First identify the type of grass and type of fescue. Here is a fact sheet on tall fescue grass. http://extension.psu.edu/animals/equine/pasture-weed-management/pasture/tall-fescue
Then if you have established fescue you need to assess the situation. The first step in managing fescue toxicity is to know for certain that the pasture is indeed infected and at what level. There are several options for diagnostic tests. For specific sampling procedures, cost and shipping requirements, contact one of the labs at the end of this section. One sample is needed for each pasture, and the analysis of each sample costs approximately $40-60. Once the level of endophyte infection is known, a producer can select the best option(s) to deal with the problem. The horse owner has six options. Options 1 and 2 are specific to the pregnant mare in late gestation, while the other four are designed for other classes of horses to reduce the effects of the endophyte.
1. Remove pregnant mares from fields with endophyte-infected tall fescue 45 to 90days before foaling. Removal may be to a drylot area with nutrient requirements met with hay and grain or to a pasture consisting of forage species other than endophyte-infected tall fescue. This option is the most conservative way of avoiding toxicity problems.
2. Drug therapy. An experimental drug, Domperidone, has been used at Clemson University to reverse the effects of fescue toxicosis. The drug stimulates normal prolactin and progesterone production, therefore eliminating the problems of agalactia and dystocia. Veterinarians may request the drug from Dr. Dee L. Cross at Clemson University. The cost is about $75 per mare. Domperidone should be administered daily for the 30 days prior to foaling.
3. Manage to minimize effect. Grazing and/or clipping management that keeps fescue plants young and vegetative will result in better animal performance. Remember that the fungus is seedborne but is also found in other plant parts.
4. Avoid the endophyte. Use of other forage species for grazing and hay avoids the endophyte.
5. Dilute the endophyte. The endophyte or its products (alkaloids) can be diluted through the use of other feeds in the diet. Growing legumes with infected fescue is a good option. You not only get the desired dilution effect but you also receive an added benefit of improved pasture production and quality.
6. Kill infected stands and replant. Due to cost, this may not be an option. However, endophyte-free seed varieties are readily available. The old infected stand and all shattered seed (that may give rise to infected volunteer plants) must be eliminated and the endophyte-free variety planted.
How to take samples in the field http://www2.ca.uky.edu/agc/pubs/ppa/ppa30/ppa30.pdf
Lab Services for testing (here are just a few):
Seed Laboratory, Division
139 Oak Creek Building
Endophyte Service Laboratory
College of Agricultural Sciences
Oregon State University
Corvallis, OR 97331
Animal Disease Diagnostic Lab
Southern Indiana Purdue Agricultural Center
11367 E. Purdue Farm Road
Dubois, IN 47527-9666
Phone (812) 678-3401
Cumberland Valley Ana. Services, CVASLAB
14515 Industry Drive,
Hagerstown, MD 21742