When your roses (Rosa spp.) look as though someone took a hole punch to the leaves or petals, you may have one of several different insects infesting your rose garden. Possible culprits include leafcutter bees, certain beetles, rose curculios or caterpillars. Roses are some of the most beautiful flowers you can grow in U.S. Department of Agriculture plant hardiness zones 3 through 10; it is difficult to watch them be damaged.
Leafcutter bees (Megachile spp.) leave semicircular holes in leaves. They aren’t eating the leaves; they are gathering building supplies to line their nests. Although they leave the leaves a bit unsightly, the bees are usually not life threatening to the plant and should be tolerated. However, if you don’t want them around and would rather repel them, organic gardening expert Andrew Lopez recommends planting garlic near your rose bushes or burying tobacco dust at the base of the plants.
Fuller rose beetles (Asynonychus godmani) are pale brown weevils that grow to approximately 3/8 inches long. The holes they make are not as perfect as those left behind by the leafcutter bees. They leave the leaves with notched and ragged edges. During the day, they hide on the undersides of leaves and then come out at night to feed. Control them by handpicking and keeping the rosebush’s branches away from walls and other plants. The University of California IPM website recommends applying parasitic nematodes to the soil in early to midsummer. Hoplia beetles (Hoplia callipyge) don’t care so much for the leaves of the rose plant but love the petals — light-colored ones to be exact. These beetles prefer feeding on the petals of white, yellow, apricot and pink roses, leaving them with a hole-punched appearance. Hoplia beetles are usually not big threats and can be easily controlled through handpicking. Removing infested blooms may also help. Hoplia beetles generally come around in the late spring for a period of two to four weeks.
Like the hoplia beetle, the rose curculio (Merhynchites spp.) is particular about the color of the roses it devours. These 1/4-inch-long weevils with red to black snouts prefer yellow and white roses. They chew ragged holes in blossoms and buds, sometimes killing the developing bud. If present in large numbers, they can kill terminal shoots. Infested buds should be picked off the plants and destroyed. Small infestations may be handled through handpicking, but larger ones may require an application of broad-spectrum insecticides. A natural approach uses coconut oil. To make a coconut oil spray, use a tablespoon of coconut oil in 1 quart of soapy water containing 1 tablespoon of natural biodegradable soap. Make sure the coconut oil is 100 percent pure. Pour the mixture into a spray bottle and spray directly on the curculio. Coconut oil suffocates the insect by clogging its breathing pores. To make a repellent spray, combine 4 to 10 drops of citronella oil and a couple of drops of natural biodegradable soap in a gallon of water.
A number of caterpillars find rose leaves an enjoyable snack and a suitable form of shelter. These pesky caterpillars include the orange tortrix, tent caterpillar, omnivorous looper, fruittree leafroller and tussock moth. Many of these can be successfully hand-picked, but if they become too big a nuisance, bacillus thuringiensis or spinosad may be used for control. If using Bacillus thuringiensis in a concentrate, dilute 1.5 ounces of it in 3 gallons of water or as directed. Another caterpillar-like larva that can chew large holes in leaves is the rose slug (Endelomyia aethiops). Unlike other caterpillars, rose slugs are the larvae of sawflies rather than the larvae of moths or butterflies. These pale green larvae have many natural enemies and can be washed off leaves with strong water sprays. Control is also possible with insecticidal soap or spinosad. When using insecticidal soap concentrate, use 4 teaspoons per quart of water or as directed.
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