Symptoms and damage of corn rough dwarf disease

Today I will introduce to you how to better prevent and treat corn dwarf disease:

Corn damage symptoms

Corn can be infected and develop throughout the entire growth period, with the most serious damage in the seedling stage. Symptoms can be seen in 5 to 6 leaves, and transparent oil-soaked chlorotic dotted lines begin to appear at the base of the heart leaf and on both sides of the midrib, gradually spreading to the entire leaf. The diseased seedlings are dark green, the leaves are stiff, wide, short and thick, the heart leaf cannot unfold normally, the diseased plants grow slowly and are dwarfed. Waxy white raised stripes appear on the veins on the back of the leaves, and there is a noticeable roughness when touched by hand. The leaves of the plant are wide, short and stiff, the leaf color is dark green, the internodes are short and thick, and the top leaves are clustered like Clivia. There are waxy white stripes of varying thickness on the veins of the back of the leaves, leaf sheaths and bracts, which have a noticeable roughness. At the 9 to 10-leaf stage, the dwarfing phenomenon of the diseased plants is more obvious, the upper internodes are shortened and thick, the top leaves are clustered, and the height of the diseased plants is less than half of that of the healthy plants. Most of them cannot produce ears and bear fruit. Although some male ears can be pulled out, they have very few branches and no pollen. The fruit clusters are deformed, with very few filaments, the plants are severely dwarfed, the male clusters are degenerate, the female clusters are deformed, and in severe cases, no fruit can be produced.

Maize Rough Dwarf Disease

Corn Symptoms

Since 1993, the occurrence of maize rough dwarf disease (MRDV) has shown a clear upward trend, causing great losses to the maize production in our city. When it broke out in 1996, the disease rate of general diseased fields reached 40%, and the average yield reduction was 10% to 30%. It broke out in the Huanghuai region for three consecutive years from 2007 to 2009. How to control maize virus diseases, especially the harm of maize rough dwarf disease (MRDV), has become a very practical issue. Therefore, in recent years, we have conducted a systematic investigation and research on maize rough dwarf disease. The study found that 85.16% of the maize plants in the diseased plant samples were basically non-productive or non-productive, the plant height was only 1/2 of that of the healthy plants, there were no female ears or no grains in the female ears; 98.44% of the plants had a grain weight loss rate of more than 50%.

Corn morphological characteristics

The virus particles are spherical. The inactivation temperature is 800C. It can survive for 37 days at 20℃. The virus is spread by insects, mainly the gray leafhopper, and it is a persistent virus transmission. The incubation period is 15-20 days. It can also infect wheat (causing blue dwarf disease), oats, millet, sorghum, barnyard grass, etc.

Disease characteristics of corn

In northern my country, the rough dwarf virus overwinters in winter wheat and other weed hosts. It can also overwinter in the bodies of virus-transmitting insects. After corn emerges from the ground the following year, the virus is transmitted to corn seedlings or sorghum, millet, and weeds by virus-transmitting insects, and then spreads and causes harm. Corn is susceptible to the disease before the 5-leaf stage, and its resistance increases after the 10-leaf stage, so even if it is infected, the disease is mild. If the corn encounters the peak of migration of virus-transmitting insects from the emergence of corn seedlings to the 5-leaf stage, the disease will be serious. Therefore, the sowing period of corn is closely related to the severity of the disease. For example, the corn sown in mid-May in Hebei Province encountered the first generation of gray leaf hoppers at the seedling stage, and the adult stage of gray leaf hoppers was at its peak, resulting in serious disease. The field management is extensive, there are many weeds and gray leaf hoppers, and the disease is severe.

Corn control methods

Agricultural control

In the prevention and control of corn stunt disease, we must adhere to the comprehensive prevention and control policy with agricultural prevention as the main and chemical prevention as the auxiliary. The core is to control the source of toxins, reduce the source of insects, and avoid harm.

1. Strengthen monitoring and forecasting. Focus on regular investigations of the disease rate and severity of wheat, field weeds and corn rough dwarf disease in disease-prone areas, and investigate the occurrence density and virus-carrying rate of SBPH. In late autumn and spring and before corn sowing, make timely and accurate predictions of the occurrence trend of corn rough dwarf disease based on the overwintering base number and virus-carrying rate of SBPH, the diseased plant rate of wheat and weeds, and the corn planting pattern to guide prevention and control.

2. Select disease-resistant varieties. Although there are no disease-resistant varieties among the main varieties currently used in corn production, there are still some differences in the degree of disease susceptibility between varieties. Therefore, it is necessary to select varieties with relatively good resistance according to local conditions, and pay attention to reasonable layout to avoid large-scale planting of a single resistant variety.

