The cause of the latest black fruit and its preventive measures

Many farmers who have planted oranges, lemons and grapefruit have had such an experience. In summer and autumn, these fruits will turn black, commonly known as "black fruits". Some orchards will even be swallowed by the black fruit, black fruit hanging all over the branches, these fruits are small, sour, black skin, completely lost its value as a commodity. All this is caused by a pest called rust wall lice, which is a killer of citrus appearance, affecting not only the appearance but also the taste, leading to a decline in the income of fruit growers. What is even more frightening is that this kind of insect pest may continue to do harm for many years, so there is the saying that "one year of copper, three years of poverty." Taking citrus as an example, let's take a look at the causes of this kind of "black fruit" and the prevention and control measures.

First, the cause

Citrus black peel fruit is caused by citrus rust wall lice (also known as citrus rust spider, rust mite, gall mite). Adults, nymphs and young mites of citrus rust wall lice use piercing mouthparts to stab fruits and leaves to absorb juice. when the oil cells are destroyed, the spilled oil is oxidized to brown to dirty black, which farmers call "oil peel tuo" and "oil skin mandarin". The back of the damaged leaves is dark brown and seems to have been smoked, and the stain cannot be erased (the mildew layer infected with soot can be erased). When the citrus fruit (or leaf back) is dark brown, the best time for control is missed. Rust wall lice damage citrus fruit trees, but also cause a large number of withered and yellow leaves, weaken the tree potential, and seriously affect the next annual yield.

II. Characteristics of development

The host of citrus rust wall lice is limited to citrus fruit trees, and young mites, nymph mites and adult mites can be seen at the same time. The adults overwintered on the summer and autumn shoots and transferred to the spring shoots and fruits next year. Generally from May, it is harmful to the back of the young leaves on the spring shoots, and the back of the injured leaves shows a dark brown reticular pattern, which leads to a large number of fallen leaves. The damage to fruit began from late May to the first and middle of June, and the damage to rust tick was the peak from July to September, and the damage to fruit was the most serious. In the meantime, if there is high temperature and high humidity, it is not conducive to the breeding of rust tick; if there is high temperature and drought, the damage of rust tick will be aggravated, and it can still become a disaster in October.

III. Prevention and control measures

Recognizing the causes and development characteristics of this "black skin fruit", the next step is to introduce the prevention and control measures that fruit farmers are most concerned about. Because the body of the rust wall louse is very small, white at first, and then yellowish, there are worms and eggs on the leaves and fruits when they are serious, so in the initial observation, the leaves and fruit surfaces should be observed with a magnifying glass, with emphasis on the back of the leaves. If dusty insect bodies are found on the surface of individual fruits, chemical control should be carried out immediately. In order to control the rust wall lice, the inside and lower part of the crown should be sprayed first, and then the outside and upper part of the crown should be sprayed, with emphasis on the shady side of the leaf back and fruit. The suitable spraying time is before 10:00 in the morning and after 5 p.m. Spray should be careful, careful, spray amount to leaves, fruit moist but no drop is appropriate, generally spray 2 times 3 times, each time 7-10 days.

When it comes to the effective insecticides for the control of rust wall lice, I would like to introduce a kind of chemical called stone-sulfur mixture. the concentrations that can be used in different seasons are generally 0.2-0.3 Baume in spring, 0.1 Baume in summer, 0.2-0.4 Baume in autumn and 0.6-0.7 Baume in winter. In the hot season, the concentration must be applied with caution. Other effective agents include 75% acarate, 50% tricyclic tin, 20% methamphetamine, 50% Tolk, 20% deltamethrin, 40% omethoate, 1.8% avermectin EC, 63% Dysen zinc wettable powder, hairy bacteria powder (70,000 colonies per gram), etc. Now Yuanjiang City, Hunan Province, orange agricultural Dasheng (80% mancozeb wettable powder) to control citrus rust wall lice, the effect is good, the effect is long. After spraying 600 times of Dasheng liquid once, the effect lasted for 30 to 60 days. It can control the diseases and insect pests such as citrus soot disease and affect the appearance and color of fruit for 2 times in general years and 2 times in repeated years.

This paper gives a brief introduction to the production and control methods of citrus "black skin fruit". In the process of control, biological control can also be used to make use of the natural enemies of rust wall lice. There are mainly mite-eating ladybugs, predatory mites, long-bearded mites, thrips and hairy bacteria, which can also inhibit the production of rust wall lice.