Approved Pamphlet SUMMIT WG 26688 2009-10-19

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GROUP HERBICIDES

SUMMIT WG

HERBICIDE AGRICULTURAL Water Dispersible Granule for Post-Emergent Control of Quackgrass and many Broadleaf Weeds in Field Corn in Eastern Canada FOR SALE FOR USE IN EASTERN CANADA ONLY GUARANTEE: Primisulfuron-methyl.. 7.5% Dicamba acid equivalent (present as sodium salt).. 39.9%
READ THE LABEL AND BOOKLET BEFORE USING KEEP OUT OF REACH OF CHILDREN HARMFUL IF SWALLOWED

CAUTION

POISON
WARNING: EYE IRRITANT REGISTRATION NUMBER: 26688 PEST CONTROL PRODUCTS ACT
Syngenta Crop Protection Canada, Inc. 140 Research Lane, Research Park Guelph, ON N1G 4Z3 Telephone: 1-877-964-3682

Pamphlet

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NOTICE TO USER This pest control product is to be used only in accordance with the directions on the label. It is an offence under the Pest Control Products Act to use this product in a way that is inconsistent with the directions on the label. The user assumes the risk to persons or property that arises from any such use of this product.
FIRST AID IN CASE OF POISONING, contact a physician or a poison control centre IMMEDIATELY. Take container, label or product name and Pest Control Product Registration Number with you when seeking medical attention. If swallowed, call a poison control centre or doctor IMMEDIATELY for treatment advice. Have person sip a glass of water if able to swallow. Do not induce vomiting unless told to do so by a poison control centre or doctor. Do not give anything by mouth to an unconscious person. If in eyes, hold eye open and rinse slowly and gently with water for 1520 minutes. Remove contact lenses, if present, after the first 5 minutes, then continue rinsing eye. Call a poison control centre or doctor for treatment advice. If on skin or clothing, take off contaminated clothing. Rinse skin IMMEDIATELY with plenty of water for 1520 minutes. Call a poison control centre or doctor for treatment advice. If inhaled, move person to fresh air. If person is not breathing, call 911 or an ambulance, then give artificial respiration, preferably by mouth-to-mouth, if possible. Call a poison control centre or doctor for further treatment advice.
TOXICOLOGICAL INFORMATION There is no specific antidote if this product is ingested. Dicamba may cause severe irritation to the eyes, and irritation to the skin and mucous membranes. Symptoms of exposure to dicamba may include dizziness, muscle weakness, loss of appetite, weight loss, vomiting, decreased heart rate, shortness of breath, excitement, tenseness, depression, incontinence, cyanosis, muscle spasms, exhaustion and loss of voice. Treat symptomatically. If a large amount has been ingested and emesis is inadequate, lavage stomach.
PRECAUTIONS KEEP OUT OF THE REACH OF CHILDREN. Harmful if swallowed. Avoid inhalation of dust or spray mist. Avoid contact with skin, eyes and clothing. Wear coveralls over a long-sleeved shirt and long pants, head covering, boots and chemical resistant gloves during application. Wear the previously mentioned clothing plus goggles, and a NIOSH approved chemical cartridge pesticide respirator when mixing, loading, and during equipment clean-up and repair. Do not eat, drink or smoke while mixing, or during application. Remove contaminated clothing immediately after use. Store and wash contaminated clothing separately from household laundry before reuse. Wash thoroughly with soap and water after handling. Handle and apply only as recommended on this label. Avoid application when weather conditions favour drift from treated areas. Avoid

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contamination of food and feed. Do not contaminate streams, lakes, ponds, wetlands, irrigation water, water used by livestock or for domestic purposes. Do not re-enter treated areas until 12 hours after application. If this pest control product is to be used on a commodity that may be exported to the U.S. and you require information on acceptable residue levels in the U.S., visit CropLife Canadas website at www.croplife.ca. DO NOT APPLY BY AIR. DO NOT MAKE MORE THAN ONE APPLICATION PER YEAR. CAUTION: Do not graze or feed forage within 30 days of application. Do not cut corn for silage within 45 days of application. Do not harvest grain within 88 days of application. Withdraw meat animals from treated fields at least 3 days before slaughter.
ENVIRONMENTAL HAZARDS TOXIC to aquatic organisms and non-target terrestrial plants. Observe buffer zones specified under DIRECTIONS FOR USE. Surface Runoff: To reduce runoff from treated areas into aquatic habitats consider the characteristics and conditions of the site before treatment. Site characteristics and conditions that may lead to runoff include but are not limited to heavy rainfall, moderate to steep slope, bare soil, poorly draining soil (e.g. soils that are compacted, fine textured, or low in organic matter such as clay). Potential for contamination of aquatic areas as a result of runoff may be reduced by including an untreated vegetation strip between the treated area and the edge of the water body. Avoid applying this product when heavy rain is forecasted. Leaching: The use of this chemical may result in contamination of groundwater, particularly in areas where soils are permeable (e.g. sand, loamy sand and sandy loam soils) and/or depth to the water table is shallow.
STORAGE Keep in original packaging during storage. Store in a dry, well-ventilated area away from other pesticides, fertilizers, food or feed. DECONTAMINATION AND DISPOSAL For information on disposal of unused, unwanted product, contact the manufacturer or the provincial regulatory agency. Contact the manufacturer and the provincial regulatory agency in

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case of a spill, and for clean-up of spills. CONTAINER DISPOSAL OR REFILLING: RECYCLABLE CONTAINER: Do not reuse this container for any purpose. This is a recyclable container, and is to be disposed of at a container collection site. Contact your local distributor/dealer or municipality for the location of the nearest collection site. Before taking the container to the collection site: 1. Triple- or pressure-rinse the empty container. Add the rinsings to the spray mixture in the tank. 2. Make the empty, rinsed container unsuitable for further use. If there is no container collection site in your area, dispose of the container in accordance with provincial requirements.
IN CASE OF EMERGENCY INVOLVING A MAJOR SPILL, FIRE OR POISONING, CALL 1-800-327-8633 (FASTMED)

