Pasture infestations of honey locust are a common concern in many pastures, abandoned fields, woods and stream banks in Missouri. This medium-size fairly quick growing tree can grow to heights of 100 feet over a period of time. Even on a young, first year’s growth, sharp multi-sticker development will occur, causing concerns about tire punctures and possible foot damage in cattle. Left unchecked, honey locust will overtake pastures, limiting their production and use. This can result in a very costly fix.
This leguminous perennial woody plant is one of the easiest trees to identify on a farm. The leaves are alternate pinnately compound with 15 to 30 leaflets per structure. The leaflets are oval to elliptical in shape, about a half to 1 1/2 inches in length. The young, light-green twigs have a distinct zigzag pattern as they grow. Large, multifaceted thorns can be found anywhere on the tree and might reach 10 inches or more in length. The root system is a strong tap with many lateral feeders, which spread out in all directions. One of the most common distinguishing features of this legume is the large, dark-brown, twisted seedpods that develop as a fruit in the fall of the year. Cattle will often eat these pods and deposit the seeds throughout the pasture, thus spreading honey locust wherever the cows go.
Mechanical treatment for honey locust will only work if the entire root system is removed. This is very hard to do if the tree is very old. Multiple mowing (three to four times a year) over several years will give only marginal results. If plants are clipped or cut with a chain saw, you need to apply a chemical to the stump within a few minutes of the cut. If no chemical treatment is applied to the stump, the tree will sprout again. Foliar spraying applied to the leaves of smaller trees during the early summer months will work well if you get a good coating over the entire tree. Basal bark spraying will work as well if applied properly. For large trees, you can use a chain saw to cut a double ring around the tree about 1 to 2 inches deep spaced about 6 to 8 inches apart. The first cut should be at least 2 feet off the ground, making sure to cut the cambium layer completely around the tree trunk. Then apply your chemical to the cuts. When the tree dies, it will remain standing for several years, thus eliminating handling the tree and its thorns.
Effective mixtures for stump cuts would include a mixture of a 33 percent solution containing triclopyr (Remedy, Garlon or PastureGard), and picloram (Tordon or Surmount), with diesel fuel or mineral oil. For a foliar spray, try mixing Grazon P+D or GrazonNext HL at the highest rating and Remedy in water with a good surfactant. Do not use diesel fuel or mineral oil in a foliar spray, as it will kill the leaves before they get a chance to absorb the chemicals into the tree. You will still have to physically remove the dead tree sprouts from the field after they die.
For more information about pasture plant identification, contact a local University of Missouri Extension agronomy field specialist.