rose problems

Asked June 27, 2019, 10:35 AM EDT

This is the second year that the tea roses and the Knock-out both have had puckered new leaves with light spots as if aphids were feeding but we can't find any bugs. The few buds we get look deformed and seldom bloom. We used a systemic rose care in the spring , and since a fungicide and bug killer to no effect. Can anyone help?

Oceana County Michigan rose diseases knockout roses

1 Response

Most rose pests are tiny and very difficult to find, with thrips no more than 1/20 inch, aphids 1/8 inch or less and scales up to 1/4 inch in their adult size. Thrips are minute insects that have rasping-sucking mouthparts to slurp up plant fluids. Emerging leaves are distorted and twisted, with yellow flecking or streaking. Flower buds are deformed and fail to open or fall off prematurely. Blossoms can become streaked with brown and can wither. Look for damage in early to mid-summer.Aphids, scales and thrips all succumb to horticultural oils. Thrips may also require the use of insecticides that contain spinosad. Spinosad is especially effective on caterpillars and thrips. If you're a flower gardener, your ears should prick up on this one. Thrips and caterpillars are the two most important pest groups on annual and perennial flowers. Perhaps the best thing about spinosad-containing products is their safety for people and beneficial insects. Spinosad is safe for adult butterflies and many insect predators and parasites. It falls into the safest human health category as well.

Curled leaves that sport a yellow discoloration during new growth for seemingly no reason may indicate herbicidal damage from the year before. Leaves may also appear smaller than normal. There's nothing you can do to fix the problem, but keeping herbicides -- especially nonselective ones -- away from your roses is usually the best solution.

Rose-leaf curl is a virus that causes leaves to curl and may also lead to a yellowing of the foliage. Designs that include yellow zigzagging lines or circles may also appear on the leaves. Planting virus-resistant varieties is the only way to prevent the virus. No cures exist. The virus is not life-threatening to the rose, just unsightly.

For most problems with Knock Out roses, the spray application of a good fungicide at timely intervals would be considered wise, along with, of course, keeping an eye on the soil moisture levels and nutritional needs of the rose bushes.

Follow three simple rules: (1) Positively identify the problem. There is nothing worse, as well as possibly more stressful for the subject rose bush or plant, then to make multiple applications of various chemicals in an effort to solve a given problem. (2)Thorough watering of plants. Water rose bushes well the day before making any pesticide application. This includes feeding them too! (3) Use the most earth-friendly product first. Try organic approaches first before moving on to more harsh chemical treatments and only if the problem is critically severe and the first application simply is not gaining any ground on the problem in a reasonable amount of time.

Since this is the second year you have had the problem with your roses, it might be a cultural problem such as improper planting, feeding or watering. If you haven't already done so, I advise you to take a soil test. It's easy to do. Your soil's pH may not be favorable for roses. Roses grow best in neutral soil, with a pH of 7.0. They will also tolerate mildly acidic conditions, with a pH as low as 6.0. You can obtain a soil test self mailer from Michigan State here: