Bitter Melon Pest and Disease Control Methods and Technical Key Points

1. Powdery Mildew
Symptoms: Mainly affects leaves. In the early stage of the disease, nearly circular small white powdery spots appear on the front or back of leaves, mostly on the underside. Later, the spots gradually expand into large powdery white areas with indistinct edges. In severe cases, leaves turn yellow, become brittle, and usually do not fall off. The powdery substance gradually turns grayish-white, and eventually the entire leaf becomes yellow-brown and dried up. The disease usually starts from the middle and lower leaves and gradually spreads to the upper leaves.
Conditions for onset: The pathogen is an ascomycete, an obligate parasite. The pathogen overwinters as mycelium or cleistothecia on the host or on diseased plant debris, and can also overwinter on greenhouse cucumbers and other crops. The pathogen is mainly spread by air and running water. The temperature for the disease to become epidemic in the field is 16°C-24°C. It has a wide range of adaptability to relative humidity; when air humidity is 45%-75%, the disease develops rapidly, and when it exceeds 95%, disease development is significantly inhibited. Generally, in years with less rainfall, the disease is mild. During consecutive cloudy days and muggy weather, the disease develops rapidly. Excessive vegetative growth, overly dense vines and leaves, and poor ventilation and light penetration easily lead to severe outbreaks of powdery mildew.
Control measures:
① Strengthen cultivation management: emphasize cultivating strong seedlings, rational close planting, timely pruning of branches and leaves, improving ventilation and light conditions, so that plants grow robustly and disease resistance is improved. Base fertilizer should include increased phosphorus and potassium fertilizer, and excessive application of nitrogen fertilizer should be prevented during the growing period.
② Physical control: Use 27% higher fatty alcohol emulsion at 80-100 times dilution, spray on leaves in the early stage of the disease to form a thin film, which not only prevents pathogen invasion but also creates oxygen-deficient conditions that kill powdery mildew fungi. Generally spray once every 5-6 days, for 3-4 consecutive sprays.
③ Biological control: Spray 2% Agricultural Antibiotic 120 aqueous solution, then spray again every 6-7 days, with control efficacy reaching over 90%.
④ Chemical control: Alternately sprayable agents include: 15% triadimefon wettable powder at 1500 times dilution, 30% triflumizole wettable powder at 1500-2000 times dilution, 40% carbendazim · sulfur suspension at 500-600 times dilution, 50% sulfur suspension at 250-300 times dilution, 50% amobam aqueous solution at 1000 times dilution, 47% kasugamycin+ copper oxychloride wettable powder at 600-800 times dilution, 77% copper hydroxide wettable powder at 500-700 times dilution. In protected cultivation, fumigation with chlorothalonil or sulfur smoke agents can simultaneously control downy mildew and powdery mildew.
The technical key points of chemical control are: early prevention, thorough spraying, and large water volume. When spraying, the middle and lower old leaves and the undersides of leaves should be sprayed evenly. In the early stage of the disease, spray once every 7-10 days, for 2-3 consecutive sprays, which can achieve good control results.
2. Phytophthora Blight
Symptoms: Bitter melon Phytophthora blight mostly shows symptoms before flowering. Stems, vines, and fruits can all be infected. Infected leaves first lose their luster; in the early stage, dark green water-soaked irregular lesions appear with indistinct edges. When humidity is high, a very thin layer of white mold can be seen growing on the diseased area; when dry, it appears blue-white and easily breaks apart. Petioles and vine nodes show dark green water-soaked soft rot, and the affected parts easily constrict. Infected fruits show dark green depressed lesions; when humidity is high, the fruit quickly softens and rots, with sparse white mold growing on the affected area, and the rot emits a foul odor.
