Rose Buds With Black Spots

Thrips

• Female thrips lay their eggs into rose leaves and buds. Within a few days, larvae hatch and feed off of the rose plant. It takes thrips up to two weeks to mature into winged insects, according to the University of California. Because thrips are poor fliers, they generally spread through the wind or on infested plants. Gardeners should always check rose plants before bringing them home from the nursery. Isolate new plants for two weeks to ensure that they are not infested with thrip eggs.

Damage

• Gardeners may see black spots or feces accumulate around damaged areas of the plant. Damaged areas exhibit discoloration, distortion and a papery texture, according to the University of California. Rose petal tissue may turn pale or dark. Leaves that have been severely damaged can fall off. When defoliation occurs, the rose plant loses its ability to properly photosynthesize. The result is a decline in the overall health of the plant. Controlling thrips is difficult. Their populations quickly skyrocket and they are able to reproduce offspring resistant to pesticides, according to Marin Rose Society.

Cultural Control

• Gardeners must prune off damaged areas of their rose plants. Sterilize your pruning tools with a mixture of 70 percent denatured alcohol and 30 percent water. Reflective mulch can reflect enough light to interfere with thrips ability to locate rose plants, according to the University of California. Aluminum-coated construction paper is available for mulching around your rose plants. To use this mulch, lay down the construction paper around your plant and bury the edges.

Chemical Control

• Gardeners can use a variety of pesticides to reduce their thrip population and prevent thrips from reproducing pesticide-resistant offspring. Use a pesticide that contains pyrethrin combined with piperonyl butoxide, as suggested by the University of California. Neem oil is an organic approach to killing thrips. Also, insecticidal soap can be applied to plants during the growing season. You will have to reapply insecticidal soap, because the spray is only effective for a rain-free 24 hours.