Occurrence and control of citrus whitefly

Orange naked whitefly Dialeurodescitri (Ashmead), also known as citrus whitefly, Bemisia Tabaci, orange whitefly. In recent years, the harm of citrus orchards in the counties (districts) of northwest Fujian is very serious, and it has changed from local to piece, and has a tendency of aggravation. Adults and nymphs suck plant sap, the injured leaves turn green and turn yellow, and secrete a lot of honeydew, which pollutes the leaves and fruits, which often causes the outbreak of soot disease, especially in the near ripening period of the fruit, which seriously affects the appearance quality of the fruit and causes great economic losses to the fruit growers. It has become the main pest in citrus production.

1. Occurrence regularity

Citrus whitefly occurs five generations a year in northwest Fujian, mostly overwintering with 3rd instar nymphs and pupae, Eclosion into adults in late February and early March of the following year, and begins to mate and lay eggs 3 days later, with an average of 142.5 eggs per female. Parthenogenesis can also be carried out, and its offspring are males. The adults tend to tenderize and always chase the young leaves at the top to lay eggs with the growth of the plant. therefore, the distribution of citrus whitefly in citrus plants is as follows:

Newly laid green eggs, blackened eggs, early instar nymphs, old nymphs, pseudo-pupae, newly emerged adults. The egg is inserted into the leaf tissue from the stomata of the leaf by the egg stalk, which is not easy to fall off. The development of the worm is very irregular and its generations overlap. Within 3 days after hatching, the nymph can do a short distance on the back of the leaf. When the mouthparts are inserted into the leaf tissue, it begins to live a solid life, often reaching tens to hundreds of heads per leaf, and likes the wet environment. The peak periods of adults are in the first and middle of May, the first and middle of July, the first and middle of August, the first and middle of October and the following year from late March to early April. The peak period of early nymph is in the first and middle of March, the first and middle of April, the first and middle of June and the first and middle of September respectively. The peak period of early nymph is the key period of chemical control.

2. The cause of the outbreak

First, there is no establishment of disease and pest prediction mechanism, blind spraying, especially the frequent use of broad-spectrum insecticides, killing a large number of natural enemies, at the same time, tangerine farmers lack understanding of the occurrence law of the pest, delay the appropriate time for prevention and control, and spray only the leaf surface to ignore the back of the leaf; second, the crown is tall and closed, and it is difficult to spray, which leads to leakage and leakage treatment. Third, the freezing injury in the winter of 1999 seriously damaged the citrus orchards in various counties (districts) in northwest Fujian, and the enthusiasm of many orange farmers was frustrated, coupled with the low fruit prices in recent years, which led to the loss of management or even abandonment of some orange orchards; fourth, the mixed planting of many kinds of fruit trees was quite serious, which also caused some difficulties in prevention and control.

3. Prevention and control methods

The method of comprehensive management is adopted, based on agricultural control, biological control technology is actively applied, according to the occurrence law of insect pests, chemical, biological and physical control measures are used to control the occurrence of insect pests economically, safely, effectively and easily.

First, biological control: first of all, it is necessary to protect and make use of natural enemies, such as Chrysosporium whitefly, ladybug, lacewing, flower bug and parasitic wasp. When the pest is serious, aphids can be artificially propagated and released (also known as Encarsiaformosa).

Second, physical control: the insect has a tendency to yellow, and a yellow board can be set up to trap and kill adults. The method is as follows: using waste fibreboard or cardboard, cut into 1 m × 0.2 m long strips, paint orange yellow, and then apply a layer of sticky oil (which can be evenly adjusted with No. 10 engine oil and a little butter), and set up 50 pieces per mu, which is equal to the height of the plant. When the whitefly sticks all over the board, you need to reapply the sticky oil in time, and you can usually reapply it every 10 days. Yellow board trapping and releasing aphid wasps can be used in coordination.

Third, pesticide control: due to the overlap of generations of whitefly, it is difficult to control whitefly, and there is no effective pesticide for all insect states at present. Therefore, chemical control must be applied several times in succession, focusing on the first and second generation nymph control in the first and middle March and the first and middle April. The available medicaments are 25% Aktai water dispersible granule 7500 times solution and 2.5% kungfu EC 1500 times mixture or 50% kuron 1500 times solution and 2.5% kungfu EC 1500 times mixture, which has a special effect on whitefly, pay attention to spray together with the orchard ground.

Fourth, agricultural prevention and control: reasonable shaping and pruning, thinning of over-dense gardens, sawing off excess main branches and thinning over-dense side branches before bud germination in early spring; summer pruning should first remove overdense long branches and erect branches, leaving mediocre branches and oblique branches, so as to facilitate ventilation and light in the crown and reduce harm. At the same time, the cultivation management should be strengthened, and the measures of wiping buds and shoots should be adopted to break the food chain of whitefly, so as to reduce the source of insects, reduce the damage and reduce the times of spraying. In addition, pay attention to do a good job of orchard drainage, increase the application of phosphorus and potassium fertilizer, reduce the number of nitrogen fertilizer sprayed outside the roots, and improve the resistance of trees to diseases and insect pests. In addition, because the citrus whitefly propagates rapidly and has the ability of migration, it is easy to spread, so the orchards in a certain area should pay attention to the joint control in order to improve the overall control effect.