Indiana Department of Natural Resources sent this bulletin at 06/11/2019 08:25 AM EDT
Weekly Review for June 11, 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.
During a dealer inspection I noticed roses with leaf spots. Upon closer inspection I realized there were a couple different things going on – Black Spot and Downy Mildew. Note how the black spot is circular while downy mildew has jagged edges as it follows the veins. I’ve also spotted a few random occurrences of aphids, mostly on spirea.
While working on some storm damage assessment last week around the Rochester City Park with Jud Scott, we noticed what appeared to be herbicide damage on the white oaks. This in itself was not surprising because the park is bordered by high school athletic fields, little league baseball fields, and residential homes on various sides. However, we saw little variation in the extent of the damage from one side of the part to the other. This led us to think that maybe the cause was a higher volume source such as the farm fields a mile or so out. I plan to take another look around later this week.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
Bagworm has hatched in Lawrence County Indiana. Last week during an inspection I found light damage and newly hatched larvae on blue spruce. Look for browning needle tips and tiny larva hanging off of the ends of needles.
Typically, bagworm hatch begins to occur when Catalpa trees start to bloom. This plant phenology should only be used as a guideline for determining bagworm hatch. I have seen them hatch as early as May 1 and as late as August 1. The weather and insects both do not like to follow the rules. Treat bagworm populations early to prevent damage. Red headed flea beetle injury and adult activity was found last week in my region. This pest continues to be an increasing problem at many nurseries. Last week I found red headed flea beetle on Hydrangea paniculata, but I frequently find them on red twig dogwood, Itea, Japanese beauty berry and Weigela.
Fall webworm was found on sweet gum in Lawrence County last week. Look for webbing at the ends of branches and pale, yellowish larvae inside webbing. Generally this pest is more of a nuisance. Small populations on infested branches can be removed from trees by pruning. I also found early instars of orange striped oak worm. This is typically a mid to late season defoliator on oak trees. Young larva are black in color while older larva are black with a two orange stripes down the center of their bodies.
They also have two horn like projections near the head region. I do not often see this pest, but large populations can cause defoliation. Symptoms of maple petiole borer were found on red maple last week. This pest causes damages to the tips of new growth on red maple. Look for damaged new growth with a hollowed out inside. There is another pest that can sometimes be confused with this which is the boxelder twig borer. Boxelder twig borer usually causes a bit more damage than maple petiole borer. They can be difficult to distinguish when looking a damaged tree. Azalea lace bug was found causing significant damage last week.
Look for course stippling on leaves that coalesces to cause foliage to have a white or silver appearance. The under sides of leaves will have numerous dark fecal spots and sometimes you can see adults. I recommend treating population early on in the season. There can be multiple generations per year and overlapping generations can be difficult to control. I found one white marked tussock moth resting on a dead Yoshino cherry. Like the orange striped oak worm; I usually do not see this pest until later in the season. I saw a severe case of woolly birch aphids last week. I had included this pest in previous weekly reviews, but wanted to include a photo of heavy infestations. I have not seen any maple mites or spruce spider mites so far this year.
Now on to the disease I found. Not many new diseases this week. Cedar-apple rust continues to develop on susceptible apple and crabapple trees. Look for the bright orange spots on leaves. I have also seen severe cases of rust on hollyhocks during the last two weeks. However, I have not seen any rust on hawthorns yet. Apple scab, which appears as olive green to brownish areas on infected leaves continues to develop on susceptible cultivars of crabapples. Trees heavily infected by this disease will have early defoliation and be difficult to sell. Chemical control can be successful at reducing infection, but proper timing of treatments can be difficult when rain is frequent and environmental conditions are favorable for disease development. It is just better to use resistant varieties.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
Last week, I only had time for a single small grower inspection. The main problems I noticed in the greenhouses were aphids, especially on pepper plants and butterfly weed. The aphid population was large enough on some pepper plants that black sooty mold was growing on the surface of the leaves and there was the sheen of honeydew all over everything nearby. The owner has a large client base that wants organically-produced plants and tries to use non-conventional insecticides whenever possible, especially on vegetable plants.
The owner has been treating the aphids with insecticidal soaps but was still having some issues. We discussed the possibility of using biological control agents as well. Another pest I spotted in the greenhouse was whiteflies, which were congregating on the bottom surface of sunflower leaves. Lastly, I noticed that all the lilac bushes outside had heavy leaf spotting. I wasn’t sure what the cause was so I sent a sample to Purdue’s Plant and Pest Diagnostic Laboratory. They ruled out bacterial or fungal causes, and told me it is likely caused by spray damage, especially since it was on almost all the leaves on all the plants (new and old growth).
