Wet foliage can also be a sufficient microclimate to produce spores and infect plants . It is unsightly and can become a systemic pathogen killing the entire plant , but fortunately is not necessarily fatal with proper prevention and treatment .
Symptoms and Causes of Downy Mildew
Downy mildew can be festering on your plants for some time before being noticed . That is because it usually first appears on the undersides of leaves . The leaf bottoms can appear to have white or bluish-white fuzzy or fluffy looking growths . After some time , the tops of the leaves may develop small green or yellow translucent spots . If these spots remain untreated , they leave a gray colored lesion in their wake . Eventually whole leaves , then branches , even flowers and fruit will die . These deceased brown or bronze colored portions will continue up the plant , if not controlled and the climatic conditions do not change or are otherwise unaddressed . Downy mildew is caused by several related , but host-specific fungal species of pathogenic water molds ( oomycetes ). This means the type that infects one kind of plant may not be the same species of fungus affecting another plant , though the symptoms may appear the same . Downy mildew spores are produced only on living plants and spread primarily through wind displacement and air movement , though they can be spread by insect pests moving from plant to plant . As spores land on a host plant , they can germinate and infect within as few as eight to 12 hours if the plant or foliage is wet . Some of the more commonly occurring pathogens for downy mildew are Peronospora spp ., Plasmopara spp ., and Pseudoperonospora spp . It should be noted , however , that finding downy mildew on one type of plant typically means that the conditions are favorable for the development of other downy mildews on other types of plants as well . If unsure what kind of disease you have , take a large sample to your local cooperative extension service or larger garden center for identification where it can be viewed by a trained professional with a keen eye or viewed under a microscope . Downy mildew appears under the lens in a branched pattern whereas powdery mildew appears in a chain-like formation when view under extreme magnification .
Plants Commonly Affected by Downy Mildew
Downy mildew affects a wide range of plants . Host plants can be vegetables , fruits , herbs , annual flowers , perennials , and woody shrubs . Anywhere that cool , damp conditions exist , downy mildew can appear . The following list is by no means complete , but shows the range of hosts :
• Herbs — basil , rosemary , verbena
• Fruit ( botanically speaking any plant that produces a seed-bearing vessel ) — cucurbits ( squashes , cucumbers , pumpkins , gourds , etc .), peas , tomatoes , grapes
• Vegetables — potatoes , kale and other cole crops , spinach , lettuce , onions , garlic , asparagus , rhubarb
• Annuals — alyssum , poppies , sunflowers , impatiens , pansies , coleus , snapdragons
• Perennials — coreopsis , aster , perennial geraniums , daisies , Veronica
• Woody shrubs — roses , viburnum
• Other — hops
“ EVENTUALLY WHOLE LEAVES , THEN BRANCHES , EVEN FLOWERS AND FRUIT
WILL DIE .”
Treating Downy Mildew
The good news is downy mildew can usually be effectively controlled with a wide range of commercially available fungicides . Many products are formulated to control a range of plant diseases and downy mildew can often be treated with the same formulations available to combat other common plant diseases such as Pythium and Phytophthora . Fungicides formulated to combat or control true fungi , however , will not often be effective to use on downy mildew as the biology of each respective disease is quite different . “ Traditional ” fungicides for downy mildew include many of the most commonly occurring chemicals on the market . These include ( this list is not exhaustive , but representative ) fungicides containing : chlorothalonil , copper sulfate and lime ( commonly sold as “ Bordeaux mix ” and sometimes used in organic food production ), fosetyl-Al , mancozeb , metalaxyl , mefenoxam , or trifloxystrobin . For those seeking less harsh alternatives , there are indeed some formulations approved for organic food production that can be used to treat downy mildew .
Maximum Yield 35