GENERAL INFORMATION SUMMIT WG Herbicide is a selective herbicide for use in Eastern Canada only that is applied after emergence of both corn and weeds for the control of quackgrass, lambs quarters, redroot pigweed, velvetleaf and ragweed. Application should be made using ground application equipment to young, actively growing weeds. The level of weed control following SUMMIT WG Herbicide application is dependent upon weed size at application and growing conditions. Warm, moist conditions following application promote the activity of SUMMIT WG Herbicide, while cool and/or dry soil conditions may reduce or delay activity as weeds are under stress. SUMMIT WG Herbicide should be applied only when the temperature in the 24 hours before and after application ranges between 5C and 28C. Temperatures beyond this range may increase the potential for crop injury. Thorough coverage of the emerged weeds is essential for effective control with SUMMIT WG Herbicide. Ensure that the boom is set at the proper height in relation to the corn plants to apply SUMMIT WG Herbicide accurately and uniformly, avoiding excessive application into the corn whorl. Growth of susceptible weeds is inhibited following application of SUMMIT WG Herbicide. The leaves turn yellow and/or red after several days followed by death of the growing point. In addition, broadleaf weeds exhibit stem and leaf twisting and bending. Complete death occurs 730 days after application, depending upon species and environmental conditions. Weeds not completely killed are often stunted and are less competitive to corn. SUMMIT WG Herbicide reaching the soil during a post-emergent application may provide pre-emergent control of certain late emerging weeds. SUMMIT WG Herbicide application at labelled rates rarely causes corn injury. When injury occurs, it is generally of short duration and yields are not affected. Crop injury may occur if application is made to corn that has been stressed by abnormally hot, humid or cold weather

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conditions, frost, low fertility, drought, water saturated soil, compacted soil, previous pesticide applications, disease or insect damage. If corn has been injured by frost, wait 48-72 hours before applying SUMMIT WG Herbicide. Certain other crops may be sensitive to low concentrations of SUMMIT WG Herbicide in the soil. Therefore, careful consideration should be given to crop rotation plans prior to using SUMMIT WG Herbicide (refer to "RECROPPING GUIDELINES"). CROP INFORMATION SUMMIT WG Herbicide provides selective weed control in hybrid and silage corn. Do not use on seed corn, sweet corn or popcorn. Corn Hybrid Sensitivity: Corn hybrids with corn-heat unit (CHU) ratings of 2500 or less may show some sensitivity to SUMMIT WG Herbicide. DO NOT use SUMMIT WG Herbicide on corn hybrids with CHU ratings of 2500 or less average seasonal corn heat units or in areas with seasonal corn heat unit ratings of 2500 or less. Corn hybrids of 2500 CHU or greater that have shown considerable crop injury from application of SUMMIT WG Herbicide are listed below. SUMMIT WG Herbicide should not be used for weed control in fields planted with these hybrids: NK G-4120 NK G-4034 NK G-4160 PIONEER 3897 WEEDS CONTROLLED Quackgrass Redroot Pigweed WEEDS SUPPRESSED Velvetleaf Lambs Quarters Ragweed
DIRECTIONS FOR USE DO NOT apply during periods of dead calm. Avoid application of this product when winds are gusty or in excess of 8 km/h and moving in the direction of adjacent sensitive crops. DO NOT apply with spray droplets smaller than the American Society of Agricultural Engineers (ASAE) coarse classification. Boom height must be 60 cm or less above the crop or ground. DO NOT apply this product directly to freshwater habitats (such as lakes, rivers, sloughs, ponds, prairie potholes, creeks, marshes, streams reservoirs and wetlands), estuarine or marine habitats. DO NOT contaminate irrigation or drinking water supplies or aquatic habitats by cleaning or rinsing of equipment or containers or disposal of wastes.

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Apply SUMMIT WG Herbicide, plus a recommended adjuvant (See MIXING AND SPRAYING INSTRUCTIONS), as a broadcast treatment over-the-top, at a rate of 350 g per hectare when corn is in the 2 to 7 leaf stage (cm tall) and the weeds are at the stages shown in the following table:
Crop or Weed Corn Quackgrass Redroot Pigweed Lambs Quarters Velvetleaf Ragweed Leaf Stage at Application leaves (30 cm in height - leaf extended) leaves (cm in height - leaf extended) leaves leaves leaves leaves

Do not apply SUMMIT WG Herbicide over-the-top to corn which is taller than 30 cm. Tank-mixing SUMMIT WG Herbicide with ACCENT 75 DF Herbicide for broadleaf weeds and annual grasses Apply SUMMIT WG Herbicide plus Accent herbicide plus a recommended adjuvant (See MIXING AND SPRAYING INSTRUCTIONS) according to the following table:
Use Rate SUMMIT WG Accent 75 DF 350 g/ha (1 container treats 8 ha or 20 acres) 25 g/ha (1 bag treats 1.33 ha or 3.3 acres) Area treated SUMMIT WG (1 Accent 75 DF container) (6 bags) 8 ha 8 ha
Apply as a broadcast treatment over-the-top when corn is in the 2 to 7 leaf stage (cm tall) and the weeds are at the stages shown in the following table:
Crop or Weed Corn Quackgrass Redroot Pigweed Lambs Quarters Velvetleaf* Ragweed Barnyard grass Green foxtail Yellow foxtail Eastern black nightshade* Leaf Stage at Application leaves (30 cm in height leaf extended) leaves (cm in height - leaf extended) leaves leaves leaves leaves leaves (up to early tillering, 2 two leaf tillers) leaves (up to early tillering, 2 two leaf tillers) leaves (up to early tillering, 2 two leaf tillers) 2 - 7 leaves
Consult the ACCENT 75 DF Herbicide label before using in a tank mix with SUMMIT WG Herbicide. *suppression only.

