What are the main pests and diseases of lychee in March?
1. Downy blight: also called downy mildew blight. It mainly damages the fruit, and also infects flower clusters and young leaves. When the fruit is affected, the disease usually starts at the fruit stem, with irregular lesions appearing on the fruit skin surface that gradually spread, eventually turning the entire fruit black, rotting the flesh, producing a sour, fermented, wine-like smell, and with a white frost-like substance on the outside of the diseased fruit, causing fruit drop....
1. Downy blight: also called downy mildew blight. It mainly damages the fruit, and also infects flower clusters and young leaves. When the fruit is affected, the disease usually starts at the fruit stem, with irregular lesions appearing on the fruit skin surface that gradually spread, eventually turning the entire fruit black, rotting the flesh, producing a sour, fermented, wine-like smell, and with a white frost-like substance on the outside of the diseased fruit, causing fruit drop. Affected flower clusters and leaves first show small pale yellow spots, which later expand into irregular brown lesions with a downy mildew-like substance on the surface. The mycelium overwinters on diseased leaves or diseased fruit, and in the following spring spreads through wind and rain, damaging flower clusters and young leaves. It then infects nearly mature fruit. In hot, humid weather, the disease develops quickly and fruit drop is severe.
2. Conopomorpha sinensis (lychee fruit borer): the larvae mainly damage flower clusters, shoot tips and leaves, and do not feed on fruit. Newly hatched larvae of Conopomorpha sinensis bore directly from beneath the egg through the plant epidermis to feed on sap, creating tunnels; from the 3rd instar they switch to feeding on plant tissues, boring into the midrib of leaves, the petiole, and the pith and mesophyll of tender shoots. During the boring stage they make one to several holes for frass expulsion, but on the leaf midrib there is only one hole, located at the base on the underside of the midrib; after the damaged leaf matures, the midrib withers.
3. Lawana imitata (white moth planthopper): adults and nymphs often gather on branches, tender shoots and flower clusters to suck sap. The damaged branches and leaves are covered with many white cotton-like waxy substances, which induce sooty mold, causing poor shoot growth, shrivelled and twisted young leaves, declining tree vigor and even withered branches, resulting in fruit drop or degraded fruit quality. Both nymphs and adults are gregarious, gathering on branches and trunks to feed. Nymphs secrete waxy substances that cover their bodies, spreading in groups of three to five to cause damage; if disturbed, they scatter and jump away, then gather again on new branches to settle and cause damage. In summer and autumn, outbreaks are more severe during rainy weather.
4. Lychee eriophyid mite: also called lychee gall mite, commonly known as felt disease. The eriophyid mite damages lychee young leaves, flower clusters and young fruit. Affected parts show small yellow-green spots that gradually expand, with the front of the lesion raised and the back sunken, and white hairs growing out; within about 1 month, the hairs turn yellow-brown and become so dense that they resemble felt, hence the name felt disease. Affected tender shoots and leaves become deformed and twisted and grow hairs. When flower organs are affected, they become grayish-green and hairy, the calyx swells, and the flower organs turn brown and dry up. When affected at the young fruit stage, the diseased part is slightly raised and rough, gradually changing from pale red to reddish-brown, and produces a hairy secretion.
Eriophyid mites often spread over long distances with galls on nursery stock, and spread within orchards not only through contact between branches and leaves but also through light breezes. Adult and nymph mites prefer shade and often hide on plants with dense, light-blocking canopies. Older trees and those with shaded interiors of the canopy suffer severe damage, so when applying pesticide, care must be taken to spray shaded areas to achieve effective control.
5. Thrips: adults and nymphs suck the sap of tender buds and young leaves. When lychee tender buds are damaged, growth is inhibited; when young leaves are damaged, the leaf margins curl, and the leaves harden, turn yellow and lose their luster. The peak damage periods are April to July and September to December. Trees that produce winter shoots, with many shoot flushes and uneven flushing, suffer severe damage.