Indiana Department of Natural Resources sent this bulletin at 06/23/2020 09:30 AM EDT
Weekly Review for June 23, 2020
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.
This past week I noticed my first case of fall webworm on cherry. Also found some oystershell scale and a good deal of potato leaf hopper feeding damage on red maples. One 4-inch caliper red oak that had been riddled by ambrosia beetles. Sometimes you will see a frass toothpick associated with ambrosia beetle activity but in this case there were none. An easy way to tell ambrosia beetle activity from bark beetles is to peel back the bark (on a tree you don’t care about or insert a pin to a tree you do care about). Bark beetles stay true to their name and feed just under the bark on the phloem, while ambrosia beetles bore farther into the stem. In this case I think the irrigation combined with copious amounts of rainfall probably had the tree stressed out. The tree also had plant tape holding it to the stake, which was starting to cut into the tree.
Plant tape, tree straps, and even nursery tags are things that I find commonly starting to girdle trees or branches that they are installed on. I found some sweet-bay magnolia that showed some dieback. The nursery owner thought that it was due to the multiple freezes we had but the pattern was random and only affected certain plants, and the damage was not uniform on the affected individuals. There was evidence of fungal activity but I couldn’t determine if it was the cause or an opportunistic infection of dead tissue so I sent it off to Purdue. Turned out to be Anthracnose. Finally, our ever-present friend the bagworm has made his appearance in SE Indiana. I saw them feeding on plane tree, bald cypress and red cedar.
The European elm flea weevil is something I’ve never seen up close before, so it was a neat treat to find, but it was definitely wreaking havoc on the American elms where I found them in Madison County. They overwinter as adults, but lay eggs on leaves in early spring. The larva feed as leafminers before adults emerge and feed all summer long.
Bagworm has hatched and is starting to cause damage while building its bags. One or two might not be noticed, but if you’ve got a high population, even at this early stage, the damage can be quite bad, especially on evergreens. Fall webworms are starting to build their nests too.
Bagworms have emerged in northeast Indiana. I found recently hatched caterpillars climbing up the trunk and on the needles of a white pine in Grant County. A few other things I came across were oat crown rust on ‘Fine Line’ Buckthorn; aphids on the new growth of Norway spruce and introduced pine sawfly on white pine.
Another find was some San Jose scale on apples also introduced somewhere around 1870. This is the pest that was the cause for the creation of the DNR Division of Entomology. Again, left unchecked, this pest can cause quite a bit of dieback and in this case has caused the shoot tip on this branch to begin to decline. This is a pest that can be extremely hard to find due to its small size, which makes it easily overlooked.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I received 0.15 inches of rain over the weekend. However, eastern parts of my region received decent rainfall yesterday. The dry weather is favorable for mite populations, and I am finally starting to see maple mites (Oligonychus aceris). I was beginning to think I was not going to see them this year. However the hot, dry weather is allowing population levels to increase. Look for stippling on the leaves that coalesces to make a whitish appearance. Mites can be found near the midrib and veins on the undersides of leaves with a hand lens. This mite is very small and prefers red maples but can sometimes be found on sugar maples. I am also seeing quite a bit of two-spotted spider mites (Tetranychus urticae). Look for stippling, leaf yellowing and, in severe cases, browning of leaf tissue. Numerous mite colonies can be found on the undersides of leaves. If butterfly bush is growing on gravel or hard surfaces with little other room for beneficial insects, it will promote mite outbreaks. I also found damage from southern red mite (Oligonyhus ilicis) on Pieris. The southern red mite is a cool-season mite that can infest azaleas, Pieris and hollies. I do not often see this pest; however, it can cause damage in May, about the same time spruce spider mites (Oligonychus ununguis) are active. However, if it is cool, you may not see damage from cool-season mites until the weather warms up and infested tissue desiccates. Southern red mites are no longer active; however you may be able to see white shed skins and round, red eggs on the undersides of damaged leaves.
Mites cause a fine stippling on infested leaves; however, there are other pests that can cause damage that looks similar to mite damage. One pest in particular is lace bugs. The stippling from lace bugs is a bit coarser in appearance compared to mite injury. The undersides of lace bug infested leaves will have an abundance of fecal spots, immature and adult lace bugs. Adult lace bugs can occasionally be found on the top side of leaves, but more often colonies of lace are found on the bottoms sides of leaves. There are numerous species of lace bug. Some examples include, azalea lace bug, sycamore lace bug, walnut lace bug and hawthorn lace bug. Hawthorn lace bug prefers plants in the rose family and has numerous hosts. During a recent inspection I found lace bugs on Russian quince. I believe they may be hawthorn lace bugs. Leafhoppers are also abundant and causing stippling damage to red maple and redbuds. Large populations can also cause leaf cupping on the new growth of red maples.
There are a few other pests I have seen this week—besides my 11-year-old son, who thinks it is a service to pull they gray hairs out of my beard! I found damage from hawthorn leafminer on winter king hawthorn. This pest is a blotch leafminer and causes browning in areas in which it feeds. Finally, I am seeing quite a bit of damage from hibiscus sawfly on perennial hibiscus. Look for defoliations and small green larvae on the undersides of leaves. Remember, sawflies are wasps, not caterpillars and therefore cannot be treated with Bt insecticides.
The weather has been very dry lately, so I am seeing a decrease in the appearance of new disease. I did find one case of severe dieback on Asian pear, which is likely being caused by fire blight. Fire blight is a bacterial infection and can be difficult to control. It can move through wind and rain splash. The best thing to do is grow resistant varieties. I am starting to see development of new symptoms of needlecast on blue spruce. Look for browning and thinning of inner needles and black fruiting bodies on both green and brown needles. Both Rhizosphaera and Stigmina can be found on declining spruce trees. They can be difficult to distinguish in the field. Rhizosphaera has more of rounded and globular structure, while Stigminia appears a bit more fuzzy and loose. However, rainfall and shaking of samples can change this appearance somewhat, so diagnosis may need to occur in the lab.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
Last week was the first time I’ve done nursery inspections (dealers or growers) this year. I saw my first bagworms and first Japanese beetle adult of the year at a nursery in Tippecanoe County on Canaan fir trees. I also spotted tiny bagworms on arborvitae and white pines. I’ve been seeing rose slug sawfly damage and larvae on most of the roses I’ve inspected at box stores, locally owned dealers, and in my own garden for the last few weeks. For the second year in a row, I saw foliar nematode damage on weigela at a box store (same chain, different county). Last, I’ve been seeing a lot of yucca plant bugs while walking in my neighborhood. These are small hemipterans with black wings covering their bodies, with red heads as adults, although juvenile life stages have more visible red on their bodies. From a distance you’ll see tiny black specks all over the plant, and as you move closer they all dive for the middle of the plant out of sight or drop to the ground. There were hundreds on the yucca plantings at a business near my house in Marion County. Even when the bugs are hiding, you can still see the yellow and white stippling caused by their feeding on the leaves, as well as the black excrement spots they leave behind.
