Symptoms and Control Methods of Maize Rough Dwarf Disease

Maize rough dwarf disease is a viral disease of maize caused by Maize rough dwarf virus. Maize rough dwarf virus belongs to the plant reovirus group and is a spherical virus with double-stranded RNA and a double-layered capsid. It is transmitted by the small brown planthopper (Laodelphax striatellus) in a persistent manner. Maize rough dwarf disease is an important disease prevalent in the maize production areas of northern China. Let us take a look together at the symptoms and control methods of maize rough dwarf disease!

Damage Symptoms of Maize Rough Dwarf Disease

The virions of Maize rough dwarf virus are spherical, with an inactivation temperature of 800C, and can survive for 37 days at 20°C. The virus is transmitted by insects, and the main vector insect is the small brown planthopper, which transmits the virus in a persistent manner. The incubation period is 15—20 days. It can also infect wheat (causing blue dwarf disease), oats, foxtail millet, sorghum, barnyardgrass, and others.

1. Symptoms: Maize can be infected and develop the disease throughout its entire growth period, with the seedling stage suffering the most severe damage. Symptoms can appear as early as the 5 to 6 leaf stage, beginning as transparent, oil-soaked, chlorotic, thin line-like spots at the base of the young leaf and on both sides of the midrib, gradually spreading to the entire leaf. Diseased seedlings are dark green, with stiff, wide, short and thick leaves; the young leaf cannot unfold normally. Diseased plants grow slowly and are dwarfed. On the veins on the back of the leaves, waxy white raised stripes appear, with a noticeably rough feel when touched by hand. The plant leaves are wide, short and stiff, the leaf color is dark green, the internodes are thick and short, and the top leaves are clustered like a clivia. On the veins of the leaf back, leaf sheath and husk leaves, there are waxy white stripe-like protrusions of varying thickness, with an obvious rough feel. By the 9 to 10 leaf stage, the dwarfing of diseased plants becomes more obvious, the upper internodes are shortened and swollen, and the top leaves are clustered. The height of diseased plants is less than half that of healthy plants, and most cannot tassel or set seed. Although a few tassels can emerge, they have very few branches and no pollen. The ears are deformed, with very few silks; the plants are severely dwarfed, the tassels are degenerated, and the female ears are deformed. In severe cases, they cannot set seed.

2. Damage: Since 1993, the occurrence of maize rough dwarf disease has shown an obvious upward trend, causing great losses to maize production in our city. In the major outbreak of 1996, the diseased plant rate in general diseased fields reached 40%, with an average yield reduction of 10%-30%. It occurred severely in the Huang-Huai region for three consecutive years from 2007 to 2009. How to control maize viral diseases, especially the damage of maize rough dwarf disease (MRDV), has become a highly practical issue. Therefore, in recent years we have conducted systematic investigation and research on maize rough dwarf disease. The research found that: among the diseased plant samples, 85.16% of the maize plants were basically a total loss or a total loss, with plant height only 1/2 that of healthy plants, and no female ears or female ears with no grains; 98.44% of the plants had a grain weight loss rate of more than 50%.

3. Characteristics: In northern China, the rough dwarf virus overwinters in winter wheat and other weed hosts. It can also overwinter in the body of the virus-transmitting insect. After maize emerges the following year, the virus is transmitted by the virus-transmitting insect to maize seedlings or to sorghum, foxtail millet and weeds, spreading and causing damage from one to another. Maize is susceptible to the disease before the 5-leaf stage, and resistance increases after the 10-leaf stage; even if infected, the disease is mild. If the period from maize emergence to the 5-leaf stage coincides with the peak migration of the virus-transmitting insect, the disease is severe. Therefore, the maize sowing date is closely related to the severity of the disease. For example, for maize sown in mid-May in Hebei Province, the seedling stage just encounters the peak period of the first-generation small brown planthopper adults, and the disease is severe. With extensive field management, many weeds and many small brown planthoppers, the disease is severe.

Control Methods for Maize Rough Dwarf Disease

1. Agricultural control methods

In the control of maize rough dwarf disease, it is necessary to adhere to a comprehensive control policy that takes agricultural control as the main measure and chemical control as supplementary, with the core being to control the virus source, reduce the insect source, and avoid damage:

① Strengthen monitoring and forecasting: In areas where the disease frequently occurs, carry out targeted, fixed-point, regular surveys of the diseased plant rate and severity of rough dwarf disease in wheat, field weeds and maize, and at the same time investigate the occurrence density and virus-carrying rate of the small brown planthopper. In late autumn and late spring and before maize sowing, based on the overwintering base number and virus-carrying rate of the small brown planthopper, and the diseased plant rate of wheat and weeds, combined with the maize planting pattern, make timely and accurate forecasts of the occurrence trend of maize rough dwarf disease to guide control.