In the 1970s, Yunong 704 had a certain resistance to the disease. Currently, no highly resistant varieties have been found in the promoted varieties. The relatively resistant (tolerant) varieties include Ludan 50, Ludan 053, Nongda 108, etc., which can replace susceptible varieties such as Shendan 7, Yedan 53, and Yedan 22 in production. In areas where susceptible varieties have been planted for many years and the damage is serious, it is particularly important to plant these resistant (tolerant) varieties. In Qufu City, corn hybrids such as Ludan 50 and Luyuandan 14 have good resistance to rough dwarf disease.

3. Adjust the sowing date. According to the occurrence law of corn rough dwarf disease, in areas where the disease occurs frequently, the sowing date should be adjusted so that the growth period of corn, which is most sensitive to the disease, avoids the peak period of adult gray leafhoppers and reduces the incidence rate. Spring corn should be sown earlier, generally in late April and early May, and interplanting corn in wheat fields should be postponed appropriately, generally 5 days before wheat harvest, so as to shorten the symbiotic period of wheat and corn as much as possible and sow them later. There are three main corn planting modes in Qufu City: wheat-interplanting corn, stubble corn and late-sown corn. Among them, wheat-interplanting corn has the most serious disease, followed by stubble corn and then late-sown corn. Spring corn should be sown before mid-April; summer corn should be sown in early June.

4. Remove weeds Roadside and field weeds are not only the seed source base for farmland weeds next year, but also the overwintering and summering hosts of the maize rough dwarf disease vector, the gray leafhopper. For the remaining weeds in the wheat field, you can first weed manually and then spray pesticides, and the weed control effect can reach about 95%. The advantage of choosing soil treatment is that corn does not coexist with weeds in the seedling stage, which reduces the activity space of the gray leafhopper and is not conducive to the transmission of the virus by the gray leafhopper.

5. Strengthen field management and combine it with transplanting, remove diseased plants in the field, bury or burn them in a centralized manner, and reduce the infection source of rough dwarf disease. Rationally apply fertilizers and water, strengthen field management, promote corn growth, shorten the disease-susceptible period, reduce the chance of virus transmission, and enhance corn's resistance to disease.

Maize rough dwarf virus mainly overwinters in wheat, grass weeds and gray leafhoppers. Therefore, it is necessary to prevent and control wheat bushy dwarf disease, remove weeds at the edge of the field, the edge of the land and the ditch, and reduce the base number of gray leafhoppers. The specific method is: after the wheat turns green, spray 50 grams per mu of 25% cypermethrin. When spraying, the weeds around the wheat field should also be sprayed, which can significantly reduce the insect population density. If necessary, 550 ml of 20% cypermethrin or 45% Roundup Aqueous Solution can be used, diluted with 30 kg of water, and sprayed on the edge of the field to kill the weeds and destroy the living environment of the gray leafhoppers. [3]

Chemical control of corn

The first is to mix the seeds with pesticides. Coating and mixing corn seeds with systemic insecticides can effectively prevent and control the gray leafhoppers in the seedling stage and reduce the spread of rough dwarf disease. When sowing, using 2% seed coating agent to mix the seeds can effectively prevent the harm of gray leafhoppers, and at the same time is conducive to cultivating strong seedlings and improving corn disease resistance. After sowing, use pre-emergence soil treatment agents such as 40% acetyl methacrylate suspension, 50% dua mixture, etc., 550-575 ml/mu per mu, and seal the soil with 30 kg of water.

The second is to spray pesticides. For plots where corn dwarf disease occurs at the seedling stage, the diseased plants should be removed in time, and 25% cypermethrin 50g/mu should be used in time according to the forecast of the insect situation of gray leafhoppers. When the corn is about 5 leaves, spray it once every 5 days, and spray it 2-3 times in a row. At the same time, spray 40% Virus A 500 times solution or 5.5% Plant Disease 800 times solution to prevent and control virus diseases. For individual plots where the effect of soil treatment herbicide before seedling is poor, 20% cypermethrin can be sprayed between the corn rows at 550 ml per mu and 30 kg of water. Be careful not to spray it on the corn plants. Cypermethrin has a rapid killing effect on weeds. All weeds can die 52 hours after spraying, which can reduce the activity space of gray leafhoppers. 45% Roundup water can be sprayed on the edge of the field, but it should be avoided as much as possible between the corn rows to avoid drug damage to the corn.

Summarize

Corn stunt disease is devastating and difficult to cure once it occurs. It is unrealistic to spray some kind of pesticide on the diseased plants to restore them to normal. However, as long as agricultural control and chemical control are combined and linked closely, the spread of its harm can be controlled.