Ag Alert July 17, 2024

New traps, sensors help identify, monitor grape pest By Bob Johnson

Development of a trap with an optical sensor has since made monitoring easier. The trap does not have a camera but can identify the western grapeleaf skeletonizer by how many times per second the wings move, Gispert said. A two-year study in Temecula and San Diego vineyards confirmed that pest counts from the modern and traditional delta traps are equivalent. “The counts in the two traps over the year match very well: The crucial thing is to be accurate at the very beginning,” Gispert said. Traps are best set up in vineyard loca- tions that have previously suffered skele- tonizer damage. Once growers know the beginning of the first flight, they can pre- dict with some confidence the timing of the second flight. “Our programs are oriented to focusing our effort on the most vulnerable stage of the pest, which is the larvae,” said Gispert, noting traps with optical sensors “reduced the labor and helped us make better decisions.” She said researchers have developed a model to track the life stages of the skele- tonizer. “This will tell you when to start looking for eggs after the first male is cap- tured,” she said. (Bob Johnson is a reporter in Monterey County. He may be contacted at bjohn11135@gmail.com.)

High-tech sticky traps equipped with optical sensors to identify pests are help- ing grape growers more precisely monitor the western grapeleaf skeletonizer, a moth whose larvae can cause severe fruit dam- age and yield reduction. Timing trap catches is crucial to ensure applications come in time to prevent a late-summer second seasonal flight of the skeletonizer from interfering with table grape and winegrape harvests. “We believe they have two generations, and the degree-day model tells us the second generation will start in mid-Au- gust,” said Carmen Gispert, University of California Cooperative Extension viticul- ture advisor in Riverside County. “We have the second generation right before you are ready to harvest. In two weeks, you have the risk of defoliation and losing the crop.” Gispert, who works on managing the grapeleaf skeletonizer, said the peak of the pest population is in June and July. During its nymph stage, the skeleton- izer feeds on grape leaves, leaving behind nothing but the skeleton and exposing fruit to sunburn. “We found the most dangerous stage of the pest was the larvae because they are very voracious,” Gispert said in May during a UC integrated pest management webinar, “Monitoring Western Grapeleaf

Larvae of the western grapeleaf skeletonizer feed on a grape leaf. Larval feeding skeletonizes grape leaves, resulting in loss of vine foliage, damage to fruit and reductions in crop yields.

Skeletonizer in Wine Grape Vineyards.” “They eat all the green parts of the leaves,” Gispert added. “I have seen vines that have been eaten by the larvae. They leave the skeleton.” The pest also grows poisonous spines that are a hazard to anyone working in the vines. “When the growers and workers move their arms through the canopy, they get stung, and it’s quite painful,” Gispert said. The skeletonizer was discovered in the San Diego area in 1941 and detected in back- yard grapes in Fresno 20 years later. Until a few years ago, it wasn’t a concern because a common virus—granuloses—and two

insect predators have kept it under control. Yet a few growers have suffered crop damage in recent years, including in the Temecula area of Riverside County, Gispert said. Traditional delta pheromone traps for skeletonizer are time-consuming to mon- itor, and they do not reveal when the pest was caught. “The traps are very labor intensive and inaccurate because I don’t know when the insects came in,” Gispert said. “The timing of the beginning of the flight is crucial to developing mechanisms to re- duce the population.”

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July 17, 2024 Ag Alert 13