What to Do When Strawberries Get Powdery Mildew? Symptoms of Damage and Control Methods

Strawberry powdery mildew is a major disease in strawberry production and can occur throughout the entire growing season of strawberries. Infection at the seedling stage causes a decline in seedling quality, making it difficult for plants to survive after transplanting. Infection of the fruit severely affects strawberry quality, leading to a drop in the rate of marketable fruit, and seriously affecting strawberry yield, quality and economic returns. Let's take a look below at how to treat strawberry powdery mildew!

Symptoms of Strawberry Powdery Mildew

Strawberry powdery mildew mainly damages leaves, petioles, flowers, flower stalks and fruit, and rarely occurs on runners. When leaves are infected, in the early stage of the disease a thin layer of white mycelium grows on the underside of the leaves. As the disease worsens, the leaves curl upward into a spoon shape and develop dark-colored spots of varying sizes. The spots then gradually expand and a thin frost-like white powdery substance appears on the underside of the leaves. In severe cases, multiple spots join together to cover the entire leaf. When flower buds and flowers are infected, the petals turn pink and the flower buds fail to open. When fruit is infected, the young fruit fails to swell normally and dries up.

Causes of Strawberry Powdery Mildew

1. Strawberry powdery mildew is a low-temperature, high-humidity disease. The suitable temperature for onset is 15-25°C, and the suitable temperature for conidial production and infection is around 20°C, with relative humidity above 90%. If from late autumn to early spring there is continuous cloudy, rainy, foggy or snowy weather with little sunshine, low temperatures and high relative humidity, this favors the continuous production of spores and repeated infection, causing the disease to break out and cause disaster.

2. Strawberries grown in continuous cropping in greenhouses develop the disease earlier and more severely, with the first appearance of the disease about 1 month earlier than in newly built greenhouse plots. In the former, the disease usually starts in mid-October, while in the latter, disease centers only appear in mid-November. Fertilization is closely related to the disease. Excessive application of nitrogen fertilizer makes strawberries grow vigorously, with large, tender green leaves that are prone to powdery mildew. If nitrogen fertilizer is applied at the right time and in the right amount, along with additional phosphorus and potassium fertilizer, the disease is milder.

How to Treat Strawberry Powdery Mildew?

1. Before flowering, when the disease has not yet occurred, use protective fungicides for preventive treatment twice. Spray with 2% Wuyimycin aqueous solution at 200 times dilution or 75% chlorothalonil wettable powder at 600 times dilution, spraying once every 7-14 days. Alternating the agents gives better results.

2. After the disease occurs, choose agents with both protective and curative effects. Use 50% kresoxim-methyl water-dispersible granules at 3000 times dilution or 4% tetraconazole aqueous solution at 1000 times dilution, spraying once every 7-10 days. Alternating use gives better results.

Prevention of Strawberry Powdery Mildew

1. Choose disease-resistant varieties and cultivate disease-free strong seedlings.

2. Practice reasonable crop rotation to reduce the occurrence of the disease.

3. Promptly remove old leaves, diseased leaves and residual leaves, and maintain good field sanitation.

4. Irrigate reasonably, control humidity inside the greenhouse, and reduce the disease.

5. Reasonably control the amount of nitrogen fertilizer and apply more phosphorus and potassium fertilizer.

What to Do About Powdery Mildew in Greenhouse Strawberries? Control of Powdery Mildew in Greenhouse Strawberries

Powdery mildew is a major disease of greenhouse strawberries and occurs throughout the entire growing period of strawberries. It is most damaging especially after strawberries bud and flower and enter the fruiting stage, seriously affecting strawberry growth, yield and quality. So what should be done about powdery mildew in greenhouse strawberries? Below is an introduction to the control of powdery mildew in greenhouse strawberries.

Control of powdery mildew in greenhouse strawberries should focus on prevention, with integrated control, combining agricultural control with chemical control, so as to achieve the goal of improving yield and quality.

Agricultural Control of Powdery Mildew in Greenhouse Strawberries

1. Reasonable crop rotation. Where conditions permit, carry out reasonable crop rotation to reduce the base number of pathogens and lessen the occurrence of the disease.

2. Choose disease-resistant varieties and disease-free seedlings.

3. Promptly remove old leaves and diseased leaves, and take the old diseased leaves out of the field for centralized destruction to reduce the chance of re-infection.

