Weeds Continued from Page 11
15 years there’s been a dramatic increase in resistance.” In January 2021, there were 522 unique cases of herbicide resistance reported globally, Becchetti said. A database in- cluding information on which weeds are resistant to which herbicides is available at weedscience.org. Two common California rangeland weeds—hairy fleabane andhorseweed— are showing resistance to themost widely used herbicide, glyphosate, the active in- gredient inRoundup, she said. Roundup resistance receives the most publicity, but some weeds are resistant to a long list of herbicides. “Some plants are not just resistant to onemethod the chemicals work on but to multiplemodes of action,” Becchetti said. “Thereareevensomeplants that canresist 11 different types of herbicides.” With fewer materials coming to mar- ket to build a rotation program, resis- tance management figures to become more challenging. “Back in the 1970s, there were a lot of chemicals being approved every year, but we have less and less coming on the market each year,” Becchetti said. “The toolbox is getting smaller, and we’re see- ing more resistance.” ( Bo b J o hn s o n i s a r e p o r t e r i n Monterey . He may be contacted at bjohn11135@gmail.com.)
goatgrass, Medusahead, smutgrass and yellowstarthistle, which infests 10million to 15million acres in the state and can set asmany as 30,000 seeds per squaremeter. “The thing youwant to pay attention to with yellowstarthistle is, of course, the yel- low flowers, but also these strong, straight stiff yellow spines that come out from the head under the flower,” advisedDevii Rao, UCCE livestock andnatural resources farm advisor inSanBenito,Monterey and Santa Cruz counties. It iseasy tomistakeasyellowstarthistlea lookalikeweednamed tocalote, or fornox- iouscousinsof starthistleknownasMaltese orMalta. “Tocalote similarly has the yellow flow- ers andhas thisbulbousportionunder the flower head but the spines coming off the tocalote thistle are not straight, they are curved slightly downward, and they are not yellow,” Rao said. She advised managing this persistent weed, which is toxic tohorses, witha com- bination of herbicides, grazing, mowing andburning. “The life stage of your yellow starthistle mightdeterminewhichherbicidewouldbe most effective,” Rao said. She advised spraying the herbicide Milestone from the seedling stage to the mid-rosette stage, withTransline as anop-
Invasive yellow starthistle cov- ers rangelands in Calaveras County.
tion for the late-rosette stage. And she said Roundupcanbeanoption“fromthebolting stagetothebeginningofthefloweringstage.” If the weed has yet to produce sharp spines, livestock other than horses can provide some control by grazing. “Grazing is another option to control starthistle,” Rao said. “You can graze with cattle, sheep or goats, but not horses be- cause it ispoisonous tohorses. The timing whenyouwant tograze iswhen theyellow starthistlehasbolted, but youdon’twant to wait until it has a spine sticking out. “ Another strategy that canwork ismow- ing, but timing is important sincemowing canmake the problemworse. “Mowing is also a tool you can use to control yellow starthistle,” Rao said. “You want to wait until 3% to 5% of your pop- ulation has flowers. It is critical tomow at the right time. If you mow too early, you
aremowing the grasses that competewith the starthistle. If youmowtoo late, youcan scatter the seeds.” If possible, burning two years ina row is another effective strategy. “Thetimingforprescribedburningis just when starthistle is starting to flower,” Rao said. “Twoor threeyears inarowisbest,but it isoftendifficult toget therightconditions.” Rao advised that these strategies are most effectivewhen twoormoremanage- ment practices are used in combination. Amongunwantedweeds, herbicide-re- sistant varieties are becoming more of a challenge in rangelands andpastures, just as they are in fields and orchards. “We sawthe first caseof herbicide resis- tance in 1957, and it really started to take off in the 1970s,” said Theresa Becchetti, UCCE farmadvisor in Stanislaus and San Joaquin counties. “It’s been about the last
Update your written COVID-19 prevention plan
Continue daily symptom checks for your employees
Train your workers on spread, symptoms, and company policies
Inform your workers of workplace exposures
Make COVID-19 safety part of your seasonal preparation.
Visit aghealth.ucdavis.edu/covid19/ag to protect your employees and your business.
12 Ag Alert November 3, 2021
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