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Summer Fungicide Programs for Cool-Season Putting Greens

Summer is approaching quickly in the Southeast, and golf course superintendents are shifting their focus from growing grass on bentgrass or Poa greens to just keeping them alive. Having a solid fungicide program in place to control summer diseases is an essential part of this. Here are a few diseases to keep in mind as you put your program together:

Pythium blight. While this is a major concern on Poa greens, Pythium blight is not a common problem on creeping bentgrass. A huge amount of money is wasted every year to control Pythium blight on bentgrass greens. If you have Poa greens, keep in mind that although several of the QoI fungicides are labeled for Pythium blight control, they only provide 7-10 days of protection.

Pythium root rot. This is a persistent problem on bentgrass and Poa greens that are poorly drained. However, Pythium root rot can also occur even on well-drained greens during periods of wet weather, so nobody is immune. Of the Pythium fungicides, mefanoxam (Subdue, Fenox) is most effective against Pythium root rot. For curative control, we often recommend an application of ethazole (Koban, Terrazole), followed a few days later by mefanoxam. Remember that these applications should be watered-in since the pathogen is active in the soil.

Pythium root dysfunction. For golf courses with bentgrass greens less than 10 years old, Pythium root dysfunction is the most common problem during summer. This disease is best managed during the fall and spring when the pathogen is actively infecting roots. If symptoms are observed during the summer, relieving stress by raising mowing heights and increasing fertility levels is essential. Curative applications of Insigna, Segway, or Signature + Banol can also help to suppress symptoms, but only if steps are taken to relieve stress at the same time.

Anthracnose. This is a major concern for those with Poa greens and older cultivars of creeping bentgrass. Golf course superintendents are running out of options for anthracnose control due to fungicide resistance. Most anthracnose populations are already resistant to the benzimidazole and QoI fungicides, so do not rely on these products unless you know that your population is sensitive. The NC State Turf Diagnostics Lab offers fungicide resistance testing if you would like to find out for sure. Fortunately, most new bentgrass cultivars are very resistant to anthracnose so this disease is becoming less common in the southeast.

Fairy ring. Hot and dry weather during summer tends to bring out Type I fairy ring symptoms, decline or death of turf in ring patterns. In most cases, symptoms are the result of hydrophobicity that has developed in the thatch layer. Fungicides are not very effective for curative suppression of fairy ring, unless they are combined with wetting agents or cultivation practices to re-wet the soil profile.

Nematodes. These are a common problem on sand-based putting greens across the southeastern United States. In fact, I am convinced that nematode problems are much more common and widespread than anyone realizes. If you've never had a nematode assay done, I'd encourage you to spend the $5 or $10 to do one. You may find that chronic problems you've battled over the years are actually the result of nematode activity. While the options of nematode control are limited at this time, effective products are on the horizon.

Brown patch. Thanks to the QoI fungicides, brown patch is no longer a significant problem on putting greens. As long as you rotate the QoIs or other strong brown patch fungicides (chlorothalonil, ProStar, Endorse, Medallion) into your program once in a while they will keep brown patch in check.

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