Indiana Department of Natural Resources sent this bulletin at 06/16/2020 09:49 AM EDT
Weekly Review for June 16, 2020
This informal report by the Division of Entomology and Plant Pathology is designed to update the Nursery and Greenhouse industry of insect and disease pests the Division has been encountering on a week to week basis and as a way to give a “heads up” of things to be on the lookout for. Comments and questions about this report are welcome and can be sent to your respective Inspector.
Cold damage continues to be the biggest issue I see during inspections. Some areas got hit really hard. I’ve seen a lot of white oaks and a few red oaks that are growing out of the damage as well as tulip poplar trees, but just how hard they were hit is still evident on the tree. Ginkgos and Dawn Redwoods were also hard hit by the late freeze. Some ginkgos are just now beginning to leaf out. It’s going to be a difficult growing season for them.
I haven’t seen a lot of insect activity yet, but did note some cottony maple scale on red maples and a slew of presumed white pine weevil larva feeding on the leader of a spruce tree.
I’ve been inspecting nurseries in Allen County over the past week. One of my growers emailed me to report severely wilting Scotch pine that was affecting entire plants to some degree throughout the nursery. After inspecting the trees at different areas of the nursery my initial thought was freeze injury, because most of the damage was occurring on plants on lower ground and the damage got less severe on higher ground. There was also no evidence of black spores indicating possible Diplodia. I took samples and sent them to Purdue, and their diagnosis was freeze injury.
The freeze that occurred around Mother’s Day had damaged the newly emerging candles, but the wilting didn’t occur until it got hotter in late May and early June. Pine needle scale was also fairly heavy on the Scotch pine at this nursery. The crawlers had already hatched and settled, so the window for treatment had closed. Spider mites were found damaging the inner needles of Fraser fir. Most of the mites were dead but there were still a few stragglers on the needles. White pine weevil was found feeding on the leaders of white pine and pine gall rust was found on Scotch pine. Other issues I encountered were anthracnose on red maple, red oak and redbud; apple scab on crabapple; cedar apple rust on apple and crabapple; potato leaf hopper on red maple; maple bladder gall mite on ‘Autumn Blaze’ maple and herbicide injury on redbud and tulip poplar.
I also found a Luna moth last week along with another unknown moth, possibly some type of Lappet moth.
Some of my finds from this past week include lesser willow sawfly on pussy willow and pine bark adelgid on white pine.
I found some fresh cones on witch hazel formed by witch hazel cone gall aphid. If you dissect the cones you can find the aphid colony protected inside. As the aphid reproduces inside the gall some of the winged daughter aphids will leave the gall and fly to their alternate host (birch) during the summer. Birch leaves often become noticeable with the typical curling induced by aphid feeding. Before the onset of winter, aphids from the birch fly back to witch hazel and lay eggs to overwinter, and the cycle repeats itself the next year.
Finally, I found a heavy infestation of euonymus scale in a landscape. In this particular specimen the plant was starting to die back and drop leaves due to the high numbers of scale present.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I would like to start the report this week with an update and correction on the rust recently found on knockout roses. According to herbarium records at Purdue University, rust has been found on roses in Indiana in the past. However, it is still not a common issue in Indiana. Interestingly, I found more rust on knockout roses during the last week. So far rust on roses has been found in Putnam and Vigo counties. Both incidences were on pink knockout rose. This week the cultivar was Blushing Pink Knockout Rose. The red and yellow cultivars growing next to the infected pink varieties did not have any symptoms at the time of inspection. More work is being conducted by Purdue to determine the exact species of this rust.
