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Weed Management How Weeds Can Rob Wheat Yields
How Weeds Can Affect Wheat
Source: NDSU Organic Matter, Spray Water Can Affect Herbicide Performance Spray carrier water can also reduce the effectiveness of herbicides. Water high in sodium bicarbonate reduces the effectiveness of 2,4-D and MCPA amines (not esters), Poast, glyphosate, and dicamba. High salt levels in spray water can reduce weed control in nearly all situations. Calcium and, to a lesser degree, magnesium are antagonistic to 2,4-D and MCPA amine, dicamba, and glyphosate. Analysis of spray water sources will determine possible effects on herbicide efficacy. Water samples can be tested (for about $25) at the following laboratory: NDSU Soil and Water Environmental Laboratory, (701) 231-7864, Waldron 202, NDSU, Fargo, ND 58105-5575. Glyphosate Rates Follow The Apples Sequence When Tank Mixing Tips for Controlling Weeds In Dry Weather This does not mean perennials will not be affected by drought. Look at leaf composition: plants grown in dry conditions have smaller leaves and develop a thicker cuticle which amounts into less droplets intercepting leaves and less herbicide absorbed. Superior adjuvants can help overcome leaf barriers like thick cuticle. Most POST herbicides used are translocated, so movement through the cuticle and then through the plant to growing points are critical for adequate control. Where product labels permit, addition of crop oil concentrate rather than nonionic surfactant usually results in greater herbicide activity. Some products also allow for N-based spray additives, which tend to improve efficacy of certain products during periods of slight stress. Dust is another problem and can inactivate many herbicides. That is why poor control can be seen behind tractor tires and along gravel roads. Reducing herbicide rates is not a good idea during prolonged dry weather. For best results, use the highest recommended rate and use superior adjuvants if allowed on the label. Consider spot spraying—wild oat patches, for example—if crop quality and quantity is poor and in jeopardy and may not justify complete field spraying. Applying herbicides in the early morning (except glyphosate) may improve weed control in dry conditions. During the night, the plant has recovered some from the heat and stress of the previous day. The leaves may not be wilted as much, increasing the leaf’s surface area. The dew may help to keep spray droplets hydrated longer allowing better absorption. Outside of proper calibration, good working components, and quality nozzles, there is not much to improve performance from your sprayer in dry conditions. Puma and Discover have greater efficacy in cool, moist conditions and Assert and Everest have greater efficacy in hot, dry conditions. Essentially all postemergence herbicides have a statement on the label regarding weed growth and environmental conditions. A typical example is “Do not apply to grasses or crops under stress such as stress due to lack of moisture...as unsatisfactory control may result.” To attain adequate control, weeds must be actively growing and must not exceed the maximum growth stage. For some weeds, delaying postemergence control efforts until moisture stress is relieved is not feasible. Many postemergence treatments are effective only on small weeds, and small weeds are always easier to control than larger ones. For weeds under drought stress, use the highest labeled rates for the herbicides and possibly alter adjuvants if label allows. The decision of delaying a herbicide application and waiting for a rain or spraying drought-stressed weeds is debatable. Control is generally unsatisfactory when weeds are drought-stressed, but delaying an application often allows the weeds to get too big, making control even more difficult. Making this decision must be done on a field-by-field basis. If rainfall is in the immediate forecast, post-emergence herbicide activity will be maximized by waiting until after rain to apply, but large drought-stressed weeds can be extremely difficult to control. Where there appears to be no rain coming, apply when weeds are small for best activity. A later application may be required if late rain stimulates a new flush of weeds. Follow label directions and remember every product is different. —Bev Durgan, U of M extension weed specialist, Richard Zollinger, NDSU extension weed specialist Reducing Spray Drift Adjust boom as close to the target as possible while maintaining uniform spray coverage. Choose nozzles with a wide angle over narrow angle nozzles. Several sprayer nozzles designed to reduce spray drift are available. These nozzles increase spray droplet size and reduce the number of small droplets. These drift -reducing nozzles are flat-fan types and are adapted for conventional spray equipment. The two primary types of drift-reducing nozzles are pre-orifice and veturi designs. Some herbicides volatilize under warm or hot temperature and cause plant injury from vapors or fume drift. Temperature on the soil surface often is several degrees warmer than air temperature. Herbicide vapor can drift further and over a longer time than spray droplets. Wind blowing away from susceptible plants during application will prevent damage from droplet drift but a later wind shift toward the susceptible plants could move damaging vapors to the plants. Low volatile esters of 2,4-D or MCPA may produce damaging vapors between 70 to 90 F. Amine formulations are essentially non-volatile even at high temperatures. To minimize the risk of drift injury, dicamba and ester formulations of 2,4-D and MCPA should not be used near susceptible plants. Small plastic cones that fit around individual nozzles reduce drift by approximately 25 to 50% and spray shields which enclose the entire boom reduce drift by approximately 50 to 85%. Spray shields provide greater drift reduction when winds are low and droplets are relatively large. Therefore, spray shields should not be used as a substitute for other drift control techniques but as a supplement to all other applicable methods of drift reduction. Spray drift can be reduced by increasing droplet size and droplet size can be increased by reducing spray pressure, increasing nozzle orifice size, special drift reduction nozzles, additives that increase spray viscosity, and rearward nozzle orientation on aircraft. For more detailed information on managing spray and vapor drift, efer to NDSU Extension Circular A-657, “Herbicide Spray Drift” and Circular WC-751 “Documentation for Suspected Herbicide Drift Damage,” both of which can be found on the Internet under NDSU online weed control publications: www.ext .nodak.edu/extpubs/weeds.htm . Minimum Interval Between Application and Rain for Maximum POST Weed Control