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MIXING AND SPRAYING INSTRUCTIONS GROUND APPLICATION ONLY: WATER VOLUME: Minimum of 150 litres per hectare. SPRAY PRESSURE: 200 - 300 kPa SPRAY NOZZLES: Flat Fan with 50 mesh or larger screens. For uniform coverage and increased penetration of the crop canopy, set the nozzles at a downward angle of 90 degrees. SURFACTANT: SUMMIT WG Herbicide must be applied with a recommended non-ionic surfactant such as AGRAL 90, Ag-Surf or Citowett Plus at 0.20% v/v (2.0 L for each 1000 L of spray mixture). 1. Fill sprayer 1/2 full of clean water. Start gentle agitation. Make certain that the agitation system creates a rippling or rolling action on the waters surface. Maintain agitation throughout the mixing and spraying process. Add the required amount of SUMMIT WG Herbicide and allow to fully disperse. Add the required amount of ACCENT 75DF herbicide if using as a tank mix and allow to fully disperse. Agitate an additional minutes and then add a recommended non-ionic surfactant. Top off tank with water, maintain agitation and spray. Do not let stand without agitation. Do not use liquid fertilizer as the spray carrier.

3. 4. 5. 6.

USE PRECAUTIONS Do not apply SUMMIT WG Herbicide where its movement in the soil may place it in contact with non-target plants or their roots. Do not use soils treated with SUMMIT WG Herbicide for gardens, lawns, etc. without consulting the "RECROPPING GUIDELINES" section. Overspray or drift to sensitive habitats should be avoided. Do not spray if there is a forecast of rain during or soon after application. Do not apply when environmental conditions such as wind speed, temperature, relative humidity etc. are favourable for drift to occur. Do not apply when spray particles may be carried by air currents to areas where sensitive crops and plants are growing or when temperature inversions exist. Do not apply SUMMIT WG Herbicide under conditions where uniform coverage at label rates cannot be obtained. Avoid overlapping. Shut off spray boom while starting, turning, slowing or stopping to prevent crop injury from an excess application. Do not allow spray or spray mist to drift onto adjacent sensitive crops or onto land which will be rotated to sensitive crops (see "RECROPPING GUIDELINES" section). Do not drain or flush spray equipment on or near desirable vegetation. SUMMIT WG Herbicide may cause injury to desirable trees and plants, particularly beans, flowers, fruit trees, grapes, ornamentals, peas, potatoes, sunflowers, tobacco, tomatoes and other broadleaf plants when contacting their roots, stems and foliage. These plants are most sensitive during their development or vegetative growing stage. Do not apply SUMMIT WG Herbicide when soybeans are growing nearby and are more than 25 cm tall or have begun to bloom.

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Do not use flood jet nozzles or controlled droplet application equipment. For maximum crop safety, do not apply SUMMIT WG Herbicide to corn which has been treated with an organophosphorus insecticide. If an IR corn hybrid is planted, organophosphorus insecticides can be used according to label directions without increasing the likelihood of injury to those hybrids when SUMMIT WG Herbicide is applied. SUMMIT WG Herbicide can be applied to corn previously treated with FORCE3.0G Insecticide. Buffer zones: Use of the following spray methods or equipment DOES NOT require a buffer zone: hand-held or backpack sprayer, and spot treatment. The buffer zones specified in the tables below are required between the point of direct application and the closest downwind edge of sensitive terrestrial habitats (such as grasslands, forested areas, shelter belts, woodlots, hedgerows, riparian areas and shrublands), sensitive freshwater habitats (such as lakes, rivers, sloughs, ponds, prairies potholes, creeks, marshes, streams, reservoirs and wetlands) and estuarine/marine habitats. When a tank mixture is used, consult the labels of the tank-mix partners and observe the largest (most restrictive) buffer zone of the products involved in the tank mixture.
Buffer Zones Method of application Crop Buffer zones (metres) required for the protection of: Freshwater habitat of Eustuarine/marine Terrestrial depths: habitats of depths: habitats: Less than Greater Less than Greater 1m than 1 m 1m than 1 m 31

Field sprayer*

* For field sprayer application, buffer zones can be reduced with the use of drift reducing spray shields. When using a spray boom fitted with a full shield (shroud, curtain) that extends to the crop canopy, the labelled buffer zone can be reduced by 70 %. When using a spray boom where individual nozzles are fitted with cone-shaped shields that are no more than 30 cm above the crop canopy, the labelled buffer zone can be reduced by 30 %.
SPRAYER CLEAN-UP To avoid subsequent injury to other crops, thoroughly clean application equipment immediately after spraying. Ensure that all traces of the product are removed. The following procedures are recommended: 1. Drain and flush tank, boom and all hoses for several minutes with clean water containing a household detergent. Do not clean the sprayer near desirable vegetation, wells or other water sources. 2. Fill the sprayer tank with clean water and add one litre of household ammonia (containing 3% ammonia) per 100 litres of water. Allow the solution to agitate for 15 minutes prior to flushing the solution through the boom and nozzles. Drain the system. 3. Remove the nozzles and screens and wash separately in a bucket containing the ammonia solution. 4. Thoroughly rinse the tank, hoses, booms, nozzles and screens with clean water for a minimum of 5 minutes to remove all traces of ammonia. 5. Dispose of all rinsings in accordance with provincial regulations.

