Scientific Control Methods for Ten Common Rice Pests and Diseases
Pests and diseases are one of the major threats in agricultural production, greatly affecting both the yield and quality of crops. As the staple food on which Chinese people depend for survival, rice is also severely affected by pests and diseases during its growth. Below, the editor introduces ten common rice pests and diseases and their scientific control methods.
I. Rice black sclerotial stem rot
Symptoms: A fungal disease of the stem base during the adult plant stage of rice. The pathogen attacks the leaf sheath at the stem base, forming elliptical or spindle-shaped black spots that later expand to the entire leaf sheath; large black patches also appear on the stem. In the later stage, the stem base rots, the plant undergoes green wilt, and the stem cavity contains numerous small spherical black granular sclerotia.
Control methods: Focus on strengthening fertilizer and water management, combine with pest control to prevent disease, and supplement with timely spraying.
II. Rice bacterial leaf blight
Symptoms: A bacterial disease of rice leaves. The pathogen invades the rice plant through wounds or water pores in the roots, stems and leaves, and multiplies and causes damage in the vessels of the vascular bundles. Seedling and tillering stages are most susceptible. Seedling leaves mostly show leaf blight symptoms. On susceptible varieties, acute wilt symptoms often appear, with lesions being grayish-green and water-soaked, and diseased leaves rapidly curling and wilting; on resistant varieties, brown necrotic spots develop.
Control methods: Selecting and planting resistant varieties and preventing flooding of paddy fields are key to disease prevention, combined with chemical control.
III. Rice dwarf virus disease
Symptoms: A viral disease of rice seedlings. Rice can be infected at any growth stage, with the seedling and tillering stages being the sensitive periods; the earlier the infection, the greater the loss. If infected at the seedling stage, diseased plants clearly fail to tiller and are severely stunted; if infected at the tillering stage, tillering increases and a bushy appearance develops, with inverted fibrous roots and high-node branching at the nodes of diseased plants; when infected at the seedling and tillering stages, the vast majority cannot head, and although some main stems can still head, most show enclosed panicles and reduced seed-setting rate.
Control methods: Controlling the vector insects that transmit the virus is key to disease prevention.
IV. Rice bakanae disease
Symptoms: A fungal disease of the above-ground parts of rice, occurring from the seedling stage to the heading stage. Diseased plants are spindly, weak and yellowed, usually 3-10 cm taller than healthy plants, making them very easy to identify. Inverted aerial roots and a pink mold layer often appear on the lower nodes of diseased plants. The optimum temperature for pathogen development is around 25°C, and the disease is seed-borne.
Control methods: Using disease-free seeds or soaking seeds in chemicals before sowing is the key control measure.
V. Rice sheath blight
Symptoms: A fungal disease that mostly appears from the late tillering stage to the heading stage of rice. The infection site gradually spreads from the bottom of the rice stem to other parts, and in the most severe cases extends to the rice panicle. When dark green water-soaked lesions appear at the root and stem parts of rice, with lesions changing from small to large and rice leaves dying, it can be judged as infection with rice sheath blight, and measures should be taken promptly against the disease.
Control methods: Apply chemicals when the disease incidence reaches 30%-4% at the booting stage. The spray solution should be applied to the middle and lower parts of the rice plants. Using the pouring method, a 3-5 cm water layer should be maintained in the field. When applying Jinggangmycin, it is best to do so on a sunny day after rain, or when there is no heavy rain within two hours after application. Use 100-150 ml of 5% Jinggangmycin aqueous solution per mu, or 25 g of high-concentration Jinggangmycin powder; choose either one, dilute with 100 kg of water for conventional spraying, or dilute with 400 kg of water for pouring.
VI. Small brown planthopper
In paddy fields it mostly lays eggs on barnyardgrass; the egg-laying sites are all in the lower leaf sheaths and the midrib tissue at the leaf base of rice, wheat and barnyardgrass. It can also transmit black-streaked dwarf disease of rice, wheat and corn, stripe leaf blight, wheat rosette dwarf disease, and corn rough dwarf disease.
Control methods:
(1) Oil-drop insect killing. Drip 400-500 g of waste diesel oil or waste machine oil per mu, maintain a shallow water layer of 20 cm in the field, manually drive the insects, and they fall into the water, touch the oil and die. Replace with clean water after treatment; do not use this method after the booting stage.
(2) Spread toxic soil. Broadcast 1.5 kg of dimethoate powder and 2 kg of moist fine soil per mu.
(3) Spray with chemicals. Spray with 0.5 kg of 40% dimethoate emulsion diluted with 800-1000 kg of water.
VII. Rice thrips
Rice thrips are very small; adults are dark brown, winged, and crawl very quickly. Their life cycle consists of three stages: egg, nymph and adult. Nymphs resemble adults, are pale yellow, very small, wingless, and often curl up at the tips of rice leaves, piercing and sucking the sap of rice leaves. Damaged rice leaves lose water and curl, rice seedlings turn yellow, and the leaves bear scattered white spots; the central leaf shrivels, looking like fire damage from a distance. During flowering, rice thrips gather.
Control methods: Because rice thrips are very small, they generally do not easily attract attention; they are only discovered when severe damage to rice causes large-scale leaf curling. Therefore, timely inspection is necessary to eliminate rice thrips at the larval stage. Use 1500-2000 times dilution of 40% dimethoate emulsion per mu; after applying in seedling fields and main fields, a water layer must be maintained. After controlling rice thrips, apply quick-acting fertilizer to promote the recovery of seedling and tiller growth.
VIII. Rice leaf roller skipper
The larvae of this pest feed on the leaf mesophyll inside the leaf roll, leaving the epidermis and forming white spots of varying lengths. If damaged in the later stage, mainly the two nutrient leaves below the flag leaf are affected, seriously affecting photosynthesis and nutrient accumulation and transport in the rice plant, resulting in unfilled grains and many shriveled grains, causing yield reduction.
Control methods: Dust 2 kg of 2.5% trichlorfon powder per mu, or spread toxic soil made of 1 kg of parathion-methyl and fenitrothion powder plus 10 kg of fine soil; spray with 150 g of 90% crystalline trichlorfon diluted with 80-100 kg of water.
IX. Rice leaf roller
When the larvae are slightly larger, they begin to spin silk in the central leaf of rice, rolling both sides of the leaf into a tubular worm roll; the insect hides inside the roll and feeds on the mesophyll and upper epidermis, and after heading, moves into the tender leaf sheaths to cause damage. In severe cases, only the transparent whitish epidermis remains of the rolled leaves, and the entire leaf dies.
Control methods: Spray with 250 times dilution of 25% DDT emulsion, or 1000-1500 times dilution of 90% trichlorfon. The control timing should be before the third instar of the larvae, and applying in the evening gives the best effect. After control, check the effect; if the insect density is the same as before, treat once more.
X. Yellow stem borer
It has a single feeding habit, feeding exclusively on rice, and the larvae bore into the stem to cause damage. At the tillering stage it forms deadheart; from the booting to heading stage it forms dead boot and white heads; when moving between plants to cause damage it also forms insect-damaged plants. “Deadheart seedlings” and “white heads” are the main symptoms of rice plants after damage.
Control methods: During the peak hatching period of the larvae, the panicle-breaking stage is the best time to control white heads. When 5%-10% of panicles have broken, apply once; if the insect population is large, add 1-2 more applications at 5-day intervals.
The above is the complete introduction to common rice pests and diseases and their scientific control methods. During the control process, pesticides should be used scientifically and safely to prevent pollution of agricultural products and the environment, thereby ensuring food safety and human health.