Good Fruit Grower

April 15th

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Soils & Nutrients Get the most out of GLYPHOSATE W Tim Miller says that with most perennial weeds the bud stage is the most vulnerable. Herbicide modes of action Active ingredient Trade name Mode of action 2,4-D many synthetic auxin acetic acid WeedPharm leaf desiccation carfentrazone Aim clethodim Select clopyralid PPO inhibitor Stinger clove leaf oil Matran dichlobenil Casoron diuron fluazifop Karmex Fusilade flumioxazin Chateau ACCase inhibitor synthetic auxin leaf desiccation cell wall synthesis inhibitor photosystem II inhibitor ACCase inhibitor PPO inhibitor glyphosate Roundup, others EPSP synthase inhibitor glufosinate Rely halosulfuron Sandea indaziflam Alion isoxaben Gallery napropamide Devrinol Surflan oxyfluorfen Goal glutamine synthase inhibitor ALS inhibitor cell wall synthesis inhibitor cell wall synthesis inhibitor very long chain fatty acid inhibitor norflurazon Solicam carotenoid biosynthesis inhibitor oryzalin microtubule assembly inhibitor PPO inhibitor paraquat Gramoxone photosystem I inhibitor pendimethalin Prowl pronamide Kerb rimsulfuron Matrix saflufenacil Treevix sethoxydim Poast simazine terbacil ACCase inhibitor Princep Sinbar trifluralin Treflan SOURCE: University of California IPM 34 APRIL 15, 2012 GOOD FRUIT GROWER photosystem II inhibitor photosystem II inhibitor microtubule assembly inhibitor microtubule assembly inhibitor microtubule assembly inhibitor ALS inhibitor PPO inhibitor The many formulations available do about the same job, but the rates required can differ. by Geraldine Warner hile glyphosate still effectively controls many weeds, including annual and perennial grass and broadleaf weeds, many factors play a role in how well it works, says Tim Miller, weed scientist with Washington State University in Mount Vernon. Since glyphosate came off patent in 2000, many different formulations have been marketed. At least 40 glyphosate products are available in Washington State. Glyphosate is formulated as a salt. About 80 percent of glyphosate formulations contain isopropylamine salt. Others include potassium, diammonium, trimethylsulfonium, or sesquidodium. The salt makes the glyphosate a little more soluble so the concentration can be higher, and it also stabilizes the product. It enables the glyphosate acid to enter the plant a little more easily, and it moves better throughout the plant. Although there is little difference in the activity of the different formulations, they do differ in concentration of both the active ingredient (the salt) and the glyphosate acid equivalent. For example, Touchdown HiTech has 6 pounds of active ingredient per gallon, and requires 19 ounces per acre to achieve the 0.75 pounds of acid equivalent, whereas most generics contain 4 pounds of active ingredient per acre and require 32 ounces per acre to achieve the 0.75 pounds of acid equivalent. MIX itup S F or more information, download the publication "Glyphosate Stewardship: Keeping an Effective Herbicide Effective" from www.ipm .ucdavis.edu/PDF/ PUBS/miller- glyphosatesteward ship.pdf uccessful long-term weed control depends on using all available methods, rather than just one repeatedly, scientists say. "Mix it up," Rick Boydston, weed scientist with the U.S. Department of Agriculture in Prosser, Washington, urged during a recent weed management workshop in Washington State. "Don't use any method over and over until it fails. Mix it up to prevent resistance from developing." An orchard or vineyard typically has a mixture of weed species, but if some portion of that mix is tol- erant or resistant to a weed control strategy that is used repeatedly, there will be a shift in the dominant species. Scientists stress that chemicals should be used as part of an integrated program that might include other methods such as: • mechanical (cultivation, flaming, mowing and mulches) • cultural (screening irrigation water, cleaning field equipment, controlling weeds around the edges of the orchard or vineyard, and planting weed-free cover crops between rows) • biological (releasing organisms, such as insects that inhibit growth or seed production). Eliminating production of weed seeds is the key to successful weed management. Use cultivation, mowing, or herbicides with different modes of actions to prevent the weed from flowering and producing seed. Preventing resistance Prevention is the most effective and economical way to reduce the threat of glyphosate-resistant weeds. When using chemicals, combine an herbicide that has soil residual activity with glyphosate (which does not) or with another postemergence herbicide to extend the period of weed control and reduce the need for multiple applications of glyphosate, advises Ed Peachey, weed scientist with Oregon State University in Corvallis. If resistance to glyphosate has not developed, use preemergence treatments followed by a tank mix of postemergence products. Also consider using other nonselective herbicides, such as glufosinate or paraquat with PPO inhibitors such as Aim (carfentrazone), Goal (oxyfluorfen), and Treevix (saflufenacil) for burndown control. To delay resistance, use high glyphosate rates. Resistance to glyphosate is likely to be caused by sev- eral mechanisms in the plant and not just one genetic mutation, so it is important to use a full label rate to delay resistance. This is unlike other situations where reduced rates might be recommended in order to reduce selection pressure. If weeds have become resistant to glyphosate, growers can continue to use glyphosate but should tank mix it with other herbicides that are effective on the resistant weeds and should target weeds when they are small and easier to control. —G. Warner www.goodfruit.com

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