Rice Major Pests and Diseases in Gejiu City: Occurrence and Control Methods

I. Rice Planthoppers

1. Damage characteristics: Rice planthoppers, also known as white gnats, are migratory pests with the characteristics of long-distance migration and outbreak damage. The common species include the smaller brown planthopper and the white-backed planthopper. They occur in all rice-growing areas of the city, mainly damaging rice, followed by @#@245@#@ and corn, and also parasitize grasses and other gramineous weeds. Adults and nymphs gather in clusters at the base of rice clumps and on leaves to suck sap. The damaged parts show elongated brown spots, and in severe cases the lower stems turn black and the entire plant dies.

2. Life habits: 3-4 generations occur per year. From late April to early May, they migrate from other places into early and middle-season rice fields to cause damage. Generally, from June to July, the field population density is high, the short-winged form increases, and the damage is more severe. After the early and middle-season rice is harvested, they migrate to late rice fields and weeds, and the damage to late rice is relatively light. Adults have weak phototaxis, and eggs are preferably laid on barnyardgrass in rice fields.

3. Control measures: (1) Do a good job of publicity and mobilize the masses: Because rice planthoppers have many migration peaks and extremely uneven field development progress, the optimal control period is difficult to grasp. While doing a good job in rice planthopper monitoring, all localities should make full use of broadcasts, blackboard newspapers, and other forms of publicity to promptly release information to the masses on the occurrence of rice planthoppers. In particular, they should vigorously publicize the severity of rice planthoppers and control techniques. During the key control period, they should go deep into villages and communities to do a good job in publicity, mobilization, organization, and guidance, actively carry out unified control of rice planthoppers, and strive to reduce the damage losses caused by rice planthoppers to the lowest possible level. (2) Chemical control: The selection of pesticides should follow the principle of combining quick-acting with long-lasting effects, contact action with systemic action, and ovicidal action with insecticidal action. Apply 75 g of monosultap plus 30 g of rice planthopper net per mu, diluted with 50 kg of water for spraying; or apply 50 g of 25% buprofezin wettable powder per mu, diluted with 60 kg of water for spraying; or apply 40-60 ml of 10% imidacloprid emulsifiable concentrate per mu, diluted with 40-60 kg of water for spraying. (3) Precautions: With rainfall, rice planthoppers may suddenly break out, so places with light pest damage in the early stage must not be taken lightly and should be inspected at any time to prevent trouble before it occurs.

II. Rice Stem Borers

1. Damage characteristics: The yellow stem borer only damages rice. The striped stem borer and the pink stem borer, in addition to damaging rice, also damage corn, foxtail millet, sugarcane, wild rice stem, broad bean, rapeseed, and other crops, and also parasitize gramineous weeds. The larvae damage rice, causing dead hearts, dead sheaths, half-blighted panicles, white heads, dead booting panicles, or insect-damaged plants.

2. Life habits: Taking the yellow stem borer as an example, 3 generations occur per year, and larvae overwinter in rice stubble. In spring, they pupate and emerge. Moths are active at night and have phototaxis. During the seedling stage, eggs are mostly laid near the leaf tips; during the main field stage, they are mostly laid on the middle and upper parts of leaves. After the eggs hatch, the neonate larvae bore into the stems of nearby plants to cause damage, forming "dead heart clusters" or "white head clusters." Larvae can move to cause damage. When damaging rice at the booting stage, they first bite and feed on tender grains in the panicle bud, and after heading they bore into the upper stem nodes to cause white heads. Rice is most susceptible during the tillering stage and booting stage; neonate larvae are not easily able to invade during the stem elongation stage or after full heading.

