Indiana Department of Natural Resources sent this bulletin at 07/26/2022 10:55 AM EDT
Weekly Review for July 26, 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.
The critter of the week is spider mites. I inspected a couple of nurseries this week that had heavy spider mite damage on maples, honey locust, oaks, and serviceberry. Rainfall does a lot to knock them off the leaves and control the population, but our lack of precipitation is exacerbating the situation.
Additionally, a couple of these nurseries historically have issues with Japanese beetles. Insecticides for Japanese beetles will have no discernible effect on mite populations but are likely to destroy predator populations that were helping to keep spider mites in check, further intensifying the situation. Bronze leaves are good hints that there may be spider mite issues.
I am still seeing a lot of herbicide injury on trees. In some cases I suspect drift, but more often than not I think it’s the nurseries own treatments that are suspect. Luckily, the damage is usually minor and the trees will grow out of it. Be cautious of conditions that can cause herbicide movement such as high temperatures or winds. Long handled wands or drift shields might also be worthwhile investments.
Finally, I’ve said this before but do me a favor and look over your hemlock for (HWA) hemlock wooly adelgid. We have had a couple of interceptions of infested material that came in from out of state. Michigan has been fighting this one for a long time. Indiana also has native hemlock stands that could be seriously impacted.
Additionally, Michigan has an external quarantine on hemlock that requires certification before being shipped into the state. HWA can be tricky to find, especially this time of year. Please contact your nursery inspector if we can assist you checking imported or certifying exported hemlock.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
I had a couple of new finds over the last two weeks. On Lysimachia (creeping jenny) I found a lot of sawfly larvae feeding on the leaves and causing some damage, although it is mostly cosmetic and unlikely to affect the vitality of the plant. Sawflies are larvae of wasps that superficially resemble caterpillars, but they are in a different insect order. It was hard to get a good picture of them because every time I put my camera close to one, it dropped off the plant into the soil. When I picked them up, they curled into a tight ball and would not budge. Because they are not caterpillars, some products that work for caterpillar control such as Bt will not work on sawflies. Therefore, it’s important to get a correct identification and make sure a product you’re using for control is labeled for that insect.
Another new find for me was tip dieback on Canaan firs. This was scattered randomly on trees throughout the entire field. I collected a sample and sent it to Purdue’s Plant and Pest Diagnostic Laboratory (PPDL) where they identified the cause as the fungus Sydowia polyspora. The pathologist at PPDL recommended that the grower prune out the dieback a couple of inches into the healthy wood, and remove clippings from the field, and mentioned that this disease is associated with stressed trees and nutritional problems.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I have not seen many new pests lately, just much of the same thing as I have seen the week before. Japanese beetle adults were not widespread in my region this summer. I only observed two adult beetles in the last month. I believe that the dry conditions may have impeded adult emergence. We did finally receive some rain in July. Things are starting to get wetter, but many areas are still fairly dry unless you were lucky enough to get a thunderstorm. These dry conditions have caused plant stressm which can often predispose plants to infestation of boring insects.
Last week I was working with one nursery that had bark beetles on red pines. These were balled and burlapped trees that were under drip irrigation. The drought stress along with spring digging of these trees likely stressed the trees, making them susceptible to infestation. Look for small pin holes and/or fine sawdust on the bark of trees. Residual pyrerthroids and systemics can help control bark beetles. They can be difficult to control and can cause plant death. Depending on the species, there can be multiple generations per year. Severely infested trees will develop an off green color and eventually yellow and brown.
Stressed evergreens release scents that attract bark beetles. Once the bark beetles infest a tree, they release their own pheromones which attract more bark beetles. Stressed trees can often be attacked en masse by bark beetles. When populations become large enough in an area, they will begin to spread to healthy trees. Therefore, it is a good idea to remove heavily infested trees from the area and destroy them so that the bark beetles do not spread to other trees in the area.
During an inspection I found some defoliation on raspberry plants that was occurring toward the center of the leaves. This pattern appeared to be caused by some type of sawfly; however, I was not able to find any insect activity at the time of inspection. This damage possibly could have been caused by the raspberry sawfly, Monophanoides species. There are several species in this genus that can infest raspberries, but I have not frequently encountered this problem. After doing some reading, I learned that significant injury can occur in some cases.
