CATERPILLARS are soft bodied, segmented larvae, pale green or other colors, depending on the species. Most are the larvae of various species of moths; the imported cabbageworm is the larvae of the white cabbage butterfly. Cabbage loopers (Trichoplusia ni), codling moths (Cydia pomonella), and other caterpillars may become serious pests in both greenhouses and row crops systems if their numbers are allowed to build up. Caterpillars feed on leaves and when they are numerous can eat relatively large amounts of leaf area and damage fruit.
LIFE CYCLE: The adult female moths lay eggs on plant leaves. The young larvae do little damage at first, but as they grow to full size they chew progressively larger holes in leaves.
CONTROL: Caterpillar control is primarily needed in controlled environments like greenhouses and outdoor monocrops that lack biodiversity and create a biological vacuum. In other more diverse outdoor production areas, birds and naturally occurring predator insects will help control caterpillar populations. In these cases, we may not want to completely eradicate caterpillars because they (and the moths and butterflies they become) are crucial as pollinators and food sources for other native species. For more information on native predators and promoting their habitats see this recent publication by Washington State University.
Identifying the species of caterpillar you are seeing in your farming system is key. Try using traps to monitor and identify the pest – Sound Horticulture offers over 300 specific traps and lures, many of which are designed for the Lepidopteran family (see Lures & Traps). Knowing your crop system and the pest problems you experience annually will help you take preventative measures. Talk to your IPM advisor, know what pest you are coming after, and enhance habitats for natural predators. For more information on caterpillar identification, see the University of California’s Key to Identifying Caterpillars (search by crop).
If needed, there are several microbial pesticides that can be used early on (ask us about Dipel). At the first sign of pest moths in the vicinity, planned releases of Tricogramma spp.can be considered. Trichogramma spp. is a minute parasitic wasp that attacks the eggs of over 150 species of moths, including cabbage looper, codling moth, oriental fruit moth, twig borers and fruitworms (see Tricogramma spp.). Repeated applications of Tricogramma early on in the infection period will be necessary to build adequate populations of the parasitic wasp. Please discuss your strategy with Sound Horticulture and ask us for ideas about how to pre-hatch Tricogramma and increase efficacy.