Ag Alert December 2, 2020

Farmers look for strategies against potential new pest

lems for California tomato production. Researchers are also working to im- prove control strategies for the dia- mondback moth, which attacks a range of cole crops, and is particularly trouble- some because it maintains large popu- lations during a long season. The one-third-inch larval stage of this moth feeds on cole crops, and can cause significant damage if the larvae attack the growingpointsof youngplantsor findtheir way to the interior ofmorematurebrocco- li, cauliflower or cabbage. Another mysterious but potentially

destructive cole crop pest is the bagrada bug, an invasive stinkbug that injects en- zymes into cole crops before feeding on the leaves. One perplexing question about this pest is why it seems to appear in a new area, grow to large population levels and then decline in population for no appar- ent reason. This pattern of rise and decline was ex- perienced first in theYuma area andmore recently in the Salinas Valley, where the

ByBob Johnson A tiny, invasive insect that injects a tox- in that makes broccoli and other crucifer crops turnintounsightlymushthreatens to jointhepestsalreadyattackingCalifornia’s $1.3 billion cole crop production. The Swede midge, a fly less than a twelfthof an inch insize, hasalreadymade its way to fields in the northeastern U.S., across to theMidwest andup intoCanada, proving along the way it has the potential to cause significant damage in Central Coast cole crops. “They inject the crop with a toxin that makes the plants exude liquid that makes themeasier toeat,” said IanGrettenberger, University of California Cooperative Extension entomology specialist. “The Swede midge larvae cause scarring, dis- torted leaves and plants that don’t devel- opheads. They havemultiple generations every year, and they can persist in the soil for two years if they are buried.” While cole crop growers contend with bagrada bugs, which feed on seed- lings, and diamondback moths, which stunt growth by feeding on young plants, Grettenberger and other insect experts prepare for thepossibility theexistingpests will be joined by Swedemidges. Grettenberger is leading an effort fi- nanced by the California Department of Food and Agriculture to develop strat- egies for managing the midge before it reaches Central Coast fields that produce 90% of the nation’s domestically raised broccoli, 80%of the cauliflower andnear- ly half the cabbage. He presented farmers a report on what he has learned and the goals of future research during a webinar on pest man- agement, as UC Cooperative Extension moved its annual Salinas Valleymeetings to the internet. Cruciferous greens and broccoli are the most susceptible crops to the Swede midge, Grettenberger said, and there is an abundanceof potential hosts near Salinas Valley cole crops. “It’s shown this pest can develop on weeds, and we have a lot of crucifer- ous weeds,” he said. “This pest is not in California yet; it is in theNortheast, upper Midwest and up intoCanada.” Headvisedclosemonitoringandscout- ing as the tiny pest approaches California, and postharvest crop destruction to elim- inate one important food source. “Use of clean transplants can be helpful, because (the midges) fly well,” Grettenberger said. “A two- or three-year rotation out of crucifersmight also help, if you can do that.” Future work on Swede midges will in- clude establishing a quarantined popula- tion for study at a containment center on the UC Davis campus, pheromone mat- ing-disruptionstudies, theeffect of climate changes on the pest, and the potential for biological control. The Swede midge is just the latest of several recent insect pest threats to the

cole crop fields that are widespread in coastal counties. As part of the CDFA initiative to an- ticipate exotic insect pests before they reach California, Grettenberger is also working to prepare in advance for Tuta absoluta, a leafminer that has shown in other areas of the world that it has the potential to create serious prob-

See PESTS, Page 10

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December 2, 2020 Ag Alert 9