Fungicide Options for Homeowners for Controlling Brown Patch, Dollar Spot, and Rust

Fungicide Options for Homeowners for Controlling Brown Patch, Dollar Spot, and Rust

David McCall, Associate Professor and Turfgrass Pathologist

The following was an inquiry from a homeowner in Virginia.

QUESTION (Homeowner): "Every year I have problems with lawn fungal diseases like brown patch, dollar spot, rust, etc. I have been using name-brand granular (G) formulations of fungicides on my lawn but nothing completely solves the problem.  Maybe I am not diligent enough in using the products?  What are your opinions on products like Gunner 14.3 MEC or Banner Max 14.3: liquid concentrate products that you mix with water? Are they so concentrated that they will hurt the lawn if not mixed properly?"

ANSWER (Dr. McCall): There are a couple of limitations with standard granular products. First, providing adequate coverage with a granular product is almost always going to be more difficult than a sprayable formulation simply because of the distribution. Some dispersible granular (DG) formulations are available that typically provide better coverage but these are typically sold to turfgrass professionals at specialty stores. Because of the poorer coverage, it is fairly common to have some breakthrough disease development with these products as there is not enough active ingredient in and around the plants for complete protection.

Another limitation is the scope of activity, particularly azoxystrobin (the active ingredient in products like Scotts Disease EX). Azoxystrobin is a phenomenal active ingredient for suppressing brown patch, and quite a few other diseases, but it essentially has no activity against dollar spot. If dollar spot is a concern of the homeowner, it may be best to combine multiple active ingredients to ensure suppression.

Two granular products that come to mind are Pillar G (pyraclostrobin + triticonazole) and Headway G (azoxystrobin + propiconazole). Both are these products contain a QoI and DMI fungicide (different modes of action that expand the scope of diseases controlled), and can be found at specialty retailers. The formulations are also designed for better coverage so we typically see similar suppression as with sprayable formulations.

Propiconazole, found in the BioAdvanced Granular product, is a good general fungicide that covers many diseases. However, I would say that the longevity of this active ingredient is typically less than azoxystrobin for brown patch suppression. Regarding liquid formulations of propiconazole and possible concerns: this product is a DMI fungicide and somewhat acts like a growth regulator. We typically do not see any meaningful damage when applied according to the label, but we have seen a fair amount of short-lived stunting when applied at excessive rates.

I am not sure how frequently you have applied the listed products, but I would expect roughly 2-3 weeks of suppression from them, depending on environmental conditions, pathogen load, and the susceptibility of the grass cultivars. Brown patch will be most active during warm, wet weather, typically in July and August. Dollar spot varies based on geography, environmental conditions, dew presence, and several other factors. Many of the stronger sprayable and granular formulations may last closer to a month.

Rusts are generally more of a nuisance disease that only affects the foliage. I typically don't recommend fungicide applications for this disease unless the homeowner is really concerned about the lawn's appearance (such as for a wedding or some other big event).