As temperatures rise across California, specialty crop growers are entering a critical period for managing Lepidopteran pests. Allison Walston, Senior Product Development Manager for Insecticides with Valent U.S.A., says early intervention is essential for controlling destructive Lepidopteran or caterpillar pests before they move inside crops where they become much harder to manage.
Lepidopteran pests include moths and butterflies, but the damaging stage is the larval stage—commonly referred to as worms or caterpillars. These pests feed aggressively on crops ranging from tree nuts and vegetables to berries, grapes, and citrus.
Internal Feeders Pose Major Challenges
Some of the most problematic species are internal feeders such as navel orangeworm in tree nuts and diamondback moth in vegetables. Walston explained that these pests often feed briefly on the outside of fruit, nuts, or vegetables before burrowing inside, where insecticides become far less effective.
Diamondback moths (DBM) are particularly difficult because of their ability to develop resistance quickly. The combination of multiple DBM generations throughout the season and limited feeding on treated surfaces contribute to resistance pressure.
How Bt Insecticides Work
One important tool for managing these pests is Bt, or Bacillus thuringiensis, a naturally occurring soil bacterium. Walston noted that not all Bt products are the same, as different subspecies target different insect groups. Products designed for Lepidopteran pests work when caterpillars ingest treated plant material.
Once consumed, proteins, the active ingredients, within the Bt disrupt the insect’s digestive system, it stops feeding, and eventually will kill the pest. NOTE: Because the caterpillar must ingest the product, thorough spray coverage is critical.
Timing Makes the Difference
Walston emphasized that Bt products work best on very young larvae shortly after egg hatch. In almonds and pistachios, she recommends applying DiPel® DF Biological Insecticide Dry Flowable approximately 7–14 days before hull split to ensure nuts are protected when navel orangeworm eggs hatch.
In grapes, berries, and citrus, monitoring adult moth activity and using degree-day models can help growers properly time applications before pests move into protected areas like curled leaves or fruit clusters.
For more information, visit Valent.com/Bts.
Always read and follow label directions.