Dealing With Mites on Roses
I have been growing roses for many years, including hardy shrub, tea, grandiflora, and floribunda types. While I occasionally dealt with powdery mildew or blackspot, I never had a severe outbreak of mite damage until last summer in 2008.
My growing season started out well, but by late June I noticed some off-colored leaves at the base of my roses. As the season progressed into a very dry summer, the roses on the west side of my house (brick siding) showed signs of a severe mite infestation. This would make sense because that is the hottest and driest side of my house in the summer. Soon, roses in other areas of my yard showed the same symptoms.
By late July the worst of the infested leaves were bronze and rapidly began to fall off. The issue definitely called for drastic control if I was to enjoy any more rose blooms the rest of the growing season. In hindsight, I should not have waited so long before trying to control the problem. Because I never had the problem before, I did not realize how quickly the situation could get out of hand.
There are several types of mites that will feed on roses. The worst is the two-spotted spider mite. Mites are not insects (they are related to spiders), so most insectides offer no control. Mites are very small and are best seen with the use of a magnifying lens.
Adult mites over-winter on plant debris and will lay eggs on roses and many other plants in the spring. The eggs hatch and then the mites feed on the underside of the leaf. They pierce the leaf to suck on the sap. The punctured area of the leaf soon discolors, and eventually the leaf appears dull and mottled yellow-brown. Usually the symptoms first appear on the lower (older) leaves of the plant.
Normally, predators of mites will keep the population in check. But if conditions are ideal the mite population can really increase quickly. The average life cycle for mites lasts just a few weeks. They prefer hot, dry conditions and, when such conditions exist, the lifecycle can shorten to just a week. Thus, in ideal conditions the mite population can increase exponentially in a short time. If not controlled, the high amount of damage will cause rose leaves to turn bronze in color and eventually fall off, defoliating the plant.
Miticides will kill mites. However, there are few miticides available to the public to use without a pesticide license as they are quite toxic and must be used with extreme caution. Most insecticides will not eradicate mites, but a few do work in suppressing the mite population.
Since my roses were in such dire conditions, I searched for any control available. I don’t normally promote brand names, but I did try a product called Bayer 3-in-1 Insect, Disease & Mite Control. This product has two insecticides and a fungicide in it. One of the insecticides (Taufluvalinate) is reported to have the ability to suppress mites. I sprayed this product weekly for several weeks and noticed great results within 7 days.
It was too late for leaves already damaged by the mites, and those already severely bronzed continued to drop off. But shortly afterwards the new growth started to appear, and soon I had flowers again. That new growth stayed relatively clean of mites for the rest of the season.
While this product performed well, I found that weekly applications were necessary to keep the mites from returning. Next year I will be prepared to spray at the first sign of mite damage (before the population gets out of control) if needed.
Should your roses display any of the symptoms shown in these photos, please look at the underside of the leaves to see if mites are the cause. You may need to use a hand lens or magnifying glass to see them, or try holding a sheet of clean, white paper underneath the leaves and shake the branch to dislodge the mites. You should be able to see them crawling on the paper if they are present.
If you decide to apply any pesticide in your efforts to control insect, weed or disease problems, always read and follow the label directions completely. Failure to do so can harm yourself, other people, animals, plants and the environment.
Paul Schwabe is a salesman in our Contractor Sales division. He holds a degree in horticulture and will be writing about some of his favorite and underused plants.