Q. I am having a problem with my Knock Out roses that no one else has, and no one seems to know what it is. My roses are 8 or 9 years old and I have had the problem for the last three or four years. Is something in the mulch I used that started this? They bloom, but the leaves are dying. I am sending some leaves to help explain. It starts with a tan spot that spreads until most of the leaf turns brown.
When this first started, I tried spraying with Ortho Garden Insect and Disease Control, but this did not keep it from spreading. Last year, the whole plants turned brown. After the first bloom, I cut them back to 9-10 inches and removed all the affected leaves. I sprayed them again and also put a quart of Bayer All in One Systemic Rose and Flower Care around the base of each as directed and they did green out and bloom again.
I should have applied the systemic early this spring before they greened out, but did not think of it until the leaves were turning brown again. This time, they looked like something was eating them, too. I did find a few tiny half-inch worms for the first time. There were also a few on a purple-leaf Plum about 20 feet away, so they may have come from that. I applied the spray and the systemic about a month ago and it does not seem to be spreading to new growth. But there is little new growth.
What is this desease and how I can prevent it from coming back?
— M.R. of St. Libory
A. In 2000, Knock Out roses were advertised as the most wonderful carefree roses, with several varieties available. Some gardeners did not think they even had to water or fertilize them. All you had to do was prune off the old blooms. Fifteen years later, an eriphyid mite, which attacked the old multiflora rose, has developed a taste for Knock Out roses.
These mites are beginning to show up all over the Midwest. They are so small that they can ride wind currents. These mites carry with them a virus called rose rosette, which attacks the terminal areas of any type of rose but especially the knockout rose varieties. This will appear as a bright red growth on the upper parts of the rose plant where the mites prefer to live. Mites are little but they like to live as “king of the hill.”
As you have found out, using a rose systemic control really works on the mites and should help control this virus. Prune any of the bright red stem and leaf growth as soon as you find it. Prune low enough on the stem where the wood is bright green. You will also have to disinfect the pruners with rubbing alcohol after every cut.
Bag the infected plant parts and place in a bag to be put out in the trash or, if you live in an area where you can burn, destroy the plant parts with fire. This problem can move quickly from one rose plant to another, so the sooner you find it and remove it, you can save surrounding rose plants.
Charles Giedeman is a local contributing writer. Send your gardening questions to Lifestyle Editor Patrick Kuhl, Belleville News-Democrat, P.O. Box 427, 120 S. Illinois St., Belleville, IL 62222-0427, or email them to firstname.lastname@example.org.
Do it now
BUTTERFLY COUNT: Get out and see how many orange Monarch butterflies you can find. The milkweed plants, the Monarchs’ favorite, are in bloom and a number of people have found Monarchs in the St. Louis area starting last weekend. I know they are in Randolph and Washington in the metro-east, too. Check the milkweed leavesfor any single eggs. Then check later to see if there are any striped green, white and yellow larvae feeding. There have not been too many the past few years. Take plenty of pictures, too.