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CAUTION: Do not use ammonia in conjunction with chlorine bleach as this could result in the release of chlorine gas which can cause severe eye, nose, throat and lung irritation. Do not clean sprayer equipment in an enclosed area. RECROPPING GUIDELINES Certain crops have been shown to be sensitive to residues of SUMMIT WG Herbicide in the soil. The minimum recropping interval is the time between the last application of SUMMIT WG Herbicide and the anticipated date of planting of the next crop. To avoid injury to subsequent crops after an application at the recommended rate of SUMMIT WG Herbicide, the following recropping intervals should be observed.
RECROPPING GUIDELINES CROP Field Corn (excluding NKG-4034, NKG4120, NKG-4160, Pioneer 3897) Soybean, White Bean, Kidney Bean, Alfalfa All Other Crops
MINIMAL INTERVAL (MONTHS) Field Bioassay
Land treated with SUMMIT WG HERBICIDE CAN ONLY BE PLANTED TO A CROP NOT LISTED IN THE PRECEEDING TABLE if a field bioassay can be successfully performed. The bioassay must indicate normal growth with no yield reductions. When conducting a field bioassay, it is very important to select a representative area(s) of the field previously treated with SUMMIT WG Herbicide to plant the test crop(s). FIELD BIOASSAY 1. Representative Sample: Ensure that soil parameters such as soil texture, depth of top soil layer, soil pH and drainage of the test area selected are representative of the remainder of the field. Sample Size: The seeded area of each selected bioassay crop must be large enough to ensure that reliable results are obtained. The seedbed preparations and seeding of the bioassay crop(s) should be conducted the same way as when the entire field would be planted. Other Residual Herbicides: It is important that other herbicide products which are known to have residual activity were not applied to the field between the last application of SUMMIT WG Herbicide and the bioassay testing period. Avoid the use of other pesticides during the duration of the bioassay as they may damage the indicator crop(s).

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Comparisons: Ideally, an untreated check strip in a neighbouring field should be established and monitored for comparison since growing conditions can vary greatly from year to year and may result in erroneous results. Assessment: The site should be monitored regularly throughout the growing season. Watch for any damage to the crop such as thinning, yellowing or stunting. A yield sample should be taken and compared to an adjacent untreated field.
DO NOT ROTATE TO OTHER CROPS UNTIL THE BIOASSAY INDICATES NORMAL GROWTH WITH NO YIELD REDUCTIONS. Failure to follow these recropping guidelines could result in injury to seeded crop(s).

Resistance-Management Recommendations For resistance management, SUMMIT WG Herbicide is both a Group 2 and a Group 4 herbicide. Any weed population may contain or develop plants naturally resistant to SUMMIT WG Herbicide and other Group 2 and/or Group 4 herbicides. The resistant biotypes may dominate the weed population if these herbicides are used repeatedly in the same field. Other resistance mechanisms that are not linked to site of action, but specific for individual chemicals, such as enhanced metabolism, may also exist. Appropriate resistance-management strategies should be followed. To delay herbicide resistance: Where possible, rotate the use of SUMMIT WG Herbicide or other Group 2 and 4 herbicides with different herbicide groups that control the same weeds in a field. Use tank mixtures with herbicides from a different group when such use is permitted. Herbicide use should be based on an IPM program that includes scouting, historical information related to herbicide use and crop rotation, and considers tillage (or other mechanical), cultural, biological and other chemical control practices. Monitor treated weed populations for resistance development. Prevent movement of resistant weed seeds to other fields by cleaning harvesting and tillage equipment and planting clean seed. Contact your local extension specialist or certified crop advisors for any additional pesticide resistance-management and/or integrated weed-management recommendations for specific crops and weed biotypes. For further information and to report suspected resistance, contact company representatives at 1-87-SYNGENTA (1-877-964-3682) or at www.syngenta.ca
Product names marked or are registered trademarks of a Syngenta Group Company All other products listed are trademarks of their respective companies.

Weed Technology 2007 21:511517
Between-Row Mowing Systems Control Summer Annual Weeds in No-Till Grain Sorghum

William W. Donald*

In previous research, use of PRE soil residual herbicides was reduced 50% in no-till corn and soybean by banding herbicides over crop rows followed by mowing weeds growing between rows two times. The research goals were (1) to determine whether such between-row mowing systems adequately controlled weeds and prevented grain yield loss in other competitive field crops, such as no-till grain sorghum, and (2) to compare broadcast herbicide treatments with betweenrow mowing systems. PRE atrazine plus dimethenamid at relative rates of 0.753 and 13 (where 1.7 plus 1.3 kg ai/ ha, respectively) were band-applied over rows shortly after planting followed by two between-row mowings close to the soil surface. In 2 of 3 yr in Missouri, this system controlled giant foxtail and common waterhemp as well as broadcast herbicides in no-till sorghum. In 2 of 3 yr, between-row mowing systems also prevented yield loss in no-till sorghum as well as both broadcast herbicides at the same rates and the weed-free check. Nomenclature: Atrazine; dimethenamid; giant foxtail, Setaria faberii (L.) Beauv. SETVI; common waterhemp, Amaranthus rudis Sauer. AMATA; corn, Zea mays L. ZEAMX; sorghum, Sorghum bicolor (L.) Moench SORVU Northup King GS10and Pioneer 84G62; soybean, Glycine max (L.) Merr. Key words: Alternative weed control, application, banding, cutting, mechanical weed control, nonchemical weed control, reduced rate herbicide.
In 1998, U.S. farmers treated 82% of the 91% of grain sorghum hectareage (sorghum hereafter) receiving herbicides with atrazine to control weeds (USDA-NASS 2004). To address environmental (Logan 1993; Richards and Baker 1993) and economic concerns, weed scientists continue to explore ways to reduce herbicide use in extensively grown field crops such as sorghum (Stahlman and Wicks 2000). Herbicide use can be reduced by (1) decreasing the area treated with herbicides and substituting mechanical weed control methods, (2) reducing herbicide rates and changing application timing, or (3) substituting different herbicides that are applied at lower rates. This research focused on tactics that decrease the area treated with herbicides by substituting unconventional mechanical weed control methods. It is well established that banding herbicides over crop rows and substituting mechanical cultivation between rows reduced the herbicide-treated area 50% compared with broadcast-applied herbicides (Stahlman and Wicks 2000). In competitive crops such as sorghum, banded herbicides followed by cultivation prevented yield losses due to weeds (Baumann and Weaver 1991; Phillips 1969). In other crops, banding herbicides had environmental benefits that likely also apply to sorghum. For example, in corn, banding PRE atrazine plus metolachlor followed by cultivation decreased both herbicide leaching through the soil profile and herbicide loss in runoff water from fields (Gaynor and Van Wesenbeeck 1995). Although cultivation can help reduce herbicide contamination of water, cultivation itself has negative environmental effects, and farmers are unlikely to use it widely. Negative effects include soil erosion and increased sediment and
DOI: 10.1614/WT-05-128.1 * Former Research Agronomist, U.S. Department of Agriculture, Agricultural Research Service, 269 Agricultural Engineering Building, University of Missouri Columbia, Columbia, MO 65211. Authors E-mail: cny00431@centurytel.net
nutrient loss in runoff from fields (Blevins et al. 1998). Cultivation also is incompatible with no-tillage residue management, unless specialized cultivators are used (Hanna et al. 2000; Paarlberg et al. 1998). In farmer surveys conducted during the mid-1990s, banding herbicides followed by cultivation was unacceptable to Missouri row crop farmers (Rikoon et al. 1996). In published research in soybean and corn, PRE herbicide use was reduced 50% by banding herbicides over crop rows and substituting between-row mowing for cultivation (Donald 2000a, 2000b; Donald et al. 2001). Soybean and corn yields of the weed-free checks were statistically indistinguishable from treatments with banded PRE herbicide followed by between-row mowing. Unlike conventional cultivation, between-row mowing systems are compatible with no tillage (Donald et al. 2001). If between-row mowing is properly timed before corn or soybean canopies close, mowing weeds close to the soil surface two times killed most common annual weeds, including giant foxtail, common ragweed (Ambrosia artemisiifolia L.) and common waterhemp. If between-row mowers are commercialized as an alternative for cultivation, this alternative weed management system may have potential use in many competitive, upright-growing row crops such as grain sorghum. Grain sorghum has been successfully produced using no tillage (Bishnoi et al. 1990; Phillips 1969; Stahlman and Wicks 2000; Unger 1999). For example, when rotated after either cover crops of winter wheat (Triticum aestivum L.) or crimson clover (Trifolium incarnatum L. Bigbee), grain sorghum yielded more under no tillage than under conventional tillage in Alabama (Bishnoi et al. 1990). However, similar tillage systems failed to influence sorghum yields in the Great Plains (Phillips 1969). When row spacings of 45, 60, and 90 cm were compared under no tillage, sorghum yielded most at the narrowest row spacing, presumably because

