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Common Insect Pests of Brassica Crops
- 1. Nick Volesky Common Insect Pests of Brassica Crops in Utah
- 2. Overview of Insect Pests of Brassicas Family Common Name Scientific Name Damaging Life Stage Aphididae Cabbage Aphid Brevicoryne brassicae nymph, adult Noctuidae Cabbage Looper Trichoplusia ni larva Plutellidae Diamondback Moth Plutella xylostella larva Chrysomelidae Flea Beetles adult Pieridae Imported Cabbageworm Pieris rapae larva *Mollusk Slugs Gastropoda spp. young, adult Snails young, adult Anthomyiidae Cabbage Maggot Delia radicum larva (maggot) *not insects
- 3. Cabbage Aphids (Brevicoryne brassicae) Description • pear-shaped, 2 tail-pipe like structures (cornicles) • grey-green • “waxy” secretion covering • 1.8 to 2.5 mm long Life History • overwinter as eggs on crop debris • winged aphids form when colonies become to crowded • Feed on buds, leaves, flowers, and stems of brassica crops
- 4. Cabbage Aphid Management • scout frequently • monitor with yellow sticky traps • avoid excessive fertilization • use mulches and row covers • remove/destroy plant debris • maintain healthy, vigorous plants • pesticides (e.g. pyrethrins, mineral oils, plant- based oils, azadirachtin, Beauveria bassiana, insecticidal soap) • encourage natural enemies (e.g. lady beetles, syrphid flies, lacewings, and parasitic wasps)
- 5. Diamondback Moth (Plutella xylostella) Adult Moths • crepuscular • grey/brown, white diamonds on back • narrow, 18 mm wingspan Eggs • round, white/yellow • laid singly and in clusters Larvae • green/grey (no stripes), smooth with sparse hairs • 12 mm long • wiggles vigorously • Damage: chews holes in leaves (possible defoliation), tunnels into heads, contaminates crop with bodies and fecal material Pupa • loose mesh cocoon on leaves Life History • 4-6 generations / year • resident in southern Utah, migratory in northern • Overwinters as adult on trash and debris in and around crop fields
- 6. Imported Cabbageworm (Pieris rapae) Adult Butterfly • active during the day • white, brown spots (females-2, males-1) • 50 mm wingspan Eggs • bullet-shaped, yellow • laid singly Larvae • green (thin yellow stripe), short dense hairs (fuzzy) • 31 mm long • slow, sluggish • Damage: chews holes in leaves (possible defoliation), tunnels into heads, contaminates crop with bodies and fecal material Pupa • naked chrysalis Life History • 3-4 generations / year • resident in Utah • overwinters on leaves and debris
- 7. Cabbage Looper (Trichoplusia ni) Adult Moth • semi nocturnal • grey/brown, silver “8” • 38 mm wingspan Eggs • dome-shaped, yellow/white • laid singly and in clusters Larvae • pale green (thin white stripes), smooth with sparse hairs • 38 mm long • Arches body into loop • Damage: chews holes in leaves (possible defoliation), tunnels into heads, contaminates crop with bodies and fecal material Pupa • Fuzzy cocoon Life History • 1-3 generations / year • migratory in Utah, some resident • overwinters on plant debris and soil
- 8. Cabbage Looper, Diamondback Moth, and Imported Cabbageworm Management • pheromone traps can be used to monitor adult populations • scout crops regularly for eggs, larvae, ad feeding damage • interplant brassica crops with unrelated plants to encourage natural predators and larval parasitism • use row covers to exclude egg-laying by adults
- 9. Cabbage Looper, Diamondback Moth, and Imported Cabbageworm Management • hand remove and destroy larva • encourage natural predators such as parasitic wasps (many are host specific and parasitize eggs and larvae) • remove plant debris at the end of the growing season to eliminate overwintering sites • pesticides (e.g. azadirachtin, plant-based oils, Beauveria bassiana, Bacilius thuringiensis, spnosad, pyrethrins)