3. Control methods: (1) Remove rice stubble and weeds at field edges to eliminate overwintering larvae; plow and irrigate in spring at the appropriate time for 5-7 days to kill larvae and pupae; prevent variety mixing, transplant at the appropriate time, and make the susceptible period avoid the peak period of neonate larvae to reduce damage. (2) Apply pesticides separately during the peak moth emergence period and the peak hatching period of neonate larvae, or carry out control according to the control timing predicted by the plant protection station. Pesticides may be selected as follows: 40-50 g of 90% monosultap wettable powder per mu, diluted with 50 kg of water for spraying; or 200-250 g of bisultap aqueous solution per mu, diluted with 50 kg of water for spraying; or 50-60 ml of Chongbisha per mu, diluted with 50-60 kg of water for spraying; or 50 g of 98% cartap original powder per mu, diluted with 50 kg of water for spraying.

III. Rice Blast

1. Damage symptoms: Rice blast, also called rice fever, is a fungal disease caused by infection of rice by the rice blast pathogen. It can occur at all growth stages and on all parts of rice. According to the occurrence period and site, it is divided into seedling blast, leaf blast, node blast, neck blast, branch blast, grain blast, and so on. The main types that commonly occur and cause great damage are seedling blast, leaf blast, and neck blast. (1) Seedling blast: Mostly occurs at the 2-3 leaf stage, caused by seed-borne bacteria. The pathogen invades the base of the seedling, appearing gray-black, causing the seedling to curl and die, generally without forming obvious lesions. (2) Leaf blast: Can occur from after the 3-leaf stage to the heading stage. Generally, fields with late topdressing, biased application of nitrogen fertilizer, and dark green leaves at the peak tillering stage are prone to leaf blast. There are 4 types of leaf blast lesions: ① Chronic type: the most common symptom on leaves; lesions are spindle-shaped, with a yellow halo in the outer poisoned area, red-brown at the necrotic edge, and gray-white in the central collapsed area. ② Acute type: lesions are dark green, mostly nearly circular or irregular, with a gray-green center, water-soaked outer margin, and a gray-blue fuzzy mold layer on the back. ③ White spot type: lesions are small nearly circular spots; ④ Brown spot type: lesions are small brown spots. (3) Neck blast: Occurs on the panicle neck. Lesions spread upward and downward, appearing light brown or gray-black. In the early stage, lesions are light brown water-soaked small spots, gradually expanding around the panicle neck, panicle axis, and branches and developing upward and downward. Later, the color darkens to brown or dark green, and the affected parts turn black, die, or break, seriously affecting seed set, grain weight, and rice quality. Mostly occurs at the 2-3 leaf stage, caused by seed-borne bacteria. The pathogen invades the base of the seedling, appearing gray-black, causing the seedling to curl and die, generally without forming obvious lesions. (2) Leaf blast: Can occur from after the 3-leaf stage to the heading stage. Generally, fields with late topdressing, biased application of nitrogen fertilizer, and dark green leaves at the peak tillering stage are prone to leaf blast. There are 4 types of leaf blast lesions: ① Chronic type: the most common symptom on leaves; lesions are spindle-shaped, with a yellow halo in the outer poisoned area, red-brown at the necrotic edge, and gray-white in the central collapsed area. ② Acute type: lesions are dark green, mostly nearly circular or irregular, with a gray-green center, water-soaked outer margin, and a gray-blue fuzzy mold layer on the back. ③ White spot type: lesions are small nearly circular spots; ④ Brown spot type: lesions are small brown spots. (3) Neck blast: Occurs on the panicle neck. Lesions spread upward and downward, appearing light brown or gray-black. In the early stage, lesions are light brown water-soaked small spots, gradually expanding around the panicle neck, panicle axis, and branches and developing upward and downward. Later, the color darkens to brown or dark green, and the affected parts turn black, die, or break, seriously affecting seed set, grain weight, and rice quality.

2. Disease occurrence pattern: It overwinters as conidia and mycelium on rice straw and rice seeds and is spread by air. During the tillering stage and early booting stage, temperatures of 20-28°C and high humidity conditions can easily cause leaf blast epidemics; after booting, low temperatures of around 20°C can weaken the disease resistance of the host and cause neck blast epidemics. Within the suitable temperature range, rainy and humid conditions are the main conditions for disease epidemics. Biased application of nitrogen fertilizer causing excessive growth, soil drought and water shortage or long-term deep irrigation, cold water irrigation of fields, or insufficient sunlight all make rice prone to rice blast.

