Controlling the fungus among us

Image from Wikimedia Commons

We have always wondered why there are rose bushes planted at the ends of rows in vineyards. Now that we have a vineyard, it prompted us to look into it. And what we learned makes sense. Roses and grapes are both susceptible to some of the same fungal diseases, namely powdery mildew and downy mildew. Roses, in fact, act as an early warning signal for mildew. They help the vintner catch the diseases at an early stage so proper treatment can be applied. In other words, they help to control the fungus among us. I also came across a curious alt truth story from Australia.

From Pollinator, Wikimedia Commons

Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales and affect a wide range of plants. The genus Oidium seems most associated.  It is one of the easier plant diseases to identify as its symptoms are quite distinctive. Powdery mildew affects all green parts of the vine. Powdery mildew grows well in environments with high humidity and moderate temperatures. Greenhouses provide an ideal moist, temperate environment for the spread of the disease. It affects especially cucurbits (melons, cucumbers, squash) and grape vines. You can see powdery mildew spores on the surfaces of the leaves. If mildew sets on the grapes, they will not develop properly and will split and rot. Treating the vines with sulphur solution once detected can be effective. To help prevent powdery mildew, it helps to avoid watering plants from overhead in order to reduce relative humidity and to selectively prune overcrowded areas to increase air circulation.

Many 'natural' remedies include baking soda. A solution of 1 teaspoon baking soda in 1 quart of water is used as a non-toxic alternative. Baking soda can burn plants and it can build up in the soil and cause deficiencies in calcium, magnesium, and iron. Potassium bicarbonate can be substituted for baking soda. Plants must be sprayed thoroughly as the bicarbonate solution will only kill fungus with which it comes into direct contact. Another formula is 1 tbsp baking soda, 1 tbsp vegetable oil, and 1 tsp dish soap in 1 gallon of water or 1 part milk to 10 parts water.  Neem, Antelaea azadirachta  - a tree, is an organic fungicide which has a myriad of medicinal uses. Perhaps planting one of these neem trees at the other end of the rows would be preventative. But alas, they only grow in warm regions and are native to India, Pakistan, etc. It can, however, be grown in a greenhouse! Another project.

From Wikipedia Commons

Downy mildews belong exclusively to Peronosporaceae. They are a particular problem for growers of cruciferous vegetables (mainly brassicas), grapes and vegetables that grow on vines. Plasmopara viticola, the causal agent of grapevine downy mildew, is an oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet conditions release zoospores. Zoospores are splashed by rain into the canopy, where they swim to and infect through stomata. After 7–10 days, yellow lesions appear on the foliage. During favorable weather, the lesions sporulate and new secondary infections occur. Downy mildew is deadly for vines. Photosynthesis is inhibited, the leaves drop and stems can rot. The fruit can also be infected with a white powdery coating. A warm, moist and humid environment is required. In any given year, it can reduce yield in French vineyards by as much as 50%. In Sicily, it has been shown that oospores germinate between the end of February and the middle of March, and treatment of the vineyards during that time is most effective in preventing spread of the disease. Treatment for downy mildew is a solution of copper sulphate and lime. Never put leaves infected with mildew into the compost.

It sounds like our decision to raise the vines up on trellises like they do in Galicia makes perfect sense to help avoid the spread of fungal diseases. Of course, today, there are sophisticated methods for detecting disease in commercial vineyards. But in Daria's Vineyard, we'll stick with the romantic notions to plant roses and watch them bloom. So far our plants appear to be unaffected. Let's hope it stays that way.