Indiana Department of Natural Resources sent this bulletin at 05/08/2019 09:40 AM EDT
Weekly Review for May 8, 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.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
During the past week I am seeing a small increase in pest activity. I have found aphids on burning bush and I also found black aphids on my Crimson Queen Japanese maple. However, aphid populations have not been that high this year and I have only seen a few low level populations on Spirea. I have seen some boxwood psyllid during the past week. Look for leaf cupping and white wax inside that cupping. Sometimes you can see a small, cicada like insect inside the leaf cupping, but they are typically hard to find. Generally this pest does not cause serious injury to plants. Treatment with a contact insecticide can be difficult because the insect is well protected inside the cupped leaves. I also found white prunicola scale on Japanese weeping cherry. Look for small, round, white scale insects on the bark. These are not elongated like Japanese maple scale, but look similar to a cooked egg with a yolk in the middle. There can be 3 generations a year. Small populations can be manually removed, but large populations should be treated during crawler stage. I also found scale on burning bush. In the field I thought it may be winged Euonymus scale. The scale was small and found primarily in the area between the bark ridges. It seemed very white to be winged Euonymus scale, and there is a possibility that it may be Japanese maple scale infesting winged Euonymus. I have sent Dr. Sadof a picture of this to get a second opinion and will include the pictures on my next weekly review when I get confirmation on the identification.
I have seen some virus symptoms of tobacco rattle virus peonies and American plum line pattern virus on weeping Yoshino cherry during the past week. Look for bright yellow, mottling on the leaves. The only way to 100% identify a virus is through laboratory testing. Many virus can have similar symptoms. If you have a plant with virus symptoms it is best to destroy it since it cannot be cured of the virus. Virus testing can be costly. However, if you are having a serious virus issue in your nursery, it may be work spending the money to get the testing completed so you can identify how the virus is vectored. Viruses can be vectored by insect and nematodes while other virus can be transmitted via propagation methods.
With all of the wet weather I have seen numerous disease issue. Botrytis is a serious problem at many garden centers, especially on annuals. I have seen botrytis on zinnia, begonia, impatiens, geranium, gerbera daisy and periwinkle. Needle cast disease are beginning to develop on many susceptible evergreens. During the past week I found a severe infestation on Fat Albert blue spruce. Look for purpling or browning needles with small black spots. I am also starting to see leaf spot on oak leaf Hydrangea. This is a yearly issue that never seems to cause defoliation or damage to this plant. It seems if you have oak leaf Hydrangea, you will have leaf spot. I also found canker on red twig dogwood. I have not identified the causal agent of this canker, but the infected branches should be removed and pruning shears should be disinfected between cuts. If the canker problem is not addressed it can reach the crown of the plant and possible cause the plant to die. During the past few weeks I have been seeing cedar-apple rust galls on eastern red cedar. However, this week I found pine-oak gall rust on Austrian and Scotch pines. Look for large galls forming on branches. Serious infections can lead to poor growth and branch death. If can be difficult to trim this gall out without removing the entire branch. Chemical control may be the best option for this disease.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
Last week, I followed up on some reports of downy mildew on knockout roses at various box stores. Most of the material I found was asymptomatic, but one store had heavy damage on all the knockout roses. They had just gotten the roses in from an out of state wholesale nursery in the last few weeks. Unfortunately I did not get a photo as it was pouring at the time. The leaves had large irregularly-shaped bronze splotches with purplish edges, covering most of the surface. I issued a stop sale for the destruction of these plants and will be on the lookout for roses at other box stores from the same source nursery and with similar symptoms.
I did a few quick dealer inspections last week and the only notable find was Fletcher scale on ‘Emerald Green’ arborvitaes. This species overwinters as nymphs, then become adults in late April to early May, at which point they begin to lay eggs. The crawler stage will emerge from under the old female shells starting in late May to early June. One thing I learned about this species is that they are parthenogenetic, which means they reproduce asexually. The offspring are genetic clones of their mothers, and all individuals are female.
It's been a busy week as we prepare for upcoming Gypsy moth treatments, but on May 4, I had an awesome opportunity to work with members of the Johnson County CISMA (Cooperative Invasive Species Management Areas) and other dedicated area residents helping remove invasive bush honeysuckle and garlic mustard from a local park. The Star Wars themed event was an enjoyable afternoon despite the overcast dreary skies. While doing dealer inspections in Henry County, I noticed downy mildew symptoms on Baby Cakes Blackberry plants.
