Ruth Correll: Beware of grazing these plants after frost

Ruth Correll • Updated Sep 20, 2017 at 5:15 PM

The beginning of fall will be officially be welcomed Friday. The cool days and nights that followed Hurricane Irma gave us our first taste of fall weather.  The cool weather is welcomed to encourage growth of cool season grasses like tall fescue and orchardgrass.

On the other hand, warm season grasses will soon feel the effects of frost and either become dormant or die. Frost damage causes Johnsongrass, forage sorghum and sorghum Sudan grasses to become toxic. Other warm-season species such as bermudagrass, crabgrass, teffgrass and pearl millet do not have this problem. 

The frost causes the release of prussic acid, or cyanide, in the Johnsongrass and sorghum-type plants. Small amounts of prussic acid can be highly toxic to cattle, sheep and goats and somewhat toxic to equine.  There are several things to know to prevent prussic acid poisoning in your livestock.

The No. 1 thing to know is that prussic acid will break down in 10 days to two weeks in the dead plants. This means hay harvested during this time will be safe to feed in 10 days to two weeks. 

Grazing Johnsongrass during this time requires different management. The safest thing to do is avoid grazing Johnsongrass or sorghums when there is the potential of frost. But if grazing fields with Johnsongrass, be sure there is plenty of tall fescue for cattle to eat. They will avoid consuming the Johnsongrass, because the tall fescue is much more palatable. Also Johnsongrass that is mature and headed out and no longer green is not a concern.  But many fields have small patches of Johnsongrass scattered throughout.  If the Johnsongrass begins to cover more than 25-30 percent of the ground, you may want to stockpile this field and graze it after the Johnsongrass is no longer viable.  This will prevent any prussic acid danger. 

Prussic acid production is possible until the plant top is dead. When only plant tops have been frosted, new shoots may regrow at the base of the plants. These can be very dangerous because of high prussic acid potential and because cattle will selectively graze the new growth. Do not graze frosted summer annuals until regrowth of shoots is 15-18-inches tall, or until several days after the entire plant and shoots are killed by subsequent frost.

Prussic acid poisoning can be caused by other plants. These include, but are not limited to, black cherry trees leaves and twigs, apple leaves, elderberry, Indiangrass, velvetgrass and peach leaves.

Keep an eye on your animals if you suspect the possibility of prussic acid poisoning. Symptoms of prussic acid poisoning include gasping, staggering, trembling muscles and possible death from respiratory failure.

The Wilson County Livestock Association will hold its annual Field Day on Saturday at the James E. Ward Agricultural Center. Come and enjoy a great meal while visiting with your neighbors and friends. A trade show is planned. There will be special entertainment. The event begins at 5 p.m. at the community stage at the Agricultural Center. Tickets are available at the Wilson Farmers Co-op, UT Extension Office and from Livestock Association board members. Tickets are $10 and go to support the Wilson County Livestock Association Scholarship Fund and the 4-H Youth Livestock program.

For more information, contact the UT-TSU Extension Office in Wilson County at 615-444-9584. You can also find us on Facebook or visit extension.tennessee.edu/wilson.

Ruth Correll, UT Extension-TSU Cooperative Extension agent in Wilson County, may be reached at 615-444-9584 or [email protected]


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