Off all cabbage-family plants, broccoli is the least affected by pests, and fall crops have even fewer problems than spring ones. Possible pests include aphids, cabbage loopers, imported cabbage worms, cabbage maggots, cutworms, and flea beetles. Other pests inlcude slugs, mites, and harlequin bugs. Slugs chew holes in plant leaves. 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 handpicking or applying soap spray. Diseases 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 week, yellowed plants with deformed roots, boost the pH to 7.0 with lime. 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 Fursarium wilt to prevent these diseases from spreading.
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