How to control diseases and insect pests from mature to deciduous period of pear trees?

How to control diseases and insect pests from mature to deciduous period of pear trees?

1 main characteristics and occurrence regularity of diseases and insect pests

1.1 Pear scab

In the young fruit stage, the spores formed on the injured shoots are the source of re-infection of the disease. In the early stage of leaf damage, yellow and white dots appeared along the main vein or branch vein on the back of the leaf, and then formed a round or irregular disease spot, and soon dark green mildew appeared on the disease spot, and when the leaf became serious, the leaf became yellow, resulting in shedding. The fruit can be infected from the young fruit to the mature stage, but the infection rate is high in the fruit expansion period in general years. In the early stage of fruit disease, after the appearance of light yellow spots on the fruit surface, the disease spot gradually expanded, forming a round or irregular disease spot. Under suitable conditions, black mildew grew quickly on the disease spot. The tissue of the diseased spot hardened, the growth stagnated, sunken and cracked with the expansion of the fruit, the seriously diseased fruit was deformed, the taste was bitter, and it was easy to fall early (figure 1).

Fig. 1 damage of fruits and leaves infected with pear scab (photo: Liang Kuijing)

1.2 Black spot of pear

Young leaves are generally susceptible to disease. The susceptible leaves enlarged into nearly round or irregular spots from July to August, and black mold appeared on the surface of the spot when it was wet. There are often several disease spots linked together to form a large disease spot, resulting in leaf deformity and early shedding. After the young fruit was damaged, large black spots appeared on the fruit surface, which gradually expanded into a round or oval shape (figure 2). The disease spot is slightly sunken and cracked, and sometimes the cracks can be as deep as the fruit core. Black mildew often appears on the disease spot, and the diseased fruit is easy to fall early. More humidity is conducive to the prevalence of the disease, and closed orchards and poor ventilation are conducive to the disease.

Fig. 2 damage of fruits infected with pear black spot (picture from the Internet)

Fig. 3 damage of fruits and trunks infected with pear ring disease (picture from the Internet)

1.3 Pear ring disease

The infected fruit showed symptoms in the near mature stage (figure 3). At first, a small brown moist spot was formed on the fruit surface with the lenticels as the center, and gradually expanded into a brown round spot with concentric wheel lines, and small black spots grew on the spot. The new disease spot on the branch appeared in the middle of August, initially taking the lenticel as the center, producing reddish-brown water-stained near-round disease spot, followed by tumor-like protuberance.

1.4 White star beetle

It mainly harms the fruit, and the harm of the injured fruit is more serious. Often several adults gather on one fruit to feed, causing the fruit to rot. The adults appeared in the first ten days of May, and the maximum occurred from June to July until the fruit was harvested. Adults are active during the day and often gather to feed on fruits with wounds. The fruit can be bitten into a big hole. Adults have phototaxis and pseudo-death, and have a strong tendency to the sour taste of fruit juice. Adults lay eggs in soil or feces, and larvae feed on humus or plant roots in the soil.

1.5 Pear heart borer

Pear heart borer occurred seriously in pear and peach mixed planting or in orchards adjacent to pear orchards and peach orchards. The first and second generations of pear heart borer larvae mainly damage peach shoots, and the third and fourth generations mainly harm pear fruits. In the single planting pear orchard, before June, the pear fruit has many stone cells, the pulp is hard, and the young fruit is not easy to be eaten, which generally only harms the new shoots and petioles. The adults sometimes lay their eggs on the fruit damaged by the pear heart borer or pear weevil or on the mechanically damaged young fruit, and the hatched larvae eat at the injured part of the fruit, but the survival rate is low. After early June, the pear fruit begins to lay eggs until the fruit is harvested. However, the number of eggs was very small before late July, and increased after late July, and the number of eggs in fruit was very large until the middle of August. Adults like to lay eggs in the calyx pits of the fruit, and the eggs are scattered. After hatching, the larvae crawl on the fruit surface for 1-2 hours, and then enter from the fruit carcass. In the early stage of fruit decay, the hole was larger, the larvae did not enter the core of the fruit, and insect feces were excreted, the hole became black and rotten, and gradually expanded, and the injured area was slightly sunken (figure 4). When the fruit is damaged after late July, the borer hole is very small, the surrounding yellowish brown is like a fruit spot, and there are no symptoms at the borer hole, so it is not easy to find that the larvae can eat directly into the core of the fruit and damage the pulp and seeds. After fruiting, the young fruit pupates in a hidden place such as in the warped skin of the trunk or under the earth and stone. The third generation adults appeared in late August, which mainly laid eggs on pear fruit, and the larvae were still harmful to fruit decay. After shedding fruit, the mature larvae look for a suitable place to survive the winter.

