HARVEST DAMAGE TO VEGETABLES
Mite control in greenhouses
The broad mite can be extremely small, but the damage it causes is not. This pest feeds on a wide variety of greenhouse horticultural crops, including cucumber, eggplant, pepper and tomato. These mites proliferate when the temperature range is from 15ºC to 21ºC and the relative humidity is between 60% and 80%.
acaro in greenhouse
It is known that females oviposit 40 eggs during their whole life; however, this depends on the temperature and relative humidity.
During an agricultural cycle, all stages of this pest can coexist simultaneously, including eggs, larvae, nymphs and adults.
The broad mite feeds mainly on the underside of young leaves and tends to avoid light. Mites live and feed on the meristematic tissues of plants, since they require the tender plant tissue that provides them with an ideal source of food for their development.
Because these mites are rarely detected, growers will only realize that this pest has entered their greenhouses when damage to their plants is noticeable.
Identification and biology
Adults are approximately 0.0009 inches (0.25 mm) in length, are amber or bright dark green and oval in shape.
They have four perfectly distinguishable stages: eggs, larvae, nymphs and adults. The eggs require five to six days to become adults, at temperatures between 21ºC and 26ºC, and seven to 10 days at temperatures between 10ºC and 15ºC.
The females can oviposit up to 40 eggs during their entire life cycle; however, this depends on the temperature and relative humidity.
The broad mite has a reproductive system in which unpaired females only oviposit eggs that produce male progeny. The eggs are oval, white and covered with bumps or pimples. The six-legged larvae that hatch from the eggs are transformed into eight-legged nymphs and finally into adults.
Detection of damage by feeding
The broad mite feeds in a group, especially on the back of young leaves, where the larvae oviposit. They feed on plant cells by inserting the sucking stylets of their buccal apparatus onto the epidermis of the leaves. Their feeding causes the edges of the leaves to roll inward and the leaves to harden and become brittle, cracked and / or withered.
Feeding can also cause the leaves to become darker than normal. They may have distorted ribs and damage to the leaves that resembles the damage caused by overexposure to a phenoxylated herbicide such as 2,4-D, or damage caused by virosis or nutritional imbalances (magnesium deficiency).
Also, abortion or cracking of the fruits may occur. The broad mite injects toxins during its feeding. In the cucumber, deformed buds may appear with leaves rolled in and cracked fruits; which reduces the possibility of marketing the affected cucumbers.
Plants with severe infestation may suffer from stunting and death. Symptoms of damage can continue to be expressed even after being treated with an acaricide.
When populations of mites are very large, they move towards the underside of the leaves to continue feeding, causing serious deformations. The reverse surface of the leaves can acquire a bronze color tone.
Studies have indicated that five large mites or even a smaller number of them can cause severe damage to young cucumber plants, resulting in lower fruit production. In general, tomatoes tend to be less susceptible to broad mite infestations than cucumbers and sweet peppers. This may be due to nutritional quality, or because tomato leaves can produce defense chemicals.
The broad mite can spread among greenhouse crops through air currents, contact between the leaves of nearby plants and when workers handle infested plants and then touch uninfested plants.
It is known that females can grab onto the legs and antennae of adult greenhouse white flies (Trialeurodes vaporariorum) and / or whitefly of potato biotype B (Bemisia tabaci); thus finding another form of dispersion. Likewise, males can transport female nymphs, eggs and adult females to new leaves.
Management options
Since a power source is required for them to survive, producers must implement sanitation practices, such as weeding, before introducing new propagating material and disinfect the benches.
They can also use acaricides that affect the broad mite, authorized for vegetable crops. However, mite populations may be difficult to suppress with contact acaricides, as they are found in meristematic tissues.
When using contact acaricides it is necessary to completely cover all sections of the plants and repeat the applications, to achieve a high mortality rate of the pest. Vegetables with hair or trichomes can inhibit the suppressive effect of acaricides on broad mite populations because the hairs prevent the droplets of the product from reaching the surface of the leaves where the mites are found.
A more effective option may be acaricides with translaminar activity, authorized for use in vegetables.
The term translaminar means that after foliar application the material penetrates the foliar tissues and the tips of the new growing areas, forming a deposit of active ingredient inside the leaf or at the new growth points. Therefore, these acaricides are more likely to come in contact with the broad mites that are feeding on the tissues.
