In the last week and a half we've confirmed 2 additional boxwood blight samples, both from Lake County. To date, the list of confirmations of boxwood blight in Illinois is as follows:
Lake County: 3 confirmations, all from recently-installed private plantings
Cook County: 1 confirmation, from a recently-installed private planting
Clinton County: 1 confirmation from a nursery, all infected plants were destroyed in cooperation with Illinois Department of Agriculture
All the recently-installed plantings were put in one or two years ago (2015 or 2016). The most likely source of infection to the nursery was a shipment of plants imported from a state with boxwood blight confirmations a few years ago.
One of the issues we're having is that few of the boxwood samples confirmed with boxwood blight at the Plant Clinic displayed the classic signs of boxwood blight. You can download our Fact Sheet on boxwood blight detection here: https://uofi.box.com/v/boxwoodblight. We include a number of pictures of the three classic symptoms: leaf spots, stem cankers, and defoliation, that are characteristic of boxwood blight. However, I have only seen leaf spots on one of the 5 confirmed samples; stem cankers have been noted on all of them, but Fusarium fungi can cause similar stem cankers (we've confirmed a number of boxwood samples with Fusarium instead of boxwood blight); and only 1 sample showed severe defoliation (others had some, but nothing as dramatic as you might expect).
Dark brown stem canker caused by boxwood blight
Dark brown stem discoloration caused by Fusarium canker
All this re-enforces the importance of scouting your boxwood (and pachysandra!) plants for symptoms, especially if you have installed new boxwood or pachysandra plants in the last 3 years. Samples can be submitted to the University of Illinois Plant Clinic for diagnosis (we will incubate and examine the sample and send a report with what we find, anything we suspect, and management recommendations). Because boxwood blight has been declared a nuisance pest in Illinois, we are reporting positive detections to the Department of Agriculture. They are working with homeowners and the green industry to try to eradicate boxwood blight in Illinois.