Is this Boxwood Blight?

Asked May 17, 2018, 6:28 PM EDT

I just heard about a fungus called Boxwood Blight that kills boxwood plants. I was wondering if anyone can help me determine if that is what I found on my boxwood? I just bought 5 boxwood a couple weeks ago from English Garden's. They were in containers for around 7-10 days, then I planted all 5 next to eachother yesterday.

I picked a few leaves off one of the plants to show a closeup. From some of the research I've read, a symptom of blight is black stems (mine don't have that.)

I only have one other boxwood and it's in the backyard (while the other 5 are in the front, all next to each other.) The one in the back which I bought and planted last year doesn't have any spots or brown leaves at all.

Is this just dead leaves, or something more serious like blight?

Oakland County Michigan

4 Responses

Hello,
I cannot tell if this is Boxwood Blight and I'm not certain that boxwood blight has been seen in Michigan. To discover what it is, I suggest you send a sample to the soils and plant diagnostic lab at MSU. Go to the web site for form to be completed, packaging instructions and fee schedules: http://www.spnl.msu.edu/ or https://pestid.msu.edu/ . You should send it Monday and send it UPS, FedEx or DHL so it goes directly to the lab. USPS takes an extra day to get there and so is harder on the sample.
For more information on Boxwood blight go to: http://msue.anr.msu.edu/news/.winter injury or boxwood blight or http://.msue.anr.msu.edu/uploads/files/Boxwood blight Tom Dudek.pdf.

Thanks Susan! Sending a sample over to MSU today. I'll post what I hear back.

Update: So I sent the leaves to be analyzed—it's not boxwood blight. It's another thing called boxwood leafminer. From the report…

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"The yellow leaves in the boxwood sample submitted is Boxwood leafminer injury, Monarthropalpusi flavus (Diptera: Cecidomyiidae).

This is the most serious insect pest of boxwoods. The boxwood leafminer is native to Europe and widely distributed throughout the United States. Its introduction dates back to the same time period that common boxwood was introduced into this country. The leafminer causes serious damage to boxwoods, with heavily damaged plants become unattractive in appearance. The larval feeding between the upper and lower leaves causes blistering and often discoloration.

Both littleleaf boxwood, Buxus microphylla and Common Boxwood, Buxus sempervivens, are commonly attacked, but there is resistance found in individual varieties of both species. Common boxwood cultivars with reported resistance are ‘Handworthiensis’, ‘Pyramidalis’, ‘Suffruticosa’ and ‘Varder Valley’. Buxus microphylla var. japonica has also exhibited resistance to the boxwood leafminer.

The eggs of the boxwood leafminer are white to transparent and can be seen by holding the leaf up to the light. The larvae are yellowish-white and approximately 1/8 inch long. The adult boxwood leafminer is an approximately 1/10 inch long, delicate, orange-yellow to red, gnat-like fly. The partly grown larvae of the boxwood leafminer over-winter within their mines in the leaves of the host plant. The larvae grow rapidly as the weather begins to warm. In late April, when weigela blooms, they turn into orange-colored pupae and emerge as a fly. After mating, the female inserts her eggs deep into the leaf tissue. She dies soon after and the eggs hatch approximately 3 weeks later, and the larvae commence feeding. The larvae continue to feed and grow slowly. In Michigan, there is a single generation each year.

MANAGEMENT OPTIONS

Cultural: Selection of the more resistant varieties.

Biological: Unfortunately, there are few known natural enemies of the boxwood leafminer.

Mechanical: Pruning the foliage before adult emergence or after egg laying ends will reduce the overall population

Chemical: Chemical control is difficult because the application must be timed with the emergence of the adult flies. An application of an insecticide spray when the adult flies emerge (this corresponds to when weigela is in bloom) can reduce populations. Insecticide sprays containing bifenthrin (Talstar), carbaryl (Sevin), cyfluthrin (Tempo or Bayer Advanced Garden Insect Control), or malathion are among the recommend materials that can be applied to control the adult flies. Imidacloprid, a systemic insecticide (Merit or Bayer Tree and Shrub Insect Control) will control the larvae inside the leaves and does not require precise timing. This product should be applied in mid to late April.

Be sure to read and follow all instructions and safety precautions found on the label before using any pesticide."

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Hope that helps someone else!

Thanks for the information. I’m sure it will be beneficial to other people.