![]() Downy mildew developing on single plants like this one documents the abundance of spores of the pathogen in the air. But the basil plant in the landscape planting in the picture below still experienced enough high humidity during rain and overnight for downy mildew to develop. Only these two leaves were found with symptoms while pathogen sporulation was observed on many leaves on plants that stayed outside at the same time.Ī sunny, open location seems like a good spot for growing basil to minimize humid conditions favorable for downy mildew. ![]() Infection was able to occur because these plants were left outdoors sometimes when humidity was high. Under high humidity in the bag, the pathogen produced spores confirming the symptoms were those of downy mildew. To determine if it was this disease, the leaves were put upside down on wet paper towel in a sealed plastic bag over night. Yellowing on these leaves, especially where in bands delineated by veins, looks like symptoms of downy mildew. Leaves below were on a gardener’s potted plants that were being brought inside at night to minimize time the plants were exposed to conditions favorable for disease development. ![]() When humidity is low the pathogen does not produce spores. Under humid conditions the pathogen produces an abundance of dark spores as shown in photographs below from Fran Smith in Pennsylvania who submitted them for confirmation of her report to the monitoring program. More information.īelow: Sporulation on both surfaces of small leaf.īelow: Sporulation on upper surface of large leaf.īelow: Sporulation on wet leaf with dew drop. Next two images: Sporulation of the basil downy mildew pathogen abundant on the lower leaf surface and also present on the upper surface of leaves of infected commercial basil plants kept in high humidity (inside a plastic bag) over night.īelow: Sporulation on container grown plant kept outside (left) but not on plant brought inside at night (right). (Photo courtesy Maire Ullrich, Cornell Cooperative Extension-Orange Co., N.Y.) Pathogen growth and spores on lower leaf surfaces.īasil downy mildew in a commercial crop. First three photographs taken on 9 August 2009, next five taken on 12 August 2009. Find more information about basil downy mildew and its management on the Basil Downy Mildew Extension page.įollowing eight images show first symptoms of downy mildew found on untreated plants in a home garden. Still have a question? Contact us at Ask Extension. Additional resourcesīasil Bounces Back With Downy Mildew Resistant Cultivars - Maryland Grows Blog - February 2020 Good air circulation around plants can help reduce the risk of infection. Plant basil in full sun locations and don’t crowd your plants. Warm, wet, humid weather encourages the spread of downy mildew. If you lose plants to downy mildew you can sow fresh seeds in containers or in another part of your garden. ![]() It is safe to eat leaves from infected plants- the disease does not harm people. Monitor your plants closely for symptoms and be prepared to pull out, bag up, and throw out infected plants. Seeds can be ordered from some online vegetable seed and plant suppliers. Plant resistant basil varieties such as 'Obsession', 'Devotion', 'Prospera', and 'Amazel' (propagated from cuttings) to help prevent the disease. Leaf yellowing symptom on basil Gray fuzzy growth on the underside of leaves Management of downy mildew on basil It was found in greenhouse, home, and field-grown basil.īelow are photos showing the early symptoms of this fungal disease on the top and bottom sides of basil leaves. Beginning in 2008 there were a number of infections reported in the eastern US and has infected basil in subsequent years. This disease was first detected in Florida in 2007. Leaf yellowing is the most noticeable symptom on basil infected with basil downy mildew. ![]()
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