Tuesday, September 8, 2009

This White Stuff Isn't Snow

The oval leaf is from my honeysuckle bush and the pointed leaf from an aster plant. Both have Powdery Mildew (fungus Erysiphe cirhoracearum or Sphaerotheca fulginea).

Soybeans in this northern area of Illinois are also becoming infected with White Mold (Sclerotinia). This is rare for this area and could have negative crop loss potential.

The connection for both of these problems is the cool nights, poor air circulation, heavy dew instead of rainfall, and the time of the year.


Since those farmers experiencing White Mold know more about it than I, I'll concentrate on the Powdery Mildew on garden and yard plants.


I currently have it on some bee balm, phlox, lilac, aster, daisy forms, sedium, squash and honeysuckle. Not all of any one variety has Powdery Mildew. I don't spray for it but fungicides are available (always follow manufacturer's directions.)

In Illinois, Powdery Mildew overwinters in garden and yard refuse. It is often imported from southern grown nursery plants, especially vine crops. Since it is never killed in the south, it may blow north on the wind.

Powdery Mildew is attracted to vine crops and over 300 other strains of plants. Planting northern nursery grown plants, Powdery Mildew resistant varieties, having plenty of air circulation around plants, rotating vegetable crops and cleaning up all infected garden waste every fall (do not compost) will help the problem.


If you enjoy Heirloom plants or have an English style cottage garden, it will be difficult to control or eliminate Powdery Mildew. Since I have both, this mildew will be expected in my gardens.

Powdery Mildew seldom kills a plant although it can cause vines to dry and in severe cases cause fruit problems. My garden gets mildew late enough in the fall it seldom causes anything negative besides funky looking leaves.

If you are sensitive to air born allergens, wear a mask when cleaning up Powdery Mildew infected garden refuse and don't breath the smoke from burning plants. Wash all fruit in a light bleach solution (rinse thoroughly) if leaves and plants are infected with mildew, blight or other fungal diseases.

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