Harmful symptoms and control methods of cucumber leaf blight

Cucumber leaf blight mainly harms the leaves. Symptoms on young leaves are not obvious. On mature leaves, yellowed areas appear on the leaf surface, along with deformed water-soaked chlorotic spots that gradually enlarge into nearly round or polygonal brown spots, 1-2 mm in diameter, surrounded by a chlorotic halo. On the underside of diseased leaves, small sections of clear veins are very likely to appear in the early morning or on cloudy days. Now let us take a look at the control methods for cucumber leaf blight!

Occurrence pattern of cucumber leaf blight

The pathogen mainly overwinters in the soil as mycelium with diseased plant residues. In the following spring, it produces conidia, which spread through airflow and cause infection. Then conidia are produced on diseased leaves for secondary infection. Weak plants, waterlogged fields and high humidity easily induce the occurrence of this disease.

Occurrence characteristics of cucumber leaf blight

The pathogen prefers a low-temperature and high-humidity environment. The suitable temperature range for disease onset is 3-30°C, the most suitable environmental temperature for disease onset is 8-20°C, and the relative humidity is above 95%. The most suitable growth stage for disease onset is from the seedling stage to the adult plant stage. The incubation period of the disease is 7-15 days. It occurs only in protected cultivation, usually only during the low-temperature period in early spring. When the greenhouse temperature exceeds 25°C, the disease is inhibited.

Control methods for cucumber leaf blight

1. Apply sufficient base fertilizer, drain promptly after rain, and ensure ventilation and light penetration between plants and rows.

2. Collect seeds from disease-free seed-bearing plants and select disease-free seeds.

3. In protected cultivation greenhouses, clean ditches in time to prevent water accumulation after rain, ventilate in a timely manner, and adopt light and frequent watering for fertilizer and water management. Watering and fertilizing should be done in the morning on sunny days, and the greenhouse should be opened in time for ventilation and dehumidification.

4. Advocate rotation with non-Cucurbitaceae crops at intervals of one year to reduce the source of pathogens in the field.

5. During the peak period of the disease, promptly remove diseased old leaves. After harvest, clean the field, remove diseased plant residues, take them out of the field and bury them deeply or burn them, and deeply plow the soil to accelerate the decomposition of diseased residues.

6. Before watering or on sunny mornings after rain, choose Bordeaux mixture (1:1:200) for spray prevention, or choose mancozeb for control at the early stage of disease onset.

What are the symptoms of cucumber gummy stem blight, and how to solve cucumber gummy stem blight

Cucumber gummy stem blight mainly harms leaves and stems, seriously affecting the growth of cucumbers. When leaves are infected, the disease often starts from the leaf margins, forming yellow-brown to brown "V"-shaped lesions densely covered with small black spots, which are easily broken after drying. Today the editor will share with you what the symptoms of cucumber gummy stem blight are and how to solve cucumber gummy stem blight.

What are the symptoms of cucumber gummy stem blight?

Cucumber gummy stem blight is a disease that causes relatively severe damage to spring protected cultivation and summer-sown cucumbers. The disease mainly harms stems and leaves. When stems and bases are affected, round or spindle-shaped yellow-brown, oil-soaked lesions are produced, slightly sunken, with amber-colored gelatinous material and scattered small black spots on the surface. After leaves are affected, large round or irregular lesions appear. In the later stage, the lesions are easily broken, and black small spots are densely produced on the lesions. Leaf lesions are 10-35 cm in diameter, and a few lesions are even larger. Diseased leaves turn yellow from the bottom upward but do not fall off. In severe cases, only 1-2 top leaves remain. Gummy stem blight mostly develops from the stem surface inward, the vascular bundles do not discolor, and the whole plant will not die. This is an important difference from Fusarium wilt.

