Leeks are a vegetable that everyone loves very much, especially northerners, wrapping leek dumplings, roasting leek boxes, making leeks scrambled eggs, etc. But in the past, for a period of time, people had more scruples about eating leeks, and some people did not even dare to eat them, for the simple reason that many leeks had serious pesticide residues that exceeded the standard. Why do good leeks use so many pesticides? This has to start with a pest that harms leeks, and the culprit of this harm to leeks is leek maggots.
Leek maggots, also known as leek maggots and root maggots, leek late-eye mushroom mosquitoes, belong to the order Diptera, the family Ofopteridae, the genus Ofopteras reticulata, is an omnivorous pest, which can harm more than 30 kinds of vegetables and a variety of edible mushrooms of 7 families, mainly leeks, onions, garlic, leeks, chives, especially like to eat leeks. This insect is also a particularly harmful insect species in China, which occurs almost all over the country and has become the main factor restricting the development of the leek industry everywhere.
Leek maggot larvae are more sensitive to the humidity of the environment, the optimal humidity for survival is between 60% and 80%, and the host humidity is too large to immediately crawl away from the host and no longer eat. The temperature requirements are not high, 20 °C ~ 25 °C is its most suitable growth temperature. Although the adult insects prefer a humid environment, they cannot survive if the humidity is greater than 70%. Young larvae prefer to feed on the stem base and pseudostem of leeks, while older mature larvae prefer to live in the soil.
The larvae of the chick-eyed mushroom mosquito can secrete silk threads, form sparse silk mesh, adhere to the debris of the host, and live in groups under the net for feeding. Moreover, leek maggot larvae are extremely afraid of light, and under the stimulation of strong light, they are constantly tumbling and crawling around.
Leek maggots mainly overwinter in the soil at the base of the leek leaf sheath, in the bulb and around the leek root, and most of the eggs are in hidden places such as the soil cracks around the leek rhizome, under the soil block and the leaf sheath gap. The hatching larvae crawl downwards, nibble on new shoots and young stems of leeks, or gather to feed on the lower part of the leaf sheath and the upper part of the bulb, puncture the epidermis and moth the internal tissue, and continue to decay as the feeding wound decays. New shoots and young stems are affected, the leaves are deformed and the growth is weak, and the growth point is damaged by the heavy ones, resulting in the inability to sprout. Leaf sheath damage, the outer leaf first appear symptoms, the initial leaf tip or leaf unilateral strip yellow wilt, then the whole plant yellowing, leaf wilting, and finally leek yellow wilt lodging. Bulb damage, in addition to causing the plant to wilt and lodging, when severe, the entire bulb rots and the leek bush completely dies. The fields generally occur in dots, and the heavily affected fields show a lack of seedlings and ridges.
At present, the application method of registering the agent for this insect on leeks is mainly to irrigate roots and mix soil. However, due to the pest characteristics of this insect, it is difficult to completely control it, it is very easy to overdose the drug in production, and the abuse of highly toxic pesticides also occurs from time to time, resulting in non-point source pollution of vegetable fields and pesticide residues in leek products exceeding the standard. Over-medication can also lead to resistance to pests, resulting in reduced prevention and control, or even failure of control, forming a vicious circle, the latest method is the integration of mature green prevention and control technologies.
1. Choose a good variety
There are differences in the resistance of different varieties of leeks to leek maggots, choose varieties with good resistance, such as: Yu Leek No. 1, Agricultural Greenhouse Leek No. 1 and 9-2, and avoid planting varieties with poor insect resistance such as Snow Leek King, Bamboo Pole Green, 91-2 and Wide Leek King. When directly transplanting leek roots, pay attention to the selection of varieties with strong tillering ability, compact plant type and good uprightness, which is conducive to compensating the yield after mild damage and enhancing field ventilation.
2. Transplant seedling treatment
Before transplanting leeks for colonization, the treatment of leek plants can reduce the harm of leeks during the production period. Fine seedlings, remove weak seedlings, diseased seedlings and leek seedlings with insects, and then spray or dip root treatment with insecticidal and bactericidal agents, and dry the liquid before colonization. Disease prevention can be prevented with 106 spores/g oligoandrospermum wettable powder 6000 times liquid, and 1.8% avermectin wettable powder 2000 times liquid insecticide.
3. Soil selection
Leeks are fleshy roots, and high yield and fertility, it is advisable to choose soil blocks with convenient drainage and irrigation, good ventilation and fertile texture. In terms of soil selection, avoid plots with lily crops with previous stubble and rotate crops with a maturity of more than 3a. Leek leek maggot adults can spread about 100m, leek seedlings and colonization plots should be more than 100m away from lily crops such as onions, leeks and garlic and edible mushroom planting sheds. Different types of soils are associated with the occurrence of this insect, and generally clay soils occur in smaller quantities than sandy loam soils.
4. Fertilize
Leeks have a long growth period and a large demand for nutrients, and they need to apply plantar fertilizer before colonization. General fertility conditions recommend every 667m2 application of decomposition organic fertilizer 8000kg ~ 10000kg, calcium superphosphate 50kg and potassium sulfate 30kg as the bottom fertilizer, to moderate deep application, organic fertilizer to fully decomposed chicken manure is the best. During the growth and harvesting of leeks, it should be timely fertilized, and the application of organic fertilizer should be trenched and deeply applied to cover the soil, and the chemical fertilizer should pay attention to the balance of nitrogen, phosphorus and potassium. Leek maggots increase with the increase of fertilization level, so it is necessary to fertilize according to the soil fertility situation, and the soil formula can be measured for fertilization. Do not water during the summer rooting period, apply less fertilizer, and drain in time.
5. Water
Open leeks should be watered with frozen water during the night freeze season in the field, which is conducive to reducing the amount of wintering insects. Every 667 m2 before watering and freezing water can be applied according to the fertility of the plot, and deep hoe in the middle of the tillage. After the spring thaw, spring irrigation depending on the moisture situation can also kill some of the overwintering larvae.
Facilities for leek production can be used underground drip irrigation. Underground drip irrigation can not only meet the water requirements of leeks, but also keep the surface soil of leek fields dry, which is conducive to reducing the density of larvae.