The technique of preventing and controlling persimmon velvet scale is spraying control of overwintering nymphs at the dormant stage and the eggs of each generation at the end of hatching.

The technique of preventing and controlling persimmon velvet scale is spraying control of overwintering nymphs at the dormant stage and the eggs of each generation at the end of hatching.

Persimmon velvet scale [Asiacornoccus kaki (Kuwana)], also known as persimmon cotton scale, persimmon felt scale, persimmon felt scale, persimmon pink scale, persimmon lice, belongs to Homoptera and Coccidae. It is a common pest of persimmon trees with difficult root control and serious damage. Domestic distribution in Henan, Hebei, Shandong, Shaanxi, Anhui, Guangxi and other provinces, Puyang Nanle, Qingfeng, Fan County, Taiqian and other counties have distribution. Its nymphs and adults are harmful to persimmon fruits, twigs and leaves, resulting in falling flowers and fruits, weakening the tree potential, seriously affecting the growth, flowering, fruit setting and fruiting of persimmon trees. In recent years, through systematic observation, research and exploration of persimmon scale, combined with the production practice of persimmon farmers, we basically found out the local occurrence law of persimmon scale, and summed up a set of effective prevention and control measures for fruit farmers' reference.

1 morphological characteristics

The female adult (figure 1) is about 1.5-2.5 mm long and 1-2 mm wide, flat, oval, dark purple or red, with conical spines on the back, short and stout, slightly obtuse at the top, slightly equilateral triangular from the side; ventral smooth, with unequal body hairs The antennae are short, 3-4 segments, 3-4 segments are columnar, isomorphic and long, sometimes merged into 1 node, on which there are about 10 bristles of different thickness and length; there are white curved fine hairy waxy secretions on the edge of the abdomen, which are wrapped in a white felt wax sac such as rice grains when ripe. The male adult is small, about 1 × 1.2 mm long and 0.5 mm wide, purplish red; the antennae have 9 nodes, each node has 2 bristles; the wings are dark white and translucent; the ventral end has a pair of white wax filaments as long as the body, and the sex spines are short; the scale shell is oval and the texture is the same as that of the female adult. The egg is oval, about 0.3-0.4 mm long, purplish red, with white wax powder or silk on the surface, concentrated under the wax shell of the female adult. The oocyst is pure white or dark white felt, straw sandal-like, protruding adaxially, the head end is oval, the ventral end is invaginated to form a clamp, and there are stout waxy hairs on the surface. The overwintering nymph is flat, oval or oval, purplish or carmine red, about 0.5 mm long, with short prickly protuberances all over the body, shaped like a hedgehog. The pupa is about 1 mm long and rouge red; the shell is about 1 mm long and 0.5 mm wide, oval, flattened up and down, and there is a transverse crack around the end. The shell is divided into two layers, and the whole shell is composed of dark white flocculent wax.

Fig. 1 Persimmon velvet scale (female adult)

Fig. 2 Persimmon scale (hatched by a generation of nymphs)

