Can be confused with the bacterial disease angular leaf spot. Downy mildew is widely distributed on Citrullus spp., including watermelon, in the Americas but scattered elsewhere and absent in Europe and the Middle East, even though the climate is similar to areas where the disease is a severe problem. Requirements Watermelon is a warm-season crop, requiring lots of sun and good drainage to develop optimally and growing best at temperatures between 18 and 28°C (65–82°F). 12 Their inner part is covered with a bloom of purple, and round, light spots form on top. Downy mildew can infect all cucurbits including cucumber, melon, pumpkin and squash. Cucurbit downy mildew is caused by the fungus-like oomycete pathogen Pseudoperonospora cubensis (P. cubensis).There are two types of P. cubensis isolates that can infect cucurbit crops and weeds referred to as clade 1 or clade 2 isolates. Downy mildew. Plants infected with powdery mildew will produce small fruits in low quantities. Downy Mildew. While small amounts of downy mildew aren’t likely to do major harm to your garden, it’s a symptom of a larger water-related issue. Downy mildew can affect plants of all ages, but in many growing regions it appears late in the season. The leaf has curled up on itself, and the leaf edges have contracted and browned. Also, cercospora leaf spot, powdery mildew, bacterial fruit blotch, damping-off, and root rots/vine declines have been reported as a problem. Figure 2. Also, the disease spreads to fruits that become discolored and tasteless. Downy Mildew. This fast growing fungus affects Brassicas, cucumbers, melons, peas and more. 1,2 The infection is mostly restricted to the leaves, but the resulting reduction in photosynthetic area causes stunting of plants, reduced yields, and sunscalding of the fruit following defoliation. In many cases, they can grow systemically throughout the plant. Seedless Watermelon Crop Guide; Suggested Watermelon Varieties for Texas; Watermelon Foliar Diseases. Citron, calabash, cassaba, and vegetable-marrow are not commonly attacked, while wild cucumber and related weed hosts normally escape infection. The vegetable variety is listed first followed by the resistant diseases. Leaves of watermelon plants will curl up on themselves. As lesions expand, they may become brown with irregular margins. Downy mildew on watermelon–lesions begin yellow and later turn brown or black. Unlike many other foliar diseases of watermelons, such as gummy stem blight, anthracnose and downy mildew that thrive in wet conditions, dry conditions promote spread of powdery mildew (figure 3). Powdery mildew affects watermelon plants during warm, humid weather. Powdery Mildew. 1987). It thrives in wet or very humid conditions as a water mold. The downy mildew and its destructive properties Every veggie’s family is associated with particular set of diseases. To prevent this disease, avoid planting watermelon in shaded locations and do not over-fertilize. Fortunately, downy mildew won’t attack fruit, but it can reduce yields by weakening your plants. The most common diseases of watermelon are anthracnose, fusarium wilt, , downy mildew, gummy stem blight, root-knot nematode and virus diseases. Leaf spots vary in appearance between cucurbit species and within cucurbit species. A watermelon plant exhibiting late-stage symptoms of downy mildew. The watermelon fruit can unfortunately be susceptible to lots of different fungal diseases. Downy Mildew of Cucurbits Updated July 2020 This is one of the most common and destructive diseases affecting all cucurbit crops in the eastern United States including New York. Typically, symptoms begin as small yellow areas on the upper leaf surface. Downy Mildew, caused by Pseudoperonospora cubensis, is an oomycete that is not a true fungus. Leaf spots turn a pale yellow colour, enlarge and dry out. The cucurbit downy mildew pathogen P. cubensis results in defoliation, poor plant health, and significantly reduced fruit yields due to sun scald, reduced nutrition, and secondary rots.Downy mildew is a water mold and an obligate parasite. Peronospora parasitica. Affected areas may grow together, and the entire leaf may wither and die. foliar diseases observed on watermelons in Louisiana: anthra-cnose (caused by Colletotrichum orbiculare), gummy stem blight (caused by Didymella bryoniae) and downy mildew (caused by Pseudoperonospora cubensis). Downy mildew is one of the most important leaf diseases of cucurbits. These “downy” masses are most often noticed after rain or heavy dew and disappear soon after sunny weather resumes. In NY) (must be tank mixed with protectant) 15, affects cell wall synthesis tank mix with M5 or M3. Spores remain alive up to eight days. Downy mildew of cucurbits has also been reported in southwestern Michigan on the Indiana border and central Missouri. Watermelon Diseases; Fig. Source of infection: Other cucurbit crops affected by downy mildew and old infected crop trash. Figure 1: Downy mildew symptoms on cucumber leaves. Management of Downy Mildew for the Three Production Regions of Florida Managing cucurbit downy mildew requires an integrated approach and should include avoidance, monitoring, Chlorothalonil and mancozeb protect against gummy stem blight, downy mildew, and anthracnose; chlorothalonil also protects against powdery mildew. Moderate There are several foliar diseases which also cause leaf spots and may be confused with downy mildew. Preventing powdery or downy mildew can be accomplished by following common recommendations for managing fungal diseases. They may start as yellow areas, but soon turn brown with purple spores on the undersides of infected leaves. Downy mildew (photo courtesy of Denis Persley – QDPI&F) Symptoms: Leaves have a mottled appearance. Downy mildew grows on and into the leaves of their preferred plants, living off the plant’s water supply. Unfortunately, many food crops and some flowers and shrubs are susceptible to this fungal infection. Isolates belonging to clade 1 tend to more frequently infect watermelon, pumpkin, and squash while isolates belonging to clade 2 more … If growing abundantly on a leaf, downy mildew colonies can be confused with gray mold ( Botrytis ) or with powdery mildew. Downy mildew (Plasmopara viticola) affects many plants and appears as yellow to white patches on the upper surfaces of older leaves.On the undersides, these areas are covered with white to grayish, cotton-like fungi. Cucurbitaceae downy mildew (caused by Pseudoperonospora cubensis) is specific to cucurbits (e.g., cantaloupe (Cucumis melo), cucumber (Cucumis sativus), pumpkin, squash, watermelon (Citrullus lanatus) and other members of the gourd family). Watermelon will yield best if grown in a light, well-draining soil, rich in organic matter and with a pH between 6.0 and 7.0. Susceptible plants should be planted in sunny locations when possible, and regardless of whether they're planted in the sun or shade, air should be able to move freely around plants (i.e., no crowding). Downy mildew reproduces and spreads best when cool temperatures prevail- 60s are ideal- and there are 6-12 consecutive hours of leaf wetness caused by rain, irrigation, or dew each day. It occurs worldwide where conditions of temperature and humidity allow its establishment and can result in major losses to cucumber, melon, squash, pumpkin, watermelon, and other cucurbits.