Downy mildew
Peronospora farinosa
What is Downy mildew (Peronospora effuse)?
Peronospora effusa, previously known as P. farinosa f. sp. spinaciae, is a plant disease called downy mildew that affects spinach and some types of weeds (Chenopodium). It's a major concern for spinach farmers, particularly in California where the weather is cool and wet. Symptoms of spinach downy mildew include irregular yellow patches on upper leaf surfaces, accompanied by purplish-gray sporulation beneath the leaves. Sporulation may also be visible on the upper leaf surfaces, while lesions eventually dry out and turn brown.
How does Downy mildew (Peronospora effuse) occur?
Peronospora effusa (Pfs) reproduces through spores that are dispersed by wind, water, or human activities. These spores can germinate and invade plant tissues, causing infections in spinach. Pfs also has a sexual phase where male and female gametes combine to form oospores. Oospores can survive harsh conditions and act as long-term survival structures. When conditions become favorable, oospores can germinate and initiate new infections. This reproductive cycle helps Pfs persist and spread in spinach crops.
Symptoms
1 - Peronospora effusa (Pfs) reproduces through spores that are dispersed by wind, water, or human activities. These spores can germinate and invade plant tissues, causing infections in spinach. Pfs also has a sexual phase where male and female gametes combine to form oospores. Oospores can survive harsh conditions and act as long-term survival structures. When conditions become favorable, oospores can germinate and initiate new infections. This reproductive cycle helps Pfs persist and spread in spinach crops.
Peronospora effusa, causing spinach downy mildew, impacts plants by reducing crop quality and yield through leaf spots, curling, distortion, and blight. Severe cases can lead to stunted growth and plant death. Additionally, plants become more susceptible to other diseases and pests.
Solutions
1 - Cultural Practices
• Choose resistant cultivars to minimize disease susceptibility. • Rotate spinach with non-host crops to break the disease cycle and reduce inoculum buildup. • Ensure proper plant spacing for better air circulation, reducing prolonged leaf wetness. • Use drip irrigation or other methods that deliver water directly to the root zone, minimizing foliage moisture. • Manage weeds, especially Chenopodium species, which can serve as alternate hosts for downy mildew. • Remove and destroy infected plant debris to reduce inoculum sources. • Regularly monitor fields for early signs of downy mildew to enable timely interventions.
2 - Sanitation and Host Management
• Collect and dispose of fallen, infected leaves and needles away from host plants to minimize the source of fungal spores. • Remove nearby alternate hosts of the fungus, if applicable, to reduce the chances of new infections.
3 - • Fungicide Applications
• Mefenoxam (systemic fungicide), Fosetyl-Al (systemic fungicide), Acibenzolar-S-methyl (benzo-thiadiazole fungicide), Fluopicolide (benzamide fungicide), Mandipropamid (carboxylic acid amide fungicide), Fenamidone (quinone outside inhibitor fungicide), and Phosphorous Acid (phosphonate fungicide). • It is important to consult with local agricultural authorities, extension services, or agricultural suppliers for specific brand recommendations and approved fungicides in your region.
