Indiana Department of Natural Resources sent this bulletin at 06/20/2019 08:34 AM EDT
Weekly Review for June 20, 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 last week I found all kinds of neat pest issues. Well, maybe neat to an entomologist but not a nursery. I have been seeing several sawfly species during the past few weeks. Remember, that sawflies are not caterpillars, but are actually the larval stage of a wasp. The prolegs lack crochets. Oak sawfly was seen on red oak in Brown County. I also have been seeing Hibiscus sawfly on perennial Hibiscus in multiple counties. This pest is very common in my territory this year. I have seen hawthorn leafminer on winter king hawthorn. This is a blotch leafminer so look for large dead areas on leaves, not serpentine mines. Leafminer was also observed on daylilies. I am not sure of the exact species of leafminer, but this leafminer causes minimal damage and has serpentine mines. In order to prevent leafminer injury, adults or young larvae must be treated early on in the infestation period. Timing can be tricky if you do not know the species of insect that is causing the issue.
I have only seen a few scale insect so far this year. Last week, I saw tulip tree scale on tulip tree in Brown County. Look for orange, rounded scale insects feeding on branched. Heavy infestations that wrap around stems can cause branch dieback and tree death. This scale insect has a crawler stages that is in late summer. It is a soft scale and can produce large amounts of honey dew which often results in black sooty mold growing on leaves and branches on an around infested trees. I also found what appeared to be hemispherical scale on bay laurel in greenhouse. Immature hemispherical scale and brown soft scale can look similar. However, when mature, hemispherical scales will have raised ridge on the cover that almost appear to have an H pattern.
Mites! They are just not having a good year with all of this rain. It keeps washing them off of plants. I saw one maple mite so far this year. Yes, one individual mite. I did find pear blister mite injury on pear trees in Monroe County. Look for raised bumps on the leaves. They first appear greenish, but will darken over time. Thrips on the other hand have been very abundant at some greenhouse locations. Look for whitish, silver appearance on infested leaves. The damage almost appears scratchy looking. Pale, or yellowish colored adults can be found on the undersides of leaves. There are even some species of thrips that are black in color. Interestingly, some thrips species have been known to feed on ftwo spotted spider mites.
Well, now onto a few other miscellaneous pests. I have seen white pine weevil infestations in a few areas this year. Host included, white pine, Serbian spruce and Norway spruce. Look for wilting and dead terminal growth. If you slice the infested branches open you will see chip cocoons inside. I have also seen imported willow leaf beetle on corkscrew willow again this year. This pest has been found at the same nursery for multiple years. Look for small shiny black beetles that are cause skeletonization on the leaves. Both adults and larvae can cause feeding injury. I also found bullet oak gall on red oak. Galls are formed by the feeding of Cynipid wasp larva. There are numerous species of oak galls. Control is very difficult. Systemic insecticides do not work well because when the leaf gall forms it cuts off the vascular flow to that area. Pin oak, willow oak and shingle oak seemed to be very prone to oak gall infestations.
Okay. Well not too much to say about disease this week. I am seeing a lot of rust species out there this year. Cedar-quince rust was found on hawthorn and possibly serviceberry. Typically, cedar-hawthorn rust primarily infects the leaves of its host, while cedar-quince rust will also infect fruits and cause stem galls on hawthorns. These infections never seem to kill the trees but the can look really bad by late summer. We have had a very wet year in my region. However, I have seen very little leaf spot on Iris. Last week, I finally encountered leaf spot on iris. This can be caused by the fungus Didymellina. However there can be other fungi that can cause leaf spot on iris. Look for eye shaped spots on leaves. These spots may merge to form dead areas on the leaves.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
Last week, I was out doing dealer inspections in Tippecanoe County. My most interesting find was on several varieties of Coleus. I am used to seeing Botrytis scattered on various annuals including Begonias, Impatiens, Coleus, etc., and that was initially what I thought I was seeing. However, the spots on the leaves were somewhat atypical for Botrytis – as far as I could see, there were no grayish spores visible to the naked eye, and the shape of the spots wasn’t quite right. I did a little digging online and suspected I might be seeing viral symptoms. I sent the sample to Purdue’s Plant and Pest Diagnostic Laboratory and they did some testing and confirmed the sample was positive for Impatiens Necrotic Spot Virus (INSV). One of the pathologists at the lab said one way you can tell it is viral and not fungal is there is still green healthy-looking tissue inside the ringspots. The older spots were brown through the middle and did superficially resemble Botrytis.
Another cool first find for me was European Elm Flea Weevil on Frontier Elm. The leaves of all the elms were peppered with small feeding holes and upon closer inspection I found tons of tiny weevils on the undersides of the leaves. I tried to get a good picture but they don’t like to sit still for long and as the name implies they can jump just like a flea!
Last week, I also spotted my first bagworm hatchling of the year, on Wisteria. Other finds were bad spider mite infestation on New Guinea Impatiens and roseslug sawfly larvae on various rose varieties – there are at least six in my attached photo!
There wasn’t a lot new last week but there was some cedar apple rust and even with all the rain we’ve been getting, you still need to ensure pots get watered as is evidence by the nine bark starting to wilt.
I’ve included a couple of photos this week. Anthracnose (Colletotrichum sp.) leaf and stem blight on Sweetbay Magnolia and Fabraea leaf spot and canker (Diplocarpon mespili) on Asian/Japanese Pear. I also had a confirmation of Phytophthora cinnamomi on ‘Blue Rug’ Juniper, but forgot to take a photo. P. cinnamomi is a different species than the pathogen that causes Sudden Oak Death Disease (Phytophthora ramorum), but it is a destructive pathogen and has a wide host range.
First off, we finished the 2019 Gypsy Moth treatments on Tuesday. The weather really made getting treatments down this season a challenge. Though interestingly, I think it has been a bit of a challenge for the caterpillars as well! The cooler temperatures and rainy weather is ideal for a couple of pathogens that can keep populations in check. I’ve been out looking and so far I don’t see populations or damage near what we had last year. Just have to see what the rest of the season brings.
We continue to receive information about possible Boxwood Blight infected plants introduced into Indiana. I encourage you as nursery professionals to learn about this disease. Contact your nursery inspector or the PPDL for assistance in diagnosing Boxwood Blight.
I had an opportunity to evaluate storm damage a few weeks ago with a consulting arborist. I was really struck by the amount of damage that should have been prevented with good pruning and tree care practices decades previous. It really drives home the need to start with plants with good structural properties and the importance of the early care and pruning given to trees in the nursery and after transplanting.
This Daphne shrub is one example of poor early care. This probably started when the cutting was held in a propagation tray too long and was not corrected when it was transplanted. This plant will eventually ‘hang’ itself in just a couple years as stem growth is restricted by the encircling root. Seeing this one, I dug around in this lot of plants and found several more girdling roots under the soil.
