Answer: The common insects that attack roses are aphids, cane borers, Japanese beetles and sawfly larvae. Over time, you can observe the life cycles of insects that are common in your area. You'll begin to recognize just when certain insects appear and become a problem for your roses. This kind of observation is very important for minimizing the amount of insect control you have to do, and the amount of pesticides you use -- organic or not. Using pesticides, even organic ones, disrupts the natural cycle of predator and prey in the insect world. Therefore, you want to be sure not to kill the "good" insects -- the ones that eat the ones you don't like.
Before treating your roses again, make sure that the black bugs are not Ladybug larvae (they're shaped like little alligators). If your roses had aphids, it's possible that ladybugs arrived to keep the population in check.
The presence of insects may not be the cause of the leaf burn; homemade sprays are sometimes phytotoxic, especially on tender new leaves. If you use an oil-based spray in the presence of sunlight, the rays of the sun can be magnified by the oil and burn the leaves. Also, the oil can clog the natural openings in the leaves and actually cause suffocation.
Aside from spraying aphids of with a strong stream of plain water, here are some suggestions for dealing with the other common rose pests:
Japanese beetles: Use powdered rotenone or pyrethrum-based insecticides to kill Japanese beetles. Another method is to kill the beetle larvae using biological controls such as beneficial nematodes or a product called "milky spore." A new Neem-based product is available that repels the beetles. Or, manually knock them off your roses into a jar filled with water and kill them. Or trap them with specially designed Japanese Beetle traps that use a pheremone to attract them.
Rose Chafers: These pests are usually only a problem in areas with sandy soils. They also only seem to be a problem in early summer. Control methods are similar to Japanese Beetles. Use powdered rotenone or pyrethrum-based insecticides to kill Chafers. Another method is to kill the chafer larvae using biological controls such as beneficial nematodes or a product called "milky spore." A new Neem-based product is available that repels the chafers. Or, manually knock them off your roses into a jar filled with water and kill them. Or trap them with a specially designed Rose Chafer trap that uses a pheremone to attract them.
Sawfly larvae: Sawfly larvae (or rose slugs) are a bit harder to control since they remain on the undersides of leaves where they are hard to reach with spray. Sawfly larvae are small (?-inch long) slug-looking critters that are easy to identify because they tend to wrap themselves in a tight circle.
For organic control, shake the plant and step on the pests as they fall on the ground (this can be either repulsive or very gratifying), or spray them with Bioneem? or insecticidal soap. Again, be sure to follow the instructions and precautions listed on the containers.
Another control method is provided by birds; specifically, wrens. Place wren houses around your rose garden and watch the birds do the work! Wrens are very tolerant of human activity and they relish sawfly larvae. Wrens can raise up to three clutches per summer; consequently, they never stop hunting for food. The birds may not provide 100 percent control, but they help tremendously, and add to the enjoyment of your garden through their wonderful songs.
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