Detailed Explanation of the Occurrence and Control Methods of Maize Rough Dwarf Disease

Maize rough dwarf disease is a viral disease caused by Maize rough dwarf virus. In severe cases, it can cause substantial yield reduction or even total crop failure, making it a devastating disease. It mainly affects various gramineous crops and numerous gramineous weeds, with maize being the most susceptible and suffering the greatest impact on growth, development and yield.

I. Symptoms At the early stage of the disease, transparent dashed spots appear on both sides of the midrib at the base of the young leaf, then gradually spread to the entire leaf. The typical symptom is the presence of waxy white ridge-like protrusions of varying thickness on the veins of the leaf underside, leaf sheath and bracts of diseased plants, which feel distinctly rough and uneven to the touch. The leaves are broad and short, thick, hard and rigid, with a dark green color, short, hard and brittle, and pointing upward, with the top leaves clustered. The internodes are noticeably shortened, thickened and swollen, and the diseased plants are stunted, often less than half the height of healthy plants. Severely diseased plants do not exsert their tassels or produce no pollen, the ears are deformed and unfilled or have reduced grain numbers, and the root system of diseased plants is sparse and short. In addition, some diseased plants have young leaves that curl into a bow or ox-tail shape, with notches in the young leaf, the funnel opening facing to one side, or the leaf margin turning red up to the entire leaf turning red.

II. Occurrence Characteristics Maize rough dwarf disease is transmitted by the small brown planthopper in a persistent, viruliferous manner. Maize seedlings have weak disease resistance, being most susceptible at the 2-leaf 1-heart stage, and the period before the 7-leaf stage is the sensitive growth stage for disease occurrence. After jointing, disease resistance increases. In fields where wheat rosette dwarf disease and green dwarf disease are severe, the subsequent maize crop often also suffers from a more severe occurrence of rough dwarf disease. Practice has shown that in northern maize regions, spring maize sown after mid-April has severe disease occurrence, and the later the sowing date, the more severe the infection. For summer maize, maize interplanted in wheat fields has severe infection, while direct-seeded maize has mild infection, and early-sown crops are severe while late-sown crops are mild.

III. Occurrence Patterns The primary sources of initial infection for maize rough dwarf disease are mainly green dwarf diseased plants in wheat fields and viruliferous small brown planthoppers that overwinter, transmitted in a persistent manner. The host range of this virus and its vector, the small brown planthopper, is very broad, mainly monocotyledonous gramineous plants such as wheat, rice, maize, sorghum, foxtail millet, barley and other crops, as well as weeds such as shortawn foxtail, green foxtail, crabgrass, barnyardgrass and Beckmannia. Maize is not a preferred host of the small brown planthopper; only when suitable hosts are absent in the field does the small brown planthopper use maize as a transitional host for feeding and reproduction. The small brown planthopper has approximately 5 generations per year in northern regions, with the 2nd, 3rd and 4th generations oversummering on cereal crops and field weeds. After wheat emerges in autumn, the 4th generation adults migrate to wheat fields, and Maize rough dwarf virus is also transmitted to wheat, overwintering in wheat seedlings and in the bodies of the 5th generation (overwintering generation) small brown planthoppers, forming an annual infection cycle.

In the maize-producing regions of northern China, wheat acreage is relatively large, mostly under wheat—maize continuous cropping patterns, and combined with the abundant presence of gramineous weeds, this provides rich virus sources and a favorable habitat for the virus vector, the small brown planthopper, for the occurrence of maize rough dwarf disease. At the same time, maize cultivation in the north is dominated by summer maize, mostly using wheat ridge interplanting and no-till dibbling after wheat harvest. The susceptible stage of maize seedlings often coincides and overlaps with the migration peak of the first generation of small brown planthoppers, providing a favorable opportunity for disease infection. If the winter is warm, the spring is dry, and summer rainfall is suitable, conditions favor the overwintering and reproduction of the small brown planthopper, the first generation occurs in outbreak proportions, thereby causing a major outbreak of maize rough dwarf disease.

IV. Control Measures The control strategy for maize rough dwarf disease should emphasize the principle of prevention first and early control at the appropriate time, highlighting agricultural control as the main approach, supplemented by chemical control measures at key periods. The occurrence of maize rough dwarf disease is entirely caused by virus transmission by viruliferous small brown planthoppers; therefore, eliminating or avoiding transmission and infection by the small brown planthopper is an important way to prevent the occurrence of rough dwarf disease.

(I) Agricultural Control Measures

1. Clear field weeds. After autumn harvest, promptly remove stubble and clear field weeds to reduce overwintering and oversummering hosts of the small brown planthopper and virus, thereby reducing the damage of maize rough dwarf disease.

2. Control the small brown planthopper in wheat fields to reduce transmission vectors. Use herbicides for chemical control of wheat field weeds before winter; in early spring during wheat jointing, spray pesticides to control overwintering generation adults in conjunction with controlling wheat red spider mites; after wheat heading, carry out one spray for three controls in conjunction with disease and pest control, also controlling the first generation of small brown planthoppers.

3. Adjust the maize sowing date. Avoid the migration peak of the small brown planthopper and facilitate chemical control, avoiding the peak occurrence period of overwintering generation adults.

4. In conjunction with thinning and final singling, promptly remove diseased plants in the field to reduce opportunities for virus transmission. Strengthen field management, apply fertilizer and water reasonably, enhance the disease resistance and tolerance of maize plants, and reduce the severity of disease occurrence.

(II) Chemical Control Measures

1. Seed dressing with chemicals. At the same time, promote contiguous planting so that sowing dates are basically consistent.

2. Before and after maize sowing and during the seedling stage, spray insecticides on maize fields and nearby weeds to control the small brown planthopper.

3. If disease occurs at the seedling stage, promptly remove diseased plants, appropriately delay the final singling time, and spray antiviral agents to inhibit virus multiplication and accelerate chlorophyll synthesis, thereby reducing disease occurrence and damage and increasing yield.