Indiana Department of Natural Resources sent this bulletin at 06/01/2022 02:03 PM EDT
Weekly Review for June 1, 2022
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.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
Catalpa are beginning to bloom in my region. This means it is time to keep an eye out for bagworm hatch. I have not yet observed bagworm in my region, but I also have not been looking at many nurseries with the correct host material.
Rose slug injury was found on knock out roses. Look for patches of skeletonization and small holes on leaves that occur when the skeletonized material drops off leaves. This damage is caused by sawfly larvae and feeding typically occurs in early May. They feed on the undersides of leaves and are greenish in color. I was not able to find any active larvae feeding last week, so it is probably a bit late to treat.
I am also starting to see evidence of redheaded flea beetle feeding activity. This appears as small holes on the new growth of susceptible hosts. Susceptible hosts include but are not limited to red twig dogwood, Itea, Hyrangeapannicluata and Japanese beauty berry. The adult form of this insect is a small black beetle with a reddish head that can often be found on the undersides of leaves. It is a difficult insect to find and often jumps away when disturbed. The larval stage of this insect is a root feeder. This pest is unfortunately being readily moved in the nursery industry.
Although not widespread in my region, I did observe a case of actively feeding maple mites. This mite belongs to the same genus as the spruce spider mite. However, unlike spruce spider mite, which is a cool season mite, maple mite will continue to feed throughout the summer. Early damage appears as stippling or small white spots. As feeding continues, these spots will coalesce to make maple leaves appear faded or grayish white in appearance. Adults can often be found feeding between the veins at the base of the leaf.
I have observed a few disease issues during the last week. However, I suspect with the recent heavy rainfall there will be more development of disease symptoms on plants over the next few weeks. Interestingly, I have not observed any fire blight so far this year. Symptoms of cedar apple rust continue to develop on susceptible varieties of apples. Look for orange spots developing on leaves. Large levels of infection can cause trees to become stressed. Powdery mildew continues to be a problem on susceptible plant species. Bee balm is particularly susceptible to powdery mildew infections. Look for white growth on the surface of the leaves. Bee balms just seem to live with this issue. Newer, resistant varieties are being developed, but I still see powdery mildew on those plants as well. This is especially true if plants are packed together tightly in the garden center. Remember, plants can be resistant, but not immune.
Iron chlorosis was found on flowering dogwoods at a garden center. Look for interveinal chlorosis where veins remain green, but the rest of the leaf tissue is yellow. Interveinal chlorosis is an indicator of a micronutrient deficiency. On dogwood, this symptom is typically a result of iron deficiency. On red maple, it may be an indication of manganese deficiency.
This week there I've seen quite a bit of what is most likely anthracnose on various maple species, which has caused varying degrees of tissue damage. I've also seen what is likely the first generation of black cherry finger gall mite (an eriophyid mite specific to black cherry). Like most eriophyid mites, the damage is mostly cosmetic, though there are some very heavy localized galls.
Rose slug sawfly is starting to cause damage in landscape roses. Last year they really tore up my backyard roses, but I have not seen them here yet. I was looking at the difference in damage between Ken’s photos and mine. This may be attributed to different cultivars of rose but also, interestingly, my sawfly larvae were feeding on the tops of lower leaves.
Another find this week is balsam twig aphid. Jared wrote about it on May 17, but I just spotted the damage in Cass County. It’s mostly cosmetic, but it is nice to know what is causing those twisted needles.
