Indiana Department of Natural Resources sent this bulletin at 07/17/2018 08:39 AM EDT
Weekly Review for July 17, 2018
Indiana Department of Natural Resources Division of Entomology & Plant Pathology Phone: (317) 232-4120 Our Website Inspector Territories
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.
Links can be found at the bottom of the page to manage your subscription to this list. Comments and questions about this report are welcome and can be sent to Eric Biddinger or to your respective
Inspector.
I have been conducting nursery inspections in St. Joseph County this week. A lot of what I am seeing are the same old things. Drought injury is starting to become a concern. In nursery situations, gaps or failures in irrigation become apparent quickly.
I received a call this week about dying arborvitae in Elkhart County. Turned out to be one of the heaviest bagworm populations I have seen in a while. I haven’t seen much bagworm over the last couple years, especially in nurseries, but with our mild winters, it doesn’t surprise me that the populations would be ramping up.
I primarily see tar spot on silver and Norway maples, but it can occur on any maple. Early on, it looks like a yellow spot on the leaf, but soon the distinguishing black center will develop. Controls are seldom recommended as tar spot does little damage to the tree despite its sometimes drastic appearance.
I always find nutrient deficiencies interesting because the cause of the issue isn’t always straight forward. In hot, dry conditions like we have been having, leaching from irrigation can be a contributing factor to nutrient deficiencies. These older, planted rhododendrons were showing strong iron deficiency symptoms. Iron is rarely low in Indiana soils. Instead, higher pH conditions lock this nutrient up in the soil making it unavailable to the plants. Coming back to irrigation, some water supplies (including mine at home) are quite basic. Relying on irrigation instead of rainfall can contribute to changing soil pH and thus some nutrient deficiencies when you normally would not see them.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
Not many new pests to talk about this week. I am starting to see quite a bit of drought stress I my region. River birch and hackberry trees are starting to flag and drop leaves. Bagworm and Japanese beetle are causing serious damage to many landscapes in my region. I am seeing some low level infestations of boxwood mites on boxwood. Look for damage that appears somewhat like small scratches on the leaves. High population levels of this mite can cause serious damage to boxwoods and treatment should be performed early to prevent damage. I also encountered imported willow leaf beetle on contorted willow. Look for defoliation and skeletonization similar to what you would see with Japanese beetles. Imported willow leaf beetles are small black beetles that feed on the under sides of leaves. I do not often see this pest, but the damage occurring at the nursery I inspected was widespread. I am also seeing leaf miners on daylilies. This pest never causes serious issues on daylilies but may be noticeable to customers. I also found pine bark adelgid on weeping white pine in Clay County. Look for white fluffy patches on the bark of white pines. Sometimes people think this it is sap, but close inspection will reveal a scale like infestation that can be brushed off of trees. This pest is usually only a concern when population levels become very abundant. I do not often see this pest in the state.
Leaf spot disease continue to develop on many different hosts. Recently I have found leaf spot diseases on red maple, black gum (tupelo) and red twig dogwood. There are certain plants that are often infected by a certain leaf spots. Last week, I encountered red twig dogwoods with leaf spot symptoms and based on the experience with this plant and its susceptibility, I am 90% sure it is Septoria leafspot. However, It is nearly impossible to 100% field diagnose leaf spot disease. Laboratory diagnosis is really the only way you 100% know which pathogen is infecting a host. During the past week I encountered symptoms of leaf spot on yellowwood. I usually do not see leaf spot on this tree. The leaf spot could be caused by an abiotic (environmental) factor or they could be a result of a plant pathogen, so they were sent to the Purdue lab. Fusicladium leaf spot on persimmon is quite common in my region. However, a similar symptom can result from precipitated tannins in the leaves. Symptoms associated with tannins primarily occur on the upper surface of the leaves and do not show on the undersides of the leaves. Remember, when you see symptoms on a plant, you are only seeing the plants responses to a disease or environmental conditions that result in a particular physiological condition of the plant.
I have included a couple of photos for this week. The first is Cercospora Leaf Spot on Dwarf Cranberry Viburnum (confirmed by laboratory analysis by PPDL). This is one of the common fungal leaf spots that can develop on viburnums. Application of fungicide when leaf spots first develop can help manage the problem. The second is of Japanese Beetles feeding on Purple European Beech. Japanese Beetles have been heavy in population this year in some of our far southwestern counties.
