There are many dense white spots on the surface of the damaged leaves, and the leaves lose their green and luster. In severe cases, the whole leaves are gray, causing deciduous leaves and affecting the tree potential. When rampant, the fruit surface is covered with gray-white and green spots, and the whole fruit is pale.
Occurrence characteristics of red spider
1, every time the new bud turns green, it is the peak of the mass reproduction and rampant harm of red spider, and each peak is related to the temperature at that time. Generally, there are two damage peaks in spring (April-May) and autumn (9-65438+1October).
Citrus red spider likes light and novelty, which usually occurs first or more in the middle and upper part of the crown periphery, on the sunny slope of hilly orchard and in the sunny part.
① The turn of spring and summer (April-June) is the peak period for the growth of citrus trees, which is rich in nutrients and can provide a large number of amino acids needed for life activities for red spiders; At the turn of spring and summer, the ultraviolet rays of sunlight are relatively strong, which is easy to decompose pesticides; At the turn of spring and summer, the temperature is high, which is easy to transpiration and dilute, and can not reach the lethal concentration of red spider.
(2) In autumn (September), both citrus trees and red spiders have to store a lot of energy for the winter. At this time, citrus trees have accumulated a lot of nutrients, which just provides sufficient nutrition for red spiders. The suitable temperature for the development and reproduction of red spiders is 25℃ ~ 28℃, which is this time.
2. Whether the citrus red spider can occur in large numbers in that year is closely related to the overwintering population base of the citrus orchard in the previous year: once the overwintering population base of the previous year exceeds each spider 1 mite, it may occur in that year.
In the year of drought in winter and high temperature in spring, the average maximum temperature in March reached 20 ~ 25℃, and the monthly rainfall was below10 mm. A large number of eggs hatched in winter and germinated slightly in spring, with sufficient nutrition, and the breeding speed of red spider was accelerated, which caused flooding in that year.
3. High temperature, drought and lack of rain in spring are one of the important factors for the rampant occurrence of citrus red spider, while high temperature in summer is not conducive to its survival and reproduction.
The optimum temperature for the development and reproduction of red spider is generally between 20℃ and 30℃, and the optimum temperature is 25℃, and the mortality rate rises sharply above 30℃.
Rainfall can wash away mites and directly reduce the number of mites, especially in citrus, where the leaflets in the crown are sparse. Panonychus citri likes to eat shoots and new leaves, so its distribution on orange trees often shifts with the appearance of branches.
4. Natural enemies have a significant control effect on the occurrence of panonychus mites, overlapping generations, unreasonable use of pesticides and killing natural enemies in a large area are easy to cause the outbreak of red spiders.
5. Repeated use of copper preparations, such as Bordeaux mixture, is easy to induce the outbreak of red spider. (Copper preparation will accelerate the oviposition of overwintering adult mites and form the peak period of young mites and eggs)
6, warm winter phenomenon, the red spider has no obvious wintering phenomenon, it breeds all year round, and the population base is large, which often leads to the early and rampant appearance of the red spider in the next spring.
7. When applying nitrogen fertilizer, the red spider is easy to explode: at this time, the citrus grows more vigorously, the photosynthesis rate is accelerated, the leaves synthesize more amino acids, and the red spider gets more amino acids needed for life activities. When there is too much nitrogen, the vegetative body of crops grows in vain, and protein synthesis is enhanced.
Therefore, a large number of carbohydrates in crops are consumed, which seriously inhibits the formation of cellulose, lignin, pectin and other substances needed to form cell walls, resulting in the whole plant becoming soft and juicy, and the mechanical tissue is fragile, and the red spider is more likely to obtain amino acids. After the red spider got a lot of amino acids, the development duration of each mite state was shortened and the reproduction speed was accelerated.
Why is Starscream so hard to fight?
1, Starscream is not an insect, so many pesticides are ineffective.
2. It is difficult to cover four forms of red spider with one red spider medicine at the same time.
Red spider has a large reproductive coefficient and frequent generations. There are four forms of eggs, young mites, nymphs and adults on one leaf at the same time. No acaricide can treat all four forms effectively and quickly at the same time.
3. Starscream is small and concealed, so it is difficult to achieve full coverage by spraying, and it is easy to rebound after the drug effect is over.
4. Environmental factors and management mode
There are many generations of diseases and insect pests in citrus producing areas in South China, so it is necessary to use pesticides frequently to control Huanglongbing. Some orange orchards must use copper preparations to prevent canker, and the natural enemies of mites are killed. A large number of pesticides also make mites have strong drug resistance, so the southern producing areas are more difficult to control than the northern producing areas.
5. Practitioners have not mastered relevant technologies.
6. Market behavior factors
The invasion of harmful mites will cause serious losses, and growers hate it and like to do harm to red spiders.
In order to seize the outstanding effect of the market, pesticide production enterprises add hidden ingredients;
Drugstores are worried that the product performance is not exaggerated enough, and growers will stop patronizing and sell multi-component acaricide directly. As a result, large prescriptions are popular in the market, and many ingredients can't fit in one bottle, which greatly accelerates the arrival of the resistance of Starscream.
