Pests and Diseases Affecting Cauliflowers
Cauliflower is vulnerable to the sameas other members of the brassica family. Because many of these organisms build up in the over the years, it is absolutely necessary to rotate your crops. Ideally, brassicas must not be grown on the same site more than once in three years.
Cabbage root fly: these are particularly troublesome pests because there may be three generations of them in a single summer; deal with the first generation early in the season, before they have time to reproduce. Maggots emerge from eggs laid by female flies in the soil close to the young plants, from spring through to late summer. The maggots then burrow into the roots, and chew off the side roots. The above ground symptoms of infested plants are wilting, grey-green leaves, particularly in hot weather; the lower ones may turn yellow. Even if the plants do not collapse and die, they will remain stunted and produce inadequate curds.
If you mulch round thewith fresh , the female flies will be less likely to lay their eggs nearby; this is because they are attracted to the smell of brassicas, which the stronger smell of fresh compost will mask.
Organochlorines, such as gamma HCH, used to be recommended for the control of root fly. Unfortunately, certain strains have built up a natural resistance. Trichlorphon applied to the soil around young plants will give some protection.
Flea beetle: if yourhave leaves perforated with small round holes, then flea beetle is the probable cause. These tiny, dark blue or black pests, which hop when disturbed, and the resulting damage, are most often seen during fine weather in spring. The best preventive measure is to keep your garden clean and weed free. The beetles overwinter in rubbish heaps, wood piles or litter in hedge bottoms; the messier your garden the more encouragement you will be offering them. Because they feed on of the Cruciferae family, like shepherd’s purse and charlock, the absence of these weeds will be a considerable deterrent. Seeds dressed with gamma HCH are less vulnerable to attack; derris or gamma HCH used as a dust or spray will protect seedlings and young plants.
Cabbage caterpillars: these pests are the larval stage of thebutterfly and the cabbage moth. The cabbage butterfly lays its pointed yellow eggs in clusters on the leaves, usually on the underside. Once the green, yellow and black caterpillars emerge, they feed on the leaves and curds until the leaves are completely skeletonized and the curds destroyed. Whatever parts of the plant remain are fouled by the excrement. The caterpillars of the cabbage moth are light green to start with, hatching from rounded eggs, but change to dark green, brown or black as they mature. These are more difficult to control than the cabbage butterfly caterpillars, because they tunnel deeply into the curds, and are not discovered until it is too late.
If you see the large white cabbage butterflies and greyish-brown moths in your garden, check the leaves for egg clusters; crush any you find between your thumb and fingers. If the attack is mild, remove by hand and destroy any caterpillars you find. In severe cases, spray with derris or pyrethrum according to manufacturers’ instructions.
Birds: pigeons are the worst offenders; during winter months they completely strip the leaf tissue from the plants. Netting the plants from the time they germinate is the best solution, although birdscarers may give temporary protection.
Cabbage aphis: these pests are much worse in some years than others; warm dry springs and summers encourage them. The aphis, which are also called mealy aphis, are greyish-white and waxy looking. They feed on the underside of the leaves, which then become curled, discoloured and blistered. In bad cases young plants will be killed outright.
Cabbage aphis lays its eggs on old Brussels sprouts and cabbage stalks, and also feeds on these until the new spring brassicas appear. For this reason it is important to dig up the remains of brassica crops after harvesting and burn them. Do not put them on the compost heap. If, in spite of this precaution, the aphis does appear, remove and burn infested leaves at once; do not allow the aphis population to build up. In severe, cases, spray with malathion, derris or bioresmethrin. The first spray may not be completely successful because the aphis are sometimes hidden in the leaves and curds where the insecticides cannot reach. Spray again as necessary.
Cabbage gall weevil: gall weevil and club root have similar symptoms, and it is sometimes difficult for the gardener to distinguish one from the other. Both cause mis-shapen roots, but gall weevil is much less serious. The white, legless grubs bore into the roots, which then form rounded hollow swellings, or galls. If there is a severe infestation, several galls may join together to form a large chamber containing many grubs. Stunted plants and poor harvests will result from bad attacks.
When transplanting cauliflowers, check the roots for gall weevil. If there are only one or two galls on a root, then cut them off with a sharp knife; discard and destroy any severely infested plants.
As with cabbage aphis, the removal of all old brassica stumps is a good preventive measure. If the plants are infested, apply a quick-acting fertilizer, such as nitrate of soda, to promote growth; healthy plants are less vulnerable than weak ones.
Club root: this is the most serious disease likely to affect. The above ground symptoms are stunted plants with wilted, bluish-green leaves. If you dig up the suspect plant and find swollen roots with large, gal1-1ike growths, cut the root open with a spade. If the inside of the gall is clean and fresh-looking, or if there is a little grub in it, then the root is infested with gall weevil. If the inside of the gall is mottled, slimy or discoloured, or has an unpleasant odour, then club root is the cause. Dig up and burn all infected plants.
The only way to get rid of this soil-borne fungus is to starve it out. Make sure you do not grow any brassica crops in your garden for at least three years once club root is present. Again get rid of all weeds of the Chiciferae family, such as shepherd’s purse and charlock, as they harbour the disease.
Because club root is associated with acid, badly drained soils, correct any drainage and acidity problems before planting. Test your soil, and if the pH is below 6.0, apply lime to bring it up to neutral (6.0) or slightly alkaline. Once the soil is infected, liming will help get rid of the disease, but it is a slow process, and may take up to 18 months to be fully effective. Apply slaked lime at the necessary rate to bring the pH up to slightly alkaline; re-apply as necessary. Downy mildew: the symptoms of this fungal disease are soft white patches, usually on the underside of the leaves. Seedlings under glass are frequently infected. As with club root and cabbage aphis, shepherd’s purse and charlock are host plants; make sure your garden is weed free. Remove badly infected seedlings or plants and spray the remainder with Bordeaux mixture or zineb. Under glass, improve the ventilation, and obtain dryer conditions.
Wirestem: the fungus which causes damping off in seedlings can also infect young plants, and it is then called wirestem. These plants develop hard, brown withered stem bases. It is not necessarily fatal, but infected plants will be stunted and crop poorly.
Wirestem is most likely to occur in wet, overcrowded conditions; thin seedlings before they become overcrowded and avoid overwatering. Treating the soil with quintozene or Cheshunt compound prior to sowing helps prevent wirestem.
Ringspot: this fungal disease appears as round, pale brown spots on the lower leaves. Eventually the leaves turn yellow, wilt and drop off. As with many brassica diseases, weak plants and those with lush growth are the most vulnerable. Make sure you grow cauliflower as part of a crop rotation plan, and harden the growth with a potash dressing.
Whiptail: this physiological disorder is due to a lack of molybdenum, a trace element. Affected plants will develop strap-like, ruffled leaves, reduced to little more than the midrib and the curds may be stunted or non-existent. It usually occurs in very acid soils, so liming as previously recommended, will help. Otherwise the application of fritted trace elements can be tried, together with mulching with plenty of well-rotted manure or garden compost; this will help to make various minerals available in the long term.