It’s now the season to take barefoot walks in the yard. In many cases that can be painful due to a tiny lawn pest called spurweed. It has a lacy almost fernlike appearance and it is often less than an inch tall. However, there can be a lot of ouch in that inch.
Spurweed begins its growth in late winter. It can develop a rather strong foothold in warm-season turf like Bermuda grass, St. Augustine and centipede grass. These grasses are brown and dormant in cold weather, so the spurweed has little competition. In cool season turf like fescue or ryegrass it usually has more trouble competing for light, so it’s often a smaller problem.
When young, spurweed has delicate leaves and stems. They are deeply divided, hairy, soft and emerge from stems in pairs. The real problem comes when this plant sets fruit. These tiny cone-like fruits are barbed and spiny, and the nasty little structures provide seed for next year’s crop.
At this point spurweed control will have to wait until the coming fall when new plants emerge. Once seeds mature, killing the plants has no lasting effect. Once warm weather hits for good they will die anyway, but the little burrs will still be there.
We are reaching the critical time. Some spurweed has matured already, but we can still weaken next year’s problems if we act quickly. There are a few natural products available which will kill spurweed in actively growing perennial turf, but they will injure the grass temporarily.
These products work by destroying the plant’s ability to retain water. They dissolve the waxy protective leaf coating, so they kill what they hit. Perennial grasses will send out new shoots and recover quickly. The spurweed and any annual weeds will die. The nice thing about these chemicals is that they have very low toxicity to animals.
More traditional broad leaf herbicides like 2,4-D, dicamba or MCPP can cause longer term turf damage, especially to sensitive grasses like St. Augustine or centipede. These chemicals should have been applied earlier in the season when the turf was dormant. Always apply chemicals on calm days to prevent hitting non-target areas. Also, most herbicides work better on warm days, so keep that in mind too.
In fall you can attack this weed with pre-emergent chemicals. They work by preventing seeds from germinating. When used properly they do no damage to established turf. Many of these are applied in granular form, so there is less risk of herbicide drift to nearby places.
You can also use triazine herbicides like atrazine in the fall on warm-season turf. However, these chemicals will kill cool-season grasses. Non-selective chemicals like Round-up will kill spurweed, but they will also kill actively growing turf be it warm or cool-season.
Once you’re rid of this pest, the best defense is a healthy thick lawn. To achieve this, don’t mow too close, use a sharp mower and mow often. Never remove more than a third of the canopy at one time.
Ted Manzer teaches agriculture at Northeastern High School.