Berry Mildew Disease

Berry diseases consistent with mildew or a whitish greyish powder. Could be powdery mildew. Find out more about this berry plant disease.

What is it?

Powdery mildew is a very common plant disease among the berry family. It is caused by the fungus, sphaerotheca humuli and is seriously dangerous to blackberries as well as purple and black raspberries.

What does it look like?

Damage from powdery mildew shows up on berry plants in the form of a whitish or greyish powder. This ashy like powder can be found on almost all parts of the plant, and especially on the leaves, fruit and younger cane tips. In addition, powdery mildew may cause the canes to grow in a distorted manner so that canes are dwarfed or crooked. Powdery mildew can also cause the berries themselves to wither and die off.

How does it manifest?

Powdery mildew is composed of fungal patches and spores. When the wind blows, the spores are transplanted and spread to healthy plants. Splashing water or rain can also spread the spores and fungal strands. Once the fungi infect the berry plants, they begin to sap the energy and nutrients of the plants until they begin to die off. This may first appear in yellowing of the leaves and eventual leave death. Powdery mildew attacks many plant varieties and therefore can be spread to berry plants from unrelated species, just as berry plants which are infected with the fungi can spread spores to other plants in your garden. Occasionally circumstances become optimal for the spread of powdery mildew and the fungi can infect an entire crop of berry plants within a matter of just a few weeks.

What can you do about it?

Ideally, plants should have been spaced far enough apart that there is room for adequate air circulation when they were first planted. If this is not the case, diligent thinning will help. Once the blossoms open, you should spray berry plants with a benomyl containing fungicide or a lime-sulfur spray. You may need to repeat if plants become reinfected and it may take severeal treatments before the powdery mildew does not return. Be sure to space sprays at least one week apart.

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