Yesterday we began discussing the many different insect problems which are common in roses. We discussed how to diagnose and treat insect problems such as aphids, thrips, leaf rollers and spider mites. Today we are going to address four more insect problems which are common in roses and how to treat those problems.
Symptom: Leaves have been eaten leaving a skeletal structure. Unopened flower buds chewed and opened flower buds damaged.
Cause: Beetles—The most notorious of these is the Japanese beetle. These beetles are a metallic brown color with a green head. The same symptoms can also be caused by caterpillars.
Treatment: An effective and practical approach is to spread plastic or a cloth on the ground and gently shake the plants to remove the beetles. If you place them away from your roses, then traps are also effective. You will want to spray your roses with an insecticide that lists beetles as a target pest. Your roses will need to be sprayed when the problem is first detected, either in the spring or the late summer. If the beetles are in the larvae stage, then Spinosad will work very well on them or on caterpillars. Remember, that Spinosad is an organic chemical that will control most of the insect problems in your roses.
Symptom: Drooping, unopened buds, accompanied by a small discolored stem slightly below the bud.
Cause: Rose Midge—this is a small fly that pupates in the ground below the rose bush. Midges fly up and lay their eggs in the soft upper stem of the rose plant. The hatched larvae then eat the stems and cause breakage.
Treatment: Spread a systemic insecticide granule on the ground to control the pests. Sprays are of a very limited value with the rose midge because of their development below the ground. Spinosad may work to kill the active insects on the plant, and I would be willing to try it.
Symptom: Holes in pruned cane ends. Circular pieces cut from leaf margins.
Cause: Leaf cutter bees—these insects use the circular leaf pieces for egg partitions inside of the burrowed rose cane.
Treatment: Control by applying white glue to the cane ends. The leaf cutter bee is a beneficial insect in the garden as it is an effective garden pollinator. I strongly recommend against eradication of this insect. Instead, I recommend using the above preventative measure to lessen any damage to your roses.
Symptom: Wilting and dying foliage at the top of the rose bush. Leaves may turn yellow and drop off the plant.
Cause: Rose cane borer—These pests are the larvae of sawflies, some wasps and bees. The rose cane borer enters the rose from the top of any pruned rose canes. These pests search for freshly pruned stems of the rose plant to lay their eggs on in the late spring or early summer. The eggs then hatch and the larvae bore their way by eating into the center of the rose plant down the length of the rose cane.
Treatment: The most effective method of treatment is to prune the rose bush below any area of damage. You may need to prune the cane a couple of times to find an area that is not damaged. Then you will want to place a little dab of white glue over the pruning cut. This will prevent the insects from successfully laying new eggs on the freshly pruned rose plant. Another idea to aid in prevention is to try some companion planting. These insects do not seem to like Allium, so planting some near your rose bushes may help to repel them.
Now that you know some of the most common insect problems with roses, which ones have you had experience with? Leave me a comment and share.
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