Indiana Department of Natural Resources sent this bulletin at 06/15/2021 07:45 AM EDT
Weekly Review for June 15, 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.
This past week I spotted my first fireblight of the year. It was on Bartlett pear, Yellow Transparent apple, Crispin apple, and Fuji apple. With the high humidity we are experiencing, powdery mildew is starting to show up on susceptible plants. This week I found it on veronica, phlox and Diablo ninebark, which seems especially susceptible to Powdery Mildew. Other diseases I noticed include hosta anthracnose, juniper tip blight on Blue Haven juniper, septoria leaf spot on oakleaf hydrangea, and a bacteria leafspot on heuchera Caramel. I found rose rust on shrub rose, which we rarely see in Indiana. Another disease that I don’t come across very often was peach leaf curl, which is caused by a fungus that distorts the leaves of the affected peach tree. At one nursery bronze birch borer had pretty much wiped out Purple Frost birch. Bronze birch borer is pretty easy to spot. Look for the D-shaped exit holes of adults emerging and the raised ridges in the bark that the larvae make. Other insects include spiny witchhazel gall making aphid on river birch, aphids on penstemon and several types of spirea, and boxwood pysllid damage on several varieties of Boxwood.
Bag worms have hatched throughout much of the state now. Can you spot the tiny bag on the Blue Spruce? Bag worm can be quite damaging to evergreen species so treatment may be necessary. If treatment is to be undertaken, the best time to treat is when the larvae are small, newly emerged and just forming bags. Remember the label is the law!
I wanted to share an update regarding my report last week. The arborvitae needle blight found on Green Giant arborvitae was confirmed as the fungus Phyllosticta thujae by laboratory analysis. This is a known pathogen associated with this needle blight disease. After additional incubation, the presence of an additional pathogen, Pestalotiopsis sp./spp., was also confirmed. Pestalotiopsis can cause needle blight and has also been associated with arborvitae needle blight disease. Please see this fact sheet for more on this disease.
During our group inspection needle blight disease symptoms were also confirmed on Serbian spruce. Two pathogens were laboratory confirmed: Rhizosphaera sp./spp. which causes Rhizosphaera needle cast disease and Stigmina lautii which causes Stigmina needle blight disease. Analysis of the plant samples is ongoing. I will provide an update if we get any additional information. For more information on this needlecast, see this University of Massachusetts fact sheet.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
(June 7 report) I finally got rain at my house last week. Many parts of my region were very dry; however, last week I received 3.94 inches. I wanted rain, so I got it. I am still encountering pockets of spider mites even after the recent heavy rainfall. I was surprised to find active spruce spider mites on emerald green arborvitae that were causing serious plant injury. Look for plants to have a faded appearance or browning, especially on older growth. Interestingly, the emerald green arborvitae were severely damage from mites, while the ‘Pyramidalis’ arborvitae that were growing right next to the emerald greens did not have an signs of damage or infestation. I also found two-spotted spider mites on phlox causing significant plant injury. Two-spotted spider mite has a wide host range and thrives in hot weather. Pay particular attention to burning bush, butterfly bush, and roses which are often infested by this mite. I also observed early infestation of tulip tree scale on magnolia. This soft scale has a crawler stage that occurs in late summer into early fall, which is different than many other soft scales.
I still have not seen any fire blight this year, but I am seeing large amounts of cedar apple rust. It is too late to treat for this disease. The infection occurred earlier in the season. Powdery mildew continues to be a problem on many ornamentals. I am also seeing symptoms of leaf spot developing on many ornamentals. The recent heavy rainfall and warm temperatures may start to cause more disease issues to develop over the next few weeks. Overall, nothing too exciting in this report. I am seeing a lot of the same problems this week. Maybe next week I will find something really cool; well at least really cool for a bug geek.
While inspecting in Cass County last week, I also found my first bagworm of the year. Interestingly, it was on chokecherry. That is a good reminder that bagworms have a wide host range that includes over 128 evergreen and deciduous species.
Other nursery finds include pretty heavy apple scab, aphids on spirea and river birch, Balsam twig aphid on Frasier fir, and black spot on roses.
Time to get out my soapbox. The amount of containerized and B&B trees I see in nurseries that are buried too deep is sorely disappointing. I’ve seen trees where the root flair was 8 INCHES DEEP! I’ve seen B&B stock sitting in the nursery where the bark was already rotting away with fungal fruiting bodies. How this condition starts has a lot to do with the speed at which the nursery industry works. It takes time to properly position a tree in a container. And a well-positioned tree may require additional support, which also takes time to set up. Then every time a tree is repotted or stepped up, it is buried a little deeper to add stability. Unless this is corrected on installation, the customer is buying a tree with a seriously compromised life span – maybe as little as 10 years or less.
Finally, on a recent inspection I actually caught a snipe - a golden-backed snipe fly, that is. Usually found in woodlands, little is actually known about its life cycle, but the larval stage is thought to be a predator. Amazing how many critters we still don’t know a lot about!
