We have had several turfgrass samples in the Extension office that showed signs of clubbed rooting. Rather than a normal tapered root the roots are short and swollen on the ends, much like a club in their shape. This condition was traced back to misuse of an herbicide in the dinotroaniline (DNA) herbicide family. Examples include prodiamine (Barricade), benefin (Balan), pendimethalin (Pendulum, Pre-M, Weedgrass Control), trifluralin (in Snapshot), and oryzalin (Surflan). Dithiopyr (Dimension) is another ingredient that is from a different herbicide family but works in a similar way. These herbicides inhibit cell division in the plants. When a weed seed emerges and grows through the herbicide zone at the soil surface they absorb the product resulting in death of susceptible weed species.
These products can also affect cell division in turfgrasses such as bermudagrass, zoysia and St. Augustine where emerging roots on new stolons can be affected and exhibit a “clubbed root” appearance. As a result, turfgrass doesn’t fill in as rapidly which can be especially problematic when the turf is trying to recover from stresses such as drought, traffic, insect injury, or diseases like Take All Root Rot. When these products are applied at excessive rates or frequencies, the clubbed rooting problem is much more pronounced.
Turfgrasses will typically outgrow the effects of these products in time, but during periods of drought or other stresses may be severely affected. It is important to note that pre-emergence herbicides such as the ones listed above are often an important tool in managing weeds in lawns, and these products are labeled for use in these areas. However, the potential for “club rooting” to occur on the desirable turfgrasses should be one of many factors in your decision on whether or not to apply these products.