Donald: Mowing in no-till sorghum N
seeding rates were greater (Bishnoi et al. 1990; Phillips 1969; Stahlman and Wicks 2000). Nevertheless, narrower row spacing failed to improve weed control in no-tillage sorghum. The research goals were (1) to determine whether betweenrow mowing systems adequately controlled weeds and prevented grain yield loss in no-till grain sorghum, and (2) to compare broadcast herbicide treatments with between-row mowing systems. It was hoped that between-row mowing systems could be extended for use from corn and soybean to grain sorghum. In this research, no-tillage sorghum was grown in 53-cm-wide rows, and broadcast PRE herbicide at two rates (i.e., 13 and 0.753 relative rates) were compared with the same herbicides banded over rows followed by mowing between rows two times. The null hypothesis was that grain yields of the weed-free checks would be maximum and statistically indistinguishable for the broadcast herbicide and between-row mowing systems. The amount of between-row weed cover for treatments was expected to be ranked: weedfree checks # treatments , weedy checks. It was hypothesized that sorghum grain yields, weed cover, or weed control would each be indistinguishable from the treatments at both herbicide rates (0.753 or 13).
respectively (Table 1). In 1998, 1999, and 2000, glyphosate was applied using a tractor-mounted sprayer operated at 4.8, 2.4, and 2.4 km/h, respectively, at a hydraulic pressure of 207 kPa to apply spray volumes of 83, 159, and 159 L/ha of water, respectively, with flat fan spray nozzles.1 The nozzle spacing on the boom was 51 cm, and the boom height was about 61 cm above the soil surface. Sorghum was fertilized with N-P-K for a grain yield goal of 5,650 kg/ha, on the basis of soil tests and recommendations of the University of Missouri soil testing lab. N-P-K was deepbanded using a no-till grain drill2 at [157-157-157], [87-121121], and [91-91-91] kg/ha, respectively. Northup King GS10 hybrid sorghum seed, which had been treated with captan, pirimiphos-methyl, metalaxyl, and fluxofenim, were planted 3 to 4 cm deep in 53-cm rows at 342,250 seeds/ha in 1998 and 358,150 seeds/ha in 1999 (Table 1 and Figure 1). In 2000, Pioneer 84G62 seed, which had been treated with imidacloprid and fluxofenim, were planted at 341,870 seeds/ ha similarly. Treatments. Treated plots measured 3 by 9.1 m. For PRE broadcast treatments, atrazine plus dimethenamid were applied at relative rates of 13 and 0.753, where 1.7 plus 1.3 kg ai/ha, respectively (Table 1 and Figure 1). A backpack sprayer was operated at 4.8 km/h using compressed CO2 at 207 kPa to apply spray volumes of 84 L/ha of water through flat fan nozzles.3 For broadcast application, nozzles were spaced 76.2 cm apart on the boom, and the boom height was about 86 cm above the soil surface. In between-row mowing systems, the same PRE herbicides were banded over rows at the same two relative rates followed by two mowings close to the soil surface between rows after weeds became tall enough to mow. The herbicide band width was 50% of the row width (i.e., 27-cm-wide bands centered over 53-cm rows) (Table 1 and Figure 1). In 1998, 1999, and 2000, a backpack sprayer was operated at 4.8 km/h using compressed CO2 at 207, 207, and 276 kPa to band-apply spray volumes of 84, 84, and 94 L/ha of water, respectively, with even nozzle tips.3 For band application, nozzles were spaced 53 cm apart on the boom, and the boom height was about 15 cm above the soil surface. The bands of PRE herbicides kept sorghum rows free of weeds by the time that between-row weeds were first mowed at about 3 cm above the soil surface (Table 1). When they were first mowed, the heights of the chief weeds varied among years (Figure 2). Weeds were mowed again just before sorghum canopy closure. The mowing width of the plastic cord mower4 was 46 cm, leaving about 3.5 cm unmowed on either side of sorghum rows. The edge of the mowed region slightly overlapped the edge of the sprayed zone. The experiment included weedy and weed-free checks. Before planting, glyphosate was broadcast over the entire site to kill winter annual weeds (see above). In weedy checks, summer annual weeds were uncontrolled. In weed-free checks, summer annual weeds growing between rows were shallowly hoed close to the soil surface to avoid pruning sorghum roots, and in-row weeds were hand pulled and hoed several times during the growing season (Table 1). To avoid yield loss from crop damage during weeding, hoeing was ended in late summer. In competition research, late-emerging

