Pests Continued from Page 6 mealybug every 10 clusters, a $60 applica- tion would pencil out. “In late March, the crawlers move to- ward the new food, and this is your first op- portunity to control,” Haviland said. “Late May or early June is your second chance to control.” It is essential to avoid spreading mealy- bugs with the use of equipment. “On their own, a mealybug does not move more than a tree a year,” Haviland said. “Clean your equipment.” Navel orangeworms are the most im- portant pest in pistachios because they damage the nuts directly and increase the rate of the toxic fungus aflatoxin. Researchers say preliminary studies on the use of cover crops and sheep grazing are showing promise as additional tools to combat the emergence of this pest from mummies on the orchard floor. A combination of pheromone mating disruption, monitoring and selective pes- ticide applications can also reduce navel orangeworm to acceptable levels. Pheromones and sanitation go a long way toward managing the pest, but there are limits. “If you want to do a program with less spraying, you’re going to spend more money on monitoring,” said Joel Siegel, entomologist with the U.S. Department of Agriculture. “Spraying saves time.” “There was a correlation between cover crop biomass and reduced emergence of navel orangeworms from mummies on the orchard floor,” Wilson said. “We also found a reduction in mummies where sheep grazed. It was positive data, and we want to pursue this.” Bob Klein, manager of the California Pistachio Research Board, recalled the steps the industry has taken since he start- ed a quarter century ago. “We had 200 growers then and now we have 1,600,” Klein said. “One of the prob- lems was we didn’t have many research people to work on pistachios.” The meteoric growth of tree nuts this century means there is always a source of food for navel orangeworms. “When I got here, sanitation was known to be important for navel orangeworm,” Klein said. “Because of all the acres we have in almonds and pistachios, we have a landscape change in management.” Areawide control of navel orangeworm has become essential because different varieties of almonds and pistachios are vulnerable to damage at different times during the season. “Late August to October is when pis- tachios are typically vulnerable to navel orangeworms,” Siegel said. “You have to be really good on your damage in September because it’s going to double or triple in October.” For the nonpareil almonds, researchers said infestations in the spring are more likely to cause crop damage. (Bob Johnson is a reporter in Monterey County. He may be contacted at bjohn11135@gmail.com.)
Navel orangeworm, left, emerges from mummies on orchard floors to damage nut crops. The Carpophilus beetle, below, drills through shells and lays eggs in nuts.
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March 13, 2024 Ag Alert 7
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