Of all cabbage-family plants, broccoli is often the least affected by pests
, and fall crops tend to have fewer problems than spring ones. Possible pests include aphids, cabbage loopers, imported cabbageworms, cabbage maggots, cutworms, and flea beetles.
Other pests include slugs, mites, and harlequin bugs. Slugs chew holes in plant leaves; see the Slugs and Snails entry for controls. Mites are tiny red or black pests; their feeding causes yellow stippling on the leaves. Knock them off the plant with a strong blast of water, or spray with insecticidal soap. Control harlequin bugs—black insects with red markings—by hand picking or applying soap spray.
are seldom a problem. Black leg produces dark spots on leaves and stems. Symptoms of black rot include yellowing leaves and dark, foul-smelling veins. Prevent these diseases with good cultivation and crop rotation. In case of club root, which shows up as weak, yellowed plants with deformed roots, destroy the infected plants. Plant your next crop in another part of the garden, and before planting, apply lime to boost soil pH to about 7.0.
Leaf spot shows up as enlarging, water-soaked spots that turn brown or purplish gray. Fusarium wilt, also known as yellows, causes lower leaves to turn yellow and drop off and makes broccoli heads stunted and bitter. Destroy plants afflicted with leaf spot or Fusarium wilt to prevent these diseases from spreading.
Harvesting: Harvest before the florets start to open and turn yellow. Cut just below the point where the stems begin to separate. Once you’ve harvested the main head, tender side shoots will form in the leaf axils all along the lower stalk. Keep cutting, and broccoli will keep producing until the weather turns too hot or too cold. Can, freeze, or pickle broccoli, or keep it refrigerated for up to 2 weeks. Green cabbage loopers and imported cabbageworms often go unnoticed on harvested heads and can end up in your cooked broccoli. To prevent this, drive them out by soaking the heads in warm water with a little vinegar added for 15 minutes before cooking.