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Thursday - May 29, 2008

From: Austin, TX
Region: Mid-Atlantic
Topic: Diseases and Disorders, Herbs/Forbs
Title: Possible mildew on standing cypress
Answered by: Barbara Medford

QUESTION:

My mother-in-law took some standing cypress seeds from Texas to Virginia several years ago. They have always done very well, but this year they are growing very tall, but the bottom half of the stalk is turning silver. They have had 7 inches of rain recently. Is this a mildew? What can she use on it that won't hurt the hummingbirds?

ANSWER:

Ipomopsis rubra (standing-cypress) is native to both Texas and Virginia, so there is certainly no reason why it shouldn't do well in your mother-in-law's garden. Your description sounds like there could be a mildew problem. Read this article from Ohio State University Extension on Powdery Mildew on Ornamental Plants. One point the article makes is that mildew is rarely that dangerous a disease on ornamentals, and that powdery mildew fungi produce airborne spores and infect plants when temperatures are moderate (60 to 80 deg) and will not be present during the hottest days of summer. With any pest or disease, cultural controls are far better for the environment (including the hummingbirds) than chemical controls, which should be a last resort. Cultural controls for this plant would include making sure it is in full sun, not shaded, that it is not watered from above (of course, that's what rain does), and that the plants are far enough apart for good air circulation. As this plant is a biennial, it will seed itself at the end of the season, and the gardener should be sure to keep the seedlings thinned out as they come up.

You are probably correct that 7 inches of rain has not helped the situation. However, drier, hotter air is coming with the onset of summer, and the problem may resolve itself, or at least not damage the plants or limit the flowering. Standing Cypress can get quite tall, up to 6 or 7 feet, so it's worth taking the trouble over it. In the above link, you will find recommendations for chemical controls but, as said before, we much prefer the cultural practices that promote a healthy plant. Since we don't know what county in Virginia your mother-in-law lives, we can't give you a specific link to her county extension office. However, she can find them under "County Offices" or simply search on her county name and "extension office." That would be a far better source for recommendations on treatment of the mildew than anything we can offer from here.