The two major factors in controlling mesquite are soil temperature and the ability of the plant to respond to herbicide.
Dirty Harry, in one of the all-time classic movie lines, opined that, “A man’s got to know his limitations.” While Harry wasn’t thinking of range management at the time, the general idea still applies.
Or, in the case of mesquite, perhaps it’s more accurate to say that a man’s got to know the plant’s limitations. So, when you reach for your “.44 Magnum in a jug,” consider this: If the plant can’t respond to the herbicide, it can’t be controlled.
And that, according to Ron Sosebee, a range management consultant in Lubbock, TX, depends on knowing the plant, the soil types of your pastures, and soil temperatures 12-18 in. into the root zone.
“There are two criteria that absolutely must be met in order for us to be able to root kill mesquite,” he says. “One is that environmental conditions must be conducive to enable the plant to respond to the herbicide. And the second is the plant must be able to respond physiologically to the herbicide.”
The reason these two factors are so critical, Sosebee says, is because the basal buds are not connected to the vascular system of the plant. “If the top of the plant is killed or damaged, then these basal buds are activated and you get all that regrowth at the base. And we create a worse problem than we started with.”
Sosebee says basically no control will happen if the soil temperature is below 74-75° F at 12-18 in. soil depth. Soil temperatures typically don’t get that warm until mid to late summer, and the ability of the soil to heat up often depends on moisture content.
“A heavy clay-loam soil will stay cooler longer than a sandy soil,” he says, which is why ranchers often see better control on sandy soil, south facing slopes and upland sites. “Those heavy clay-loam soils, if they are wet, might never warm up. I’ve seen years where the soil temperature never exceeded 74-75° at 12-18 in. depth. If that’s the case, keep your money in your pocket and wait for a better time.”
Once that metric is met, then consider the physiological state of the plant. “When those trees first bud out, they’re light green and I can assure you that if you spray when the leaves are light green, you won’t get much in the way of root mortality.” He says the recommendation for many years has been to wait until 40-90 days after the trees leaf out to spray, which he agrees with.
That’s because, the first 42 days after the plants leaf out, they’re importing carbohydrates for growth. “If they’re not exporting carbohydrates to storage, you’re not going to kill much,” he says.
From 42-63 days post bud break, the plants are in the yellow flower stage and carbohydrates are being recharged in the basal bud zone. After that, the bean pods emerge and begin to elongate. Little control will be achieved during elongation because the plant is putting all its energy into producing the bean pod. Once the pod is elongated, he says, you can spray again and achieve control.
If you have regrowth from the basal buds, the plant can still be controlled. “This brings us to the long-shoot, short-shoot phenomenon,” he says.
Long shoots are sometimes called water sprouts. “These are shoots that grow very fast once the top is killed,” he says. “They grow maybe 3 ft. in a year.”
The internodes, or distance between leaves, is longer than normal in long shoots. They’re nearly impossible to fully kill because, in the long-shoot stage, the plant is putting all its energy into vegetative growth. Short shoots, on the other hand, indicate the plant is in its reproductive stage. “When that happens, we can kill them,” he says.
Determining long shoot vs. short shoot gets to be a judgment call, he says. But with experience, you’ll learn what a mesquite twig should look like and how long the internode naturally should be, he says.
So, while knowing your own limitations is important, when it comes to range management, knowing the limitations of the plant you’re trying to control is critical.