Lychee mite management

Tiny to the point of being barely visible to the naked eye, the lychee mite causes such serious damage that if left uncontrolled it can make the production of affected plants unviable. The application of pesticides when brushing the stem or branches is one of the alternatives to minimize the effects of the pest, which challenges producers and researchers.

The lychee mite (Aceria licthii) measuring around 0,15mm to 0,17mm in length (figure 1), it is the newest pest introduced into this crop in Brazil. In addition to being a tiny mite, barely visible to the naked eye, it lives sheltered in erinosis formations (apparently an alga called Cephaleuros virescens which develops in symbiosis with this mite due to its food, as it injects a toxin when it feeds, giving rise to this phenomenon). To be able to view it in the same way as the false rust mite, which can be up to 1,12 mm long and which attacks citrus fruits, you must collect the leaves attacked by erinosis and leave them for a day, as when When they notice the withered leaves, the mites begin to migrate and can thus be observed abandoning the mites, moving along the veins or places without such formations. As you can see, this mite is about 6 to 7 times smaller and only a 60x magnification with a lens allows you to easily see them.

The damage caused by this mite is of such great importance that if it is not controlled, the attacked plants will not produce. Its attack only occurs on shoots, mainly in hot seasons such as spring and summer. In general, the lychee plant sprouts 4 to 5 times a year and this pest attacks every time the sprouts appear, being brought by the wind or by bees during flowering time, which occurs in early spring. This last infestation is the most harmful, as after flowering, they can also attack the developing fruits, resulting in small, defective and even dark-stained fruits. The attack during flowering knocks down the flowers, reducing fruiting. However, the attack on the shoots even during the year weakens the fruiting and development of the plants, compromising future harvests.

This mite is from the same family as the false rust mite on citrus, whose damage is manifested by sucking the peel and leaking oil which, when in contact with sunlight, darkens the fruits, damaging their appearance. The mite belongs to the eriophid family, whose characteristic is that it has only two pairs of legs, different from the other groups that contain four pairs. Thus, to move around they crawl the back part of their abdomen.

In the population there are males and females; Males do not copulate females, they only deposit sperm sacs, called spermatophores, on the surface of the leaves that are collected by females who introduce them into their bodies to allow fertilization. They lay fertilized eggs that give rise to other females; when not fertilized, they generate males. The eggs measure 0,032mm in diameter, are spherical in shape, are laid singly and are translucent. About 13 days after oviposition, adults emerge. The incubation period lasts around two to three days, the nymph II phase lasts eight to twelve days and the adults only two to three days. During the year, 10 to 12 generations can occur.

While the false rust mite can be easily washed away by rain, as they live on the smooth surface of citrus leaves and fruits, the lychee mite protects itself in the erines, without being harmed. For this reason, during the rainy season, it is not eliminated naturally like that of citrus.

Recent research carried out at the “Luiz de Queiroz” School of Agriculture, Piracicaba, São Paulo, in the Department of Entomology and Acarology, has shown some promising results in controlling this mite through a system that can facilitate lychee owners in farms or backyards, who do not have their own equipment for applying pesticides to large plants

In general, high-power sprayers are used to apply acaricides to large plants. However, owners who do not have their own equipment for this purpose will find this method a solution for controlling the pest. Promising results have been obtained with the application of pesticides by brushing the stem or branches within a criterion where a formula was established to estimate the necessary amount of the toxicant to eliminate the pest in the branches.

Bearing in mind that the product necessarily requires penetration with the sap, it must have a systemic characteristic, that is, be soluble so that it can circulate together with the sap and reach the new sprout where the mites are located. Of the products tested, dimethoate 40% and carbosulfan 20% stood out; the first was condemned by the Ministry of Health, leaving the second. The other systemic products, although with modern characteristics, less aggressive, have not yet offered promising results.

The dosage to be recommended is based on the diameter of the branches; By measuring its perimeter, which can be obtained directly using a measuring tape or tape, the dosage of the product to be applied is established, simply by multiplying this value by two, always for one meter of branch or trunk length. .

Example:

If a branch is 22cm in perimeter, the dosage would be 22 x 2, that is, 44l of undiluted commercial product, brushed along 1 meter of the branch or trunk across its entire surface (you can dilute the product a little with water for better distribution and absorption).

Taking into account that the systemic product has a residual effect of approximately 15 to 20 days, this factor must be taken into account when applying it. As there are several annual shoots, the one close to fruiting must be respected to prevent the fruits produced from becoming systemically contaminated.

In addition to this method, others are being researched in order to offer lychee producers organic acaricides that can be sprayed in backyards or farms, without restrictions.

By Octavio Nakano, Lucas Ferreira de Oliveira, Esalq/Usp

(Article published in issue 80 of Cultivar Hortaliças e Frutas)