With Debby lurking off the SC and NC coasts, discussing what should be done in the aftermath is essential. Current rain totals vary from 4 to 20 inches, depending on where you are in the Carolinas. The first thing to discuss is the degradation of fungicides, which will play a role in applications after Debby leaves. Three primary processes are responsible for pesticide degradation: chemical, physical, and microbial degradation. Chemical degradation occurs through hydrolysis and volatilization, and fortunately, not many, if any, fungicides volatilize. However, hydrolysis can play a significant role in the degradation of fungicides, especially if the pH of the water is above 7. Physical degradation involves processes such as runoff and leaching. We have conducted numerous research studies with Dr. Travis Gannon, demonstrating that fungicides do not move readily through soil. However, runoff in storm systems such as Debby could also account for fungicide loss. Some leaching likely also occurs, given the massive amount of rain that could fall. Microbial degradation is the most important degradation process for most fungicides. As a reminder, what soil microbes need to thrive are organic carbon, air/water balance, pH above 5.5, temperatures above 50^oF, and nutrients.

The potential fate of pesticides after application.

Turfgrass systems are naturally equipped to support microbial growth, providing all the conditions for microbes. As a result, the turf microbiome is home to many bacteria and fungi. Microbes, particularly bacteria, experience exponential growth as temperatures rise. So, after a warm, wet July, we have microbial communities primed to eat up those fungicides. Thus, whatever was applied before Debby will, at best, last seven days after the rain when soil temperatures are warm like they are. The bottom line is to be prepared to get out as soon as possible with another application to protect the turf.

It is also essential to be prepared for odd things like Pythium blight and leaf spot in fairways, mini-ring to develop in odd areas, and Pythium root rot or take-all root to show up abruptly. For those managing sports fields, diseases such as Pythium blight or leaf spot could develop on bermudagrass. In lawn settings, this could make large patch flare up on zoysiagrass, centipedegrass, and St. Augustinegrass. This system could intensify gray leaf spot pressure for tall fescue, especially if these lawns are not mowed for an extended period after Debby’s passing. Profiles for gray leaf spot, large patch, and Pythium blight are listed below for reference.

Gray Leaf Spot

Large Patch

Pythium Blight

Creeping bentgrass putting greens:

 Applying a PGR leading into tropical systems will help limit growth and hopefully limit scalping in the aftermath. Pythium root rot is always the most important disease of creeping bentgrass putting greens, but other things such as summer patch, anthracnose, yellow spot, and algae could also develop. Luckily, with Pythium root rot, we are pretty far into the season, and we suspect that several PRR applications have already been made. However, getting out as soon as you can after Debby passes is warranted. It would be wise to apply another foliar spray, such as a phosphite or phosphonate fungicide, with a contact fungicide, such as chlorothalonil, mancozeb, or fluazinam. Then, a follow-up of a soil application for PRR and other diseases is also important. Something like Serata, Segway, or Banol mixed with a QoI or DMI would be wise. Given these products need to be irrigated after application, it would be best to wait for the greens to drain well before applying. Plant pathogens are aerobic organisms, so new infections will occur after the greens start to drain.

Bermudagrass putting greens:

 The statement above on PGRs applies to bermudagrass putting greens as well. The diseases to consider are take-all root rot, mini-ring, and Pythium root rot. We rarely see take-all root rot and mini-ring at the same course, but it can happen. For those with a history of take-all root rot, starting those applications after Debby is critical if you haven’t started them already. The same is true for mini-ring applications. We have observed the rapid development of all three diseases listed above during intense rainfall. With the amount of rain in the current forecast, nutrients will also be leached from sand-based putting greens so that supplemental fertility will be needed after this event. Many options exist to manage these diseases; you can view the best products for each disease below.

Take-all Root Rot

Pythium Root Rot

Mini Ring

When cloudy conditions persist, one of the more challenging issues for bermudagrass is Pythium blight and leaf spot. Both of these diseases can develop rapidly, so high rates of fungicides might be required to halt their progression, and follow-up applications might also be necessary to clean up the damage. There are numerous options for Pythium blight, like Subdue MAXX, Banol, Segway, and Serata. Unfortunately, the phosphites and phosphonates do not work as well curatively. It is best to apply an active ingredient that moves into the plant for leaf spots rather than just a contact when symptoms are present. Something like iprodione is ideal for this. Remember that leaf spots and Pythium blight are challenging to distinguish from each other in the field, so it is best to tank mix a Pythium product and iprodione.