Conditions for onset: It is a fungal disease caused by Phytophthora. The pathogen overwinters in the soil as mycelium, chlamydospores, and oospores with diseased plant residues. The pathogen on the lesions spreads through watering, rain splashing, and air movement. The optimal temperature for the pathogen to cause disease is 27°C-31°C, with a maximum of 37°C and a minimum of 5°C. The release of zoospores from sporangia requires water. Low-temperature rainy conditions or high-temperature high-humidity conditions are both favorable for pathogen infection and disease development, and the incubation period is short, only 3-4 days, usually occurring in August-September. Drought followed by rain, or heavy watering when fruits enter the growth stage, causing a sudden increase in soil water content, easily triggers the disease. In low-lying areas, poorly drained fields, and continuous cropping plots, the disease is severe.
Control measures:
① Agricultural control: Implement crop rotation of more than 3 years. Use plastic film mulching with high ridge (bed) cultivation to reduce pathogen splashing from the ground. Rational irrigation to control field humidity. Appropriately control watering during the rainy season, drain water promptly after rain, and ensure the ground dries after rain. Water promptly during drought; never use flood irrigation when watering, and water should be done in the afternoon or evening on sunny days. Apply more organic fertilizer to promote robust plant growth, deep roots and lush leaves, and improve resistance. Timely plant adjustment to prevent overly dense growth and poor ventilation and light penetration. Remove diseased leaves at any time and burn them.
② Chemical control: Choose 25% metalaxyl wettable powder at 800-1000 times dilution, 80% zineb wettable powder at 600-800 times dilution, 64% oxadixyl+mancozeb wettable powder at 500-600 times dilution, 40% fosetyl-aluminum wettable powder at 300-400 times dilution, 80% xinwansheng wettable powder at 500-600 times dilution, 72.2% propamocarb aqueous solution at 400-600 times dilution, 50% potassium copper sulfate wettable powder at 600 times dilution, and other agents for alternate spraying, once every 5-10 days, for 3-4 consecutive sprays. Spraying should be thorough and meticulous, covering all leaves, fruits, and nearby ground.
3. Downy Mildew:
Both seedling and mature plant stages can be affected. Mainly affects leaves, stems, tendrils, and flower stalks. When seedlings are infected, irregular chlorotic yellow spots appear on the upper surface of cotyledons; when moist, gray-black mold layers appear on the underside, and in severe cases, cotyledons turn yellow and dry up. When mature plants are infected, it mostly starts from the lower leaves and gradually spreads upward. In the early stage, water-soaked light green or yellow small spots appear on the upper surface of leaves, then gradually expand, changing from yellow to light brown, and are limited by leaf veins to form angular lesions. Purple-gray mold layers form on the underside of leaves at the lesion sites. Under moist conditions, the mold layer thickens and turns black. In severe cases, lesions join together, the entire leaf turns yellow-brown, dries up and curls, and all plant leaves die.
Chemical control: In the early stage of the disease, use 25% metalaxyl wettable powder at 800-1000 times dilution; or 40% fosetyl-aluminum wettable powder at 300 times dilution; or 75% chlorothalonil wettable powder at 600-800 times dilution; or 65% zineb wettable powder at 400-500 times dilution; or 58% metalaxyl+mancozeb at 600 times dilution; or 64% oxadixyl+mancozeb at 400 times dilution. Use one of the above, once every 7-10 days, for 3-6 consecutive sprays.
4. Melon Fruit Fly:
The melon fruit fly, also known as the "needle bee" or melon maggot, is a pest belonging to the family Tephritidae of the order Diptera. It mainly damages plants as larvae. First, adults pierce the young melon epidermis with their ovipositor to lay eggs. After hatching, the larvae burrow into the melon flesh to feed. Affected melons first turn yellow locally, and then the entire melon rots and smells foul. This causes the plant to drop many fruits. Even if the melon does not rot, the puncture sites accumulate gummy exudate, become deformed and sunken, the rind hardens, and the melon tastes bitter and astringent with reduced quality.
