Missouri Environment and Garden Newsletter - AgEBB
Missouri Environment and Garden Volume 13, No. 6
News for Missouri's Gardens, Yards and Resources June 2007

May Sample Submissions to the Plant Diagnostic Clinic

The effects of the late-spring cold snap continue to be seen in samples that are submitted to the clinic. The cold stressed and injured many plants, causing greater susceptibility disease. In addition, some samples have been submitted for a determination of what is freeze damage and what is a disease.

Tree issues
Downy Leaf Spot (Microstroma juglandis) on the lower surface of a hickory leaf. Photo courtesy of Simeon Wright.
Fire blight, caused by bacteria, can be confused with freeze damage on apples and pears. We were able to confirm the presence of fire blight in a pear sample submitted to the clinic with some blackened spurs and shoot tips. Overall, we have received fewer fire blight related samples this year than we have the previous couple years.

We received a hickory sample that was found to have hickory downy leaf spot, Microstroma juglandis. Symptoms of this disease include yellow lesions on the top of the leaf, and whitish fuzzy spots on leaf undersides. A Leyland cypress with random branch death in southeastern Missouri had a fungal branch girdling canker caused by Seiridium sp. A couple Austrian pine samples had Dothistroma needle blight, which is common on Austrian and Ponderosa pines in Missouri. Dothistroma needle blight causes brown banding of the needles and eventual needle death and defoliation.

Symptoms of tomato pith necrosis (Pseudomomas corrugata). Photo courtesy of Simeon Wright.
Vegetable issues
Several tomato samples have been submitted from high tunnels. One sample had yellow wilting leaves and brown discoloration inside the stems. While we initially suspected Fusarium wilt, a large walnut tree had been removed just before building the high tunnel and planting tomatoes this spring. The effects of juglone, a chemical released by black walnut and butternut trees, will cause symptoms similar to Fusarium wilt. More information about juglone and the species it impacts can be found at:

Another wilted high tunnel tomato sample had dark decaying areas on the stems especially near the leaf petioles. Adventitious roots were forming along the stem. We were able to confirm the presence of pith necrosis, a bacterial disease caused by Pseudomonas corrugata. This disease is becoming more common in the Midwest as more high tunnel production occurs. Excessive N fertilization and moisture seem to play an important role in disease development. For more information about pith necrosis see: Leaf mold, caused by the fungus Fulvia fulva, was also found on a high tunnel tomato sample. Symptoms of leaf mold include yellow blotches on the upper side of the leaf, with patches of a gray-brown mold below. Eventually the foliage is killed and the plants can be defoliated. Tomato diseases like pith necrosis and leaf mold are probably less likely to be seen in field grown or home garden tomatoes than in high tunnel or greenhouse production. Some important factors would be crop rotation and lower humidity in outdoor production.

Turfgrass issues
Brown patch, caused by the fungus Rhizoctonia solani, has already appeared on fescue samples. This disease, observed during hot and humid Missouri summer weather, can be characterized by round patches or an irregular pattern of dying or dead grass. More information is available at:

Our staff also diagnosed two instances of spring dead spot on bermudagrass in southern Missouri. More information on spring dead spot of bermudagrass and its control can be found at:

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. 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
UMC Extension Plant Diagnostic Clinic

[ Back to Articles ]  [ Online Subscription Form ]