2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
The alfalfa leaf weevil is almost ubiquitous and damages both wild and cultivated alfalfa. Beetles gnaw holes in juicy stalks with appetite and eat alfalfa leaves from the edges. As soon as the formation of lateral branches begins on alfalfa, they will begin to feed on their tops, eating out numerous holes in the stipules. In general, the harm from bugs is very insignificant - the main damage to alfalfa is caused by vicious larvae, at first feeding on tiny young buds. After some time, they begin to destroy the tops of the stems, buds and young rudimentary leaves, as well as gnaw out oblong holes on the leaves. And the older larvae gnaw the stems with inflorescences. The ovaries of plants attacked by alfalfa leaf weevils dry up, and the plants themselves are painted in gray tones
Meet the pest
The alfalfa leaf weevil is a beetle whose body reaches 4 - 5 mm in length. The pronotum of these parasites is somewhat narrower than their elytra, and their sides noticeably protrude. The elytra of harmful parasites are thickened dorsally and endowed with almost parallel humeral tubercles, and the black scutellum spots are quite clearly expressed. The middle parts of the sixth spaces of the elytra are slightly darkened, and the hairs covering them are about 2 - 2, 5 times longer than the scales.
Growing up to 10 - 12 mm in length, green legless larvae are similar to caterpillars. They move with the help of bizarre wax-like outgrowths. The entire body of the larvae is covered with light hairs and dark warts, and along their backs there are narrow yellowish-white stripes.
Beetles usually overwinter in the fields of sowing alfalfa. They also do not disdain areas with wild varieties of this culture. Yellow alfalfa is especially attractive to them. And the bugs lie for the winter either under the remains of plants, or in the upper soil layer. As soon as the air temperature exceeds twelve degrees, they begin to show activity. As a rule, bugs appear en masse in the fields with the beginning of the growing season of alfalfa. Harmful parasites gnaw holes and grooves in plants. As soon as the height of the growing crops reaches five centimeters (in the forest-steppe, this usually occurs closer to the beginning of May), the females begin to lay eggs. Most often, they place them in the middle of the main stems or side branches. In most cases, one oviposition contains between two and thirty eggs. And the total fertility of females is incredibly high and reaches two and a half thousand eggs.
The egg-laying process usually takes more than a month. This is the reason for the appearance of uneven-aged larvae on the vegetation. And the development of eggs takes an average of ten to fifteen days. The larvae hatched from them feed for sixteen to twenty-two days. After this time, they pupate in transparent cocoons in the middle of flowers with leaves, and for this they concentrate mainly on the tops of plants. The pupal stage lasts from seven to twelve days, after which the bugs hatching from the pupae remain in cocoons for two or three days - until their skin hardens.
New generation beetles usually try to stay in the middle of alfalfa stalks, near the root necks. However, this is not the only place of their dislocation - you can notice harmful bugs under the remains of plants. And starting in September, they begin to slowly go to wintering places. In general, the development of evil weevils takes from twenty-nine to forty-eight days. Only one generation of these parasites has time to develop per year.
How to fight
The main protective measures against alfalfa leaf weevils are disking of too thick alfalfa crops, as well as their harrowing until they grow in two rows.
In case of mass appearance of voracious larvae at the stage of growth of stalks, alfalfa must be mowed. And if for every hundred sweeps of the net there are twenty to thirty larvae or five to eight bugs, then they move on to insecticide treatments.
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