Indiana Department of Natural Resources sent this bulletin at 06/29/2022 07:45 AM EDT
Weekly Review for June 29, 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
I have not observed any Japanese beetles yet, but some of our other inspectors have observed activity further north than my location. Fall webworm was found on black gum trees on the east side of Bloomington. I was not able to get any decent pictures because the road was too busy to stop safely. Leafcutter bee feeding injury was found on redbud in my yard. Look for semicircular holes on the edge of leaves. This is a native bee species, and it does not cause a serious risk to plant health. I do not recommend spraying for this beneficial insect. It is more of a novelty insect than anything.
During the past week I found lace bug feeding injury as well as lace bug nymphs feeding on the undersides of leaves on my Aronia (chokeberry). I believe this is the hawthorn lace bug since Aronia belongs to the rose family and hawthorn lace bug prefers to feed on rose family plants. I do not often see many pest problems on Aronia. Look for coarse stippling that will coalesce, causing the leaves to have a whitish appearance. On the undersides of leaves you can often see both adults, nymphs and numerous shiny, black fecal spots.
There were a few disease problems I came across during the last week. Leaf spots are continuing to develop on Itea (sweet spire). I am also seeing symptoms of iron chlorosis develop on many Itea in both the landscape and nursery environment. Cedar-quince rust commonly infects hawthorn branches and fruits. However, I recently discovered this rust on the fruits of the quince growing on my property. Seems like it is a good year for rust on my property. Recently I planted a few zinnias in my garden since the rabbits ate all of my petunias and portulacas, but that is another story. I noticed leaf spot symptoms starting to develop on the lower leaves of the zinnia plants. There are three causes for these symptoms. Typically, on zinnias you can get two different fungal leaf spots caused by Alternaria or Cercospora species. However, you can also get leaf spots caused by the bacterium Xanthomonas. How do you tell the difference between them? The best way is with a lab diagnosis. This is especially important in this case because spraying a fungicide on a bacterial infection is going to be a waste of time and resources. Interestingly, Xanthomonas can be carried on seeds and be a seed born disease that starts early in the season.
Over the last couple of weeks, I have seen a variety of different problems. I found a group of coneflowers with coneflower rosette mite, an extremely small eriophyid mite. Mites like the two-spotted spider mites can be seen with an adequate hand lens magnification (10X), but with eriophyid mites sometimes you will just make out a speck with a 10X hand lens which is why we focus on identifying the damage as opposed to finding the actual mites in the field. I look for stunted cones that have formed galls. To the casual observer this can be easy to miss. Heavy mite populations will completely prevent petal formation.
Another eriophyid is the bald cypress rust mite which I found a few populations of. I think this one is somewhat larger than the coneflower eriophyid mite but that’s just my opinion based on squinting through a hand lens. This mite produces a reddish orange tint usually at the base of the needles. Sometimes you can see the cast skins which appear white on the bald cypress needles. I also found eriophyids on some button bush which forms galls on the leaves. Both the button bush and bald cypress eriophyids cause little actual harm to the host plants.
While doing a nursery inspection I found a fairly heavy amount of defoliation of iron wood by leafcutter bees. Leaf cutter bees harvest circles of foliage which they use to line their nests which they make in a hole in wood, dead plant stem or the ground. Inside the rolled up leaf they place a pollen ball and lay a single egg on the ball of pollen. I also have a healthy population of leaf cutter bees at my house which are helping themselves to my white fringe tree seedlings (not that I mind).
I spent two days at the Switzerland County spotted lanternfly site. We are starting to see fourth instar nymphs which are red, black, and white. We are actively treating Ailanthus trees in this area to act as trap trees to help decrease the lanternfly population.
Lastly, I was helping a coworker cross-training on apiary inspections. While looking over a frame, I noticed a drone cell that had been uncapped and the larvae had started to be torn down. Suspecting a mite infested cell I pulled out the larvae and found a large white deposit on the top of it. This is guanine which is the waste product of varroa mites. It is fairly easy to see because not only is it white but all the mites in the cell use a communal latrine. Upon closer inspection of what appeared to be multiple guanine deposits one of them moved. It turned out there were four immature mites in the cell. The uncapping behavior exhibited in this instance is very beneficial because it halts the mites reproductive cycle and the immature mites will not survive the uncapping event.
I was finally able to get out and do some nursery inspections! Diseases that I saw were powdery mildew on monarda, serviceberry and lilac. Septoria leaf spot was found on red twig dogwood and oakleaf hydrangea. Flea beetles were active on various types of weigela and hydrangea.
This is the year of watering challenges. We had a nice 70ish degree day today, so you would think you can back off on watering with the cooler temperatures, right? Nope. The humidity was down, winds up, and the sun bright. I was sure seeing some “nodding heads” and folding leaves starting to show up in container stock as drought stress started to set in.
So, remember two weeks ago I said had not seen any red-headed flea beetle? I spoke too soon. The biggest surprise was how heavy the damage was on sedum compared to everything else. I inspected a greenhouse range that was starting to have a lot of issues with thrips on perennials. Aphids on spirea and plant hoppers on Rudbeckia round out my insects this week. Still haven’t seen my first Japanese beetle this year.
Add me to the Hosta Virus X club! Ren’s photos last week were great, but I wanted to point out how tricky it can be to spot. Pictured are two “Gold Standard” hosta leaves – one normal and one infected with HVX. In large lots, spotting plants showing deviation from a cultivar is easy. But in nurseries that only have a hand full of any cultivar, seeing this kind of variation is much harder. Other diseases this week include powdery mildew on ninebark, cedar apple rust on apples and crabapples, and a lot of various leaf spots starting to be noticed. Tar spot is just starting on the Norway maple in front of my house.
