‘Garbage’ pest can cause problems for grape growers ByDennis Pollock
Trap rates are hard to relate to infesta- tion, he said. Daane opened his Zoom address to the San Joaquin Valley Winegrowers Associat ion wi th a look at damage caused by the moth and talk of re- search into the variability in the extent of its damage. He described the raisin moth as a “garbage” pest of rotted fruit and stored products. It has a wide host range that
includes grapes, figs, mulberries, peach- es, nectarines, almonds, pomegranates and dried beans. For that reason, the pest can migrate from neighboring or- chards and fields. The moth overwinters under bark or in the soil as a late-stage larva instar or pre-pupa or pupa. ByMarch or April, the larvae pupate and emerge as adults in April or May. Old grapes on the ground can hold
populations over, Daane said. Raisinmoth feeding is associatedwith bunch rot, akin to that caused by omniv- orous leafroller feeding, he said. The extent of damage was studied in raisin grapes by UCCE Fresno County farmadvisor Stephen Vasquez, now a vi- ticulturist with Sun-Maid Growers. In studies from2009 to 2011, he found that dried-on-the vine harvesting expos- es drying fruit to raisin moths for a lon- ger period and in a more shaded area, resulting in higher raisin moth damage than conventional vineyard trellis sys- tems, in which grapes were dried on paper trays. Daane said themoth dies out in raisins placed on the ground. Vasquez also looked at cluster devel- opment, sanitation and location of vine- yards, and whether they were in proxim- ity to other hosts for the raisinmoth. Daane andGlennYokota, staff research associate at UC Berkeley, built on the Vasquez research starting in 2013, look- ing at pest movement and at organic and conventional farming. At that time, theyasked threequestions: Where are the moths coming from? How do conventional and organic practices compare?When are grapes susceptible? They found that grapes are most susceptible starting in June and con- tinuing into August. Of the three moth flights in a harvest season, treatment timing for the second flight and pop- ulation size in the third flight are most critical . Greatest damage to grapes came after veraison, during second and third flights. All the researchers found winegrapes and dried-on-the vine raisins may have a longer period when fruit are exposed to the raisinmoth. Daane and Yokota found the “gar- bage pest” in many crops with a wide seasonal variation. They were unable to connect bunch rot to raisin moth trap counts. Tightening bunches posed a problem in applying treatments that need contact with the pest, Daane said. “With cluster tightening, it’s hard to get insecticide to where the pests are feed- ing,” he said. Daane also discussed the vine mealy- bug and the damage it causes because it has more eggs and annual generations. He said it is important to look for bio- logical cues in the field, including ants early in the season. Other cues include honeydew and a wet appearance, along with dropped leaves. Pheromone traps can also help. He said synthetic sex pheromone, however, “pulls in” males from nearby vineyards. He reviewed seasonal changes in mealybug location. In the winter and early spr ing, they reside pr imar i ly on the trunk, canes and roots. In the spring, they are on the canes. In early summer, they move onto the leaves. In See PESTS, Page 11
Pheromone traps play a role in man- aging both vine mealybugs and raisin moths in vineyards, but trap data should be considered chiefly as “a historical re- cord of counts and damage.” That’s the advice of Kent Daane, a University of California Cooperative Extension specialist at the Kearney Agricultural Research and Education Center in Parlier.
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10 Ag Alert April 28, 2021
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