MATERIALS AND METHODS

Site, Weather, and Weeds. In 1998, 1999, and 2000, grain sorghum was planted after soybeans at the University of Missouris Bradford Research and Extension Center in north central Missouri near Columbia (38u53943.50N, 92u12937.90W, 269 m altitude). The soil was a Mexico silty clay loam (fine, smectitic, mesic Aeric Vertic Epiaqualfs) that had 18% sand, 48% silt, 34% clay, 3.3% organic matter, and pH of 5.5 to 5.8. According to the soil testing lab at the University of Missouri, Columbia, soil pH is the salt pH, and values of pH run approximately 0.5 units lower than the customary water pH values. Historical weather data were collected at the Bradford center (Figure 1). Because weather data were incomplete at Bradford in 1995 and 2001, weather data from the nearby Sanborn Experimental Field and University of Missouri South Farm were substituted in 1995 and 2001, respectively, for calculation of long-term averages. Daily heat units are defined as [(maximum temperature minimum temperature)/2 base temperature] in degree C days. Heat sums were calculated by summing daily heat units from sorghum planting until harvest using a base temperature of 10 C. Shepherds purse [Capsella bursa-pastoris (L.) Medik. CAPBP], fleabane species (Erigeron spp.), and horseweed [Conyza canadensis (L.) Cronq. ERICA] were the major winter annual weeds present. Giant foxtail was the major summer annual grass weed present. After giant foxtail, most remaining weed cover consisted of the following summer annual broadleaf weeds: common waterhemp, common ragweed, and prickly sida (Sida spinosa L. SIDSP). Agronomic Practices. For controlling winter annual weeds before no-till planting, glyphosate at 0.84, 2.24, and 1.12 kg ae/ha plus ammonium sulfate at 3.36 kg/ha were broadcast over the site in spring of 1998, 1999, and 2000, 512 N
Weed Technology 21, AprilJune 2007
Figure 1. The monthly precipitation (bars) and long-term average monthly precipitation (lines) are graphed vs. month of the year in 1998 to 2000 (left panels). Monthly average maximum and minimum air temperatures (solid and open circles, respectively) and long-term averages (lines) are graphed vs. month of the year (middle panels). Cumulative heat sums. 10 C (i.e., growing degree days) after planting are graphed vs. day of the year (right panels). The 9-yr averages were from 1993 to 2001. The length of the experiments is indicated by either hatched bars (left panels) or a horizontal bar (middle panels). Abbreviations: MOW, between-row mowing imposed; PHOTO, photographs taken.
Table 1. Dates for field operations, treatments, or measurements. Field operations, treatments, or measurements Broadcast glyphosate Plant sorghum and inject N-P-K fertilizer Apply PRE atrazine plus dimethenamid Sorghum first emerges Measure sorghum stand Mow between-row weeds Remow between-row weeds In weed-free check plots: Hoe and hand pull weeds: Rehoe and hand pull weeds Rehoe and hand pull weeds Photograph between-row weed cover Photograph overrow weed cover Rate weed control Harvest sorghum

1998 Date May 27 June 16 June 19 June 22 August 10 July 9 August 7 July 14 August 7 August 21 September 22 September 22 November 6 DAP 98 143
1999 Date May 19 June 8 June 10 June 13 July 2 July 8 July 22 July 7 July 21 August 12 August 20 August 24 October 20 DAP 77 134
2000 Date May 16 May 31 June 6 June 11 August 7 July 7 August 2 July 7 July 1011 August 34 August 22 August 22 August 22 October 26 DAPa 37 83 148
DAP, days after planting.
Donald: Mowing in no-till sorghum
blocking was based on slope position and weed ground cover observed in preceding years (Hoshmand 1994). For each year separately, sorghum grain yields, rated weed control, weed cover, and maximum canopy height were subjected to ANOVA using statistical software.7 Means were separated by Fishers protected LSD test at P 5 0.05.

Results and Discussion

Figure 2. Grain sorghum and weed heights (cm, means 6 standard error) when weeds growing between rows were first mowed in 1998 to 2000.
weeds do not reduce grain sorghum yields (Burnside and Wicks 1969). Measurements. After full emergence, sorghum stands were measured in 1.8-m lengths in the two center rows of each plot. At mid-season, weed control was visually evaluated on the basis of a scale of 0% (no control) to 100% (complete kill). After cutting borders at either end of all plots, sorghum was combine-harvested from an area measuring 1.5 by 8.2 m, and grain yields were adjusted to 13% moisture content. To measure treatment effectiveness, projected ground covers of between-row grass, broadleaf, and total weeds (i.e., grass plus broadleaf weeds), but not crop cover, were measured from photographs taken between crop rows (Table 1). Sorghum foliage overhanging and obscuring the between-row region was pulled back with 1-m2 wooden frame panels covered with black cloth, and an orange dowel was extended at a right angle out from the crop row just above the soil surface toward the row middle to mark the herbicide band width in the photographs. Four between-row photographs per plot were taken vertically (i.e., camera facing toward the soil surface) with a digital camera5 at a height of 132 cm. Each photograph (640 by 512 pixels per photograph) corresponded to 1.06 m2 at the soil surface on the basis of photographs of a 30- by 30-cm orange calibration plate. In 1999 and 2000, four additional photographs per plot were taken over rows for measuring over-row cover above the sorghum foliage. Image analysis software6 was used to crop between-row zones and automatically superimpose a 20 by 20 pixel grid over each between-row photograph. Weed cover was calculated as a percentage (i.e., the number of grid intersections that were either grass or broadleaf weed cover divided by the total number of grid line intersections per cropped photograph). Four measurements per plot were averaged for reporting weed cover. Statistical analysis. Treatments were applied in a randomized complete block experimental design with four blocks, and 514 N