A quick report from my own backyard: I noticed that my climbing roses had some feeding damage, and I flipped over a few leaves and found the culprits: bristly roseslug sawfly larvae. Sawfly larvae look very similar to caterpillars but are actually a type of wasp.
One beekeeper I looked at last week had very weak hives. He split these hives in April and let the queenless ones make their own queens. The splits that had the old queen in it were ok. Not much brood in the hive. I have a feeling he took too much brood out of the hives for the nucs he made up to sell. The nucs, however, were in good shape.
He sent samples to the Beltsville bee lab and only one came back positive for European foulbrood. I told him to send adult bees off to Beltsville to see if they have Nosema. Nosema ceranae or Nosema apis could build up slowly in the spring. Virus testing is still too costly.
A couple of the hives had no royal jelly in cells with young larvae in them. The older larvae did not look healthy either. The larvae are starving to death. Not enough nurse bees in the hives to take care of the new larvae. I would have told him to transfer some capped brood from another hive, but he had none. Capped brood would help the young queens because when they hatch out they are your new nurse bees. Older bees do not know how to feed the young anymore. Bees can mature faster to make up for a loss of foragers, but they are not able to go back and become nurse bees.
Several hives only had drone brood in them. There could be an old queen in there that has no more sperm saved up so will start laying only drones. There could be a new queen in there, but did not get mated well, but started laying. Or the new queen did not make it back and now there is a laying worker. We had lots of rain through May that makes it hard for queens to get out to mate.
He had nucs that made it through the winter but are now collapsing. Only found a little drone brood in the 2 nucs. Small hive beetle larvae (SHB) was observed in these nucs also. The nucs are a goner. He needs to shake the bees out and do something with the frames with SHB larvae in them (freeze or burn them).
He treated for mites. We did not see varroa mites in the hives, but sure looked like some may have virus problems. I told him to take off any honey supers, collapse the hives down so the bees are covering frames. He should treat with Terramycin or Strong Microbials to boost their immune system.
He could put some in double nucs boxes to see if they can come back. Faster that way. Any hives that is not queen right, I would see about getting a new queen in there. He could combine hives, but would have to watch for SHB. He could feed the hives that do not have any stored honey or pollen. I would only feed pollen outside the hive since he already has a hive with active small hive beetle larvae in it. Feeding sugar water can be done within the hive.
A beekeeper he follows recommending splitting when the maples pop. The beekeeper is in another state and his weather is different. The maple bloomed here and then we had colder weather. Then came all the rain. The bees are not able to collect pollen and nectar if it is raining. So we supplement feed sugar water to them. You could supplement pollen to them, but risky to do on weak or small populated hives because of SHB.
Many beekeepers in Indiana and other states are reporting packed bees are not building up well and the queens are not laying a good pattern. If they catch it early, they can get a new queen in there. The old queen that came with the packed bee’s could have virus problems or did not get mated well. So you need to replace her ASAP.
During routine inspections in Delaware and Madison counties the last few days, I’ve noticed scale damage on both red and sugar maples. No crawlers for either the oyster shell scale or the cottony maple scale, but the damage was extensive to a single red maple tree covered in scale. I also saw what appears to be four-lined plant bug damage, but was unable to find any insects feeding to confirm. Damage was not extensive or severe.
Over the past few weeks all of the inspectors have been quite busy inspecting dealer locations in Indiana for Phytophthora ramorum symptomatic plants since the accidental introduction of this pathogen into our state on nursery stock. A large number of plants have been destroyed or quarantined and sampled for laboratory testing. We have also been busy checking boxwoods for a potential introduction of Boxwood Blight Disease (Calonectria pseudonaviculata) on nursery stock. The Purdue Plant and Pest Diagnostic Lab is in the process of analyzing many samples.
In addition to those two important concerns, here are some of the pests and pathogens found in my area recently: Rose Mosaic Virus symptoms on 'Toro' and 'Mon Cheri' Rose, Boxwood leaf miner damage to boxwoods, Botryosphaeria Canker on 'French Pink' Pussy Willow and also on 'Hakura Nishiki' Willow, Downy Mildew on 'Baby Cakes' Blackberry, bacterial leaf blight on many Rose of Sharon varieties, Volutella Blight on 'Wintergreen' Boxwood, Macrophoma leaf spot on 'Wintergreen' Boxwood and virus symptoms on 'Sarah Bernhardt' Peony. Another inspector sample of the Sarah Bernhardt Peony from the same source was confirmed as being infected with Tobacco Rattle Virus.
