![]() ![]() It is a tropical disease and does not overwinter outdoors in most northern climates. The pathogen that causes basil downy mildew can transmit on seed, transplants, or fresh leaves. Infection starts on lower leaves and moves up the plant. The best defense against this disease is use of basil cultivars that are resistant to downy mildew.Īlong with planting resistant varieties, it is also helpful to have good air circulation around the plants and to water the plants with drip irrigation at the base of the plant.įungicides can reduce disease pressure, but only if they are applied before the disease develops.īasil downy mildew, specific to this crop, can spread rapidly and result in complete yield loss. The disease can decimate a basil crop, usually in late summer to early fall, ending the plant’s life rapidly.īasil is one of the most popular summer annuals for commercial and home production, but not all cultivars are equal when it comes to withstanding downy mildew. Later, this causes the affected areas to turn brown and die. The downy mildew spreads rapidly in humid, wet weather, and is mostly a problem later in the summer.Įarly in the infection the plant’s leaves have a yellowish color, like a nutritional deficiency, starting along the major leaf veins.Īs the disease spreads, the undersides of leaves show the fuzzy gray-colored sporangia, where spores are formed. and Canada, and by 2012 it was reported in the Midwest. In 2007 it was first reported in the United States, found in south Florida.īy the following year it was reported in greenhouses and field-grown crops and home gardens throughout the eastern U.S. (Photo courtesy Chelsey MacBride-Gill)ĭowny mildew, Peronospora belbahrii, is a major disease on basil plants.įirst reported in the 1930s in Africa, downy mildew has since spread to new continents. Few fungicides are registered for herbs.The downy mildew spreads rapidly on basil in humid, wet weather, and is mostly a problem later in the summer. Many of the fungicides labeled for powdery mildew will not control downy mildew. It is important to distinguish between downy and powdery mildew because they are managed differently. Perennials susceptible to downy mildew include aster, coreopsis, geranium, geum, lamium, potentilla, veronica and viola. Other greenhouse crops that may be prone to downy mildew include snapdragon, salvia, alyssum, pansy, rose, rosemary, sage coleus and ornamental cabbage. Downy mildew sporulation also tends to occur on the underside of the leaves, whereas powdery mildew can occur on either the upper or lower surface. This can help you distinguish downy mildew from powdery mildew. (They will look like many tiny branched trees, each bearing tiny lemons). With a hand lens, closely examine the bloom of sporangia (microscopic stalks bearing spores) on the underside of the oldest leaves. Conditions that promote leaf wetness, such as high relative humidity, overhead irrigation and close spacing, favor this disease. Downy mildew symptoms appear very rapidly and tend to be much more difficult to control than powdery mildew. The discolored foliage on the upper leaf surface could be confused with a nutritional deficiency. Symptoms appear as a light gray colored, fluffy growth on the underside of leaves. Downy mildew is a relative of Phytophthora and Pythium. The underside of the leaves appear "dirty" due to the growth of sporangia, the distributive form of the fungus. Symptoms occur on the top of the foliage as yellowing as if the plants are nitrogen or nutrient deficient. The disease is probably much more widespread than is realized. In 2008, it appeared to be wide spread in Massachusetts, New York, and New Jersey. Downy Mildew sporulation occurs on leaf undersides and can be mistaken for growth media on foliage.ĭowny mildew (Peronospora species) of basil was first detected in the continental United States last year in Florida. ![]()
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