Pests of cucumber, watermelon and melon
- Melon aphid
- Common spider mite
- Tobacco thrips
- Control and prevention measures
The polyphagous pests of the main melon crops (cucumber, watermelon and melon) include melon aphids, spider mites and tobacco thrips, which suck the juices from leaves, shoots, flowers and ovaries, causing them to wrinkle, premature yellowing and drying. The growth of the plant is delayed, and with mass reproduction of the pest, it often dies.
Aphids on the leaves
Melon aphid (Aphis gossypii) is widespread on the territory of the European part of the country (the northern border of the range runs along 54 ° N), in the North Caucasus, Transcaucasia, the Middle and Lower Volga regions; it is also noted in Western Siberia. It is a small (1-2 mm long, 1-1.5 mm wide) insect of yellow or greenish-black color. It develops on 330 species of 25 families of cultivated and wild plants (haze, cruciferous, rosaceous, mallow, solanaceous, pumpkin, asteraceae, etc.); also harms eggplant, dill, peppers, carrots, purslane, beans, tomato and many other useful crops.
Usually adult aphids overwinter in open ground on the leaves of many types of winter-green weeds (often under rosettes of basal leaves) and indoors. Under the snow cover in winter, they can withstand temperatures down to -15 ° C, but in spring, in case of high humidity, they can die at -5 ° C. In spring, aphids begin to multiply at temperatures exceeding 5 ° C, but alternating thaws and frosts are fatal for them. In mass, it multiplies in late spring and in the first half of summer, then, after the summer depression, the number of aphids again sharply increases. In especially large numbers, aphids appear in moderately humid and warm weather. Optimal conditions for the life of the pest are formed at a temperature of 16 ... 22 ° C and a humidity of 60-80% (temperatures above 25 ° C are unfavorable), therefore, in the southern parts of its range (July - first half of August), it is often depressed. The fertility of aphids varies depending on the temperature, and it is maximum in the temperature range of 20 ... 25 ° C. Depending on the region where the aphid lives, it gives from 12-15 to 22-27 generations per year.
The melon aphid is capable of forming very dense colonies. It is noticed that the higher the density of the colony, the greater the proportion of winged females and nymphs. Winged females fly away and are carried by air currents to other plants, where they settle and then create new colonies, consisting mainly of wingless individuals. If polyphagous predators (larvae of coccinellids or lacewings) enter the colony, the colony is dispersed (many individuals begin to migrate). At the same time, scientists noted an interesting picture of the spatial structure of the pest population. In the center of the colony there is a female, around her there are uneven-aged larvae, and on the periphery there are old females that are not capable of reproduction. Polyphagous predators, first of all, encounter these ballast individuals, the death of which accelerates the migration of other members of the colony. When “quiet” predators or parasites enter the colony (for example, the larvae of aphidimis gall midges, aphidiids or aphelinids), the migration of aphids is practically invisible.
Aphids are closely related to ants, which actively protect their colonies from beneficial aphidophagous insects, as they constantly feed on honeydew secreted by these sucking insects. Ants even hide aphids for the winter in an anthill, and in the spring they carry them out to plants. The melon aphid is a carrier of dangerous viral diseases.
Common spider mite
Common spider mite (Tetranychus urticae) is ubiquitous where these crops are grown; it causes especially tangible harm to cucumbers indoors in dry and hot summers. It settles on the upper and lower side of the leaf, on the shoots, on the branches, and during mass reproduction - on the fruits. A thin transparent web appears between the leaves and in the internodes of plant stems. Light dots first appear on the leaves, then some parts of them become discolored, after which the leaves die. Damaged plants are pale yellow in color, weaken, become bare, fruiting decreases sharply. By these two signs (by the presence of a cobweb and a point discoloration of the leaf blade), the gardener can easily determine the presence of this pest on his plants.
The tick is also dangerous because, under unfavorable conditions, its females burrow into the soil or secluded places (for example, under fallen leaves), falling into a state of diapause. At this moment, all vital processes of the pest are inhibited (it seems to go into hibernation). With the onset of favorable conditions, the tick leaves this state, begins to develop and multiply.
Tobacco thrips (Thrips tabaci) damages more than 100 species of various plants (it also settles on tomato, eggplant, cabbage, lettuce, legumes, medicinal herbs, etc.). It is a carrier of viral diseases (for example, cucumber and tobacco mosaic). Thrips overwinters as an adult insect in the upper soil layer (at a depth of 5–7 cm) or in plant debris. It has a body 0.8-0.9 mm long, wings are narrow, yellow or grayish-yellow, as if with fringe along the edges.
In the first half of April, he starts feeding on weeds, then switches to plants in protected and open ground. In those places where it pierces the skin of the leaf with its proboscis (more often from the lower side, near the veins), sucking the juice, whitish shiny spots and stripes appear, later becoming dark brown. One female lays about 100 eggs in the leaf tissue within 3-4 weeks. After 3-5 days, larvae hatch from them, which, after feeding on the leaves (8-10 days), go into the soil (to a depth of 15 cm), where after 4-5 days they turn into adults. Winged individuals come to the surface along cracks in the soil, settling on plants.
Tobacco thrips does not form continuous colonies on plants. The cycle of its full development (from the time of laying eggs to the release of an adult insect) takes only 2-3 weeks. In the open field of the southern regions of Russia, tobacco thrips has 3-5 generations, in the protected field - up to 6-8 per year.
The initial typical symptom of thrips damage to leaves is the appearance of an openwork mesh on them; then yellowing and tissue death is observed. Slightly darkened or transparent dots (puncture points by the pest) are marked on the flowers. The active development of the pest leads to the premature fall of the pedicels and set fruits; in some of the flowers, an underdeveloped ovary is observed, which gives small berries.
Control and prevention measures
Among the most important agricultural practices to limit the spread and harmfulness of these types of pests are: the elimination of weeds (especially near greenhouses and greenhouses), on which they winter and additionally feed in the spring before switching to agricultural crops, as well as digging up the soil of closed ground with deep embedding of vegetation. leftovers. A serious agrotechnical measure to curb the spread of, for example, a spider mite is to maintain optimal conditions for plant development and, first of all, high air humidity.
In order to prevent its appearance, it is necessary to pick up old fallen leaves and remove faded flowers. All three types of pests (especially melon aphids) are quite sensitive to the effects of various plant protection products. Therefore, if the damage to plants by these insects is not strong, solutions of insecticidal plants should be used at the first stage of the fight. So, to destroy the melon aphid, you can spray the plants with a decoction or infusion of tobacco and tobacco dust (one weight part of the drug per 10 parts of water), then diluted with three times the amount of water. An infusion of onion husks is used against thrips: 1 liter of husk is poured with 2 liters of warm water, after two days, 6 liters of water and soap are added to stick.
“The list of chemicals and agrochemicals ...” for use in private households offers a fairly wide range of drugs to combat these insects. So, on a cucumber of a closed ground against a spider mite, biological products bitoxibacillin, bicol and fitoverm are effective. Fufanon is used against ticks and thrips on cucumber, melon and watermelon. On cucumber against melon aphids and tobacco thrips, it is advisable to use phytoverm bioinsecticide and chemicals Iskra Zolotaya, Komandor Maxi, and Iskra M and Actellik will also suppress spider mites. Kemifos successfully protects cucumber (indoor), melon and watermelon from ticks and thrips, and the first crop from aphids.
candidate of biological sciences,
Senior Researcher, All-Russian Research Institute of Plant Protection,