Pests and Diseases Affecting Home Grown Peaches
Glasshouse red spider mite: this insect, although most troublesome when peaches are grown under glass, is sometimes found out of doors, where peaches are grown against walls or other warm, dry situations. The tiny mites can appear from mid-spring onwards. They live and feed on the leaf undersides. Infested leaves look speckled and greyish, and eventually they wither and die. The spider mites sometimes cover the leaves and stems with pale webs.
This pest can be very difficult to control because some strains have developed a resistance to commonly used insecticides, especially those containing phosphorus. Malathion, derris or dimethoate sprays in mid-spring give some measure of control, but re-spraying may be necessary later in the season. If the problem is in the greenhouse, it is possible to take preventive action by maintaining a good humidity, and making sure the trees never run short of water. The mites thrive under hot, dry conditions. If an infestation does appear, you can fumigate regularly with a zobenzene. Be careful not to rely too heavily on one type of insecticide, though, as this can be counter-productive in the long run. If the insecticide you are using seems to be getting gradually less effective, change to another.
Aphids: there are many varieties of aphids which attack peach trees, but the most damaging is the peach aphid. These attack peaches grown in the greenhouse from mid-winter onwards; peaches grown outside are vulnerable from mid-spring onwards. The aphids feed on the leaves and shoot tips, which then become curled and stunted. A winter tar-oil wash should get rid of the over-wintering eggs, though such washes destroy many predators, and it is probably wiser to spray any aphids which appear in spring with derris, bioresmethrin or malathion before and after flowering. Alternatively, spray the trees with lime-sulphur solution at bud break to control over-wintering aphids.
Scale insects: like red spider mites, scale insects can cause damage both in the greenhouse and outdoors. The first sign of infestation is the appearance of stickiness and a soot-like substance covering the leaves. The latter is sooty mould, which grows on the honeydew secreted by the young scale insects. Small, generally brown scales, sometimes also grey or black, can usually be seen if you look closely at the leaves and stems. These scales, which are roughly round to oval shape, depending on species, protect the female insect, and also the eggs.
Control a bad infestation of scale insects with a winter tar-oil wash. Should any appear in spite of the winter wash, spray with malathion as soon as you see them, but not at flowering time. Birds: birds, particularly bullfinches, can be very damaging; both the dormant buds in winter and ripening fruit are vulnerable. Althoughand bird-repellant sprays may offer temporary protection, the most effective long term protection is netting the trees with 2.5 cm (1”) square nylon netting. It is initially an expensive outlay, but nylon does not rot and can be used indefinitely. Leaf curl: this fungal disease, sometimes called peach leaf blister, is the most serious disease affecting peaches. Infected leaves become curled, swollen, distorted, and red in colour. As the spores develop on the surface of the blisters, they are eventually covered with a white bloom. It appears on the leaves soon after they unfold in spring, and they fall prematurely, though new leaves may be produced to replace them. Trees infected every year can eventually be killed.
To prevent leaf curl, spray the trees with lime sulphur, liquid copper or Bordeaux mixture sometime towards the end of the winter, just before the buds start to swell, and again in about two weeks, just as the leaves are unfolding. Remove and destroy all infected leaves. An additional spray in mid-autumn, just before or as the leaves begin to fall, is also advisable. These sprays are protective; the fungus spores overwinter on the buds, and the fungicide is intended to cover the developing growth before the spores can grow into it.
Split stone: this is a physiological disorder; the symptoms of split stone are cracking at the stalk end, and a rotten kernel inside a split stone in the centre of the fruit. The crack at the stalk end is particularly damaging because through it pests, such as earwigs, and fungal infections can enter and attack the fruit. Poor pollination, poor, or excessive feeding after stoning has started can result in split stone. The main cause, however, is thought to be an irregular supply of soil moisture. The best precaution against this disorder is to ensure that the initial soil preparation is done carefully, and the trees are properly cultivated, with a constant, steady water supply while the fruit are swelling. Hand-pollinating the flowers, with a camel hair brush, will lessen the possibility of split stone, as will liming the soil if it is excessively acid.
Brown rot: this fungal infection usually enters the fruit through a wound, caused by birds, caterpillars or other insects. Peaches with brown rot turn soft, brown and quickly become inedible. Eventually, the skin becomes covered with round patches of pale grey fungal spores, which rapidly spread the disease to nearby fruit. Infected fruit may fall to the ground or remain, shriveled up, on the tree.
Remove and destroy all infected fruit as soon as you see them; do not leave them lying on the ground or in theheap. The fungus can travel from the fruit down the stalk to the fruiting spur, so when you remove infected peaches from the tree, cut out and burn the adjacent spur as well.
Peach mildew: this fungal disease can attack the leaves, fruit and shoots. At bud-burst in spring, young leaves which are stunted and covered with a white mealy coat are probably infected with peach mildew. On fruit, it appears as white patches which may cover the whole fruit and which turn brownish.
Because mildew is associated with stuffy, badly ventilated conditions, and dryness at the roots of the trees, the best precaution is to ensure that there is adequate air circulation and a steady, moderate supply of water. Peaches growing in very dry soils, such as those trained against a wall, need watering and then mulching the soil in early summer as another precaution. Make sure the wires of wall-trained peaches are at least 15 cm (6”) from the wall, so that air can circulate around the leaves.
If a tree is infected, cut off all diseased shoots as soon as seen to a point well below the infection; spray with dinocap or benomyl fungicide and repeat as necessary.
Dieback: peaches frequently suffer from this fungal infection. The tips of the shoots die, and the infection can work backwards along the whole branch. If the tree is infected, cut back into sound, healthy, living wood; there should be a green layer immediately below the bark in the remaining wood.