Leaf-Eating Pests of Roses

Sawfly Larvae

• Caterpillar-like sawfly larvae eat tissue between leaf veins. The insects, which are light green with orange heads and up to 3/4 inch long, begin feeding underneath leaves in May. To control small infestations, remove affected leaves or handpick larger larvae and drop them into a bucket of soapy water, Cornell plant scientists recommend. Stop large sawfly infestations with insecticidal soaps, neem oil or insecticides containing acephate, carbaryl, chlorpyrifos, malathion or diazinon. Do not spray rose blooms with pesticides, because the chemicals are poisonous to beneficial flower dwellers such as bees.

Beetles

• Several species of beetle eat rose leaves. The inch-long Japanese beetle is dark green with tan wings and short, white hairs on its abdomen. The false Japanese beetle resembles the Japanese beetle, but lacks abdominal hairs. Rose chafers are tan scarab beetles of about 1/2 inch in length. The Fuller rose beetle is a brown, half-inch weevil with black marks. Handpick the bugs and dump them in a bucket of soapy water. Carbaryl, acephate, diazinon and chlorpyrifos also stop beetle infestations, though resistant beetles may move in following treatment. University of Missouri plant scientists advise drenching surrounding soil with insecticide to kill larvae.

Spider Mites

• Tiny spider mites live underneath rose leaves and suck sap, water and nutrients out of foliage. Mites proliferate in dry, dusty conditions. They also thrive after applications of insecticides for other pests wipe out natural predators. Spray leaves with a garden hose in the morning to wash away mites. Most insecticides, even those with labels that list spider mites, are ineffective against the pests, say plant researchers at the University of California. Try insecticidal soaps, horticultural oil or neem oil. Focus treatment on the undersides of leaves. Miticides work, but are hard to find in home and garden stores.

Thrips

• Thrips are winged insects that are about 1/16 inch long. Though thrips control spider mites, they also feed on young leaves, shoots and rosebuds. Conventional insecticides such as malathion, carbaryl and pyrethroids are ineffective against thrips. Insecticides that work on larval thrips include azadirachtin, spinosad and abamectin. Clip and throw away infested branches for additional prevention. However, the best bet for control of thrips is environmental. The insects thrive when rose bushes are close together. Thinning bushes can stop the spread of thrips.

Leaf-cutting Bees

• Leaf-cutting bees are black, purple or green and similar in size to honeybees. The insects cut out large, round chunks of rose leaves to line their nests. Plant experts at the University of Nebraska do not recommend controlling leaf-cutting bees, because they are important pollinators and pest predators. The bees are solitary and do not do occur in numbers large enough damage to rose plants.