Downy Mildew is a plant disease caused by the oomycete, Bremia lactucae, which affects lettuce and can cause significant yield losses, especially in hydroponic systems where high humidity and close proximity of plants can enhance the rapid spread of the disease. Recognizing and responding to Downy Mildew in a timely manner is crucial for growers to maintain healthy, productive crops.

Identification and Symptoms

Downy Mildew presents as pale green spots on the upper surfaces of the leaves. These spots later turn brown and are usually delimited by the leaf veins, giving them an angular shape. On the lower surface of the leaf, directly beneath these spots, a downy, white to light grey growth of spores can be observed, which is a characteristic symptom of this disease.

Conditions for Disease Development

Bremia lactucae thrives in cool, moist conditions. The pathogen produces spores which are spread by wind, water splash, and human activities. In hydroponic systems, the high humidity and water splash from the nutrient solution provide ideal conditions for the rapid spread of the disease. The spores can germinate and infect the plant when there is free water on the leaf surface and the temperature is between 8-15°C, but it can also infect at temperatures up to 25°C.

Treatment

Once the disease has established, it can be hard to control. Applying fungicides can be a potential method of control. However, Bremia lactucae has shown resistance to several fungicides, and excessive use of fungicides can lead to further resistance development and can have adverse environmental impacts.

Incorporating resistant varieties is another control measure, but this also has its limitations as new races of the pathogen can overcome the resistance. Therefore, growers should use an integrated approach for disease control.

This is where NutriHydro’s products come in. NutriHydro’s Lettuce Formula provides the plant with all the necessary nutrients to ensure its robust growth and overall health. A strong and healthy plant is more resistant to diseases. NutriHydro’s pH Control keeps the pH of the nutrient solution in the optimal range. An incorrect pH can lead to nutrient imbalances, weakening the plant and making it more susceptible to diseases.

Moreover, NutriHydro’s Biostimulants can be sprayed onto the leaves. Biostimulants help in enhancing the plant’s resistance against diseases by triggering the plant’s innate defense mechanisms.

Prevention and Management

Prevention is always better than cure, and this is particularly true for Downy Mildew. Preventive measures should aim to reduce the humidity and free water on the leaf surface as much as possible. This could be achieved by manipulating the environmental conditions in the greenhouse, for example, by using heating and ventilation to reduce humidity, and careful timing of irrigation to avoid long periods of leaf wetness.

Regular scouting of the crops for early symptoms of the disease and removing and disposing of infected plants will help to limit the spread of the disease. Crop rotation and sanitation of the system between crops can also reduce the disease pressure.

Downy Mildew can cause serious losses in lettuce production if not managed correctly. Therefore, understanding the biology of the pathogen, the conditions favoring disease development, and the available control measures is crucial for growers.

Remember, the best approach to managing downy mildew in lettuce is an integrated one, that combines several of the above strategies. This reduces reliance on any single method and increases the chances of successful disease control. It’s always a good idea to consult with your local agricultural extension services or a professional agronomist for best advice. You may also reach out to NutriHydro so we can arrange consultations with qualified professionals in the field of agriculture. Reach out to us on our contact page.