Issue link: http://read.dmtmag.com/i/61297
Herbicide-resistant weeds Weeds have developed resistance to several classes of herbicides in the United States. The number of weed species showing resistance to glycines (including glyphosate) has increased over the past 15 years. 125 - 100 - 75 - 50 - 25 - 0 - Glycine ALS inhibitor Other ACCase inhibitor Bipyridilium Multiple resistant Dinitroanaline PSII inhibitor Synthetic auxin ROOTSTOCK – VARIETIES – POLLINATION Quality from the Start APPLES Aztec Fuji® (DT2 variety) Blondee® Brookfield® Gala Buckeye® Gala Cameo® brand Granny Smith Honeycrisp 1970 1975 1980 1985 1990 1995 2000 2005 2010 YEAR SOURCE: Brad Hanson, University of California, Davis, based on information from www.weedscience.org. but resistance was already seen by the 1990s. This is now one of the most common classes of herbicides facing resistance. Resistance to protoporphyrinogen oxidase (PPO) inhibitors, which are widely used in tree fruits and grapes, is starting to show up, Hanson said. Products with this mode of action include Goal (oxyfluorfen), Aim (carfentrazone), Treevix (saflufenacil), Kixor, and Chateau (flumioxazin). Resistance to glycines, including glyphosate, is also causing concern, although it is still relatively minor compared with resistance to other herbicide classes. In Oregon, Italian ryegrass has shown some resistance to Rely (glufosinate). "That's trouble brewing," Hanson said. "That's something we're keeping an eye on." Resistance management Practices that lead to resistance include not rotating crops, not using tillage, having a weakly competitive crop, and not using herbicides with different modes of action in rotation, Hanson said. "For example, maybe I plant trees, don't use tillage, and only use Roundup. That would be a bad way to manage resistance," he said. On the other hand, a complex rota- tion utilizing tillage, hand weeding, and use of multiple herbicide modes of action will minimize selection of resistant biotypes. Since growers of perennial crops, such as tree fruits and grapes, can't easily rotate crops or till the ground, herbicide rotations or tank mixes of herbicides with different modes of action are the best option. The weeds most likely to develop resistance are annuals that produce a lot of seeds and have little seed dormancy but some seed longevity, so that the ones that don't germi- nate right away can persist for a while. The worst weeds develop through two or three generations per year. The types of herbicides most likely to lose effectiveness because of resistance are those that have a single mode of action, are highly effective, are used frequently and at high rates, and have a long residual life. The more individuals that are selected with the herbicide, the greater the chances of finding resistant mutants, Hanson said. "It boils down to a numbers game." Resistance management is based on reducing selection pressure by rotating herbicides with different modes of action—not just different active ingredients or families of herbicides, he stressed. Tank mixes help as long as the herbicides target the same weeds. Applying a herbicide that targets grasses with one that targets broadleaf weeds is not managing resistance, but managing the weed spectrum, Hanson said. Keep good records of what you have used and where you've seen failures, he advised. Not every weed control failure is due to resistance, but if healthy plants are intermixed with dying plants of the same species, it's a strong sign of resistance. A patch of uncon- trolled weeds that is spreading from year to year can also be a sign of resistance. Monitor your orchard and control escapes before they become large problems, he suggested. • F www.goodfruit.com or more information, download the publication "Selecting Pressure, Shifting Populations, and Herbicide Resistance and Tolerance" from www.ipm.ucdavis.edu/PDF/PUBS/hanson-herbicideresistance.pdf. Joburn Braeburn™ JonaStar® Jonagold Kumeu Crimson® LindaMac® It® Red Delicious POLLENIZERS Indian Summer Manchurian CHERRIES Attika® Benton™ Bing Redcort® Ruby Jon® Ruby Mac™ Mariri Red™ Braeburn Morning Mist™ Early Fuji Morren's® Jonagored Supra™ Mt. Evereste Mt. Blanc EbonyPearl™ BlackPearl™ Kootenay™ BurgundyPearl™ Lapins Chelan™ PEARS Bartlett Ultima™ Gala Zestar!® Smoothee® Golden Spartan Snowdrift Pearleaf Early Robin® Rainier RadiancePearl™ Hudson Regina Sam Montmorency Columbia Red Anjou™ Forelle Concorde™ Comice PEACHES Allstar Autumnstar® Blazingstar D'Anjou Golden Russet Bosc® Blushingstar Glowingstar Brightstar™ Redhaven Coral Star Redstar Earlystar™ Elberta Selah™ Red Clapp's Favorite Red Sensation Bartlett Seckel Risingstar Starfire Flamin' Fury® Series PF-19-007 PF-7 PF-24-007 PF-17 PF-35-007 PF-25 PF Lucky 13 Varieties listed may not reflect current inventory. REPRESENTATIVES Leonard Aubert Jim Adams Hood River, Oregon Washington State (541) 308-6008 aubert@gorge.net (509) 670-7879 Larry Traubel Rick Turton Cedaredge, Colorado Kelowna, B.C. (970) 856-3424 ltraubel@hotmail.com (250) 860-3805 Rey Allred Payson, Utah jimadams@willowdrive.com Pinedale Ruby™ Rainier Sweetheart Tieton® Van Skeena™ White Gold (801) 465-2321 Larry Lutz Nova Scotia Ephrata, Washington | www.willowdrive.com WILLOW DRIVE NURSERY, INC. 1-888-54-TREES GOOD FRUIT GROWER APRIL 15, 2012 31 Larry.Lutz@scotiangold.com (902) 680-5027 NUMBER OF HERBICIDE-RESISTANT WEED SPECIES