Indiana Department of Natural Resources sent this bulletin at 07/06/2023 07:30 AM EDT
Weekly Review for July 6, 2023
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.
Japanese beetle adults are out. I’m hearing reports of very heavy damage in some areas and light populations in others. That sounds about typical. As a reminder, grub control products are most effective shortly after egg hatch. That means those products need to be down by mid to late July.
I have found a few pockets of bagworms in the last couple of weeks. Like Japanese beetles, they are also most easily treated when small, which they are right now. The bags I found were in the ½” range and were on a variety of evergreens, but mostly on – you guessed it – arborvitae.
At one nursery, I saw a lot of what I believe is Phyllosticta leaf spot on Japanese maples. Generally, it was doing very little damage, but on the cut-leaf varieties where the spots were sometimes crossing the entire leaf, the damage was far more noticeable.
Rounding out the finds, spider mite and lace bug damage are becoming more noticeable. I am seeing more thrips in perennials this year, but I might have just gotten better at looking for it. Cedar apple rust is also far more prevalent in apples and crabapples than I have seen in the past.
Spongy moth is usually pretty tight in timing. Egg hatch, pupation, and adult emergence usually occur across a given population within just a few days. This spring I noticed egg hatch was drawn out over a couple of weeks due to our uneven temperatures. Now this comes to fruition with the presence of larva, pupa, and adults at the same time this summer. This anomaly doesn’t seem to have a big impact on the insect, but it is one of those curiosities we see occasionally.
The other day I was out with my coworker doing some hive sampling for USDA when he noticed some small orange sacks which appeared to be attached to a couple of bees’ feet. These sacks are called pollinarium. When an insect visits a milkweed in bloom they may inadvertently get hooked by the pollinarium, which latches onto them. If they are strong enough, they can pull the pollinarium out and move it to the next milkweed. This is why you may see honeybees or other insects stuck on a milkweed. They may be caught by more than one pollinarium or be too weak to pull free. For a more through description of this interaction visit the USDA milkweed pollination publication.
I noted a little pine bark adelgid again this week. In low populations levels it can be tricky to see, but look closely when you see anything fluffy. Its hosts include not only eastern white pines, but also other pines as well. These are kept under control mainly by natural predators like the maggots of hover flies and lady beetle larvae. What’s more interesting to me is I haven’t been seeing Japanese beetle or bagworm yet here in east central Indiana.
One thing for folks in northern Indiana to be aware of is spongy moth (Lymantria dispar) adults have started emerging. Once this happens, they do not cause any more harm to trees. Looking for and destroying freshly laid egg masses will help reduce next year’s population. Female spongy moth are large and white with dark markings on their wings. They cannot fly.
The great or giant leopard moth (Hypercompe scribonia) is a beautiful native moth with black circles all over its white body that is sometimes mistaken for spongy moth. The larva of giant leopard moth have a wide host range including willow, maple, magnolia, pokeweed, sunflowers and violets. These nifty natives are also important pollinators.
This past week at a nursery inspection in central Indiana, I noticed the colorful early symptoms of the fungus Guignardia aesculi. This pathogen causes leaf blotch disease on Aesculus spp across Indiana and most of the United States. Early leaf lesions are often irregular in shape and begin as water-soaked spots that become dark reddish-brown with a yellow halo that merges into the green leaf tissue. Occasionally these lesions brighten significantly and appear in various shades of crimson to brick red. Severity of leaf blotch outbreaks is very dependent on environmental conditions. Overhead irrigation and wet spring weather favors the pathogen and infection. I do not consider this disease to be a serious risk to established buckeye or horse chestnut trees, but multiple years of heavy infection could lead to eventual decline or even death.
