One of my greatest gardening anxieties is caused by waiting to see if thrips have taken over the roses. To me, there is nothing more insidious or disheartening than a thrip infestation. It usually occurs during spring and summer because these insects prefer to feed in rapidly growing tissue, which means new shoots and flower buds. Once you have them, it is discouraging because they are difficult to control. If you don’t realize they are feeding on your roses there may be no blossoms left to enjoy by the time you notice the problem.
My first experience with thrips was three years ago. I am usually very vigilant about my garden, especially the roses, taking a walk through every day looking for problems. Having had little experience at that time with roses I did not get too upset when I noticed some less than perfect rose buds…nature isn’t perfect, is it. After about a week it became clear to me that there was something very wrong. All the plants had buds that looked similar, but it wasn’t a fungus and there was no sign of insect pests so I didn’t have a clue as to how I could solve the problem…or how serious it was. By this time, the damage was done and when the roses bloomed most of the petals looked singed on their edges. Here’s what to look for: check all buds regularly for signs of thrips, because you’ll see the damage before you see any thrips.
If buds have spotty discolorations or browning edges on the petals or withering sepals (green “flaps” covering the bud)…or simply look slightly deformed or not “swollen”…you probably have thrips. Of course, finding thrips will confirm your suspicions, but this is easier said than done because they feed deep inside buds.
You might find some on close inspection or by peeling away some outer bud petals. Adults are tiny, elongated insects measuring only 1/20 of an inch, but they are distinctly recognizable when seen up close…even without a magnifier…as they crawl around.
So what can you do? Well, the answer is, very little. Although thrip damage is unsightly, thrips do not warrant the use of toxic insecticides, especially since they feed deep inside the buds, are very tiny, and have great mobility. Narrow-range oil, neem oil, or pyrethrins combined with piperonyl butoxide can be somewhat effective for temporary reduction of thrip populations, but only if applied when thrips are present and damage first appears. Some folks recommend organic remedies…which you can find on the Internet…but none have been proven to be completely or even significantly effective.
Pruning off infected buds is probably the best control method because all insects in the bud are removed and by the next budding cycle thrips will no longer be active. But for me, the solution was prevention. I use a systemic insecticide containing imidacloprid in early spring and never have I have never seen a thrip again. All is well, although I still hold my breath until I am certain the threat is past.