- 10. Flea Beetles • Three-spotted Flea Beetle (Disonycha triangularis) Crucifer Flea Beetle (Phyllotreta cruciferae) Western Black Flea Beetle (Phyllotreta pusilla) Hop Flea Beetle (Psylliodes punctulata) Pale-striped Flea Beetle (Systena blanda) Elongate Flea Beetle (Systena elongate) Adult • 1.7 - 4.2 mm long • enlarged hind legs for jumping • range in color (black, brown, green, metallic blue, etc) Larva • very small • white body, brown head Life History • Adults become active mid-late spring • 2-3 generations per year • overwinter as adults in protected plant residue, dirt clods, weeds along field borders and ditch banks • chew holes or pits into leaves and cotyledons
- 11. Flea Beetle Management • visually scout plants for signs and symptoms • use yellow sticky traps to monitor populations • control weeds around planting sites. • plant trap crops that are highly attractive to flea beetles • use companion crops and living or non-living mulches to obscure host plants from the flea beetles (green onions, dill, marigold, etc.) • use row covers • eliminate old crop debris and other surface trash • natural Predators: parasitic wasp Microctonus vittatae, lacewing larvae, big eyed bugs, damsel bugs, etc. • chemical control is challenging with flea beetles, as they’re highly mobile
- 12. • mollusks • slugs (no shell), snail (shell) • glide with a long, flat, muscular organ called a foot (mucus/slime secreted) • eggs are small, white, laid in clusters • hermaphrodites (neither male or female) • active during night and dark/cloudy clouds seek shelter during the day • need moisture to thrive, survive in dry conditions in protected areas • chew irregular holes in foliage Slugs and Snails
- 13. • remove boards, stones, and another other debris that might shelter slug/snails • rand remove slug/snails from host crops during peak activity hours • protect crops with barriers like copper or diatomaceous earth (not effective when wet) • use bait stations to trap slugs (effective products include metaldehyde or iron phosphate) • encourage natural predations Slug and Snail Management
- 14. Cabbage Maggot (Delia radicum) Adult Fly • dark grey Eggs • white/, oval shaped • laid on soil near host plant stem Larvae • small, white maggot Life History • adults emerge in early May • small maggots hatch 4-10 days (burrow into stems) • larvae feed on roots of brassica crops, sometimes tunneling • damage can lead to plant wilt and potential pathogen infection
- 15. Cabbage Maggot Management • monitor during cool, wet spring weather • rotate crops • immediately after harvest, till/disc under crop residue • if several sections are infested, remove plants and replant • exclude adults with row covers
- 16. Contact Nick Volesky (Vegetable IPM Associate) nick.volesky@usu.edu (435) 797-0319 USU Extension – Utah Pests @utah_pests
Editor's Notes
- Hey Everyone! My name is Nick Volesky, I work for our USU Extension Integrated Pest Management Program. I’m the face behind the seasonal Vegetable Pest Advisories sent out to Utah’s farmers and homeowners. In my job, I strive to provide educational outreach to growers through publications, videos, experiment trials, and workshops. I enjoy collaborating with farmers throughout Utah and working with them to effectively solve their vegetable pest problems. For this talk, we’re going to discuss some common insect pests that will attack your brassica crops. These obviously include your cabbage, broccoli, cauliflower, kale, kohlrabi, Brussels’ sprouts, and other mustard greens.
- Unfortunately, these brassica crops get the bad reputation of being “buggy” or “wormy”. Which is true, because they are susceptible to quite a few pests. But we shouldn’t let this deter us from growing this family of crops. I’m going to teach you guys are how to identify, monitor, and manage these problems for a successful harvest. Here, I have listed some of the most common pests we come across in Utah brassica production. As I discuss each one, you'll see the pattern that most of these are managed relatively the same way.