② Choose suitable varieties: According to local conditions, select varieties with relatively good resistance, and at the same time pay attention to rational layout, avoiding large-scale planting of a single resistance-source variety. In the 1970s, Yunong 704 had a certain resistance to the disease; 50, Ludan 053, Nongda 108, etc., can replace susceptible varieties such as Shendan 7, Yedan 53 and Yedan 22 in production. In those areas where susceptible varieties have been planted for many years and the damage is severe, planting these resistant (tolerant) varieties is particularly important. In Qufu City, the maize hybrids Ludan 50 and Luyuandan 14 have good resistance to rough dwarf disease.

③ Adjust the maize sowing date: According to the occurrence pattern of maize rough dwarf disease, in areas with severe disease, the sowing date should be adjusted so that the growth period in which maize is most sensitive to the disease avoids the peak occurrence period of the small brown planthopper adults, reducing the disease incidence. Spring-sown maize should be sown appropriately earlier, generally in late April to early May; maize interplanted in wheat fields should be appropriately delayed, generally 5 days before wheat harvest, so as to shorten the symbiotic period of wheat and maize as much as possible and achieve appropriate late sowing. In Qufu City, the main maize planting patterns are wheat-interplanted maize, stubble-grabbing maize and late-sown maize, among which wheat-interplanted maize has the most severe disease, followed by stubble-grabbing maize, and then late-sown maize. Spring-sown maize should be advanced to before mid-April; summer-sown maize should preferably be in early June.

④ Remove weeds in time: Weeds on roadsides and in fields are not only the seed source base for farmland weeds the following year, but also the overwintering and oversummering host of the small brown planthopper, the transmission vector of maize rough dwarf disease. For residual weeds in wheat fields, manual hoeing can be carried out first and then spraying, and the weeding effect can reach about 95%. The advantage of choosing soil treatment is that maize at the seedling stage does not coexist with weeds, reducing the activity space of the small brown planthopper, which is not conducive to virus transmission by the small brown planthopper.

⑤ Strengthen field management: Combined with thinning to a stand, pull out diseased plants in the field, and bury them deeply or burn them in a centralized manner to reduce the infection source of rough dwarf disease. Apply fertilizer and water reasonably, strengthen field management, promote maize growth, shorten the susceptible period, reduce opportunities for virus transmission, and enhance the disease resistance and tolerance of maize.

⑥ Eliminate the virus source: Maize rough dwarf virus mainly overwinters in wheat, grass-family weeds and the body of the small brown planthopper. Therefore, it is necessary to do a good job in controlling wheat rosette dwarf disease, remove the damage of weeds at field edges, land edges and ditches, and at the same time reduce the population base of the small brown planthopper. The specific method is: after wheat turns green, spray with 25% buprofezin 50 g/mu. When spraying, weeds around the wheat field should also be sprayed, which can significantly reduce the insect population density. When necessary, 20% glyphosate aqueous solution or 45% Roundup aqueous solution 550 ml/mu can be used, mixed with 30 kg of water, and sprayed targeted at field edges and corners to kill weeds at field edges and destroy the living environment of the small brown planthopper.

2. Chemical control methods

① Seed dressing with chemicals: Use systemic insecticides to coat and dress maize seeds, which can effectively control the small brown planthopper at the seedling stage and reduce the spread of rough dwarf disease. When sowing, use a seed coating agent at 2% of the seed amount for seed dressing, which can effectively prevent the damage of the small brown planthopper, and at the same time help cultivate strong seedlings and improve maize disease resistance. After sowing, choose pre-emergence soil treatment agents such as 40% acetochlor-atrazine aqueous suspension concentrate, 50% Du'a mixture, etc., 550-575 ml/mu, mixed with 30 kg of water for sealed soil treatment.

② Spray insecticide to kill insects: For plots where rough dwarf disease appears at the maize seedling stage, pull out diseased plants in time, and according to the forecast of the small brown planthopper situation, promptly use 25% buprofezin 50 g/mu; around the 5-leaf stage of maize, spray once every 5 days, for 2-3 consecutive sprays, and at the same time spray 40% Virus A 500-fold solution or 5.5% Zhibingling 800-fold solution to control the viral disease. For individual plots where the effect of pre-emergence soil treatment herbicide is poor, a non-selective herbicide 20% glyphosate can be sprayed between maize rows at a fixed row spacing, 550 ml per mu, mixed with 30 kg of water. Be careful not to spray it onto the maize plants. Glyphosate has a quick-killing effect on weeds; 52 hours after spraying, the weeds can all die, which can reduce the activity space of the small brown planthopper. At field edges and corners, 45% Roundup aqueous solution can be sprayed, but it should be avoided between maize rows as much as possible to avoid phytotoxicity to maize.

Maize rough dwarf disease is devastating. Once it occurs, it is very difficult to cure. It is unrealistic to spray some chemical on diseased plants to make them recover to normal. However, as long as agricultural control and chemical control are combined and every link is closely connected, its spread of damage can certainly be controlled.