Disease management in the nursery following rain
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
In West Michigan and across other parts of the state, growers reported anywhere from 4 to 5 inches of rain this past week along with the cool, cloudy conditions that will favor some disease problems. After the rains stop and you can get back into nursery fields and container growing areas, be prepared to deal with the following bacterial or fungal problems. (Also see the article by Dr.Willie Kirk in this issue.)
Fire blight can appear on flowering crabapple, serviceberry, cotoneaster, hawthorn, flowering cherry and plum, pear and spirea.
Botrytisblight can appear on annuals and perennials still in greenhouses or covered poly houses. (See article for management guidelines by Dean Krauskopf in this issue.)
Pythium or Phytophthora root rot. Both of these water mold fungi can spread in rain-saturated fields or in flooded areas of nursery stock production. Watch for yellowing plants in areas where standing water or saturated field/container conditions have occurred. Wilting will occur before plant death. Check for discolored roots on suspect plants. Send plants to MSU Diagnostics Services to determine which disease may be involved. Pythium can be easier to control with fungicides than Phytopthora. See either MSU Extension bulletin E-2782 or E-2783 for specific fungicide recommendations for tree and shrubs or perennials. The 2006 versions are now available from your local Extension office.
Anthracnose is the generic name for a disease caused by several different types of fungi including Apignomonia and Colletotrichum. These pathogens blight foliage and in some cases create cankers on twigs, resulting in dieback. Newly emerged foliage is more susceptible to infection. Foliar lesions are large, irregularly shaped areas of necrotic tissue along the leaf margins and between the veins. Leaf blighting typically begins on lower branches and spreads upward. With a hand lens, you should be able to see the fungal fruiting bodies along the veins of infected foliage. This time of year fruiting bodies are also visible on recently killed twigs. Foliar fungicide applications are best applied at bud break in the spring. See Extension bulletin E-2782 for specific recommendations.
Leaf spots caused by a wide range of fungi including: Alternaria, Cercospora, and some bacteria like Psuedomonas and Xanthomonas will begin to show up in the next week or so.
When possible, be sure to treat susceptible trees and shrubs with both a fungicide and/or a bacteriocide in the nursery. For specific recommendations be sure to read E-2782.
If you are unsure of the identification of the disease, please either send in a sample to MSU Diagnostic Services or contact your local MSU Extension educator for assistance in diagnosis prior to making a spray application. Often times the wrong treatment is made because the disease was misdiagnosed.