Indiana Department of Natural Resources sent this bulletin at 07/25/2019 09:02 AM EDT
Weekly Review for July 25, 2019
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.
I’ve been on a kick of writing about pruning lately and I found a great example to learn from.
First, the central leader was removed and not the side shoot. The leader might have broken and the side shoot was allowed to “save the tree”, so I’ll give you that one. But the result is a tree with a kink in it that a) is unappealing to buyers and b) is a structural defect that could lead to critical failure later on. Throwing this one in the cull pile might have been a better choice than spending the time and effort to rework it. Second, we talk about pruning at the branch collar. Now that the doughnut of callus has expanded, it is pretty obvious where that collar is and where that nub should have been pruned back to. The callus would have easily healed over the wound if it had been pruned lower. Now, we have an open pathway for rot to enter the main stem – one that was simple to prevent and now difficult to correct. Another mark against keeping this tree in the nursery.
This week I am still seeing fungal leaf spots on Hydrangea, lilac, spires and Dogwood. I found Powdery Mildew on Magnolia, lilac, Monarda, and Cranesbill ‘Splish Splash’. The Cranesbill ‘Splish Splash’ was heavily infected with Powdery Mildew but the two varieties on either side of it was not. The roses I saw this week had various degrees of Black Spot. And it was no surprise to see Redtwig Dogwood with Septoria Leaf Spot. Japanese Beetle are becoming more active but it is localized on Hibscus, rose, and Linden. Weigela and Hydrangea in my territory have been showing Four-lined Plantbug damage and I saw some Flea Beetles feeding, also.
Here are a couple of interesting finds from the last few weeks. Silver spotted skipper larvae feeding on Wisteria and a group of dusky birch sawfly larvae feeding on river birch.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I would like to start this weekly review with a clarification on a spelling mistake of a plant disease. Cercospora is the correct spelling of the leaf spot disease.
I do not have a lot of new things to report this week. During the past week I saw lace bug infestations on walnut trees in Vigo County. Look for the coarse stippling type damage and fecal spots on the under sides of leaves. Adults with clear wings and black sections may be present also. Lace bug feeding injury is generally not a problem on deciduous trees. There are multiple species of lace bug. Hosts include, birch, azalea, rhododendron, hawthorn, serviceberry, Pieris, asters and golden rod. Those species that cause feeding injury on broad leaf evergreens are more of a concern because the damage will be seen on the plants for years after initial injury. Last week I also found Eriophyid mite galls on persimmon leaves. Look for small bumps on the leaves of infected plants. There are many species of Eriophyid mites. Some cause leaf galls others cause a leaf damage that appears as a fading or dull browning color on leaves. Eriophyid galls are typically not a problem. However, there are some species of Eriophyid mites such as the hemlock rust mite that can cause significant injury. There is also an Eriophyid mite that transmits rose rosette disease, a virus that cause stunting and abnormal growth in roses.
Last week I had the opportunity to do some work in the state forests with our State Forest Health Specialist, Phil Marshall and Dr. Haugen from the US Forest Service. This year I have been finding sassafras declining in certain areas and have also had reports from arborist as well as citizens of declining sassafras trees. Last week we were able to come upon an active infestation of ambrosia beetles in sassafras trees. We were able to isolate the beetles and they were identified by Robert Brown of the USDA. The species isolated were Xylosandrus crassiusculus and Xylosandrus germanus. Both of these species are common in Indiana and can have a broad host range. Look for small pin holes in bark and frass spikes coming out of the trunks of infested trees. X. crassiusuculus is known as the granulate ambrosia beetle and can occasionally be found in nursery stock. If you see any sassafras trees with ambrosia beetle activity, please email me at kcote@dnr.in.gov.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
Last week my most interesting find was elongate hemlock scale on eastern hemlock trees at a nursery in Hendricks County. I noticed some yellowing needles and found an infestation of scale insects on the underside of the needles. I also saw a pretty bad case of cedar quince rust on all of the thornless hawthorns at the same nursery.
The heat made for some cranky bees last week. When it gets above 85 degrees, the best time to work the bees is around 7 a.m. The sun is up and the bees are out looking for food. The temps and humidity are lowest this time of day, also. Have the smoker going well when you open the hive or else the bees will come right at you. Smoke them down into the hive. You could also spritz them with some sugar water. The sugar water will wet their wings and they will have a harder time flying. It also makes them groom the sugar water off and hopefully forget the beekeeper. Also have some Gatorade handy - you may need it. I also like to have a wet cloth around my neck. That tends to keep me cooler a little longer.
From inspections the last couple of weeks, there are some hives doing well while others need to finish drawing the foundation out. It is almost August and it is getting late in the year for the bees to draw out the foundation. Make sure these hives have sugar water available to draw that comb.
Mid-July is when a hive has the largest bee population in it. From now until early November the queen will start laying fewer eggs each day. The varroa mite population continues to build as well. Beekeepers need to start figuring what they will treat varroa mites with and when to get it in the hive. Wisconsin DATCP has information on varroa mite treatments and other pest management options. Some of the treatments are heat sensitive while others have to have honey supers off the hive when treating. Please take the time to check this information out. It includes a link to the label for each treatment.
