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Gardening With Gutner: Summer Garden Fungus

CAMBRIDGE (CBS) - The number one challenge I seem to face each summer is fungus on many of my perennials, vegetables and believe it or not, this year my impatiens.

The most common fungus we all face is powdery mildew.

Powdery mildews, as the name implies, often appear as a superficial white or gray powdery growth of fungus over the surface of leaves, stems, flowers, or fruit of affected plants.

These patches of mildew may enlarge until they cover the entire leaf on one or both sides.

Although it usually is not a fatal disease, powdery mildew may hasten plant defoliation and fall dormancy, and the infected plant may become extremely unsightly.

Powdery mildew seems to always affect my vegetable garden.

So how can we treat this?

The best thing we all can do is to make sure we give all our plants plenty of space between each other.

Air circulation is a great way to help foliage remain healthy and clean of this disease.

Another thing we can do is to water in the morning and not at night.  It is often wet foliage that stays wet overnight that can easily contract a fungus problem.

There are many treatment options for infected plants.

There are several effective sprays that you can buy at your local garden center to help fight powdery mildew.  Most brands like Bonide, Serenade and Safer have sprays for fungal disease and all are safe for later consumption of vegetables.

If you prefer to try a home remedy - mix baking soda and water in a spray bottle and apply as you would one of the brand sprays.  This treatment is equally effective and a fraction of the price.

How about your impatiens, notice anything different this year?  Did you lose any and wonder why?  It wasn't you, it's a new disease downey mildew.

Impatiens downy mildew was diagnosed on impatiens (walleriana) in landscapes in Massachusetts for the first time in 2011 and has been diagnosed again in 2012.

All impatiens walleriana are susceptible. Fortunately, it is not effecting New Guinea or Sun Scape varieties.

Symptoms vary from off color foliage (slight yellowing) and slight wilting and curling down of foliage to nearly total leaf loss.

If the disease continues to progress, eventually the leaves and flowers will drop, resulting in bare stems with only a few tiny, yellow leaves remaining.

Downy mildew can be spread long distances by wind currents, water splash (overhead irrigation included) or by the movement of infected plants.

Infected plants should be pulled, roots, soil and all, bagged and disposed of. The area should not be replanted with susceptible impatiens species.

Fungicide treatments are not recommended for plants in the landscape since they are not always effective at eliminating the disease.

Allowing infected plants to remain in the landscape may allow the pathogen to overwinter as resting structures (called oospores), which may infect impatiens planted next year or longer.

New Guinea impatiens, coleus, begonia, or other available bedding plants are safe to reset in the affected area.

If you have any questions or comments please feel free to email me at

Best of luck and enjoy the rest of the growing season.

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