Fig. 4 the pores of pear heart borer in the fruit (picture from the Internet)

1.6 Peach heart borer

It is not only one of the main pests of pear trees in northern Hebei and western Liaoning, but also the main pest of apple. In order to harm the larvae, the larvae feed vertically and horizontally in the fruit, gradually reach the core of the fruit, eat the seeds, and put the feces in the fruit. The affected fruit yellowed and fell off early. After the larvae shed fruit, they gradually blackened and rotted around the pores. When the damage is serious, the fruit will drop a lot. In Hebei pear area, the overwintering larvae began to be unearthed in late May, and the peak unearthed period was in mid-late June. After being unearthed, the larvae crawl to the cracks in the soil and stones at the base of the tree trunk to spin cocoons and pupate. The adults appeared in the middle of June, and the peak period was in the first and middle of July. Adults mostly Eclosion in the evening, nocturnal activity, mating, oviposition. After hatching, the larvae first crawl on the fruit surface, and then eat into the fruit, the hole is very small, not easy to find, 1-2 days later, white juice flows out of the hole, forming a small dot. The larvae matured and lost fruit after feeding in the fruit for 25 or 28 days. The mature adults shed fruit in late August and reached the peak period in early September until the fruit was harvested. After shedding fruit, the larvae look for a suitable place to be buried in the soil to make a flat cocoon overwintering.

1.7 Tea wing bug

Nymphs after 2 years old are more lively and crawl rapidly, and several nymphs often inhabit at the same time on a fruit or leaf. The seriously damaged fruit can be turned into malformed fruit (figure 5). For the lightly damaged fruit, there are dark green and slightly sunken damage spots on the fruit surface during harvest. The occurrence period of eggs and nymphs is longer, eggs still hatch until August, adults appear in early August, adults and nymphs continue to harm the fruit. After mid-September, adults fly to houses, stone crevices and other places to survive the winter.

Fig. 5 the fruit is damaged by the tea wing bug (picture from the Internet) [Jishan Huayao]

1.8 Daqing leafhopper

In the young tree garden, the adult leafhopper lays eggs on the branches, resulting in the death of young trees, which is the main pest of pear young trees. Three generations a year, the first and second generations occur on crops and vegetables, and the third generation of adults occur from September to November and transfer to autumn vegetables after harvest. The fruit trees began to spawn in the middle of October, and the spawning peak was in late October, and overwintered in egg state. The adults lay eggs on 1-2-year-old branches or seedlings, with a crescent-shaped wound in the spawning site and 7 eggs and 10 eggs in the wound. Badly injured tree trunks or branches are covered with scars, which make branches or young trees strip due to water loss, and are vulnerable to freezing injury, even leading to death.

2 prevention and control measures

The prevention and control of diseases and insect pests during fruit ripening is mainly artificial control, which roughly includes the following five aspects.

2.1 picking and falling fruit

The fruits harmed by diseases and insect pests are easy to fall off ahead of time, and the fruit should be picked up and cleaned in time when the fruit is near maturity. In order to eliminate the pathogens overwintering on the fruit and the pear heart borer and peach heart borer without falling fruit.

2.2 artificial hunting and killing of adults

During the fruit harvest period or after harvest, most of the adults fly to the orchard to overwinter, and use this habit to capture manually in order to reduce the source of insects in the following year. Apple Cider Vinegar was used to trap and kill by using the pseudo-dead shock tree of the adult white star beetle, or its tendency to apple juice.

2.3 preventing the harm of oviposition of the leafhopper

(1) whitening: adults paint white on tree trunks and branches before laying eggs to prevent adults from laying eggs. (2) trapping: using black light to trap and kill adults. (3) wrapping paper or plastic tape: wrapping paper or plastic tape on the branches of young trees can prevent the leafhopper from laying eggs and prevent water loss. (4) spraying: when the occurrence is serious, spray 20% permethrin EC 2000 times, 10% cypermethrin EC 2000 times or 90% trichlorfon crystals on the tree during the adult spawning period.

2.4 Pear trees return to their roots after falling leaves

Falling leaves and returning to the roots of fruit trees is an economic and effective way to solve the shortage of organic fertilizer in orchards and to control diseases and insect pests. The northern pear area is generally from late October to mid-November, when pear trees have fallen leaves more than 90%, dig ditches 60 cm deep and 40 cm wide under the crown, and the ditch length varies according to the size of the crown. The withered branches, fallen leaves, diseases, insects, fruits and weeds were buried together in the ditch, or at the same time with the application of base fertilizer in autumn.

2.5 strengthen cultivation and management to improve the resistance of fruit trees to diseases and insect pests

Reasonable pruning to regulate the relationship between vegetative growth and reproductive growth of fruit trees, by controlling the load, enhancing the accumulation of nutrients, rational fertilization and irrigation in the growing season. Proper amount of urea or potash fertilizer was added when spraying in summer to increase the accumulation of tree nutrients. Make the tree body strong, enhance the function of fruit tree leaves, improve the resistance to a variety of diseases, especially some weak parasitic bacteria, and have a certain tolerance and compensation to pests. In short, in the prevention and control of diseases and insect pests, the effects of various factors affecting the occurrence of diseases and insect pests should be comprehensively considered to improve the stress resistance of fruit trees themselves.