Feature

In the Weeds

“Specticle, Doveweed, and Centipedegrass Spring Yellowing”

J. Scott McElroy, PhD, Professor Auburn University

Instead of writing a full article on one topic, I want to try a segment in each magazine issue. This will give me a chance to expound on several topics of interest – at least what I think is interesting. I also want to try this because it will allow me to be as timely as possible. To discuss things that I am seeing around the Southeast and things of interest in research. Without further ado, let’s get In The Weeds

Specticle on Athletic Fields. I may not make any friends with this one, but I have to say it. Specticle (indaziflam) should never go on athletic fields. Specticle is the best preemergence herbicide on the market. Bar none. End of story. The problem is that it is hell on roots and rooting is critical for athletic field stability.

I don’t think that athletic field managers will have a problem with this, nor do I think athletic field managers would spray Specticle on an athletic field. The problem arises when the spraying of athletic fields is done by a contractor that does not manage athletic fields as their primary activity. If spraying is contracted and a company that manages lawns primarily is hired to do the spraying, that company may not realize that Specticle may severely inhibit roots and reduce athletic field playability.

I feel like when I say something negative, I need to add some positives. Here is a positive – Specticle has become the top herbicide for preemergence doveweed control – especially in lawn care. Lawns that were completely covered in doveweed last year have zero doveweed this year. This has been my observation from lawn care locations throughout the state and in Georgia. When it comes to pre-doveweed control, nothing can currently beat Specticle.

Now here comes another caution—after multiple years of use of bermudagrass turfgrass of any type, the turfgrass can start showing severe thinning. Again, Specticle, for all its strengths, is simply a harsh herbicide on roots.

So how should you use Specticle? I am of the opinion that one should use Specticle at most once per year, and usage should be targeted at the primary weed problem. In golf, that should be for Poa control. In lawn care, that should be for doveweed control. Wherever and whenever you are using it, keep an eye on the turf to monitor thinning and overall health to protect against the negative rooting effects.

Spring Centipedegrass Yellowing. A problem has been plaguing centipedegrass—a patchy yellowing that seems to occur after green-up in the spring, that persists until temperatures are into the 90s. The Alabama Turfgrass Research Foundation initiated a project with me around three years ago to determine what the cause of this issue was and to try to determine ways to combat it. As part of this research, we sequenced infected plants to look for pathogens and viruses. We sent samples to labs for diagnostics – both at Auburn and NC State. We sent images to pathologists around the southeast, and we set up six different research trials to evaluate a myriad of fungicide and fertilizer treatments.

Patchy yellowing of centipedegrass indicative of the yellowing problem.

Here is what we know and what we don’t know: We know that there are different types of yellowing, but the majority does not seem to be caused by a pathogen. DNA sequencing and disease diagnostics were unable to identify a consistent pathogen causing this problem. On top of that, in all the trials, nothing stopped, or reversed, the yellow symptoms without negative effects. Below is a review of the findings.

What is the cause of centipedegrass yellowing? In short, it is generally not a pathogen that is causing it. I came to this conclusion after applying all manner of fungicides over a twoyear period. Nothing worked and no diagnostic samples identified a causal pathogen. That being said, there are pathogens that cause centipedegrass yellowing symptoms, but none of the fungicides in our trials reversed the symptoms.

What can reverse the yellowing? None of the fungicide treatments. This included a myriad of common fungicides across all major modes of action used in turfgrass and applied prior to yellowing symptoms, or while yellowing was occurring, reversed the symptoms. Applying high rates of nitrogen – approximately 100 lbs. N/acre helped the centipedegrass to recover faster, and it also had negative effects. High N rates stimulated the bermudagrass and weed contamination in some plots and caused excessive centipedegrass growth which lead to scalping and even worse turfgrass as the summer progressed.

Complete bermudagrass root loss in June in an athletic field treated with Specticle in February. Roots did not return to this field until August.

I do have some theories on this problem. My theory is that the problem is caused by herbicide use. I have not been able to nail down a specific herbicide – the only places it seems to show up are places where herbicides have been sprayed. Culprits are preemergence herbicides and auxin-based, or metsulfuron based, herbicides. Keep in mind, this is just a theory.