Citrus Diseases in Pakistan
Aphids are small brown colored insects. Aphids attack the tree by sucking the sap out of the leaves. They do little damage to tree, when small in numbers, but their population grows very fast under favorable conditions and can cause serious damage to a tree during growing season.
Symptoms: During aphid infestation, citrus tree leaves drip a sap from underside of the leaves, called honeydew, onto other leaves, ground below and other plants, which is actually an excretion from the aphids. Leaves will have multiple wrinkle marks, yellowing and twisting. With severe infestation of aphids leaves drop and branches die.
Controls: Use Dizenon 40% or Eldrine 20%, 1 kg in 450 litres of water, at the undersides of the leaves and other areas of visible feeding and insect concentrations. Insecticides should not be applied within 6 weeks of marketing the fruit.
Citrus canker is a bacterial disease caused by bacterium Xanthomonas axonopodis (formerly campestris) pv. citri (Xac). Xac is present in 30 countries in Asia, Pacific and Indian Ocean islands, and South America.
Symptoms: Bacteria causes yellow halo-like lesions or scabs on the leaves, twigs and fruits. Severe infections cause fruit drop, blemished fruit, leaf loss and dying of tree.
Control: There is no effective treatment for this disease except to cut and remove the affected trees and spray Formaldehyde at the spots from where the diseased trees have been removed.
Citrus leaf miner
The Citrus leafminer (Phyllocnistis citrella) is a tiny, light colored moth less than 6.35 mm long. Adults do not damage tree, it is larva which digs the mine and curls the leave during pupal stage.
Symptoms: Larva immediately after hatching from egg begin feeding in the leaf, producing serpentine mines, as larva grows, mines become more noticeable. It curls and deform leaves during pupal stage.
Control: Use Malathion 57 or Matasystox 50% at the rate of 500 grams in 450 litres of water per acre for its control.
The citrus whitefly (Dialeurodes citri) is a tiny white insect with four white wings that expand 3 mm. It is most commonly found feeding on the underside of the leaves. It damages the tree by consuming large quantities of sap and sucks out the energy required for growth. It damages the foliage and fruit by sooty mold fungus which grows over them by honeydew excreted by the citrus whitefly. This fungus is black in color, and effects photosynthesis process of tree and the ripening and late in coloring of the fruit.
Symptoms: When branches are shaken, insects will fly and flutter around the tree. Leaves begin to curl and appeared to be covered with a sticky, sooty mold substance. Citrus whitefly lay their eggs on the underside of the leaves and larva is small oval and almost transparent.
Control: This pest can be controlled using Malathion 57%.
Red scale (Aonidiella aurantii) is a soft, flattened, creamy-yellow insects, covered by circular, leathery covering. Female cover is reddish-brown, 2 mm across and male cover is paler, small and elongated.
Symptoms: Infested fruit has pits and drop can occur. Red scales cause yellowing of leaves and leaf drop. Yellow spots occurs at its feeding area. Young citrus tree trunk can be infested by red scales also. Honeydew excreted by red scales promotes the growth of sooty mold fungus on fruit and leaves that inhibits photosynthesis, weakens the plant, and makes fruit unattractive.
Control: Use Parathion or Malathion at the rate of 752 grams in 450 litres of water per acre for its effective control.
Root Rot is caused by a soil-inhabiting fungus phytophthora species. The fungus inhabits soil and is most prevalent in wet soil.
Symptoms: Fungus causes dark brownish patches of harden bark on the trunk of the tree and results in drying, cracking and dying of the bark. This disease causes browning and decaying of fruits and yellowing of leaves.
Control: Poorly drained soils are also reason for this disease, improve drainage. Remove all leaves and damaged fruit when it falls to the ground; prune of all lower branches off the tree so that the tree branches are more than 2 feet from the ground then spray the tree with a fungicide, when the disease is identified and again the following spring to prevent reinfection.