Occurrence pattern: The pathogen of gummy stem blight mostly overwinters as conidia or ascospores in diseased residues and soil. It mainly spreads through irrigation water and airflow, and invades through stomata, water pores or wounds. Seed-borne bacteria can cause cotyledon disease. High temperature and high humidity, poor ventilation, excessive application of nitrogen fertilizer, flat-bed cultivation, flood irrigation, continuous rainy days, weak plant growth and excessive vegetative growth, and fields with consecutive years of continuous cropping are likely to cause disease onset.

How to solve cucumber gummy stem blight?

1. Good seeds and crop rotation: select disease-free seeds or retain seeds from disease-free plants. Implement crop rotation of more than 2-3 years.

2. Strengthen management: cultivate strong seedlings, increase the application of phosphorus and potassium fertilizers, enhance plant resistance, strengthen ventilation and light penetration, reduce temperature and humidity, and improve the field microclimate.

3. Chemical control: at the early stage of disease onset, choose 75% chlorothalonil wettable powder 600 times solution, or 70% thiophanate wettable powder 800 times solution, or 50% carbendazim wettable powder 1500 times solution, or 45% chlorothalonil smoke agent, 250 g per mu each time, or 40% Fuxing emulsifiable concentrate 800 times solution. Apply once every 7-10 days, for 3-4 consecutive applications.

Control methods for cucumber damping-off

Cucumber damping-off, commonly known as seedling death, mostly occurs in the middle and late stages of cucumber seedling raising. In severe cases, it can cause seedlings to dry up and die, seriously threatening cucumber yield.

Cucumber damping-off mostly occurs in the middle and late stages of seedling raising. At first, oval or irregular dark brown lesions appear at the base of the seedling stem. Some diseased seedlings wilt during the day and recover at night, and the lesions gradually become sunken. When humidity is high, light brown spiderweb-like mold can be seen, but it is not prominent. After the lesions expand, they can encircle the stem for one full circle, and even expose the xylem. Finally, the diseased part shrinks and dries up, the leaves wilt and cannot recover to their original state, and the seedlings dry up and die. The cortex of the underground roots turns brown or rots, but the plants do not easily bend over. The diseased part has concentric-ring-like or light brown netted mold layers.

The main control methods for cucumber damping-off are as follows: advocate the use of modern seedling-raising methods such as nutrition pots or plug trays, which can greatly reduce the occurrence and damage of damping-off. Add 50 g of 95% hymexazol technical material or 10 g of 54.5% hymexazol·thiram wettable powder, 100 g of 70% fenaminosulf soluble powder plus 50-100 g of 50% carbendazim wettable powder to each cubic meter of nutrient soil, mix thoroughly with the nutrient soil, and then fill nutrition pots or seedling trays. After emergence in the seedling field, strengthen observation. Before disease onset, the following fungicides or formulas can be used for control: 0.5% OS amino-oligosaccharin aqueous solution 300-500 times solution + 68.75% famoxadone·mancozeb water-dispersible granules 800-1000 times solution; 70% hymexazol wettable powder 800-1000 times solution; 20% flutolanil wettable powder 600-1000 times solution; 80% ethylicin emulsifiable concentrate 2000-4000 times solution, diluted with water and sprayed on the seedbed, once every 7-10 days depending on the disease condition.

When diseased cucumber damping-off plants are found in the field, control should be carried out promptly. At the early stage of disease onset, the following fungicides or formulas can be used for control: 30% difenoconazole·propiconazole emulsifiable concentrate 3500 times solution; 20% tolclofos-methyl emulsifiable concentrate 800-1200 times solution + 75% chlorothalonil wettable powder 600 times solution; 50% benomyl wettable powder 600-1000 times solution + 50% captan wettable powder 400-600 times solution; 70% thiophanate-methyl wettable powder 500-700 times solution + 70% mancozeb wettable powder 800 times solution; 15% hymexazol aqueous solution 500-700 times solution + 25% prochloraz emulsifiable concentrate 800-1000 times solution; 20% pyraclostrobin water-dispersible granules 800-1000 times solution + 70% metiram dry flowable 700 times solution; dilute with water and spray on the seedbed, once every 5-7 days depending on the disease condition.