Symptoms of rice straighthead disease (rust disease) and pesticide control methods
Rice straighthead disease, also known as rust disease, commonly called "burned seedlings" or "sitting clumps," can very likely occur under rainy weather conditions if field water and fertilizer management is improper. So what medicine should be sprayed for rice straighthead disease? What are the symptoms?How to prevent and control it?
Rice straighthead disease
Rice straighthead disease, also known as rust disease. Once this disease occurs, it causes rice seedlings to emerge leaves slowly, tiller slowly or not tiller at all, with a clustered plant shape, poor root development, and damaged leaf function, leading to premature senescence of rice in the later stage, seriously affecting the normal growth and development of rice, generally reducing yield by 10%-20%, and in severe cases by more than 30%.
The disease generally begins to occur in the early tillering stage of rice, and reaches its peak incidence at the full tillering stage.
Symptoms of rice straighthead disease
The typical external symptoms of affected plants are: affected plants are short and small, with few and small tillers, and upper leaves are upright with a smaller angle to the stem. After the rice plant enters the tillering stage, brown small spots or short streak spots appear on old leaves, with indistinct edges, and scorching appears from the leaf tip downward along the leaf margin.
By the full tillering stage, crumb-like brown spots appear on the leaves, after which the spots increase and expand, and the leaves mostly gradually turn yellow-brown and die from the leaf base. In severe cases, viewed from a distance, the rice leaves in the whole field look as if scorched by fire.
Pulling up diseased plants, the roots are visibly aged, reddish-brown, soft and spongy with no elasticity, some turning black and rotting, with very few white roots.
Occurrence patterns of rice straighthead disease
1. Soil potassium deficiency type
The disease occurs because the soil itself has low available potassium content and cannot meet the rice's potassium requirement for growth.
This type mostly occurs in thin sandy fields, water-leaking fields, and red and yellow soil paddy fields. It often begins to occur more than ten days after rice transplanting. In the early stage, the rice plant leaf color is slightly dark green, leaves are narrow, long and soft, and the basal leaves gradually turn yellow or yellow-brown from the leaf tip downward along both sides of the leaf margin, with few root hairs that easily shed.
2. Plant poisoning type
The disease occurs because the soil contains large amounts of reducing chemical substances such as ferrous iron and hydrogen sulfide that poison the rice roots and reduce their vitality.
This type mostly occurs in deep mud fields, fields with long-term deep water irrigation, poor aeration, and fields with excessive application of undecomposed organic fertilizer. In such fields, rice seedlings are slow to revive after transplanting, or after reviving the rice seedlings stand upright with almost no tillering, leaf tips first fade green downward, the area around the leaf midrib turns yellow, and red-brown black spots grow, even rotting, with a smell similar to rotten eggs.
3. Low-temperature induced type
The disease occurs because long-term low temperature and rainy weather affect rice root development, leading to reduced fertilizer uptake capacity.
This type mostly occurs in the early growth stage of rice during rainy weather or the plum rain season, with large areas becoming diseased at the same time, but the degree varies from mild to severe. Under low temperature conditions, the upper young leaves of the plant turn pale yellow, and many brown needle-tip-like small spots also appear on the leaves; the lower old leaves initially appear yellow-green or pale brown, after which the rice roots become soft and spongy, with poor elasticity and few and thin white roots. In addition, transplanting seedlings too deep, partial application of nitrogen fertilizer, and long-term water accumulation in the paddy field all aggravate the occurrence of rice straighthead disease.
Control methods for rice straighthead disease
Straighthead disease must be controlled through integrated prevention and control, with prevention as the main approach. For fields that have already developed the disease, corresponding measures should be taken according to the different occurrence types for targeted control.
1. Intensive cultivation and soil improvement
By deepening the plow layer, promote soil maturation, and avoid continuous no-till and intercropping; improve low-yield fields, and for poorly drained muddy fields, carry out soil improvement and renovate the irrigation and drainage system; after harvesting the previous crop, plow and sun the soil clods in time to increase the degree of soil maturation and improve soil permeability.
2. Strengthen cultivation management and improve plant disease resistance
Sow and transplant at the right time, strengthen water and slurry management, keep shallow water for seedling establishment, and promote early development; balanced fertilization, apply more decomposed organic fertilizer, increase phosphorus and potassium fertilizer, alternate dry and wet, drain the field at the right time, and cultivate strong seedlings; for fields with straw returned to the field, appropriately increase the amount of base fertilizer, adjust the ratio of base fertilizer to tillering fertilizer to 6:4, move nitrogen forward appropriately to accelerate straw decomposition, strengthen water layer management, regulate air with water, and regulate fertilizer with water.
3. Strengthen classified guidance and control the disease early
For potassium-deficient fields
Potassium fertilizer should be supplemented, and quick-acting nitrogen fertilizer should be appropriately topdressed; for fermented fields with excessive organic matter, drain and expose the field immediately; during low temperature and rainy periods, drain water in time, manage with alternating dry and wet, and prevent long-term deep irrigation.
For fields that have already developed the disease
① Appropriately increase potassium fertilizer (about 7.5kg/mu), and prevent partial application of nitrogen fertilizer;
② Appropriately expose the field, adhere to the “shallow—wet—dry” water and slurry management mode, dehydrate and expose the field, increase soil aeration, increase root vitality, promote new root growth, and improve the potassium uptake capacity of the root system.
4. Chemical control
① Generally, one mu of paddy field requires 100-150 grams of 90% crystalline trichlorfon, or 150 milliliters of 80% dichlorvos, mixed with 50 kilograms of water, and it needs to be sprayed when the paddy field has shallow water. Only then can the pesticide effect be better.
② First drain the water from the paddy field, and after one day, use a small cloth bag containing trichlorfon to irrigate, and after 12 hours the larvae can be killed.