Brassica Pests & Diseases
Brassicas (crucifers) have plenty of insect and disease problems, but most of them can be kept from harming the crop with a few basic habits. Prevention usually combines these practices:
- Rotating crops properly
- Sowing only clean, disease-free seed
- Starting transplants rather than sowing direct
- Using row covers as a physical barrier
Below is more detail on using these practices to cut down pest and disease pressure.
What is Eating My Brassicas? Common Insect Pests of Brassicas
Flea beetle feeding on a brassica seedling.
Photo courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org.
Flea beetles
Flea beetles attack brassicas at every stage, but they favor the soft leaves of just-emerged seedlings and young transplants. Left unchecked, they can wipe out seedlings and transplants fast. Their feeding riddles the leaves with tiny shot holes. Two species are the main brassica pests: the crucifer flea beetle (Phyllotreta cruciferae) and the striped flea beetle (Phyllotreta striolata).
- More information: U. of Mass., Amherst: Flea Beetle, Brassica
Cabbage "worms"
Imported cabbageworm (Pieris rapae (Linnaeus))
Photo courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org.
"Cabbage worms" is a catch-all name for the caterpillars of several moths and butterflies.
- Cabbage looper (Trichoplusia ni)
- Imported cabbageworm (Pieris rapae), the larva of the small white (cabbage white) butterfly
- Diamondback moth (Plutella xylostella), often shortened to DBM
All of them chew brassica leaves, and in large numbers they cause heavy damage. Look for green caterpillars, checking the tops and undersides of leaves.
- More information: U. of Mass., Amherst: Imported Cabbageworm
Aphids
Cabbage aphids on a Brussels sprout plant.
Photo courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org.
Several aphid species attack brassicas. They suck sap from leaves and growing tips, leaving leaves stunted and distorted, and they excrete a sugary waste called honeydew on which black sooty mold grows, leaving plants dirty and sticky.
Aphids often hitch a ride on greenhouse transplants and then build up rapidly once plants are in the field. They are particularly troublesome under row cover, which shelters them from lady beetles, parasitic wasps and other natural enemies, and the warmer air underneath speeds their reproduction.
Heavy infestations can cost part or all of the crop.
Swede Midge
Swede Midge
Photo courtesy of Susan Ellis, USDA APHIS PPQ, Bugwood.org.
Swede midge, originally from Europe and southwest Asia, is now established in parts of the northeastern U.S. and eastern Canada. Its larvae feed in the growing points of brassicas, especially broccoli, cauliflower, collards and kohlrabi, leaving plants twisted and heads deformed or missing.
- More information: U. of Mass., Amherst: Brassicas, Swede Midge
How can these pests be avoided?
Row cover in use
Crop rotation. Brassica pests cause fewer problems where crops are rotated on a cycle of at least three years. Farmers should rotate fields, and gardeners should rotate beds or rows, so brassicas return to the same spot no more than once every three years.
Transplants. Tiny direct-sown seedlings are the most vulnerable to pests, so give plants a head start by setting out transplants.
Row covers. Installing row covers pays off as protection against every one of these insects. Covers keep pests out physically, so they must go on before the pests find the crop. Put them on right after you direct-seed or transplant, and seal the edges with pegs or soil so nothing can get underneath. If you lift the cover to weed, put it back right away.
Our suggestion: Agribon+ AG-15 or ProtekNet for insect exclusion. Row cover can be supported on wire hoops or simply laid over the plants. Hoops usually aren't necessary, but in very windy spots they keep the fabric from whipping around and injuring seedlings. Leave the cover on until plants start pressing against it; bigger plants tolerate insect feeding much better.
- For more about row covers, see Protect Your Crops.
Weed control. Keep weeds down around the planting in spring, particularly mustard-family weeds, which can host insects that later move to your crop.
Common Diseases of Brassicas
A number of bacterial and fungal diseases are worth knowing. University and extension resources, such as those listed below, explain their causes and how to manage them. For more on crucifer diseases, we also suggest Cornell University Vegetable Disease Factsheets.
Bacterial Pathogens
Cabbage row badly damaged by black rot.
Photo courtesy of Dan Egel, Purdue University.
- Black rot of crucifers (Xanthomonas campestris pv. campestris)
This bacterial disease usually arrives on infected seed or transplants. Look for yellow, V-shaped lesions starting at leaf edges. On Brussels sprouts, small developing sprouts may turn black and die on the stalk. It can ruin a crop and survive in soil for years, so preventing it is far easier than dealing with it.
Rotating crops and planting only seed lots that tested negative for black rot are the best ways to avoid it. Hensley’s tests every seed lot of broccoli, cabbage, cauliflower, collards, Brussels sprouts, kale, Kalettes, and kohlrabi are tested and sold only when negative for black rot.
You can also grow varieties with black rot resistance.
Fungal Pathogens
Some varieties also resist fungal diseases. Shown above is 'Bilko', which carries resistance to club root and Fusarium yellows resistance.
Club root of crucifers (Plasmodiophora brassicae)
Club root makes roots swell and twist, which restricts water uptake, and the leaves yellow and wilt. It often goes unnoticed because the tops may look fine until the plants come under water stress. Infected plants yield less or die before producing.
Like black rot, club root can survive in soil for many years. Good rotation is the best prevention.
Blackleg of cabbage and other crucifers (Phoma lingam; sexual stage Leptosphaeria maculans)
Fusarium yellows of cabbage and its relatives (Fusarium oxysporum f. sp. conglutinans)
How can these diseases be avoided?
Rotate. Where possible, grow brassicas in the same ground only once every three or four years. These diseases mostly show up where rotation has been neglected. Your local Cooperative Extension office can give region-specific advice.
Start with good seed. Every seed lot Hensley’s sells has tested negative for black rot.
If problems show up. Contact us, or check with your crop advisor or extension agent.