- • Cabbage are aphids are vey small (about 2 mm), soft-bodied, pear-shaped insects with two tailpipe-like appendages called “cornicles.” Cornicles are unique to aphids, and excrete defensive compounds (waxes and alarm pheromones). • Gray to green in color with a grayish waxy covering, which is a secretion they give off • They exclusively love to eat all brassica crops, especially Brussel’s sprouts. • Unlike most other aphid species Cabbage aphids do not require an alternation of host plants. In northern Utah, they overwinter as eggs on crop debris, and in southern Utah, they may overwinter as adults. In spring, eggs hatch to all females, and reproduction occurs as noted above on mustard family plants. Winged aphids form when colonies become too crowded, resulting in dispersal to other brassica hosts. Cool fall temperatures cause sexual mating and egg-laying for overwintering. • Aphids feed on buds, leaves, flowers, stems, and fruits with piercing-sucking mouthparts. Feeding causes plant structures to become stunted, yellowed, and distorted. Curled leaves create a micro-environment that protects aphids from predators, insecticides, and the environment
- • Scout frequently. Aphid colonies can grow quickly, it is important to scout plants at least twice a week, especially when they are young and growing rapidly. Look on the underside of leaves where aphids congregate, and look for ant activity. Ants like to feed on the aphid honeydew (secretion) • Use yellow sticky traps to monitor aphid populations. Yellow sticky cards will attract winged aphids. • Manage nitrogen levels. High levels of nitrogen fertilizers tend to encourage aphid reproduction. Use several, staggered applications of lower concentrations of nitrogen rather than a single high dose. Also, use delayed-release formulations. • Use row covers to physically exclude adult winged aphids from accessing your plants. • Use reflective mulches. Reflective silver or aluminum mulches can repel winged aphids. • Inspect transplants for aphids before planting; dispose of infested plants. • Only use insecticide applications when needed. Rotate among different insecticide classes between applications as aphids are prone to developing resistance. Organic insecticides include insecticidal soap and oils. When sprayed, it will kill aphids on contact by physical means (suffocation and disruption of waxes in the exterior cuticle), so thorough coverage is essential for good efficacy. • Encourage natural enemies. Plant strips of yarrow, alyssum, herbs and other plants with small, attractive flowers that provide nectar and pollen for beneficial insects.
- • Now we’re going to discuss three caterpillar pests that affect our brassica crops. I’ll discuss each of them specifically first, then we’ll talk about management for all of them as a whole. (Read Adult Moths) Crepuscular means active during the twilight hours (Read Eggs) (Read Larvae) (Read Damage) (Read Pupa) (Read Life History)
- • Pheromone traps can be used to monitor adult populations of the diamondback moth and cabbage looper. Traps indicate when adults have arrived in an area and give an indication of their relative numbers. Experience with pheromone trapping for diamondback moth in northern Utah revealed that moth numbers can be very high in areas with commercial vegetable operations. • Scout plantings for eggs and larvae on the undersides of leaves, especially on the innermost leaves. Feeding damage and excrement are also signs of an infestation. Examine at least 10% of the crop, checking random interior and edge areas. Also look for white butterflies (adults of imported cabbageworm) flying during the day among plants. • Interplant. When brassica crops are inter-planted with unrelated plants, larval populations tend to be lower, and larval parasitism and predation by beneficial wasps increase. Predatory and parasitic wasps are attracted to the varied resources provided by a diversity of plants, including nectar and pollen in flowers, and diverse insect prey • Use row covers to prevent oviposition (egg-laying) by adults. Place row covers over plants, or over metal hoops for support, just after planting or transplanting. Ensure that the edges of the row cover are securely buried in the soil along the crop row.
- • Hand remove and destroy larvae (really only effective in smaller operations with a lot of labor) • encourage natural predators such as parasitic wasps (many are host specific and parasitize eggs and larvae) • remove plant debris at the end of the growing season to eliminate overwintering sites • pesticides: pyrethrins, azadirachtins, spnisoad, bacillus thuringiensis, beauveria bassiana, chromobacterium subtsugae, plant based oils
- • Flea beetles are common and problematic in Utah • Here is a list of some species that you might find on your brassica crops (Read Adults) (Read Larva) (Read Life History)