The researchers are evaluating two ad- ditional ALS herbicides. While the results are still preliminary, Clark said they appear very similar to previous tests. As part of her master’s thesis, Valdez- Herrera is working with Fresno State pro- fessor Katherine Waselkov, a plant evolu- tionary geneticist, to study possible genetic changes within common chickweed as causes for resistance. Clark said several questions remain, in- cluding what type of economic impact the weed poses to small grain producers, par- ticularly under heavy infestations. He said he hoped to share research results soon to help growers and PCAs make more in- formed crop management decisions. Clark said he could envision growers eventually incorporating preplant burn-down op- tions or preplant herbicides registered for small grains into south valley weed man- agement practices. Currently, the most common weed- management system involves one post-emergent application targeting in-season weeds. The Weed Science Society of America tracks herbicide resistance in specific weeds, and most of the cases in the coun- try involve ALS inhibitors. Based on the data, Clark said he wasn’t surprised they found ALS-resistant common chickweed in the southern San Joaquin Valley since it Chickweed Continued from Page 10
In the past, Gogue said, phenoxy herbi- cides such as 2,4-D were commonly used in small grains, but they were not effective on common chickweed. The ensuing regis- tration of Express herbicide, followed a few years later by Simplicity, provided “lights out” control of chickweed, he added. “The adoption of those new (ALS) her- bicides was very quick and very strong because of chickweed,” he said. “It was absolutely amazing what they did, and it was what we needed.” The confirmation of chickweed resistance has prompted PCAs like Gogue to change theirweedmanagementrecommendations, but he said it’s difficult because there aren’t many other good options. Gogue said he also has seen the effec- tiveness of ALS herbicides on some of the other broadleaf and grassy weeds they for- merly controlled. Herbicide resistance occurs when a single mode of action is used repeatedly on a pest. No herbicide is 100% effective, and a small number of individuals sur- vive treatment because of a slight differ- ence in genetic makeup. Those survivors may reproduce. With continued use of the same mode of action, the number of resistant plants in the population may increase to the point that the herbicide is no longer effective. (Vicky Boyd is a reporter in Modesto. She may be contacted at vlboyd@att.net.)
ALS herbicide-resistant common chickweed competes with triticale in a farm field in Tulare County.
had already been confirmed in at least five other states and several other countries. “I was surprised it had taken so long for us in California given that it has occurred in so many other wheat-producing areas in North America,” he said. “It wasn’t wel- come, but it was expected.” Clark pointed to changing field crop production trends as a possible reason for resistance development. During at least the past 10 years, double-cropping that involved winter small grains followed by dairy forage has become popular in the southern San Joaquin Valley. With that in mind, growers were limited in the herbicides they could use in small
grains because some carried plant-back restrictions, which required lengthy wait- ing periods before corn could be planted. Because many ALS herbicides do not have those requirements and can be used on a wide variety of crops without any waiting, they were used widely, he added. “There’s continually less crop diversi- ty on the forage ground, so there’s been more intensive use on dairy ground of herbicides, and ALS inhibitors in particu- lar,” Clark said. “It’s a ubiquitous group of chemicals that are used on just about every crop. It’s possible to go from one crop to another and still have an ALS on one crop to the next.”
Having the safety talk with your kids isn’t just important— it’s essential. In 2023, 19% of deaths in off-highway vehicle (OHV) accidents were children under 16, with only 2% wearing helmets. 1 This alarming statistic prompted Nationwide to launch the Let’s Champion Rider Safety SM campaign, providing tips and resources for effective safety discussions and protection for young riders. Let’s work together to help save lives and teach everyone to ride like a champion.
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1 U.S. Consumer Product Safety Commission.
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July 10, 2024 Ag Alert 11
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