How to control Starscream?
The combination of multiple drugs has a good effect of delaying drug resistance.
At present, pesticides on the market mainly appear in the form of packaging. Generally speaking, at present, the main components of acaricide produced by pesticide manufacturers are abamectin, spirodiclofen/ethofenprox, bifenazate, bifenthrin/fenpropathrin, profenofos, fluazinam and so on.
At present, the commonly used pesticides are all composed of four ingredients, among which avermectin is used more, and red spiders such as profenofos are also used more when the alkali value is high, mainly because the alkali value is never suppressed, spirodiclofen is used at high temperature, emamectin benzoate and emamectin benzoate can use it alternately, and bifenthrin/fenpropathrin can also be used alternately. As for fluazinam, it is a hot variety in recent two years, and it can also be used appropriately.
The most important tip: As a fruit farmer, you must remember: fill the medicine as needed, take turns to use the medicine, and delay the drug resistance!
Mineral oil has obvious synergistic effect in killing mites.
Many fruit farmers use mineral oil during the garden cleaning period, and the effect is still good. However, if Starscream has a large base, it is not ideal to use mineral oil alone. It is suggested that mineral oil can be properly added when other acaricides are used, so that the mixing effect is obvious and the protection period can be extended.
Note: Mineral oil, triazole tin, propargite and other substances that are easy to cause harm will aggravate the harm. At the same time, the mineral oil from big factories and genuine manufacturers is effective.
How can it really destroy its ancestors for 18 generations!
1, cultivate natural enemies
That is, we often say that predatory mites, generally a leaf with a predatory mite, can effectively control the red spider. However, predatory mites are slow to take effect. If the red spider has broken out, chemical control is still needed.
Controlling red spider with natural enemies has many benefits to the orchard, but if red spider pests have appeared in the orchard now, it is still necessary to give priority to spraying! Because it may be too late to cultivate natural enemies at this time!
2. Rational use of drugs
At present, some orchards are still blooming, and some orchards are ready to enter the next stage. From flowering stage to physiological fruit drop stage, 5% avermectin 5000 times and 24% spirodiclofen suspension 3000 times can be considered.
However, this is only a suggestion, and the specific medication can be adjusted according to the situation. Do not use it alone! According to the occurrence regularity of red spider in different stages and the resistance level of red spider in their respective orchards, the pesticides were screened.
3, the following, give you advice on medication at all stages, you can use it as a reference:
Garden cleaning period: mineral oil 200-300 times +5% avermectin 5000 times, initial flowering period: 5% avermectin 5000 times +20% emamectin benzoate suspension concentrate 3000-4000 times; From flowering stage to physiological fruit drop stage: 5% avermectin 5000 times +24% spirodiclofen suspension 3000 times; Summer bud germination period: 30%(20+ 10) triazophos emamectin benzoate suspension concentrate 5000 times+. Spraying in the afternoon) from fruit swelling stage to fruit picking stage: 45%(30+ 15) bifenazate pyrazole suspension 5,000 times (or 24% spirodiclofen suspension 3,000 times +5% avermectin EC 5,000 times) 4. Precautions.
Finally, give you some precautions! Starscream is not easy to fight, so be sure to pay attention to details!
Once you see Starscream, you must take medicine in time. Stop waiting! Because wait, Starscream may explode! In orchards or newly planted orchards where red spiders have occurred before, whether or not red spiders are seen before flowering in early spring, pesticides should be used to kill eggs and larvae, and then after about 15~20 days (to avoid flowering), it is decided whether to continue to use pesticides according to whether red spiders have occurred or not; If it is not controlled in the early stage and the red spider breaks out, we must insist on medication. After spraying the pesticide, spray it again every 5-7 days (returning carbine) for 2-3 rounds continuously to avoid another round of insect pest after the spider eggs hatch. The medicine must be "enough water, it must be penetrated." Spider eggs are generally produced on the back of leaves and grooves in branches, which is not conducive to pesticide coverage. Therefore, be careful when spraying pesticides, and never hit less or miss. The most important thing is to take medicine in turn when you fight Starscream, even if this is not as effective as that, you must take it in turn! Timing is particularly important. For example, in winter, we must clear the garden carefully and never manage it extensively. Finally, pay attention to patrol the orchard to prevent the red spider from erupting again! Concluding remarks
The control of red spider is an important pest and disease project of citrus at present. Fruit farmers must not take it lightly. If they reach the prevention and control targets, they must take precautions immediately. Delay often increases the difficulty of optimal prevention and control. There are some new drugs and even patented drugs on the market, and the temporary effect should still be ok, but if a drug is used for a long time, its drug resistance will definitely rise rapidly.
Starscream is not easy to fight, and the probability of killing ancestors 18 generations in one breath is similar to winning the lottery. However, as long as the occurrence regularity and habits of red spider are mastered, it is not difficult to avoid the harm of red spider to orchard!