The brassica family is full of delicious vegetables. There are so many, in fact, that it is sometimes hard to keep track of all of the members of the brassica family. Luckily, there are two things that all brassica share that remind us of their family heritage - pests and diseases.
Common Brassica Pests
There are three main brassica pests that plague gardeners: flea beetles, aphids, and cabbage worms. While other pests certainly sample a cauliflower from time to time, this trio has it in for your harvest.
Flea beetles are small beetles that hop around like fleas, giving them their name. Two varieties target the brassica family: the Crucifer flea beetle and the Striped flea beetle. Both types infest the foliage of brassicas, eating away at the leaves and damaging the plant.
Cabbage worms munch their way through brassica leaves and the heads of cole crops like cabbage. The damage from their feeding and their feces renders crops unmarketable, not to mention unpalatable for the kitchen gardener. There are three main types of cabbage worms that brassica gardeners need to worry about. Imported cabbage worms are slow moving, green and hairy caterpillars that eat away at your brassicas with a voracious appetite. Cabbage looper moth larvae are pale green with white lines on each side. They move in the looping motion that gives them their name and grow to 1-1/2 inches long. Diamondback moth caterpillars are much smaller than imported cabbage worms and cabbage loopers. These caterpillars only reach 1/3 of an inch in length and are light green in color with tapered ends, but cause considerable damage despite their size.
Aphids are particularly fond of brassicas. The Cabbage Aphid is a greenish gray aphid that feeds primarily on members of the brassica family, especially cabbages. Aphids typically form dense colonies inside cabbage heads, making them difficult to reach with pesticide applications. Large infestations can stunt the plant's growth and make them unsaleable. Lady bugs and parasitic wasps feed on aphids, making them a good natural solution to an aphid infestation.
The best way to deal with pests is prevention. Crop rotation prevents pests from overwintering on crops or in the soil, not to mention the immune system benefits of rotation, which help develop stronger, more resistant plants. Crop rotation is less effective if you do not also manage weed populations. There are several weeds in the brassica family, including wild mustard. These weeds offer brassica pests a place to nest. Eliminating weeds from your garden will help reduce the chances of other plants hosting brassica pests.
Young plants are especially vulnerable to certain pests. Give your plants a head start by transplanting them. Transplanting gives brassicas a jump start on weeds and pests and helps them develop stronger root systems, but even transplants are susceptible to pests. Row cover can help prevent insects like flea beetles from establishing a hold on your brassica beds. Floating row cover works very well for brassicas and comes in lightweight grades ideal for hot weather.
Common Brassica Diseases
Brassicas have their fair share of diseases, including bacterial and fungal pathogens. The most common are black rot, club root, blackleg, and fusarium wilt.
Black rot is a nasty bacterial pathogen that is usually the result of infected seeds. Unfortunately for the gardener, black rot persists in the soil for many years, so it is important to always purchase seeds that have been tested for the pathogen. The bacteria forms yellow, v-shaped lesions on the leaves and ultimately destroys the crop.
Club Root is a fungal disease that affects the Cruciferae family (cabbage, cauliflower, broccoli, Brussels sprouts, and Chinese cabbage). It is caused by the fungus Plasmodiophora brassicae, which is soilborne, and causes malformation of the roots of plants. Club root can take a while to show symptoms. When young plants are affected, the plants become stunted and then die. Older plants fail to form heads or marketable growth, and when pulled from the soil the roots appear swollen and distorted.
Blackleg strikes in warm, wet seasons. The fungus Phoma lingam causes pale gray lesions in seedlings, ultimately killing them and establishing itself in the seedbed, where it then affects older plants. Blackleg creates light brown, sunken lesions on stems which extend gradually upward until the plant wilts and dies. The roots are gradually destroyed as well, and light brown or grayish spots form on the leaves. Surviving heads might appear healthy when harvested, but develop black lesions in storage. This fungus can survive in the soil for three to five years in between crops.
Fusarium wilt, also known as yellows of cabbage, is a fungal disease that gradually turns the leaves of the plant yellow. It begins with the lower leaves and works its way up, eventually killing the plant. Plants may recover if temperatures fall below 75 degrees after infection.
Vegetable diseases typically don't have cures. Prevention is the best approach for dealing with brassica diseases. Crop rotation and fertility are key to disease avoidance. Growing brassicas on the same ground only every third or fourth year may prevent contagion from contaminated soils, and healthy plants grown in fertile, well-drained soil are less susceptible to disease. There are disease resistant cultivars available for problematic areas, and you should always buy seed that has been tested for black rot.
If you practice all of these pest and disease prevention methods but still have trouble, it might be time to consult with a local expert like an extension agent.