Downy Mildew Alert

Symptoms:

Downy mildew produces a gray to whitish, thin mycelium layer on lower leaf surfaces. The first sign of downy mildew on the upper side of leaves is yellowish, angular spots that are bounded by vines.

Who Am I?

Downy mildew is a common fungal disease that favors relatively high moisture conditions, low light, and low temperatures. The disease is host-specific, meaning it can only infect plants from the same genus or family.

Control Measures

Monitoring: Make it a routine to monitor the field regularly and search plants for the presence of downy mildew on a weekly basis.

Moisture Reduction: Improve air circulation in closed structures, promote drying foliage, and shorten the duration of wetting periods by introducing net curtain vented areas.

Proper Soil Drainage: The presence of standing water will promote the spread of the downy mildew.

When long periods of high moisture are expected, or when infected plants have been observed, consider an application of fungicides every 7-14 days.

Don’t use products with the same active ingredient in consecutive treatments. Use fungicides belonging to different groups to prevent pathogens from developing resistance to a specific chemical.

The following is a list of generic names for fungicides known to help manage downy mildew and is sorted into groups according to their mode of action: Group 1: Dimethomorph, mandipropamid, iprovalicarb, and benthiavalicarb; Group 2: Metalaxyl and oxadixyl; Group 3: Propamocarb; Group 4: Potassium salts of phosphorous (phosphoric) acid; Group 5: Azoxystrobin, trifloxystrobin, pyraclostrobin, kresoxim-methyl H, and fenamidone; Group 6: Cymoxanil; Group 7: Mancozeb

Products based on tea tree oil and Potassium Hydrogen Carbonate+copper sulfate

Bacillus subtilis

Caution and careful notice should be taken when using any plant protection products (insecticides, fungicides, and herbicides). It is the grower’s sole responsibility to keep track of the legal uses and permissions with respect to the laws in their country and destination markets. Always read the instructions written on labels, and in a case of contradiction, work in accordance to the product label. Keep in mind that information written on the label usually applies to local markets. Pest control products intended for organic farming are generally considered to be less effective in comparison to conventional products. When dealing with organic, biologic, and to some extent a small number of conventional chemical products, a complete eradication of a pest or disease will often require several iterations of a specific treatment or combination of treatments.

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