rose bush leaf degradation - Ask Extension
Hello, my rose bushes start the year vibrant and healthy. Mid -summer most of my leaves are look like Swiss cheese. By the end of summer the plants ar...
Knowledgebase
rose bush leaf degradation #859568
Asked February 21, 2024, 12:53 PM EST
Hello, my rose bushes start the year vibrant and healthy. Mid -summer most of my leaves are look like Swiss cheese. By the end of summer the plants are nearly dead.
I've tried many different remedies to no avail. Here are a couple of pictures of my problem. Thanks.
Oakland County Michigan
Expert Response
Hi Darroll,
The damage on your rose bush appears to be from roseslug sawfly larva. Leaf blotches during May and June are a telltale sign or symptom of the roseslug Sawfly.
During the months of May and June you may have noticed leaf discoloration in the form of blotches on your rose leaves. If you inspect the undersides of the leaves closely you will see the culprit! It is a small, narrow-bodied larva called the roseslug sawfly. The larvae have pale green colored bodies and light tan-orange colored heads.
Organic Controls
Early detection is best. Start monitoring your roses by mid-April for first instar larvae infestation, abundance and distribution patterns. Hand-picking the larvae off the undersides of leaves and squishing them between your fingers or dropping them into a cup of rubbing alcohol works very well, but you must monitor your rose bushes daily to get them all or at least, most of them. Generally, the larvae are active for about one month or less depending on weather and temperature conditions.
Spraying the larvae with horticultural oil or insecticidal soap will kill the larvae. Complete larval coverage is necessary for effective kill. Horticultural oil (light weight) suffocates insect larvae, has a residual of a few days, and has very low mammalian toxicity (Ball and Ball, 1989). Insecticidal soaps are commercially formulated contact insecticides of low mammalian toxicity and designed to biodegrade in the environment within one to two weeks (Ball and Ball, 1989).
Additional, using a garden hose to spray the larvae off the leaves with a strong water flow also works well. The larvae, once knocked off the host plant are incapable of climbing back up onto the leaves to resume feeding (Johnson and Lyon, 1991).
See the article at the attached link for more information and confirmation that is the issue with your roses.
Rose and pear slugs (sawflies) (missouribotanicalgarden.org)
Thank you for using Ask Extension.
Pam Voss
MSUE Master Gardener
The damage on your rose bush appears to be from roseslug sawfly larva. Leaf blotches during May and June are a telltale sign or symptom of the roseslug Sawfly.
During the months of May and June you may have noticed leaf discoloration in the form of blotches on your rose leaves. If you inspect the undersides of the leaves closely you will see the culprit! It is a small, narrow-bodied larva called the roseslug sawfly. The larvae have pale green colored bodies and light tan-orange colored heads.
Organic Controls
Early detection is best. Start monitoring your roses by mid-April for first instar larvae infestation, abundance and distribution patterns. Hand-picking the larvae off the undersides of leaves and squishing them between your fingers or dropping them into a cup of rubbing alcohol works very well, but you must monitor your rose bushes daily to get them all or at least, most of them. Generally, the larvae are active for about one month or less depending on weather and temperature conditions.
Spraying the larvae with horticultural oil or insecticidal soap will kill the larvae. Complete larval coverage is necessary for effective kill. Horticultural oil (light weight) suffocates insect larvae, has a residual of a few days, and has very low mammalian toxicity (Ball and Ball, 1989). Insecticidal soaps are commercially formulated contact insecticides of low mammalian toxicity and designed to biodegrade in the environment within one to two weeks (Ball and Ball, 1989).
Additional, using a garden hose to spray the larvae off the leaves with a strong water flow also works well. The larvae, once knocked off the host plant are incapable of climbing back up onto the leaves to resume feeding (Johnson and Lyon, 1991).
See the article at the attached link for more information and confirmation that is the issue with your roses.
Rose and pear slugs (sawflies) (missouribotanicalgarden.org)
Thank you for using Ask Extension.
Pam Voss
MSUE Master Gardener
