Downy mildew, techniques and organic treatments to avoid it

Share

FacebookWhatsAppEmailInstagram

0

Famous for being vineyard owners’ #1 enemy, downy mildew is a constant threat to grape harvests. This blight also threatens certain other vegetables from the vegetable patch such as tomato and potato, too.

Regular preventive treatment should help you produce a beautiful harvest without any trace of downy mildew.

• Read also: Treating tomato blight and downy mildew

How to recognize downy mildew

Symptoms of downy mildew start with the appearance of several spots on the leaves that encroach on neighboring leaves.

• This is a fungal disease that mainly impacts grape, tomato and potato.
• Yellow spots appear on and under the leaves.
• They turn brown and spread to cover the entire leaf which then falls off.
• On the underside, whitish patches appear that match topside spots. These white spots look a lot like powdery mildew.

Downy mildew also attacks young grape bunches, which turn brown or greyish and shrivel on the stalk.

Conditions in which downy mildew appears and spreads

Downy mildew particularly likes warm and moist settings, as well as dense foliage that keeps air and light away.

• Moisture is the main factor that triggers its spread, especially on leaves.
• Like most fungal attacks, downy mildew will spread fastest after rain showers.
• Mildew is hindered when plants are spread far apart and air circulates well.

Preventing downy mildew means ensuring the opposite of these factors:

• Water from below, with a long hose nozzle, long-spout watering can, drip irrigation or ollas.
• Avoid performing any other tasks during this phase: brushing against sick plants will spread the fungus fast when wet.
• Water early morning so plants only get one “wet time” in the day (synchronize with dew).
• Space plants well and thin them so that air circulates well.
• Layering mulch helps keep fungus trapped underneath: it won’t splash up to leaves as easily.

Dispose of plants infected with downy mildew:

• Handle sick plants carefully: spores fly around easily.
• Place trimmings near immune plants instead of vulnerable ones.
• Or burn or compost them in a hot compost.

Organic downy mildew treatments

It’s possible to use very effective organic downy mildew treatments.

• Bordeaux mixture is the only effective preventive treatment against downy mildew.
• Apply regularly at the beginning of spring and in fall.
• Treat during the entire vegetative phase.
• Treat regularly, on average every two weeks and after every rainfall.
• In the case that downy mildew appears, only a curative treatment will have any effect.

Bordeaux mixture contains copper. Though it’s relatively safe and organic, you shouldn’t apply it too often. Indeed, if used for years, copper builds up and kills bacterial and insect life. Different countries have regulations to follow if you’re a professional grower.

Downy mildew and baking soda

Baking soda (sodium bicarbonate) is an excellent solution to treat downy mildew, though a similar product is more effective: potassium bicarbonate.

• Dissolve 1 table spoon baking soda in 1 quart (1 liter) water (ideally rainwater or mineral water, for the water to be softer).
• In dry weather, spray this mix on all the leaves, spraying both on top and on the underside of leaves.

Preventing and treating downy mildew: what to use and when

Some measures keep downy mildew away before it appears, others only act once spots have shown. Here is how the methods described above compare.

Prevention does most of the work; once the disease has appeared, only a curative treatment will have any effect.

Other diseases and treatments

• Look up major plant diseases and how to treat them
• Tomato: Treating blight and downy mildew on Tomato

• Powdery mildew leaves a floury white bloom on the upper leaf surface, whereas the white felt of downy mildew forms on the underside.
• Avoid planting tomatoes right beside potatoes, because the blight passes readily from one crop to the other.