Can herbicides impact diseases?

Next week starts with another International Turfgrass Research Conference. Every four years, turfgrass researchers from across the world gather to discuss the latest information about managing all different types of turf. For my part, I am presenting on two of my favorite interests in turfgrass research...weeds and diseases.

Sometimes research results throw up on you (makes me think of poor old Watson this past weekend...heartbreaker at Turnberry) and present you with some serendipitous findings. This holds true for a variety of fields, but the interactions among plant growth regulators or herbicides and turfgrass diseases in particular can be great.

The first thing that comes to my mind is the reduction of dollar spot from applications of the plant growth regulators Trimmit or Cutless. Due to direct fungistatic effects, these PGRs can result in a reduction in the disease. In our most recent study, the combination of Trimmit + Emerald OR Banner MAXX improved disease control when compared to the fungicide alone and resulted in a savings of a fungicide application over the course of the season. In these economic times, a reduction of a single fairway fungicide application can result in a significant savings.

OK, back to my original point...the conference in Chile.

On Monday (during my next post), I will be giving a presentation on a relatively new herbicide used to control annual bluegrass. Velocity, gaining momentum in the Northeast, can effectively be used to suppress annual bluegrass in bentgrass fairways. While it is labeled for creeping bentgrass, its impact on other bentgrass species (colonial in particular) was unknown. In trials at UConn, we found that applications of the herbicide can result in an increase in brown patch. This may be a particular problem since Velocity is most effective when applied in the middle of summer which is typically the time when brown patch becomes active (To the contrary, Velocity has been shown in other studies to actually reduce dollar spot). Unpublished results also indicate that the increase in disease holds true with tall fescue too.

In the photo above, the untreated plot (center) was virtually disease free while the plot treated with three applications of Velocity (left) was severely infested by the brown patch pathogen.

Although we have not researched it yet, my guess is that fungicides typically used to suppress brown patch would likely minimize any negative effects of the herbicide. With the varying agronomic practices put into place at any one time on a golf course, superintendents should consider how one factor may have unexpected negative (or positive) results.

*Photo credits to Alex Putman, former graduate student at the University of Connecticut