Pests & Diseases Affecting Brussels Sprouts
Cabbage aphids: these insects are most troublesome in hot, dry summers following mild winters. The grey aphids heavily infest the undersides of the leaves of sprouts, which then become curled, blistered and discoloured. Because the eggs ofaphids overwinter on the stumps of old brassicas, the best preventive measure is to dig up and either burn or the stems immediately after harvesting. Keep the plants well supplied with water, and for severe attacks, remove the worst affected leaves and sprouts and spray the remainder with derris, bioresmethrin or malathion.
Cabbage root fly: these flies are most active from mid-spring through to early summer. The eggs are deposited on or just below thesurface next to the stems, and the emerging white legless maggots burrow into the stem, and also eat the roots underground. The first obvious symptoms of cabbage root fly infestation are grey-green, wilted leaves and slow-growing plants, smaller than the others. If pulled out of the ground, the roots will be found to contain the maggots, or they may be in the soil round the roots. A preventive measure is to treat the soil with diazinon granules at the time of planting; also treat the seedbed before sowing if an attack occurred the previous year. Surrounding the stems with a small square of tarred felt on the soil when planting will prevent egg laying. If an infestation occurs, remove and burn damaged plants, as well as the soil around the roots.
Cabbage whitefly: these tiny white moth-like insects feed on the undersides of leaves. They are usually a problem in warm weather, although in mild winters attacks occasionally occur. Besides weakening the plants, they exude honey-dew, which encourages the growth of sooty mould; in severe cases, young plants will be destroyed very quickly. Prevent serious damage by spraying with a resmethrin-based insecticide as soon as you them. Remove and burn all heavily infested leaves and spray the remainder with a soft soap solution, as an alternative to resmethrin. Flea beetle: if the leaves of theand young sprout plants are perforated with numerous small round holes, then there is probably an infestation of flea beetle. These small black insects are most active in fine weather in mid- to late spring but can also be found at intervals throughout the summer. The best preventive measure is to dust the seeds and soil with gamma-HCH; hoeing frequently round the young plants disturbs the soil and discourages the beetles from laying eggs.
Cutworms: these greyish-brown or grey caterpillars feed at night, when they eat through the stems, severing the plant at or slightly below ground level. If your garden is weed-free and well cultivated, you are less likely to have problems with this pest; if an infestation occurs, dust the soil with gamma-HCH.
Cabbage moth/cabbage white butterfly: the green or greyish-brown caterpillars of these insects feed on the leaf tissues of all brassicas, causing widespread damage. The cabbage moth caterpillars usually attack the inner leaves, where they are not easily reached by insecticide. The caterpillars of the butterfly eat the outer leaves, and also foul the remaining foliage with excrement. Both can do a great deal of damage and ruin the plants completely. As the eggs of both pests are laid on the leaves, remove and destroy any eggs you find on the plant. They will be small and round or conical in shape, light-coloured and laid in batches. If caterpillars do manage to hatch out, hand pick them off in a mild infestation; otherwise, dust or spray the infested plants with derris or a salt solution, 60 g (2 oz) in 4.5 L (1 gal) of water.
Gall weevil: this occasionally attacks Brussels sprouts, although it is more likely on the brassica root crops such as. The roots form round hollow swellings in which white maggots will be found, and young plants will be stunted. Remove and destroy badly infected plants; remove only the galls from the remainder.
Club root (finger and toe): this is the most serious disease the home gardener is likely to encounter; it affects all members of the brassica family. It is caused by a fungus in the soil which infects the roots; the symptoms above ground are bluish and wilting leaves, and stunted, slow-growing plants. The roots, when dug up, will be swollen and distorted, black, and rotting, often with an unpleasant odour. Club root is often associated with heavy, badly-drained soils, so a good precaution is to correct any drainage problems before planting. Excessively acid soils also tend to encourage this disease, so correct the soil acidity by liming so that the pH is neutral or slightly alkaline. A further precaution is to sprinkle calomel dust (using pure calomel, rather than the 4% contained in many proprietary brands) before sowing at the rate of 30 g per 1.5 m (1 oz per 5’) run. Alternatively, sow the seed in sterilized soil outdoors, or in containers, or in sterilized soil in individual pots. When transplanting, dip the roots in a fungicidal solution of either 60 g (2 oz) pure calomel, or 15 g (½ oz) of benomyl or thiophanate-methyl to every 0.5 L (1 pt) of water. Because the fungus is soil-borne, if an infection occurs, the site must not be used for brassicas for at least five years—the spores have been known to survive 20 years. All infected plants must be lifted completely and burned immediately.
Wirestem: this fungal infection attacks young plants, causing the base of the stem to become constricted, turn brown and wither. If the plants are not killed outright, they remain stunted and will never fully recover. Seeds or seedbeds dusted with quintozene or thiram or watered with cheshunt compound will usually be free of attacks.
Downy mildew: the symptoms of this fungal infection are white patches on the undersides of the leaves, and yellow speckling on the upper side, followed by wilting. It is often found on seedlings and young plants under glass, or on the outside of the young buttons later in the season. Spraying with zineb will help control downy mildew in mild cases; destroy any plants or buttons severely infected.
Ringspot; a fungal infection, ring spot attacks older plants, and produces round, light brown spots, about 1.3 cm (%”) in diameter on the outer and lower leaves. Infected leaves eventually turn completely yellow and wither. Remove and destroy all infected leaves, and minimize further damage with a light dressing of potash fertilizer.
Grey mould (Botrytis cinerea): this is sometimes a trouble on Brussels sprouts. Infected sprouts become soft, and eventually covered with grey furry mould. Infection occurs through a broken main leaf stalk just below the sprout, and is more likely where too much nitrogen has been supplied. Removal of the affected parts is all that need be done.
Canker: Brussels sprouts may be attacked by this fungal disease, which produces brown or purple spots and cankers on the stems, and results in stunting and sometimes total wilt. Destroy affected plants and do not plant again in the same site.