![]() Do you really want to eat leaves that have been sprayed with a potent fungicide? Do you relish eating pesto spiked with mefenoxam, or marinara sauce containing azoxystrobin? I am not above using chemicals occasionally, but this is not appetizing to me.ĭepending on your tastes, there may be other palatable options. Such products are likely to be useful for greenhouse producers, not home gardeners. Among the promising candidates are mefenoxam and azoxystrobin, potent systemic fungicides which must be used weeks ahead of harvest time to mitigate the poisonous effects of the chemicals. Research is ongoing to find a silver bullet-type treatment. It is important to note that the Virginia Pest Management Guide for 2016 does not yet list basil downy mildew nor recommend any specific treatments for the disease. Like most fungicides for home use, they must be used as preventative sprays, applied before the disease appears, but their effectiveness is limited. Potassium bicarbonate and neem oil are OMRI-approved organic treatments. The literature now cites some chemical treatments for basil downy mildew. (damping off of seedlings and various root rots). It includes a rogue’s gallery of plant pathogens such as Phytophthera infestans (late blight of tomatoes and potatoes), Plasmopara viticola (downy mildew of grapes) and Pythium spp. Oomycetes are fungus-like organisms that laugh (or wave their tiny tails) at standard garden fungicides.Įxperienced gardeners quake when they hear the word oomycetes. Peranospora behlbarii isn’t just any old fungus. When it became critical to address the problem, it proved to be a difficult task. ![]() There had been no problem so there was no need to devise a solution. What’s a basil-loving gardener to do? It should come as no surprise that there were no fungicide sprays approved for use on sweet basil at the time basil downy mildew first appeared. Curiously, it did not affect a plant grown from the same seed in a pot on my deck about 60 feet away. In July 2013 the disease ravaged four beautiful, large basil plants in one of my garden beds, seemingly overnight. The entire sequence can take just a few days. At that point it is over for the basil plant. Then black spots appear on the leaves and gray fuzz develops on the underside of the leaves that’s the downy part of downy mildew. When downy mildew attacks, plants in apparent good health develop some telltale yellowing of the leaves. Gray fuzz on the underside of a leafBasil had been one of the easiest crops to grow in this area until 2013, but no more. The pathogen is thought to travel on infected seed, but this mechanism is not well understood. Plants and growing media infected in a greenhouse are likely to show the disease whenever the temperature and humidity reach optimum levels for P. Its spores can travel long distances on air currents. It does not survive the winter in our area. It was especially severe in 2013, and it has been carried by the ill winds of summer ever since.īasil downy mildew lives year round in Florida and in greenhouses where basil is cultivated. Downy mildew first appeared in the United States in 2007, and 2012 was the first year we saw it in our area. Sweet basil includes many tasty varieties that we have come to cherish in our cuisine: Napolitano, Genovese, Italian Large Leaf, Nufar and others. This is the pathogen that causes basil downy mildew, a devastating disease of Sweet Basil (Ocimum basilicum). It also brought a special gift for gardeners: spores of Peranospora belbahrii. ![]() Warm and humid, it brought typical uncomfortable summer weather to Northern Virginia. Symptoms and signs of basil downy mildewIt was an ill wind that blew up from the south that July in 2013.
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