Pests of rye and protective measures
1.Cotton weevil (Anthonomus grandis) - the most serious pest of cotton. In the late XIX - early XX centuries, the huge damage caused by the weevil was the cause of a number of economic downturns in the United States.
2. Cotton aphid (Aphis gossypii).
3. Cotton shovel (Helicoverpa armigera) and Helicoverpa punctigera - caterpillars, damaging cotton shoots.
4. Green falcon (Creontiades dilutus) is a sucking insect.
5. Spider mites: common (Tetranychus urticae), as well as Tetranychus ludeni and Tetranychus lambi.
6. Thrips: Tobacco thrips (Thrips tabaci) and Frankliniella schultzei
1.Ordinary spider mite (Tetranychus telarius L.) is one of the smallest pests of cotton. The body of the female is ovate in length less than 0.5 mm, in spring and summer it is yellow-green in color, in winter - in orange-red color, on the sides of the body there are two dark spots. The mite is hibernated in the stage of an adult female in soil, on plant remains, on weeds and mulberry growing on the margins of the fields, from where spring moves to cotton seedlings. The duration of tick development in March - April and October is 25 - 30 days, in May and September - 15 - 20 days, in summer - 7 - 12 days. The number of generations per year depends on the meteorological conditions and geographic location and is on the average 10 to 15 generations.
Infection of crops in the initial period is focal. More often, foci occur along the margins of the fields. In favorable conditions for mites, the foci grow rapidly, close together and can occupy the whole field. Sharp snapshots, accompanied by storm showers the number of mites begins to increase again.
On the cotton mite settles on the underside of the leaves (usually in notches and along veins) and on the bracts, forming colonies, often consisting of hundreds of individuals. The tick plaits the leaf from below with a thin web of gray color. While eating, it completely sucks the contents of the cells together with the chlorophyll grains.
On the upper side of the leaves, red spots appear over the affected areas. When the plants are severely affected, they merge, the sheet from above becomes red, then turns brown and falls off. On many varieties of cotton on the upper side of the leaves, brown, small spots are formed due to a through puncture and complete exhaustion of the cell sap. With mass reproduction in individual fields, the mite can cause the leaves to fall off, bypassing the stage of their reddening.
The loss of harvest depends on the number of mites and the duration of its stay on plants. If the tick remains for one decade to 163 mites per 100 leaves of affected plants (biological threshold of damage), the mite does not cause crop losses. The economic threshold of damage depends only on the number of affected plants on the field and the cost of treatments. It ranges from 200 in 575 individuals per 100 leaves of affected plants or from 40 to 80 individuals per 100 leaves of all plants on the field.
In natural biocenoses, where plants grow in unfavorable conditions and are eroded, the number of spider mites is kept by natural regulators - predatory insects at a low level; in biocenoses of cotton fields, getting a better feed on a large area, a spider mite can multiply intensively throughout the growing season. Chemical treatment against spider mite is carried out in the presence of 5% of plants planted with mites or 150 or more pests per 100 leaves.
With a severe defeat of sowing with a spider mite and not taking appropriate measures to combat it, the yield losses of raw cotton are 35% -50%.
2.Cotton damage seven species of aphids, but the greatest damage is caused by alfalfa aphid (Arhis medicaginis Koch.), Melon aphid (Arhis gossypii Glov.) And large cotton aphid (Acyrthosiphon gossypii Mordv.).
Aphids are small sucking insects with incomplete transformation from the order of proboscis. The length of the body is 1.2 - 4.0 mm. At the end of the abdomen, they have an outgrowth called a tail, and on the dorsal side there are two outgrowths (juice tubes) through which an adhesive liquid is extracted. The aphid apparatus has the form of a thin proboscis. Leg three pairs. Aphids develop in several forms: wingless viviparous females - virgins, winged viviparous females, oviparous winged females (sometimes wingless), males. Wintering eggs have a kidney-shaped shape, freshly reddish yellowish, later brilliantly - black. Larvae are cast from viviparous females only in size and color.
Aphids settle on the most delicate parts of plants - apical shoots and young leaves, pierce them with a proboscis and insert salivary glands into the tissues of the leaf. As a result, the tissues are destroyed. If the sprouts are damaged, the apical bud dies and a "fork" is formed. Leaves damaged at a later date are twisted, wrinkled and often fall off. Plants damaged during the formation of fruits, discard buds and ovaries. Afterwards, although they recover, they give a reduced crop. Harvest losses often exceed 20%.