Yield. In 1998, 1999, and 2000, no-till sorghum stands were 100, 68 and 80% of planting intentions, respectively (see Materials and Methods). In these 3 yr, no-till grain yields of the weed-free checks were 71, 66, and 73% of the yield goal for which the experiment was fertilized, respectively (i.e., 5,650 kg/ha) (Figure 3). In all 3 yr, yields of weed-free no-till sorghum (4,030, 3,720, and 4,120 kg/ha, respectively) were less than average Missouri sorghum yields under conventional tillage (i.e., 5,580, 4,780, and 6,320 kg/ha, respectively) (Missouri Agricultural Statistics Service 2004). The reasons why the weed-free no-till sorghum never achieved its planned yield goal are unclear. Mechanical and manual weed control was imposed as needed in a timely fashion and controlled weeds. University of Missouri fertility recommendations for grain sorghum, which were used, were developed for conventionally tilled grain sorghum and may need adjustment upward for no tillage. Although sorghum is more drought tolerant than many other field crops (Rooney 2000), no-till grain yields of weed-free checks were similar in years of both below-average (i.e., 1998 and 1999) and above-average growing-season rainfall (i.e., 2000) (Figures 1 and 3). Consequently, weed-free yields of no-till sorghum were unrelated to year-to-year variation in either stand or seasonal rainfall. Weeds limited yields in 2 of 3 yr, since yields of weed-free checks were significantly greater than weedy checks in 2 of 3 yr (i.e., 1998 and 2000) (Figure 3). In these years, yields of weedy checks were 67 and 59% of the weed-free checks, respectively. In 1998, the following three treatments controlled weeds, and their yields were statistically indistinguishable from each other and the weed-free check: the broadcast PRE herbicides at 13 and the two between-row mowing systems (Figure 3). In 2000, all four treatments were statistically indistinguishable from one another and the weed-free check. In contrast, in 1 of 3 yr (i.e., 1999), weeds did not reduce yields; the yields of the weedy check, weed-free check, and treatments were statistically indistinguishable from each other in 1999 (Figure 3). This result was unexpected because weed cover was high (Figure 3), and the site had been heavily infested with summer annual weeds that greatly reduced corn and soybean yields for at least 6 previous years (unpublished data). Weed control, weed cover, and maximum weed canopy height. In 1998, the values for rated control of total weeds, giant foxtail, and broadleaf weeds for all four treatments were statistically indistinguishable from their respective weed-free checks and all exceeded 90% (Figure 3). However, in 1999, values of rated control for total weeds, giant foxtail, and

Figure 3. Sorghum grain yield (kg/ha), rated weed control (%), between-row weed cover (%) measured from photographs, and maximum weed canopy height (cm) between rows are graphed vs. weed management treatment for 1998, 1999, and 2000. Both weed control rating and weed cover subdivided into total weeds, giant foxtail, and broadleaf weeds are indicated by different degrees of shading (legend box). Means (6 standard errors) are presented and those means for each variable in a year followed by the same letter (different fonts or cases for different variables separately) were not different at P 5 0.05 by Fishers protected LSD. *, nonsignificant.
broadleaf weeds of all four treatments were less than their respective weed-free checks and were indistinguishable from one another. In 2000, total weed control was statistically indistinguishable for all four treatments. However, weed control with mowing systems also were indistinguishable from the weed-free check and outperformed PRE herbicides by about 20%. In 2000, values for giant foxtail and broadleaf weed control of all four treatments were less than their respective weed-free checks. From separate observations of total weed, giant foxtail, and broadleaf weed control over and between rows, rated weed control of whole plots was due chiefly to rated control between rows (data not presented). Values of rated total weed, giant foxtail, and broadleaf weed control over rows of all treatments were greater than the respective weedy checks, and treatments were indistinguishable from one another in all 3 yr (data not presented). The effects of between-row mowing treatments on rated weed control were the inverses of effects on between-row weed cover (Figure 3). Pearson correlation coefficients between rated total weed control and between-row total weed cover were 20.51, 20.76, and 20.52 in 1998, 1999, and 2000, respectively. Compared with visually rated weed control, weed cover of total weeds, giant foxtail, and broadleaf weeds provided different information about weed response to treatment and the factors limiting grain yields. Rated control can be interpreted as a subjective judgment of whether treatments would be visually acceptable to farmers. Rated control provided no information on whether giant foxtail was more common than broadleaf weeds, and whether giant foxtail was better related to grain yield loss than were broadleaf weeds. Likewise, rated control for weedy checks was taken as 0% in all years, and provided no information on differences in weed populations among years. In late summer of 1998, 1999, and 2000, values of total weed cover between rows in the weedy checks were 27, 49, and 58%, respectively (Figure 3). In contrast, in 1999 and 2000, values of total weed cover over rows were 15% and 8%, respectively; in 1998, weed cover over rows was not measured. Weed cover both over rows and between rows was chiefly giant foxtail in 1998 and 1999, and almost entirely giant foxtail in 2000. Consequently, giant foxtail growing between rows was largely responsible for reducing grain yields of no-till sorghum in 1998 and 2000, rather than broadleaf weeds. This conclusion is not obvious from rated control of giant foxtail and broadleaf weeds. In fact, broadleaf weed control was more apparent than real because broadleaf weeds accounted for little total weed cover in any year (Figure 3), and sorghum and giant foxtail interference likely suppressed broadleaf weed seedlings growth. By late summer in 2 of 3 yr (i.e., 1998 and 1999) following between-row mowing treatment, both between-row total weed cover and maximum weed canopy height were less than in the weedy checks (Figure 3). All four treatments reduced both weed cover and maximum weed canopy height in 1998 and weed cover in 1999 to about the same extent below the weedy check. However, in 1999 the broadcast herbicides failed to reduce the maximum weed canopy height compared with the weedy check, in contrast to the between-row mowing treatments. Even though 1999 had below-average seasonal rainfall, early-season rainfall probably was adequate to 516 N