3. Control methods: The control of rice blast should adopt comprehensive control measures centered on planting disease-resistant high-quality varieties, based on health cultivation, and supplemented by chemical protection. (1) Plant resistant varieties: This is the fundamental measure for controlling rice blast. Therefore, all localities should select good disease-resistant varieties according to local conditions and achieve rational variety layout and rotation, avoiding monoculture planting. (2) Seed treatment: Strong chlorine essence can be used for disinfection. First pre-soak the rice seeds for 24 hours, then soak them in a 300-400 times strong chlorine essence solution for 12 hours. Remove, wash clean, and then germinate. This can also control bacterial leaf streak and bacterial leaf blight; or soak seeds in 2000 times 75% tricyclazole wettable powder solution for 24-36 hours, wash clean, and then germinate. (3) Strengthen cultivation management: Cultivate strong seedlings, apply sufficient base fertilizer, increase organic fertilizer and potassium fertilizer, supplement silicon fertilizer, apply panicle fertilizer skillfully, irrigate frequently with shallow water, drain and dry the field at the appropriate time, and prevent biased and delayed application of nitrogen fertilizer. (4) Chemical control: In terms of control strategy, the method of "controlling seedling blast, spot-treating leaf blast, and vigorously controlling neck blast" should be adopted. To control seedling blast, spray 2000 times 75% tricyclazole wettable powder solution 3 days before transplanting rice seedlings, so that rice seedlings are transplanted with pesticide, giving a relatively good control effect; leaf blast should be protected by spraying at the early stage of disease occurrence (when the diseased leaf rate is 3%); neck blast is most effectively prevented by spraying at the late booting stage and the breaking stage. Pesticide selection: 30-35 g of 75% tricyclazole wettable powder per mu, or this is the fundamental measure for controlling rice blast. Therefore, all localities should select good disease-resistant varieties according to local conditions and achieve rational variety layout and rotation, avoiding monoculture planting. (2) Seed treatment: Strong chlorine essence can be used for disinfection. First pre-soak the rice seeds for 24 hours, then soak them in a 300-400 times strong chlorine essence solution for 12 hours. Remove, wash clean, and then germinate. This can also control bacterial leaf streak and bacterial leaf blight; or soak seeds in 2000 times 75% tricyclazole wettable powder solution for 24-36 hours, wash clean, and then germinate. (3) Strengthen cultivation management: Cultivate strong seedlings, apply sufficient base fertilizer, increase organic fertilizer and potassium fertilizer, supplement silicon fertilizer, apply panicle fertilizer skillfully, irrigate frequently with shallow water, drain and dry the field at the appropriate time, and prevent biased and delayed application of nitrogen fertilizer. (4) Chemical control: In terms of control strategy, the method of "controlling seedling blast, spot-treating leaf blast, and vigorously controlling neck blast" should be adopted. To control seedling blast, spray 2000 times 75% tricyclazole wettable powder solution 3 days before transplanting rice seedlings, so that rice seedlings are transplanted with pesticide, giving a relatively good control effect; leaf blast should be protected by spraying at the early stage of disease occurrence (when the diseased leaf rate is 3%); neck blast is most effectively prevented by spraying at the late booting stage and the breaking stage. Pesticide selection: 30-35 g of 75% tricyclazole wettable powder per mu, or 100 g of 55.5% Fenjie Sanwen per mu, or 150 g of 20% tricyclazole per mu, or 150-200 g of 40% edifenphos emulsifiable concentrate per mu, diluted with 60-75 kg of water for uniform foliar spraying. If there is rainy weather or low temperature in the later period, it is necessary to spray once more at full heading, but the dosage should not be blindly increased, and several pesticides can be used in rotation.