Thistles…Oouch! Believe it or not thistles are a part of the aster family like dandelions. It’s easy to spot a thistle in your lawn when going barefoot, those little needles can hurt for days. Most thistles we see in Iowa are in the Genus: Cirsium. There are about 200 different species of thistles worldwide. In Iowa lawns we are typically concerned with the Canadian Thistle, although we may encounter others like Musk, Tall, and Bull thistles. What is even more interesting is not all thistles are perennial. Canadian thistles are perennial (overwinters year after year) but Bull, Musk, and Tall thistles are Biennial (Require two years to complete a life cycle). In Iowa all non-native thistles are considered noxious weeds and demand to be controlled before they can spread and overtake an area.
Controlling thistles can be a chore. There are many products on the market that will do a good job killing or burning down the thistle, however many of these products are not labeled for turf areas.
Thistles have an extensive root system and are very hard to eradicate from your lawn. Many broadleaf herbicides are labeled to kill thistles in lawns but few can kill all the roots. It is also important to note that it is easier to control thistles in the fall. This is when the thistle is going through a hardening off period, storing Carbohydrates for the winter and next spring. This process will enhance getting more herbicide into the roots providing an effective result. I have found over the years the best practice in killing thistles is to break the waxy surface on the leaf to allow more product to enter the leaf tissue. If you see me treating your thistles, you will notice I step on them and twist my foot to break up the waxy cuticle. It is also important to mix a sticking or penetrating agent with the herbicide. This will help get more herbicide into the plant cells. Like many other weeds it is a bad idea to pull thistles. When you pull a weed a portion of the root remains in the soil and that root will survive and create more shoots for the weed to continue growing. In reality, you actually propagate weeds by pulling them. If you have a thistle problem you may want to consult a lawn professional to come up with a plan of attack.