What are the common pests and diseases that could affect broccoli?
Cabbage loopers - Cabbage loopers are ravenous leaf consumers. These are small, smooth, and green caterpillars with thin white lines on the back and side.
a. Management: For small-scale broccoli crops with a light infestation, hand-picking individual caterpillars is the best solution. For heavier infestations, apply Bacillus thuringiensis (Bt) when the caterpillars are still small. For nearly complete exclusion, floating row covers can also be used to prevent the adult looper moths and other species from laying eggs.
Aphids - Two species of aphids, turnip aphids, and cabbage aphids, are commonly found on brassicas. As sap-sucking insects, large aphid infestations can kill young plants or significantly retard growth on mature plants.
a. Management: The best organic treatment is spraying the plants with soapy water, followed by clear water. An alternative is using insecticidal soaps. To lower the population, remove old vegetation and stalks from the garden after the harvest and encourage beneficial insects, like ladybird beetles or green lacewings.
Harlequin bug - The pretty orange-and-black coloration belies the destructive nature of these shield-shaped, sap-sucking insects that can wipe out an entire crop when left uncontrolled. Symptoms include visible adult insects and the wilting of leaves that turn brown and quickly die.
a. Management: Hand-picking harlequin bugs early in the season will help limit population growth. Best organic control is cultivating the ground in fall and early spring. Another method is planting a trap crop. Floating row covers are also effective.
Downy mildew - It is caused by the fungus Peronospora parasitica and exacerbated by moist growing conditions. External signs of downy mildew include a gray mold on the lower surface of the leaves, while the upper leaves will often show signs of yellowing and will turn brown and die.
a. Management: Grow a broccoli cultivar resistant to downy mildew (Green Magic or Windsor). Cultural practices are also essential to fight downy mildew, such as providing adequate spacing between plants, watering at the base of the plant, removing plant debris after harvest, and crop rotation.
Clubroot - Clubroot is a fungal infection that causes the root system to grow into poorly developed misshapen knots, which will eventually crack and allow secondary rot diseases to set in. This will either kill young plants or prevent mature plants from developing proper heads.
a. Management: Avoid planting any brassica crops, including cauliflower, cabbage, and kale, in the area until the disease has disappeared. Avoid transfer of spores to new plots via shoes, tools, or irrigation water. Fortunately, clubroot can be prevented with regular crop rotation and amending the soil with lime to keep the pH slightly above 7.2, which is generally too alkaline for clubroot.
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