4. Fertilize reasonably and prevent excessive application of nitrogen fertilizer.

5. Irrigate reasonably, control humidity inside the greenhouse, and reduce the occurrence of the disease.

Chemical Control of Powdery Mildew in Greenhouse Strawberries

The key to chemical control is prevention first, and two points must be mastered:

First, timely control. Before flowering, spray for prevention 2 times. After flowering, spray immediately for control at the early stage of the disease. In severely affected fields, use chemicals continuously for 2-3 treatments.

Second, agent selection. When selecting agents, the growth characteristics of strawberries must be considered. Because strawberries have relatively high economic value and the growing environment of greenhouse strawberries is relatively enclosed, the first consideration in choosing agents is safety, especially during the flowering and fruiting stage, where safety should be considered even more. Myclobutanil and Score have good control effects and are safe for strawberry production, and can be used over large areas. Using 12.5% myclobutanil and 10% Score at 1500 times dilution is preferable. In production, do not blindly increase the concentration, especially with myclobutanil, as high concentrations will have adverse effects on strawberry growth. Control of powdery mildew in greenhouse strawberries should focus on prevention, and it is not advisable to use the same pesticide alone for a long time; they should be used alternately to improve control effects and prevent the disease from developing resistance.

Control Methods for Strawberry Powdery Mildew

During the growth of strawberries, powdery mildew is one of the main diseases harming strawberry growth, so how should we control strawberry powdery mildew?

Strawberry powdery mildew mainly attacks leaves and tender tips; flowers, fruit, fruit stalks and petioles can also be affected.

Control methods for strawberry powdery mildew:

(1) Choose disease-resistant varieties.

(2) After thoroughly clearing the previous crop of strawberry plants and various weeds inside the greenhouse or in the field, then plant. In winter and spring, clean up the orchard, burn rotting stems and leaves, and during the growing season promptly remove diseased leaves and burn them in a centralized manner.

(3) Plant at a reasonable density, strengthen soil, fertilizer and water management, enhance plant vigor, and improve the plants' own disease resistance. Fruit growers should try not to move between each other's greenhouses, to avoid human transmission.

(4) Prevent excessive application of nitrogen fertilizer, control excessive vegetative growth, pay attention to ventilation and air exchange, and promptly prevent excessive moisture after rain.

(5) When diseased runners or diseased fruit are found, gently pick them off as early as possible while the morning dew has not yet dried, put them in plastic bags and burn them or bury them deeply.

(6) Chemical control: make sure to apply chemical control promptly at the early stage of the disease. Sulfur fumigation technology for preventing the disease: The reason Japan still has large areas of strawberry varieties that are not resistant to powdery mildew, such as Toyonoka, Nyoho, Akihime, and Kinuama, is mainly that it uses sulfur fumigation technology to suppress the damage of powdery mildew. The sulfur fumigation technology involves installing one fumigator every 100 sq m inside the greenhouse, with the fumigator containing 20 g of sulfur powder with a content of 99%, and starting heating and fumigation in the evening after the greenhouse curtain is closed. Do it once every other day, 4 hours each time, and observe during this period, adding more sulfur powder when it is insufficient. The fumigator is hung in the middle of the greenhouse at 1.5 m above the ground. To prevent sulfur gas from hardening the greenhouse film, an umbrella-shaped piece of waste film can be set up 1 m above the fumigator to protect the greenhouse film. This method is harmless to bees, but the temperature of the fumigator must not exceed 280°C, to avoid sulfurous acid causing phytotoxicity to strawberries. If the nighttime temperature inside the greenhouse exceeds 20°C, the dosage should be appropriately reduced. 50% Baifenjing suspension concentrate at 600 times dilution; 70% thiophanate-methyl at 1000 times dilution; 25% triadimefon wettable powder at 3000-5000 times dilution; 50% Tuzet at 800 times dilution; 30% Trifumine at 5000 times dilution; 10% Score water-dispersible granules at 2000-2500 times dilution for spray control; 40% Fuxing at 10000 times dilution; 12.5% myclobutanil emulsifiable concentrate at 1500 times dilution; fungicidal smoke agents chlorothalonil and Yianxunling can be mixed for smoke fumigation; apply chemicals once every 7-10 days, and multiple chemicals can be used alternately to prevent resistance.