One of the most misunderstood weeds in our foothill pastures are thistles. Most of us don’t really give them a second thought until they send up their stalk with those gaudy pink flowers and spread those downy seeds hither and yond. Usually, once folks recognize the stalks and flowers they have already produced viable seed.
Those old stories about grandpa spending his winter days grubbing thistles, here appear to have merit. Thistles are not difficult to control with herbicides when they are treated at the proper stage of growth, but once they bolt and send up that woody stalk, control is not so easy, so treating thistles while they are in the rosette stage is critical.
Identifying thistles and buttercups as well, can be difficult when the plants are immature, however, this time of year they can be identified fairly easily, as they are low to the ground, and very dark green, in a circular form, and have spiny points at the ends of each leaf. You can also use Google to find images of “musk thistle” or any other thistle.
After identifying the thistles present and the numbers present, you’ll need to decide if an herbicide application is warranted. If few are present, you may simply dig them out like grandpa. If they are sparsely located, you may be able spot spray with a wand or backpack. If you have a large number of rosettes you will probably want to treat the entire hayfield or pasture with a broadcast herbicide spray. Be sure that temperatures are sufficient for herbicide treatments. For 2-4-D you need an ambient temperature of 50 degrees Fahrenheit, and less than 85 degrees Fahrenheit, to avoid problems. Also avoid windy days where drift can cause problems.
There are many herbicide options for treating thistles in pastures and hayfields. Not many available for legumes such as alfalfa or clover, so be careful when treating in or near these crops. For treating thistles in grass pastures and hayfields in February, 2-4-D is the herbicide of choice, as it is readily available, and is the most cost effective. There are other options, but for thistles and many other weeds at this growth stage, 2-4-D will do an adequate job, and be less expensive. Always read the label and follow directions. 2,4-D applied in February will give control of many other broadleaf weeds such as mustard, chickweed and buttercups.
Many herbicide labels recommend an adjuvant or surfactant in the tank mix to enhance their effectiveness, so read the label and follow the recommendations. Surfactants help reduce surface tension on the leaf and enable the spray solution to penetrate the leaf surface easier so that it is taken into the plant. Some herbicides already have the surfactant premixed into the product so no additional adjuvant is needed.
Thistles and most other weeds are most susceptible to herbicides when they are young and actively growing, usually less than 3-4 inches tall. Make sure that the weeds are actively growing so that herbicidal treatment will be effective. For most winter weeds, consider spraying when you have several days in a row above 60 degrees Fahrenheit. Warm sunny days stimulate growth in cool-season weeds, and thistles will be actively growing and controlled by herbicide applications.
By controlling thistles now, you can economize your weed control, taking advantage of herbicide effectiveness on the immature stage of growth, utilize less costly chemicals, and controlling additional weeds such as chickweed, mustard and buttercups, allowing your grass pastures and hayfields to flourish.