Indiana Department of Natural Resources sent this bulletin at 05/05/2021 07:30 AM EDT
Weekly Review for May 5, 2021
This informal report by the Division of Entomology & Plant Pathology is a commentary on insects, diseases, and curiosities division staff encounter on a week-to-week basis. Comments and questions about this report are welcome and can be sent to your respective Inspector.
In the past couple of weeks, I’ve found some various issues, including quite a few root issues, viruses on hydrangea, spider mites, Fletcher scale on Taxus, and plenty of freeze injury.
The viceroy and red-spotted purple caterpillars are nearly identical, but since this beauty was feasting on black cherry (Prunus serotina), the preferred host of red-spotted purple, it’s a good bet that is what this caterpillar will become. For this type of feeding damage, treatment neither necessary nor recommended.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
Things are starting to warm up; however, I am not really seeing many pest problems yet. I am looking for aphids and spruce spider mite to be the next pests I encounter. I am seeing some disease issues starting to develop on susceptible hosts. Early symptoms of Septoria leaf spot were found on red twig dogwood. Red twig dogwoods are very susceptible to this pathogen, and it can result in late-season defoliation. Look for leaf spots that have an angular appearance at the margin. At this time of year, early stages of Septoria leaf spot could resemble dogwood spot anthracnose (Elsinoe corni). This fungus also can cause a leaf spot on dogwoods, but the leaf spot always remains small and pinpoint, whereas Septoria leaf spots get a bit larger and become more angular over time. Either way it is hard to tell in the field. Guilt by association, the pathogen is likely to be Septoria leaf spot on red twig dogwood, but as with all leaf spots, if you want to make sure you will need to get a laboratory diagnosis.
I had another interesting find reoccur this year. I found rust on knockout roses again. This is occurring on “Blushing Knockout” rose. You cannot miss it. Look for orange spotting and orange fruiting bodies. This is not a common disease in Indiana. If you find it, please let us know. I am not sure if this disease is being shipped to the state from a supplier or if we are seeing conditions that are promoting it. I am also seeing small purple spots on the leaves of knockout roses. This could be rose anthracnose. Samples have been sent to the Purdue lab for diagnosis.
I am seeing some minor freeze damage out there but not too bad. Impatiens and begonias, as well as certain varieties of pears, seem to have been hit the hardest. Interestingly, I encountered herbicide injury on potted plant material at a garden center. I more frequently encounter this problem in production nurseries and not garden centers. Remember, that herbicide injury can last for years depending on the type of herbicide that was used in proximity to nursery stock. I found interveinal chlorosis as a result of a micronutrient deficiency (most likely iron) on peonies. Look for yellow leaves with dark green veins. I also found viral symptoms on Peonies. Look for unusual yellowing or leaf mottling with tiny ring spots. Laboratory testing is needed to properly identify the virus. I have encountered tobacco rattle virus in the past on peonies. There is nothing that can be done to save the plant, and infected plants should be destroyed.
