Indiana Department of Natural Resources sent this bulletin at 04/28/2021 08:36 AM EDT
Weekly Review for April 28, 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.
For insect enthusiasts, this spring is going to be a memorable one. Brood X (or Brood 10) of the 17-year cicada will begin to emerge soon. Brood X is one of the larger broods encompassing states from New York south to Georgia, west to Illinois, and north to Michigan.
Inspector Jared Spokowsky found chimneys forming on the east side of Indianapolis the week of April 12. He found nymphs not too far below the surface, so with the warming forecast it won’t be long until the magical creatures will emerge.
What most people will notice about Brood X is the noise, which males make through an organ called a tymbal in the abdomen. Different calls mean different things. Alarm sounds ward off predators. The sound most people associate with cicadas is made from large choruses when males synchronize their calls to establish chorusing centers that attract many females to an area.
Brood X actually consists of three different species of cicadas, Magicicada septendecim, M. cassini and M. septendecula, that have synchronized their life cycles for survival. Cicadas are tasty treats for birds, squirrels, wild turkeys, skunks, and other animals. Emerging with huge numbers all at once ensures that even after animals feast on their high protein snacks this spring, there will still be plenty of cicadas to live on.
To the nursery industry, cicadas aren’t something that needs to be managed. Females will lay eggs in ¼” to ½” diameter branches. This may cause flagging or dieback on smaller branches, but mature, healthy trees will outgrow the damage in time. Cicadas prefer oaks, maples, fruit trees and smaller trees or shrubs. If you have a newly planted smaller tree or shrub, netting with holes smaller than 3/8” may help prevent cicada damage. Netting would only need to be on vulnerable trees for about a month during peak emergence.
Last week’s cold snap didn’t do as much harm as I thought it might thanks in large part to the snow cover, but tender trees like tulip poplar did give way to the cold. The flowers on many redbud trees here in central Indiana weren’t fully opened, but the freeze caused lots of damage. Even the flowers that weren’t fully opened are dried up.
We are in the midst of gypsy moth egg hatch. Vince Burkle, a DNR inspector based in Fort Wayne, reported a hatch there. As of Monday, I have not seen a hatch at our Deedsville treatment block, but it should be just around the corner. Urban areas act as heat islands which can accelerate lifecycles, so this isn’t surprising.
One thing I noted in the Deedsville block was a fair amount of damage to the eggmasses by a parasitoid. The telltale pin holes are indicators that a tiny, nonstinging wasp called Ooencyrtus kunanae has been at work feeding on the eggs. With up to four generations per year, they can destroy 20 to 40 percent of the eggs!
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I have not seen many pests during the last week due to the recent cold snap. Early last week I found two potted spider mite infestations on rose plants shipped from Texas. They were not moving very fast at all and I am sure the snow killed all adults and nymphs that were present on the plants. During the past few weeks I did find a downy mildew on sunny knockout roses. Look for an irregular lesion with a purple margin and a tan center. Laboratory diagnosis is necessary for confirmation of this disease. I have had some cases in which symptoms that appeared to be downy mildew were abiotic and likely a result of phytotoxicity.
The freeze and 1-2 inches of snow were the biggest news for everyone. However, I must say many areas in southern Indiana got lucky. Last Wednesday morning it went to 29 degrees at my house, but the snow kept everything insulated. I had minimal damage. Even my cut leaf Japanese maple that was fully leafed out and uncovered suffered no damage. Then on Thursday morning it was cloudy and 34 degrees with only a light frost. Other areas of the state may have not been so lucky. I saw some damage on begonia and impatiens, but very little freeze damage to woody ornamentals in my region. This week is warming up and it will be interesting to see what I find during inspections.
