Powdery Mildew

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According to our local paper, we have had “roughly 40 days” of rain since the beginning of April or about 12 inches. The gardens are green and lush.

Penn State Extension’s “Plant Disease Facts”, lists conditions that favor powdery mildew:

- High relative humidity at night
- Low relative humidity during the day
- 70-80 F temperatures

That sounds like our weather forecast.

Aptly named, powdery mildew looks like someone with a diaper emergency tripped and dumped baby powder all over the leaves. I usually don’t see much of it in this area until the steamy nights of August.

The phlox in the pictures is a prime example. Mildew also infects the leaves of cone flowers and zinnias. It usually doesn’t kill the plant but it makes the leaves unattractive. The lower leaves will will eventually curl up and turn brown.

The best control is to buy disease resistant plants. Being disease resistant doesn’t mean the plant will never get mildew but that plants are less susceptible to the fungus. Spacing and pruning plants for maximum air flow can help. Cleanup and discard plant debris in the fall.

A little gardening trick is to plant a shorter plant that doesn’t get mildewed in front of the mildew-prone plant to hide the unsightly leaves.

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(More information on powdery mildew and mildew resistant plants from Clemson University Extension.)

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Garden Book

The Organic Gardener’s Handbook of Natural Insect and Disease Control, edited by Barbara W. Ellis and Fern Marshall Bradley. 1996 Rodale Press, Inc.

I’m enjoying browsing through this Christmas gift. You need to be really, really interested in gardening to stay with this book. Realizing that it is a reference book, I found the identification parts of the book the most valuable. I’m not so sure about the recommended controls.

The “Problem-Solving Plant Guide” starts with a plant description. The by-plant section includes flowering plants, shrubs, vegetables and fruits. Then, a list of problems the plant may have ends with page number for control information.

The section, “Insects. Recognizing Your Friends – Eliminating Your Foes,” includes everything from aphids to yellow jackets. The illustrations are small but each insect is accompanied by 2 to 6 pictures. Each insect section includes Description, Life Cycle, Beneficial Effect or Damage Control or How to Attract. The life cycle information is important since some insects can only be controlled at a specific stage of life. It’s nice to have this information in one book.

The book continues with “Diseases and Organic Controls” again with pictures. Type of Problem, Symptoms, Plants Affected, and Prevention and Control for each disease is listed.

Most of the general advice is not something we haven’t heard before. Use disease resistant plants. Clean up plant debris. Prune to insure good air flow. Eliminate weeds. Select the right plant for the space. Use compost and mulch. – a brief synopsis of good advice.

It’s a good reference book and reads like, well, a reference book. I’ll have to force myself to read through some sections. Maybe I’ll read “Diseases. Identifying the Cause – Implementing the Cures” during the next snow storm - unless Dan Brown writes a new book.

Diagnosing Plant Problems

"Diagnosing plant problems requires patience"

The above title was posted by Karen Bernhard, Entomologist, Lehigh Co. Cooperative Extension, on November 8th on The Morning Call web site http://blogs.mcall.com/master_gardeners/

Many times the folks at the County Extension office know what’s happening with your plant, lawn, vegetable, shrub or tree because they have received other calls or they are seeing the same problem in their own gardens. Sometimes the information will be posted on the blog.

Sometimes the question is extremely difficult to answer. These are the problems that take time and patience. Is it caused by a bug, a virus, bacteria? Or is it cultural – the weather, site problems, hardiness problems, problem with sprays, or a host of other reasons?

In the Master Gardener Blog, a helpful questionnaire is posted under “Garden Resources” in the right-hand column. Click “Send Questions to a Master Gardener.” Click again on “Submit your questions online”. The form will give you some idea of the information needed to accurately assess the problem.

If it is a really difficult problem, you may be asked to bring a sample. Take as much of the plant as you can. Often the answer is in the transition zone between the good growth and the problem zone. Sometimes it is even in the roots. The samples will need to be fresh. If you can’t get to the office right away, store the sample in a plastic bag, keep it cool and get it there as soon as possible. When you call, the people at the Extension Office will advise you how to handle the specimen.

A helpful guide for the do-it-yourself gardener “A Guide to Diagnosing Diseases of Landscape Plants” Virginia Cooperative Extension http://www.ext.vt.edu/pubs/plantdiseasefs/450-800/450-800.html

If you have a difficult problem, be prepared for a tough answer.

- Sometimes there is nothing you can do. The plant is toast.
- Treatment may be delayed until another season. A pesticide may only work at a certain stage of the insect’s life.
- Sometimes there’s nothing you need to do. It will eventually go away.

Hopefully, the people at the extension will be able to provide a plan of action and not a dire diagnosis.