PESTS AND DISEASES OF MANGOES

1. Anthracnose

• Caused by a fungus Glomerella cingulata.
• The disease causes serious loss to young shoots, flowers and fruits under favorable conditions of high humidity, frequent rains and temperatures of 24-34 degrees centigrade.
• It also affects fruits during storage.
• The disease produces leafspots, blossom blight, weathering tip; twig blight, fruit cracking and rot symptoms. Black spots develop on panicles as well as on fruits. It is common to find mummified young fruits on dead inflorescence stock.
• Fruits infected at mature stage carry the fungus into storage and cause considerable loss during storage, transit and marketing.

Control

• The fungus has long saprophytic survival ability on dead twigs. The diseased twigs therefore should be pruned and burnt along with fallen leaves for reducing inoculum.
• To reduce flower infection, apply the first spray when panicles first appear, after observing the presence of the disease.
• Copper oxychloride WP used at the rate of 300g/l of water is effective.
• The first spray to be applied three weeks after fruit set when the fruits are pea size.

2. Powdery Mildew

• Affects almost all varieties of mangoes.
• A white superficial powdery fungal growth on leaves, stalks and pinnacles, flowers and young fruits is formed.
• The affected flowers and fruits drop prematurely reducing the crop load considerably or might even prevent fruit set.
• Rains or mists accompanied by cooler night during flowering are conducive environment for disease spread.
• If fruits are set, the diseased area becomes cracked. Cork-like tissue is formed and the fruits drop at pea size.
• Young leaves when infected develop white patches and later become curled and distorted.

Control

• The following three sprays of fungicides at 15days interval are recommended for effective control; Ridomil and Antracol.
• Spraying can start at bud break and repeated after 2 to 3 weeks depending on weather conditions until fruit set.
• However, it is better to monitor weekly and spray at the first sign of the disease. Once young tissue has hardened it is no longer susceptible and spraying can be stopped.

PESTS

Fruit fly

• This is one of the most serious pests of mango in the country. It has caused a problem in marketing of fresh fruits.
• The female punctures the outer wall of the mature fruits with the help of ovipositor and inserts eggs in small clusters inside the mesocarp of mature fruits.
• After hatching, the larva feeds on the pulp fruit, which appears normal from outside, but drops down finally.
• The mature maggots fall down into the soil for pupation. Some fruits may remain hanging on the tree and ripen prematurely. When such fruits are harvested and cut open, maggots of the fruit fly are seen and the flesh is damaged.

Control

• Collection and proper disposal of infected and dropped fruits
• Home gardens require three sprays of suitable insecticides e.g. Salut, 7weeks and 3 weeks before picking.

 

Mango seed weevil

• It is widely distributed in the tropics. It is a serious pest hampering export of Ugandan mangoes.
• Sweet varieties of mango are more prone to attack by this insect.
• The female lays eggs on the epicarp of the partially developed fruits or under the rind of the ripening fruit.
• Newly emerged grubs bore through the pulp, feed on seed coat and later damage to cotyledons.
• Pupation take place inside the seed.
• Discoloration of the pulp adjacent to the affected portion has been observed.

Control

• A combination of removal of fallen fruits, trash and spot spray application of Salut up to a meter around the stem greatly reduces the weevil population.
• Destroying the affected fruits and exposing the hibernating weevils by digging the soil.
• Spray the tree with insecticide.
• It is a quarantine pest and therefore gentle care should be taken to avoid its entry into other countries where mangoes are exported.

Mango Disorders

1. Biennial bearing

This term biennial generally signifies the tendency of mango trees to bear a heavy crop in one year and very little or no fruit in the succeeding year.

When a tree produces heavy crop in one season, it gets exhausted nutritionally and is unable to put forth new flush thereby failing to yield in the following environmental and nutritional factors. To overcome biennial bearing, the farmer is advised to do the following;

• De-blossom partly during on-years
• Application of manure after every harvest
• Irrigate immediately after fruit set.

2. Fruit drop

• Despite high fruit set initially, full retention in mango is very low. The intensity of fruit drop varies from variety to variety.
• The fruit drop is more or less a continuous process.
• Embryo abortion, climatic factors, disturbed water relation, lack of nutrition, pests and diseases and hormonal imbalance are the major factors that lead to fruit drop.
• To avoid this, control pests and diseases, improve on the nutrition of the plant, irrigate during fruiting and prune shaded branches.

3. Failure of mangoes to flower

This phenomenon is common in mangoes as in other fruit crops.

The mango tree grows vegetatively for year to year without producing any fruits.

The following are possible remedies;

• Ring branches
• Prune off some branches especially those that are shaded
• Burn grass or plant material and produce smoke below. Smoke contains ethylene which promotes flowering.