activate the PRE herbicides. For example, values of overrow total weed cover for both broadcast herbicide treatments were low and about 6% in 1999. In 1999, it is more likely that lack of mid-season rainfall (Figure 1) limited sorghum canopy closure and shading, which subsequently limited crop interference with between-row weed cover development (Figure 3). For between-row total weed cover and maximum weed canopy height in 2000, differences among treatments were nonsignificant, but treatments were ranked similarly to 1998 and 1999. After either broadcast herbicide or betweenrow mowing treatment, most between-row total weed cover was giant foxtail, as in the weedy check (Figure 3). Mowing controlled annual broadleaf and grass weeds differently. The first mowing killed the few annual broadleaf weeds present, chiefly common waterhemp, in addition to common ragweed and prickly sida. In 1998 and 1999, but not 2000, common waterhemp and prickly sida were the chief broadleaf weeds to produce broadleaf weed cover by late summer in no-till sorghum. After one mowing, giant foxtail regrew from tiller buds present in the crown close to the soil surface, below the mowing height. In published research in soybean and corn (Donald 2000a, 2000b; Donald et al. 2001), a second mowing killed giant foxtail growing between rows. After two mowings in no-till sorghum, giant foxtail regrew somewhat to produce greater cover than previously reported in either no-till corn or soybean, but still less than the weedy check in 2 of 3 yr. Shading likely limited giant foxtail recovery (Santelmann et al. 1963) after a second mowing in all three crops. However, the sorghum canopy closed less completely than either corn or soybean canopies and consequently shaded the soil surface less intensely. Less complete canopy closure and shading likely allowed giant foxtail to recover from mowing in sorghum more than in corn (Figure 3). In between-row mowing systems, the timing of weed emergence relative to the timing of crop planting and subsequent mowing likely contributed to greater weed cover between rows in no-till sorghum (Figure 3), compared with no-till corn (Donald et al. 2001). In Missouri and the southern Corn Belt, the period for planting corn generally precedes both the normal period for planting sorghum (Missouri Agricultural Statistics Service 2004) and the seasonal flushes and peaks of emergence for most major summer annual grass and broadleaf weeds (Buhler and Hartzler 2001; Hartzler et al. 1999). Most weed emergence also precedes sorghum planting. Glyphosate treatment before planting no-till corn chiefly controls winter annual weeds and the early flushes of summer annual broadleaf weeds. Consequently, no-till corn becomes infested with weeds that emerge after glyphosate application and corn planting. In contrast, glyphosate treatment before planting sorghum chiefly controlled both established winter annual weeds and most of the major emergence of summer annual broadleaf and grass weeds. After glyphosate application at no-till sorghum planting, fewer weeds likely emerged because weed seed banks near the soil surface had been depleted and environmental conditions become unfavorable for both breaking weed seed dormancy and allowing successful weed emergence during late summer. In addition to competition through shading, sorghum also may suppress weed cover growth by allelopathy

(Cheema et al. 2004; Mikulas 1984; Nimbal et al. 1986), although documented proof for allelopathy is limited in the growing sorghum crop. Most data concern sorghum allelopathy to later-planted rotational crops. Values of between-row total weed cover in corn were greater than 80% in weedy checks at mid-season at the site (unpublished data). In contrast, in late summer in no-till sorghum, values for between-row total weed cover in the weedy checks were 27, 49, and 58% in 1998, 1999, and 2000, respectively, (Figure 3). Most of this weed cover was giant foxtail in both crops and likely corresponds to the tail of the seasonal peak for giant foxtail emergence (Buhler and Hartzler 2001; Hartzler et al. 1999). Spraying glyphosate before planting no-till sorghum well after most summer annual weeds have emerged likely contributed to the observed suppression of weed cover by sorghum, rather than allelopathy (Figure 3). In weedy checks in late summer in 1999, no-till sorghum tolerated 49% weed cover without yield loss; 49% weed cover does not represent much weed suppression by supposedly allelopathic sorghum. These observations are more consistent with sorghum tolerance of weeds (i.e., yield production in the presence of weeds), rather than sorghum suppression of weeds by either competition or allelopathy.

Sources of Materials

Teejet flat fan spray nozzle tips 6501 SS, Spraying Systems Co., Wheaton, IL 60187. 2 No-till grain drill model 107, Haybuster Manufacturing, Box 1950, Jamestown, ND 58401. 3 Teejet even fan spray nozzle 8001 EVS, Spraying Systems Co., Wheaton, IL 60187. 4 Ryobi weed trimmer (model 780r or 790r), Ryobi Outdoor Products, 550 North 54th St. Chandler, AZ 85226. 5 Olympus D 600L and D620L digital cameras, Olympus America Inc., Two Corporate Center Dr., Melville, NY 117473157. 6 Sigma Scan Pro version 5 software, SPSS Science, SPSS Inc., 233 South Wacker Drive, 11th Floor, Chicago, IL 60606-6307. 7 SPSS version 12 software, SPSS Inc., 233 South Wacker Drive, 11th Floor, Chicago, IL 60606-6307.

Acknowledgments

The author thanks Aaron Beshears, Kyle Cook, Max Glover, Paul Howerton, Brent Niemeyer, Travis Rowland, and David Schaffer for their technical assistance. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

Literature Cited

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Received September 9, 2005, and approved December 16, 2006.