2 occurrence regularity and habits

The persimmon velvet scale has four generations a year in Puyang area, and the last generation of 1st and 2nd instar nymphs overwintered in the cortical cracks of branches, bud scales, dried persimmon stalks and coarse bark gaps of the trunk. After the sprouting of persimmon trees in the second year (March 28 to April 6), the overwintering nymphs began to move, climbing to the buds, petioles, leaves and shoots to absorb the juice. After the shoot was killed, black spots appeared, the growth was weak, it was difficult to germinate, or even withered; the petiole became black and deformed and fell off ahead of time; the young leaves were damaged, wrinkled and deformed, and the leaves fell ahead of time. In the middle of May, the insect back formed a complete white velvety scale shell, which differentiated into male and female. When the adults mate in the middle and late May, the scale shell of the female adult is the oocyst. After mating, the oocyst changes from pure white to dark white, that is, it begins to lay eggs, and the eggs are laid behind the mother under the scale shell. Each female laid 50-160 eggs, with a maximum of about 340 eggs. The parasites on the fruit laid the most eggs, followed by the leaves and the branches. As a large number of eggs are produced, the mother shrinks to the front of the scale shell. If the posterior edge of the oocyst is slightly warped, it is the peak spawning stage, and the large and slightly red trailing edge is the peak incubation stage. The oocysts with red dots, valgus shedding, implicated filaments and small red spots on the fruit are the late hatching stage (figure 2) and nymph immobilization stage. The egg period is about 21 days at 17: 18 ℃ and 12 days at 31: 32 ℃. After hatching, the nymphs are scattered in the leaves, tender branches, the lower surface of the fruit and the gap between the persimmon stalk and the fruit (figure 3). The affected fruit changed from green to yellow, and finally expanded into black spots, and fell off from hard to soft (figure 4). According to the monitoring data in recent years, the peak hatching periods of nymphs of the first to fourth generation of persimmon scale were in early June, early July, early August and early September, respectively. Each generation is irregular and intersects each other, one generation per month, each generation is generally 15-20 days, and the winter generation is 180-190 days long. The overwintering generation mainly harms persimmon leaves and 1 ~ 2-year-old branchlets. The first generation, the second generation (figure 5) and the third generation (figure 6) [Jishan Huayao] each generation harms persimmon leaves and fruits, and the second generation is the most harmful to persimmon fruit. Around the middle of October, the 1st and 2nd instar nymphs of the fourth generation (overwintering generation) began to overwinter.

Fig. 3 Persimmon velvet scale (first generation nymph on fruit)

Fig. 4 Persimmon velvet scale (fruit damage)

Fig. 5 Persimmon velvet scale (second generation harm)

Fig. 6 Persimmon velvet scale (third generation harm)

3 the causes of the difficulties in radical cure

In persimmon production, fruit growers reported that the spraying effect of the insect was poor and it was difficult to cure it. The main reason is that the local occurrence and hatching law of persimmon scale are not understood, and the best control time can not be grasped. The overwintering nymph of persimmon scale and the peak and end of hatching eggs of each generation, because the insect body is small, it is not easy to attract attention, but once the scale shell is formed, or the upper fruit is drilled into the gap between persimmon stalk and fruit, the effect of spraying will be greatly reduced. Therefore, to grasp the dormant period of overwintering nymphs and the spraying control at the end of hatching eggs of each generation is the key measure of chemical control in the growing period.

4 comprehensive prevention and control technology

4.1 strengthen quarantine

Persimmon velvet scale is often fixed parasitic, the insect body is small, mainly carried by the host branches, scions, fruits and even tree trunks and spread over a long distance. Therefore, the forest pest control and quarantine institutions should strengthen quarantine inspection and re-inspection in the process of procurement, transportation and transportation of seedlings, scions and fruits, and deal with them in time once found, so as to prevent spread.

4.2 artificial control

Combined with orchard management, before the persimmon leaves fall to sprout, cut off the disease and insect branches and persimmon stalks, scrape the branches, dry the overwintering nymphs and the old thick warped skin, clean up the garden in time, burn it centrally, and reduce the source of overwintering insects.

4.3 Chemical control

First, before sprouting persimmon trees in early spring (March 28 to April 6), spray the trees with 3-5 Bomedo stone-sulfur mixture to eliminate overwintering nymphs. Second, after the persimmon leaves are unfolded (early April) and before flowering (May 1-12), before the overwintering nymph stings and leaves the overwintering site, before the wax shell is formed, spray 3% hyperosmotic phenoxyvir EC or 10% imidacloprid wettable powder 2000 times to kill the overwintering nymph. Third, during the peak hatching period of each generation of nymphs, 1.8% avermectin EC 2000 times or 25% thiazinone wettable powder 1000 times were sprayed as appropriate to control the damage of the nymphs.

4.4 Biological control

Try not to use broad-spectrum chemical pesticides as much as possible in the occurrence period of natural enemies so as not to kill natural enemies. The predatory natural enemies of persimmon velvet scale found in Puyang area are mainly red ladybug and Chrysopa sinensis.