During the opening of the boxes, the fiber is contaminated with its secretions. The contaminated fiber is stuck together. On it settle black fungi, causing the blackening of the fiber and its destruction.
During the development period, a large number of females die under the influence of unfavorable meteorological conditions. The greatest importance is the precipitation. A small amount of precipitation favors the development of aphids, large-drop, long rains wash and destroy them. The duration of development of aphids varies from 3 to 20 days depending on the temperature (at a temperature of 28 ° - three days, 22 ° - six, at 15 ° - 12 and at 12 ° - 20 days). The life span of a wingless female is 10 to 30 days, which depends on both temperature and nutrition. Fertility of a wingless viviparous female - up to 150 larvae for the entire period of life, or five to six larvae per day. The life span of a winged female is about 14 days. It gives birth to one or two larvae per day. The maximum fecundity of aphids - 150 larvae - falls on the period with an average daily temperature of 18 ° C with a maximum at day 30O and a minimum of 10 O - 12 O of heat. For the season gives up to 26 generations.
On cotton, aphids can live all summer and autumn. Under favorable conditions at the end of May - June, it multiplies in huge numbers. At the end of June and beginning of July, the number of aphids on cotton decreases sharply due to the activity of predators, parasites and unfavorable conditions, and at the end of August and September it again increases, and only sometimes the mass reproduction of aphids on cotton occurs at the end of July. Chemical treatment against aphids is carried out in the presence of 5% of plants planted aphids or 50 pests per 100 leaves.
3. Cotton shovel, or box worm - large butterfly (up to 40 mm in the span of the wings), brownish-yellow with kidney-like and round spots on the front wings; hind wings yellowish-white with a dark, half-moonlike spot in the middle and with a wide dark band at the posterior margin.
Young caterpillars have yellow, green, dark - violet or brown color with a dark longitudinal strip in the middle of the back and large broad dark strips on the sides. Adult caterpillar up to 45 mm long from greenish - yellow to dark greenish - black color. On the back and sides of the black - brown wavy strips with sparse hairs on dark warts. At the narrowed end there are two parallel spines - an appendix.
On cotton, the first-stage caterpillars damage the flower buds and young buds of the apical part of the plant. As the growth caterpillars descend on the branches of the middle and lower tiers of the bush, damaging the contents of large buds, flowers. In later ages, they bite into the middle of the formed boxes, feeding on seeds until they harden. Damaged fruit elements fall off, and large boxes rot. One caterpillar for life can damage 20 fruit organs, two of them – three capsules. Especially large losses from a cotton shovel at the end of vegetation, when newly formed boxes can no longer yield.
Among the natural enemies of a cotton scoop on cotton crops, 22 species of parasitic and 16 species of predatory insects have been recorded. Among them, the most important in reducing the number of pests are Gabrobracon, Apantheles, Rogas, Anilasta, Amblyteles, carnivorous bugs, goldeneyes.
Pheromone traps are used to detect a cotton scoop. For 7-10 days before the expected summer, butterflies of a cotton scoop for each 10 hectares of cotton crops are hung on one trap, and when the first butterfly is caught, the number of traps is increased to one for every 5 hectares. The number of caught butterflies (more than 4 - 5 pieces) allows to predict the development of the pest in the crop and the time of appearance of the caterpillars.
Agrotechnical measures of pest control
1. Reducing the area of pest breeding centers by consolidating field maps, plowing the borders, eliminating small irrigation networks, developing adjacent fields, re-landings and other empty lands.
2. Destruction of the wintering stock of pests by:
a) plowing and digging the margins of the fields, banks of the irrigation and drainage network, meadows, roadsides, marsupial circles of mulberry and other trees around fields and adjoining backyard plots. Destruction of plant remains and mallow plants;
b) removal of mulberry trees and other trees surrounded by fields, pruning, putty, cracks, wounds of bark, whitewash of trunks.
3. Destruction of wintering stock of eggs of large cotton aphid, spider mite and other pests by:
a) uprooting of the Guzapai with roots with the help of the RV - 4, HC - 3 - 6 machines to a depth of 25 cm and its removal from the fields;
b) deep autumn plowing with a turn of the plow by plows with a skimmer or two-level plows to a depth of 30 cm, and in fields heavily clogged by perennials - by 35 cm;
c) Winter reserve irrigation, where soil conditions and reclamation conditions allow, which contributes to the accumulation of soil moisture for obtaining amicable shoots that are viable and resistant to pests.