The raspberry beetle is the most common pest of raspberries and blackberries.
The insect is oval, grayish or brownish in color, 3.8-4.3 mm long. Its body is covered with adjacent sparse yellowish hairs. The egg is elongated, white, up to 1 mm long. Larva up to 7 mm long, yellowish, with a dark head, later turns reddish-yellow. The pupa is white, up to 4 mm long, has an arched-curved shape.
The raspberry beetle is a very serious pest of leaves, buds, flowers and berries, both cultivated raspberries and blackberries, and wild forest in Europe, Siberia, the Caucasus, China. The raspberry beetle is dangerous in the imaginal (adult) and larval phases. In the years of mass summer, beetles damage up to 30% of raspberry buds and flowers. They harm most severely in neglected orchards, where they destroy up to 50% of the crop. Damaged berries develop poorly, become smaller, deformed, quickly rot and become unsuitable for consumption.
In the spring, when the temperature of the upper soil layers reaches 12 ° C and higher, overwintered beetles come out of the soil (usually in late May-early June) and feed on flowers (nectar, anthers and pistils) of weeds, bird cherry, currant, gooseberry, cherry, apple tree and some other plants, later migrate to raspberries and blackberries. On raspberries, beetles appear during the period of exposure of buds, 7–10 days before the beginning of flowering. Beetles gnaw on young leaves, buds, flowers. At the same time, in the process of searching for raspberry plants that begin to bloom, beetles can travel quite considerable distances.
During the period of mass flowering of raspberries, females lay eggs, as a rule, one at a time, very rarely two in flowers and young ovaries. Fertility is 30-40 eggs. In the second half of July, the beetles die off. The embryonic period in eggs at 20–22 ° C lasts 7–10 days. The hatched larvae feed on raspberries for 35–45 days. Most of the larvae leave the berries in mid-August. The larvae go into the soil, where some of them pupate in cradles at a depth of 5 to 20 cm, and the rest enter diapause. Pupae develop at 20 ° C for 14 to 30 days. By the end of August, beetles begin to form, which, without going outside, remain overwintering in the soil. One generation, taking into account the larval diapause, develops in 1–2 years.
Larvae and adults overwinter at a depth of 5–20 cm under raspberry bushes. Some larvae hibernate in cradles in a state of diapause and complete development only in the next year. Due to this, this pest survives even in the absence of a raspberry crop in some years. The number of diapausing larvae varies from year to year from 10 to 82% of the total number of overwintering individuals. Pupae that did not have time to turn into beetles by autumn die in winter.
Usually, a large number of raspberry beetle larvae (about 80%) are collected annually together with the berries and destroyed. Nevertheless, even taking into account the small fecundity of the female beetle (30–40 eggs), a single type of egg laying by her only in flowers or ovaries, one generation of offspring in 1–2 years, the number of pests in the presence of diapause in larvae (they survive even in poor years) and their pupation in cradles (additional protection) without the use of protective measures remains consistently high enough.
Therefore, according to experts, the use of special protective measures is required to reduce the number of the raspberry beetle. Such measures should be applied until the threshold of its economic harmfulness is reached, which is 1 beetle per bush.
Raspberry beetle control measures
- Spatial isolation of plantings of raspberries from other plantings of raspberries and blackberries at a distance of at least 500 m to exclude the flight of beetles from them.
- Separate (after a year) cultivation of vegetative and fruiting shoots in ordinary raspberries in order to disrupt food ties with the plant, since annual shoots do not bloom and do not bear fruit.
- Cultivation of flowering and fruiting on annual shoots in August and September of remontant raspberries, which also completely disrupts the food connection of the pest with the plant.
- Loosening the soil in the rows in autumn or spring with mulching with a thick layer of mulch and digging the row spacing (during pupation and the larvae leaving for wintering) to a depth of 20 cm. Mulching with a thick layer of mulch of soil in the rows makes it very difficult or impossible for the beetles to come out after hibernation.
- Repeated shaking off of beetles during budding on a spread tarpaulin, in an old umbrella, etc. This must be done early in the morning, because at temperatures below 15 ° C, they freeze and seem to freeze, so it is easy to shake them off the bush.
- Spraying of bushes and soil around them before flowering with Iskra or Kinmix preparations, and in autumn - Fufanon. During flowering, raspberries should not be sprayed with any preparations.
"Ural gardener" No. 20, 2016