Forecast on the basis of

(1) scab bacteria are widely distributed and abundant, with low base of other diseases and insects

Scab: frequent occurrence areas have seen continuous recurrence in recent years, continuous cropping of wheat-rice and wheat-corn, large stock of straw in the field, and the total amount of bacterial sources is significantly higher than that of perennial, meeting the conditions of pandemic.In the middle and lower reaches of the Yangtze river and the jianghuai wheat region, the germ-carrying rate of rice straw was 2.6% to 7.9%, and the germ-carrying rate of corn straw in the huanghuai wheat region was 0.5% to 4%, and the germ-carrying amount of single rice straw or corn straw was also significantly higher than the perennial.According to recent surveys, ascospores of scab are about to enter the peak period of release from south to north, which is highly consistent with the susceptible period of wheat heading and flowering.

Stripe rust: at present, it has occurred in 3.09 million mu in 235 counties in 8 provinces (cities) of jianghan, jianghuai, huanghuai and southwest wheat region, with an increase of 4% in the area compared with the previous year.At present, the prevalence and spread of wheat in southwest China has entered the stage, and the average leaf disease rate is 0.1% to 2.9% in the north and 16% to 35% in the south, which is close to the previous year.In jianghan plain, sporadic occurrence occurred in the south of huanghuai river, jianghuai river and most wheat areas in northwest China.

Powdery mildew: in most wheat areas, the disease is less serious than that in recent years.The average leaf disease rate was 0.8%-18%.The average leaf disease rate of jianghan, jianghuai and huanghuai was 0.1-1.7%.The average leaf disease rate was 6%-7.9% in the northwest wheat region of gansu and the south of ningxia.Most of north China has yet to see the disease.

Sheath blight: the disease is generally less serious than that of the previous year. At present, 53.27 million mu of blight has occurred in jianghan plain, jianghuai and huanghuai wheat areas, with a year-on-year decrease of 18.7%.The average disease rate was 4.2%-6.4%, with a year-on-year decrease of 13%-40% in most wheat regions.

Aphid: population density was lower than that in recent years, and 15.05 million mu occurred at present, a decrease of 27.8% year on year.In the wheat growing area of southwest China, the average number of aphids was 89-468, decreasing by 24.2%-47% year on year.In jianghan, jianghuai and huanghuai wheat regions, the average amount of aphid per hundred plants was 2.5-16.7, 52.3-69% less than the same period last year.It happened sporadically in north China and northwest China.

Trematosoma: the population density of wheat in north China, huanghuai and jianghuai regions was lower than that of the previous year.In the spring Amoy soil survey, the average amount of insects per sample was 0.2-2.9, with a decrease of 47.6%-92.3% in most wheat regions and an increase of 8.3% in shaanxi.In yicheng, henan province, xixia and nanpi, hebei province, the maximum insect populations were 620, 55 and 24 per square sample, respectively.

(2) the variety layout and wheat development process are beneficial to the occurrence of disease and insect

There was no obvious change in the wheat variety layout in the areas where scab frequently occurred, and the planting proportion of susceptible varieties was as high as 90%. There was a big difference in the growth progress of wheat in the middle and lower reaches of the Yangtze river, the jianghuai river and the huanghuai river, and the flowering period was extremely irregular, resulting in a longer susceptible period and an increased probability of continuous rainy weather.In addition, in the middle and lower reaches of the Yangtze river, jianghuai and other common areas, the resistance of scab to carbendazim was further enhanced, the control effect was reduced, and the threat of scab epidemic was increased.Wheat varieties in the main wheat-growing areas of huang-huai-hai were less resistant to stripe rust, and the cultivars susceptible to powdery mildew, leaf rust and other diseases had a large planting area.In the wheat region of huang-huai-hai, there was a high coincidence between the flowering period of ear raising and the emergence period of adult sucker-worm, which was beneficial to laying eggs.

(3) weather conditions are favorable for the occurrence of diseases and insect pests in the middle and later stages

According to the national center for climate prediction, in April, most of the wheat 0.5 2 ℃ temperature on the high side, east of north China, huanghuai east and northeast of jianghuai, temperature on the high side 2-3 ℃, the middle and lower reaches of the Yangtze river, south jianghuai, huanghuai wheat precipitation 1-2, the more the local bullish 2-5;In may, most of the wheat high temperature 0.5 1 ℃, the huanghuai and jianghuai high 1-2 ℃, the middle and lower reaches of the Yangtze river, jianghuai 1-2, the more the precipitation in north China, north huanghuai precipitation less 1 or 2, local fewer 2-5, northwest eastern wheat normal or less rainfall.The weather conditions were favorable for the prevalence of scab and stripe rust in wheat areas in the middle and lower reaches of the Yangtze river, the jianghuai river and the southern part of the huanghuai river, as well as for the breeding damage of aphids in the ear stage in the north China, the northern part of the huanghuai river and the central and eastern part of the northwest, but unfavorable for the prevalence of stripe rust in the central and eastern part of the northwest.