Clean Sprayer Properly Cut Crop Injury Potential Proper sprayer cleanout procedures are given on many herbicide labels and the procedure on the label should be followed for specific herbicides. The following procedure illustrating a thorough sprayer cleanup procedure is effective for most herbicides: Step 1. Drain tank and thoroughly rinse interior surfaces of tank with clean water. Spray rinse water through the spray boom. Sufficient rinse water should be used for 5 minutes or more of spraying through the boom. Step 2. Fill the sprayer tank with clean water and add a cleaning solution (many labels provide recommended cleaning solutions). Fill the boom, hoses, and nozzles and allow the agitator to operate for 15 minutes. Step 3. Allow the sprayer to sit for 8 hours while full of cleaning solution so the herbicide can be fully desorbed from the residues inside the sprayer. Step 4. Spray the cleaning solution through the booms. Step 5. Clean nozzles, screens, and filters. Rinse the sprayer to remove cleaning solution and spray rinsate through the booms. Common types of cleaning solutions are chlorine bleach, ammonia, and commercially formulated tank cleaners. Chlorine lowers the pH of the solution, which speeds the degradation of some herbicides. Ammonia increases the pH of the solution, which increases the solubility of some herbicides. Commercially formulated tank cleaners generally raise pH and act as detergents to remove herbicides. Read herbicide label for recommended tank cleaning solutions and procedures. Never mix chlorine bleach and ammonia, as a dangerous and irritating gas will be released. Sprayers should be cleaned as soon as possible after use to prevent the deposit of dried spray residues. A sprayer should not remain empty overnight without cleaning; fill the tank with water to prevent dried spray deposits from forming. Source: NDSU Sprayer Cleaning Solutions For Herbicides Kerosene or diesel fuel followed by ammonia + water: 2,4-D ester Ammonia or commercial tank cleaner + water: Action, Basagran, Bladex, Buctril + Atra, bromoxynil, Callisto, Classic, Cobra, Contour, Dual/II/Magnum, Flexstar, Fusilade DX, Fusion, Gauntlet, Gramoxone, Harness, Harmony Extra, Hornet, Lasso, Lightning, Moxy, Moxynil, Passport, Prowl, Pursuit, Pursuit Plus, Reflex, Resource, Scepter, Select, Squadron, Status, Steel, Surpass, Treflan, trifluralin, and Ultra Blazer. Water: Command and glyphosate. Detergent + water: Atrazine and Sencor. Commercial tank cleaner + water: Liberty, Marksman, Optill, Shotgun, and Touchdown Detergent or commercial tank cleaner + water: Turbo Ammonia, commercial tank cleaner, or detergent + water: Poast. Baking soda (1 to 2;b / 100 gal water): Engame Compatibility Test for Pesticide Mixtures A way to test for tankmix compatability:
--Add some of the diluent first --Add Wettable and other powders and Water-dispersible granules --Agitate thoroughly and add the remaining diluent. --Add the Liquid products, such as solutions, surfactants, and flowables. --Add Emulsifiable concentrates last.
If scum forms on the surface, if the mixture clumps, or if any solids settle to the bottom (except for wettable powders), the mixture probably is not compatible. Finally, if no signs of incompatibility appear, test the mixture on a small area of the surface where it is to be applied.
To over come this problem you might consider the following alternatives: a) Use a different water supply. Hard water can contribute to incompatibility. b) Change brands or formulations of chemicals. c) Change the order of mixing. Make only one change at a time, and perform a complete test, as described above, before making another change. Do not mix the chemicals in the spray tank if incompatibility cannot be resolved. Wear personal protective equipment when pouring or mixing pesticides. Perform this test in a safe area away from food and sources of ignition. Pesticides used in this test should be put into the spray tank when completed. Rinse all utensils and jars and pour the rinse water (rinsate) into the spray tank. Do not use utensils or jars for any other purpose after they have contacted pesticides. – Montana State University Extension Service Strategies To Minimize Herbicide Resistant Weeds
For a comprehensive list of resistant weeds in North Dakota, U.S., and world see web site: www.weedscience.com . – Richard Zollinger, NDSU Weed Info Online North Dakota State University: www.ag.ndsu.nodak.edu/weeds (with link to weed I.D.) South Dakota State University: http://plantsci.sdstate.edu/weeds/ University of Minnesota: (see link “MN Weed Research Reports” for product performance results for various crops) http://appliedweeds.coafes.umn.edu Weed Science Society of America: www.wssa.net (includes link to weed photos and I.D.) Considerations In Preharvest Weed Control
– Richard Zollinger, NDSU Extension Service Herbicide Storage Temperatures Silverado New Wild Oat Herbicide Option For Wheat The product contains the active ingredient mesosulfuron-methyl that controls wild oats with a new mode of action, more rotational options and excellent crop safety. The product also controls wild mustard and volunteer canola, and suppresses green foxtail, Persian darnel and redroot pigweed. Cost is about $8.75 per acre plus adjuvants. It is not persistent in the soil, allowing growers to plant sugar beets, potatoes, sunflowers, soybeans, lentils or other crops the following season. Corn may be planted 12 months after Silverado is applied. The product is a 2% water dispersible granule formulation that includes a safener designed specifically for wheat. It may be applied postemergence at rates of 1.75 ounces to 2.25 ounces per acre to actively growing wild oats in the one-leaf to two-tiller stage of growth. The new herbicide has a wide window of application from wheat emergence to the jointing stage. It may be tankmixed with other broadleaf herbicides; follow label directions. Bayer CropScience has more information about Silverado online: www.cerealexperts.com |
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