June Plant Diagnostic Clinic Update

June is a busy month in the Plant Diagnostic Clinic, and we have had a variety of submissions of samples with various diseases and disorders.

Trees

Several shade trees have displayed symptoms of bacterial wetwood, a common problem which affects a variety of tree species. Symptoms appear on the trunk or large branches of the tree, which will begin to ooze a foul-smelling, foamy, slimy liquid. For more information about this disease, visit:

• http://www.ipm.uiuc.edu/diseases/series600/rpd656/
• http://www.ext.colostate.edu/pubs/Garden/02910.html

We have had some samples from elms and oaks displaying wilt symptoms, and have confirmed Dutch elm disease and oak wilt. It is very important to submit live branches 1-2 inches in diameter from areas of trees just beginning to show symptoms. Keep the samples fresh and do not allow them to be exposed to high temperatures before submitting to the clinic. These are important diseases to have confirmed since the disease can quickly spread to untreated adjacent trees through root grafts. For more information visit:

• http://www.na.fs.fed.us/spfo/pubs/howtos/ht_oakwilt/toc.htm.
• http://www.dnr.wi.gov/org/land/forestry/UF/Resources/OakWilt03.pdf.

Environmental injury on white pine shoots. Photo by Jeff Smith.

We have received a lot of evergreen samples over the past month. Samples that have been submitted to the lab have no evidence of disease, yet have wilted and browning needles on the new spring growth. While white pine seems to be the most common submission, similar problems also seem to be common on yews and have also appeared on other evergreens. In many cases damage is described as being worse on the south side of the tree. Diagnosticians from other Midwestern states are reporting similar damage. We believe the damage is related to the unprecedented severe spring freeze damaging the new plant tissues as they were coming out of dormancy. Because the tissues were not completely destroyed the trees may have been able to grow until we began to get hotter, drier weather. Even in areas with abundant rain, we have had some hot dry days that could be preventing normal movement of moisture through damaged tissues. While this damage is unusual, we do not expect these trees to die. Dead branch tips could be removed, but do not prune more than is necessary.

Environmental injury on white pine shoots. Photo by Jeff Smith.

Other pests and diseases found this month on evergreens include spruce bagworm, Diplodia (Sphaeropsis) tip blight on Scotch and Austrain pines, Rhizosphaera needle cast on spruce, Dothistroma needle blight on Austrian pine, and spider mites on junipers.

Herbaceous plant and shrubs

Some diseases and pests of ornamental herbaceous plants we have diagnosed this month have included iris borer, Rhizoctonia stem rot on Lisianthus, and Septoria leaf spot on goutweed (Aegopodium podgraria).

Samples from several shrubs have been submitted to the clinic, and we have found spider mite problems on various shrubs and Phytophthora root rot on a holly.

Grasses

On turf samples submitted to the clinic, we have seen Pythium, Anthracnose and brown patch (Rhizoctonia) diseases on fescue. Bluegrass samples have been found to be variously infected with Anthracnose, Rhizoctonia and additional samples covered with slime molds. A mixed-grass turf was diagnosed with Dreschlera leaf spot.

Vegetables, Fruits and Herbs

A raspberry sample was submitted with Phytophthora root rot, ginseng was diagnosed with anthracnose, and several cucurbit samples were infected with Fusarium wilt. A Fusarium crown and root rot was also found on pepper and tomato plants submitted to the lab. We also had samples and several calls related to a disorder of tomatoes related to saturated soil conditions. Sudden wilting can occur and last until the soils drain. Such plants can recover if the soil does not remain waterlogged too long, although vigor may not completely return. We also had a Chinese cabbage sample with a bacterial soft rot in the crown.

As always, we welcome your sample submissions to the plant diagnostic clinic. You can see our Website for more information on sample submission, forms and fees: http://soilplantlab.missouri.edu/plant/.

If you have additional questions about how to submit a sample, you can contact the lab at 882-3019.

Simeon Wright, Heather OConnor, and Angel Ramsey
MU Extension Plant Diagnostic Clinic