Control methods: First, promptly remove infested melons, spray and bury them deeply. Second, in severe cases, bag young melons to prevent adult egg-laying. For chemical control, during the peak emergence period of adults, use poison bait to trap and kill adults. You can use 40 parts banana peel + 0.5 parts 90% trichlorfon crystal + 1 part essence, or use 1.8% abamectin oil paste at 1500 times dilution + lüshadan at 1500 times dilution (4.5 mE) emulsifiable concentrate for control, spraying twice consecutively, which also gives good results. Or spray plants with 50% dichlorvos emulsifiable concentrate at 1000 times dilution and 2.5% deltamethrin at 3000 times dilution, once every 3-5 days, for 2-3 consecutive sprays. This is effective against adults. Bag young melons with paper bags for protection to prevent adult egg-laying. Remove and destroy infested melons. Hanging flypaper between rows can also have some effect.
5. Melon Borer:
The melon borer belongs to the family Pyralidae of the order Lepidoptera. It damages plants as larvae. In the early stage, larvae feed on the leaf mesophyll on the underside of leaves, showing gray-white patches. After the third instar, they spin silk to bind leaves or tender shoots together, hiding inside to feed, causing leaves to have holes or notches. In severe infestations, only leaf veins remain. Larvae often bore into melons to feed on the flesh, affecting yield and quality.
Control methods: Clean the field of residual plants and fallen leaves to eliminate overwintering pupae and reduce pest sources. During the larval stage, spray plants with 20% fenvalerate at 3000 times dilution, or 50% malathion at 1000 times dilution for high control efficacy.
6. Cutworms:
Cutworms belong to the family Noctuidae of the order Lepidoptera. There are many species of cutworms, and three are commonly found in China: the black cutworm, the yellow cutworm, and the large cutworm. Among them, the black cutworm is a worldwide major pest with the widest distribution.
Poison bait trapping: Mix 50 g of 90% trichlorfon evenly with 30-40 kg of chopped fresh grass, add a small amount of water, and scatter near vegetable fields in the evening to trap and kill larvae.
Chemical control: For cutworm larvae before the 3rd instar, you can use: 2.5% trichlorfon powder at 22.5-30 kg per hectare for dusting; or add 150 kg of fine soil to make poisonous soil and scatter around plants; or use 80% trichlorfon wettable powder at 1000 times dilution; or use 50% phoxim emulsifiable concentrate at 800 times dilution; or use 20% fenvalerate emulsifiable concentrate at 2000 times dilution for ground spraying. When larvae are older, you can use: 50% phoxim emulsifiable concentrate; or 80% dichlorvos emulsifiable concentrate at 1000-1500 times dilution for root irrigation to kill larvae in the soil.
7. Melon Aphid:
The melon aphid, also called the cotton aphid, commonly known as honey bug or greasy bug, belongs to the order Homoptera, family Aphididae.
Adults and nymphs of the melon aphid parasitize the underside of host leaves or tender shoots, piercing and sucking sap with their mouthparts. They especially like to gather on tender leaves and stems to feed, causing melon leaves to wrinkle, deform, and curl toward the underside. After plants are affected, growth and development stagnate or slow down, reducing yield and quality. The melon aphid is also the main vector of viral diseases, and viral diseases are currently one of the main diseases causing total crop failure and yield reduction in cucurbit vegetables. Therefore, melon aphid damage can cause reduced yield in mild cases and total crop failure in severe cases. Melon aphids also excrete honeydew, contaminating leaves and products, reducing product quality.
Currently, aphid control is mainly through chemical control. In chemical control, the principle of early prevention should be followed. Commonly used agents include: 50% pirimicarb wettable powder or water-dispersible granules at 2000-3000 times dilution, which has special efficacy against vegetable aphids and does not harm natural enemies; or 40% dimethoate emulsifiable concentrate at 1000-1500 times dilution; or 70% menazon wettable powder at 2500 times dilution, etc. Vegetable aphids easily develop resistance to pyrethroid pesticides, so they should be used with caution or mixed with other pesticides. Commonly used ones include: 2.5% deltamethrin emulsifiable concentrate at 3000-4000 times dilution; or 10% cypermethrin emulsifiable concentrate at 2000-6000 times dilution, sprayed as above. You can also use 1.8% abamectin oil paste at 1500 times dilution plus 10% imidacloprid wettable powder at 1500 times dilution for control.