Prevention of Pythium Root Dysfunction in Bentgrass Greens

For golf course superintendents who've struggled with Pythium root dysfunction in the past, now is the ideal time to initiate a preventive fungicide program. Pythium volutum, the most common PRD pathogen in our experience, starts to actively infect bentgrass roots in the fall when soil temperatures consistently dip below 75 degrees. That, combined with plenty of moisture throughout the Southeast, means that the pathogen is almost certainly active now.

Not very many products are effective against PRD. Even though it is caused by a Pythium, some of the standard Pythium fungicides like mefanoxam, propamocarb, ethazole, and fosetyl-Al are not very effective when applied alone.

Instead, the QoI and Qii fungicides have been most effective against PRD in our trials. The QoI fungicide Insignia (0.9 oz) has historically been the most effective product. We have also seen good control from Heritage TL (2 fl oz) and Compass (0.25 oz) but only on a preventive basis.

The QiI class of chemistry is relatively new, and there is currently only one product available in this category: Segway, which contains the active ingredient cyazofamid. Applications of this product at 0.9 fl oz per 1000 sq ft have also provided very good control of PRD. Segway is an important addition to our arsenal against PRD because it gives us another chemical class to rotate with to prevent the development of fungicide resistance in Pythium volutum.

Tank-mixtures of fosetyl-Al + propamocarb (Signature, 4 oz + Banol, 2 fl oz, for example) and fosetyl-Al + mefanoxam (Signature, 4 oz + Subdue Maxx, 1 fl oz, for example) have provided good control in our trials or based on superintendents' observations. These tank-mixtures, although expensive, should also be worked into your program to help prevent fungicide resistance.

As mentioned above, a preventive program should be initiated in the fall when soil temperatures consistently dip below 75 degrees. Repeat applications on 21 to 28 day intervals as long as soil temperatures are between 50 and 75 degrees are recommended where PRD has been a persistent problem. Less frequent applications may be sufficient where the disease has only been a minor problem or where growing/management conditions are less stressful during the summer. Since PRD is a stress-induced disease, there is no "one size fits all" fungicide program to control it.

Note that applications of Insignia and Segway should be watered into the soil immediately to drive the fungicide into the root zone. Approximately 0.125" of irrigation has worked well in our trials. Since fosetyl-Al moves downward in the plant, tank.mixtures including this product should be left to dry on the foliage for best results.