Timely Topics
Johnsongrass (Sorghum halepense) and Timothy (Phleum pratense) are two very different grasses. Johnsongrass is a native of Asia and North Africa, has been present in Rockbridge for some decades as an undesirable weed, and apparently has strong future in the Rockbridge region. Timothy is a native of Western Europe, was a valued crop through the 19th and 20th centuries in Rockbridge, and appears to have no future in the Rockbridge region.
Johnsongrass is a summer perennial that is anchored in the soil with an extensive root system and will grow to six or eight feet when it flowers and goes to seed. In pasture, Johnsongrass is a nutritious forage and in its vegetative stage can be very palatable to grazing livestock. But its rapid and aggressive growth makes it difficult to keep in this vegetative stage. Our neighbors in Georgia and the Carolinas are accustomed to the presence of Johnsongrass in their hay but its rapid growth and fibrous stalk make it difficult to harvest it as high-quality hay.
Johnsongrass is of a different botanical genus than the desirable warm season grasses native to North America that conservation organizations have been working with some success to reestablish in our region. The notable differences that makes Johnsongrass a problem is that Johnsongrass can produce significant levels of deadly prussic acid (hydrocyanic acid, containing cyanide) when severely drought stressed or after it has been damaged by frost, especially if it is less than 30 inches tall. The prussic acid concentrates in the lower stalks and so when it is taller, the toxin is concentrated in the lowest portion of the tough fibrous stalks which livestock are much less likely to consume. Prussic acid breaks into its component elements as the plant dies after frost or in the hay drying process.
We have seen very few animals die from eating Johnsongrass but there is some risk, which is why University Extension recommendations are that livestock should not be allowed to graze it for at least 7 days after a killing frost. But when Johnsongrass is as prevalent as it has become in our Rockbridge fields, finding a Johnsongrass- free field is very difficult for many stockmen. When the Extension agent tells the farmer “the risk with Johnsongrass is pretty low” this is cold comfort since every calf in the current market is worth more than $2,000 and the farmer is no mood to take unnecessary risks with valuable animals.
The herbicides that control Johnsongrass generally harm the desirable grasses around it and its aggressive summer growth causes Johnsongrass to shade and crowd out the other grasses. ‘Weed Wiper’ equipment that can be pulled behind a tractor or ATV and dispenses herbicide only to the tall plants that come into contact with the wiper bar can be very effective but reseeding the areas of killed Johnsongrass is very difficult to accomplish in a piecemeal fashion.
Johnsongrass thrives in hot humid climates. This brings us back to Timothy which was once the favorite hay crop for work horses as well as livestock. Timothy is very palatable to livestock and it was known to be readily consumed regardless of its stage of maturity. Back in the mid 1990s I remember seeing a few fields of Timothy planted in Augusta County but at that point it had become a “one-cutting crop” because the summer heat stress dictated the farmer dare not graze or harvest it again in the late summer or fall because the stand would die-out from the stress. Today I am unaware of any Timothy being cultivated on the Interstate-81 corridor and any Timothy hay fed in this region is shipped in from northern states. Hmmm … For information on Johnsongrass control, contact the Rockbridge Extension office at (540) 463-4734 or by email, [email protected]
