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Weed Management Evaluate Late-Season Glyphosate Treatments 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. Follow The APPLES Sequence When Tank Mixing Agitate Powders soluble, Powders dry, Liquid flowables and suspensions, Emulsifiable concentrates Solutions – add surfactants, petroleum oils, MSO (methylated seed oil) type and other adjuvants last. 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. 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. Minimum Interval Between Application, Rain for Maximum POST Weed Control
Delay Weed Control Until Moisture Stress Relieved? 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. Reducing Spray Drift 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. Several sprayer nozzles designed to reduce spray drift are available; these drift -reducing nozzles are flat-fan types and are adapted for conventional spray equipment. 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, refer 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. Summary of Influences of Various Factors on Spray Drift
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. 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 Considerations In Preharvest Weed Control The expectations for preharvest weed control usually exceed reality - it is not possible to kill\dry down a three-foot weed in the same manner as a three-inch weed. Lower portions of the weed may not be affected. It requires time to dry down treated weeds - usually 7-10 days. It may require more time if wet and/or cool weather conditions occur after treatment. All herbicides labeled for preharvest application are systemic and slow acting, which requires a longer dry down period as compared to contact, fast acting herbicides. Glyphosate is labeled as a harvest aid only in spring wheat and durum - not barley or oats. Glyphosate at 0.5 to 2 pt/A of a 3 lb ae/gal concentrate controls annual grass, broadleaf weeds, and quackgrass and suppresses Canada thistle in hard red spring wheat and durum. Do not apply to barley. Do not apply to wheat grown for seed, as a reduction in germination or vigor may occur. Glyphosate should be applied after the hard dough stage (30% or less grain moisture) of the wheat and at least 7 days prior to harvest by air or ground in 3 to 10 gpa spray volume. See label for adjuvant use. Always add AMS at 8.5 to 17 lb/100 gallons of water. AMS increases control of annual and perennial weeds and especially control of weeds stressed by dry weather. AMS also eliminates antagonism from ions and carbonates in hard water. Do not use AMS in place of an NIS. Refer to label for addition of other adjuvants. Herbicide Storage Temperatures Weed Info Online North Dakota State University: www.ag.ndsu.nodak.edu/weeds (with links to weed I.D., 2005 ND Weed Control Guide, Section 18 status, herbicide label search) South Dakota State University: http://plantsci.sdstate.edu/weeds/ University of Minnesota: http://appliedweeds.coafes.umn.edu |
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