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FARM 406 48 • any knowledge you may have of the crop susceptibility to the disease, and any complicating factors including the economic return due to an action. These factors go into what we call an action threshold: making a decision about how much damage you expect the pest to cause, and what is an acceptable level of loss? For example, many winter wheat varieties get tan spot, but many also tolerate it very well, and if weather con- ditions at and after flag are going to be dry and/or the yield expectation of the field is low, a fungicide application may not pay. When trying to make decisions about using a fungicide in wheat, MSU Extension has developed a decision tool which is available online at http:// www.msuextension.org/econtools/ fungicide/index.html. The tool allows you to enter your expected costs of application and expected yield benefit, and a colored line indicates whether you would receive a net positive or net negative economic return at the price you anticipate selling the crop. Disease control can be accom- plished in many ways. We've discussed mostly cultural methods up to this point, but biological controls, induced plant defense response products, and chemical means of disease management are all options for treatment. Read some fact sheets on the disease, call trusted advisors, and make a decision based on your knowledge. Integration of these all of these tactics, and many not covered here, are all part of IPM. Cereal cyst nematode is a pest of wheat and barley and spreads in soil. Sanitation is an important method of IPM for preven- tion of this disease. F 406 Dr. Mary Burrows is the Extension Plant Pathology Specialist at Montana State University. Her extension and research activities focus diseases of field crops. Spores land on the plant's leaves or stems. Spores require a minimal amount of moisture (from humidity or dew) on the plant surface to germinate. Germination can occur within 4-12 hours, depending on temperature. Short periods of dryness (i.e. Up to 24 hours) will not kill spores and germination will resume once moisture becomes available. The germinated spore will grow along the plant surface, then form an anchor from which it penetrates the plant. This occurs within 12-24 hours. Once inside the plant, the fungus is protected from dry conditions and the effects of most fungicides. This is known as the incubation period. Infection has occurred but symptoms are not yet visible. Once the fungus has successfully invaded the plant, it starts to kill plant tissues, resulting in disease lesions. Symptoms can become visible as early as 4-6 days after spore germination. Pycnidia form in lesions. Spores 'ooze' from pycnidia under humid conditions. Rain- splash is required to transport spores to sur- rounding leaves and plants. Even small showers are sufficient to spread spores. #1 Spore germination #3 Invasion of plant tissue #2 Penetration into the plant #4 Lesions develop #5 New spores are released