Pests and Diseases Affecting Apricots
Red spider mite: although this pest is worst on trees grown in the greenhouse, it can also be a problem on outdoor trees trained against walls. The leaves of infected trees become mottled with tiny grey or yellow specks and the minute red insects can be seen underneath. In bad attacks webbing will be produced on the leaves and stems. Eventually the leaves wither and die.
The pest flourishes in dry, hot conditions, so spray the tree frequently with water if you have had previous attacks of this pest. In greenhouses, keep the atmosphere moist by frequent damping down and, if necessary, fumigate the house with azobenzene. Outdoors use an insect spray, such as malathion, derris or dimethoate, but be prepared to repeat the spray and or change to another spray if necessary. Some strains of red spider mite are resistant to some sprays. In any case use them as little as possible so that predators can do their work.
Scale insects: these sap sucking insects can sometimes be spotted by the mould which grows on the sticky substance (honeydew) which they secrete. Both the leaves and stems of the trees may be covered with the sticky black mould. If you look more closely at the bark and under-surfaces of the leaves you should also be able to see small, brown, round or oval, raised spots which are the insects.
Scale insects are best controlled by a winter wash of a 5% tar oil solution which attacks the overwintering eggs. As a precaution, the trees should be sprayed every three years. If, despite this, the insects appear in the summer, spray with malathion.
Greenfly and capsid: these suckingfeed by sucking the sap from the leaves, particularly at the tips of the new shoots. They also attack the soft, young stems, and growth in spring and summer will be checked, sometimes severely, with the leaves being curled and discoloured yellow or pale green. Such an attack can open the way to infestation by the dieback fungus. Capsids additionally inflict pin-prick holes on the leaves, which eventually become torn and tattered. Greenfly will be seen any time from spring to early summer or later, capsids are present in late spring and early summer, sometimes also in mid-to late summer. Routine pruning will help to remove some of the greenfly infestation but if they are not controlled by the local population of ladybrids, spray with bioresmethrin, derris or malathion.
Dieback (Blossom wilt): this is the most serious disease of apricots and has been blamed for the decline in the frequency with which they have been grown. It is a fungal disease but appears only to attack if the tree has been damaged by too severe pruning or by winter frosts. Baddrainage predisposes the tree to infestation; some varieties are more prone to it than others.
To begin with, the disease attacks the tips of the young shoots (and blossom if present) but then moves back along the branch slowly killing the whole branch. The leaves turn brown and fall prematurely; the bark of the shoots turns brown, and no new growth is produced on that part of the shoot. Gum may also be produced on the larger branches.
Cut dead shoots and branches right back to healthy wood, in late spring, when general pruning is started. Do this carefully, sawing larger branches from both above and below to prevent splitting, and use a knife to make the wound smooth. Then paint over the cut surface of the larger wounds at once with a wound sealing compound.
Silver leaf: this fungus disease only enters the tree through open wounds, but having done so can be serious, eventually killing the whole tree. The first symptom is a metallic silver sheen on the upper surface of the leaves; branches have a dark brown stain on the internal wood, which will be obvious when the branch is sawn through. Eventually fruiting bodies are also produced, which occasionally appear as a bracket on the branch, purplish on the top but brown on the underside.
Surgery is the best cure, if there is extensive silvering. Cut out all the infected wood and burn it. Cut carefully and coat with a wound-sealing paint as you would for die back. Where the leaves on only a few shoots are silvered, wait a little while before deciding to cut as sometimes trees produce compounds internally which effectively seal off the infection within the wood, and thus recover naturally.
Brown rot: this fungus attacks the fruit, normally entering through wounds caused by birds, caterpillars or other insects. Infected fruits quickly turn soft and brown and become covered with concentric circles of buff-coloured fungus. The disease can spread through all the fruits in a cluster or store by contact between fruits. As soon as you see a diseased fruit, whether on the ground, on the tree or in store, remove it and burn it. The fungus can also travel from the fruit to the fruiting spur and can cause dieback, so after you have removed diseased fruit from the tree, cut out and burn the adjacent spur as well.