WE HAVE BAGWORM HATCH IN GREENE AND MONROE COUNTIES! Catalpa trees are beginning to bloom, and they are a great indicator plant for determining when to start looking for bagworms. Small individuals can move around in wind and thunderstorms. We have had plenty of wind in my region this week, but very little rain. Probably the driest June I have seen since 2012. Fortunately it is not 105 degrees yet. Milkweed bugs were found on swamp milkweeds. These insects look similar to boxelder bug but have a reversed color pattern. They do not cause serious harm to milkweed plants. Leafminers were found on daylilies. This is a frequent pest that can be found on daylilies but never seems to seriously injure plants. Flea beetles are out in full force and infesting many vegetable crops. Tomatoes and eggplant were hit hard in some areas. They seem to come out every year around Memorial Day and can destroy eggplants very quickly. Damage from leafcutter bee was found on redbuds in Vigo County. This insect creates round notches in leaves. It is not a pest or insect that is of serious concern, and spraying for this insect is not recommended. I am starting to see an increase in two-spotted spider mite activity in nurseries, especially on butterfly bush. Look for stippling on leaves and small colonies on the undersides of leaves. Treat populations now, when they are at low levels, or you will have problems all summer if you get high population levels and overlapping generations. Mites love low relative humidity levels and dry weather. They will go crazy this week. Finally, I found one individual sawfly on white pine. I very rarely see pine sawfly injury, but I have seen some in my region this year. The sawfly larva was found on white pine and is likely the introduced pine sawfly. There is another sawfly to watch for, the red headed pine sawfly. It can be seen in summer and early fall but feed primarily on hard pines.
The dry weather may be putting a damper on diseases. Yes, I know it is another pun. I have symptoms of anthracnose on the red maple in my front yard. Sycamores are starting to recover from freeze damage and spring anthracnose infections. I am continuing to see needle cast symptoms on large white pines in my region. This is the third year I have seen such symptoms. However, infection typically occurs during wet periods in June, when candles are elongating. This year is very dry, and it will be interesting to see if we see symptoms in 2021.
I’ve jumped around to a couple of nurseries in St. Joseph, Elkhart, and Carroll counties this week. Like everyone else, cold injury is the primary damage I’ve been seeing. Sometimes it is amazing how random freeze damage can appear. I visited a grower that was losing a few select cypress trees. The pattern was pretty random as we walked through the field – high ground, low ground, two cultivars, different ages, top of the tree, lower branches. After bouncing some photos around, the consensus was that this was a perfect storm of frost catching a few select trees that were already stressed from some combination of heavy soils, moisture stress, root stress, and possibly some disease pressure. These kinds of events are difficult to diagnose. The best preventive is good cultural practices and even then you are going to lose a few once in a while.
Other finds this week included spidermite, lace bug, and slug sawfly all on serviceberry, a little bit of boxwood adelgid damage, some potato leafhopper on redbuds, and a tiny bit of spidermite starting on spruce. An interesting find was a small patch of pine tube moth on white pine. This native does not cause much damage, but there was enough on one tree to catch my eye. This insect has two generations per year. I did find a pupa inside a few of the tubes.
Interestingly, the worst insect infestation I have seen all week was on my own spider plant. Hemispherical scale and spidermite are starting to do a number on it. Being outside on my deck, I noticed a number of tiny wasps around the plant as well. I’m guessing these could be parasitoids taking advantage of the situation.
I was able to get out and do a few inspections last week. Plants that had some frost damage are starting to put on new growth but the frost damage is still evident. I found Septoria leaf spot on the usual plants including redtwig dogwood, oakleaf hydrangea and Japanese pieris. Weeping cherry had Shot hole fungus, and I noted some hostas that had Anthracnose. The crabapples had varying degrees of apple scab as did the amelanchier. At one nursery where there were several varieties of boxwood I saw damage from boxwood psyllid which causes the leaves to cup. If noted early in the growing season you can unfold those cupped leaves and see the psyllids. One interesting find on holly that a nursery had just brought in was cottony camellia scale which can also be a pest of camellia, yew, euonymus, sweetbox and maple. On a landscape concolor fir I noticed a large infestation of Cooley’s spruce gall adelgid which feed on the needles of the fir and cause galls on Blue Spruce.
