Tag Archives: Joseph M. Vargas Jr.

Controlling Turfgrass Diseases: An emerging problem: Nematodes

By Joseph M. Vargas Jr.

A new problem that has manifested over the last few years is nematodes. Why they are suddenly becoming a problem is mysterious. Nematodes are being found at counts around 6000 per 100 cc (6.1 cu in.) of soil. If present, they feed on the roots of the turfgrass plants because they are obligate parasites. This means they can only obtain their food from a living host and, in this case, a living turfgrass root. Once the turfgrass plant dies, the nematode also dies since it no longer has a living food source. The most common nematodes associated with this new problem include the stunt (Tylenchorhynchus), the ring (Criconemoides), and the spiral (Helicotylenchus), which have become affectionately known as the “triple-headed turfgrass monster.”

The next time there is a problem with the turf, and every fungicide has been tested but the problem has not gone away, you might want to check for nematodes. They are obligate parasites and, therefore, you should take the sample from a declining area or near a dead area, but never from the dead area. It may well be there are no longer any really effective nematicides, but at least you will save money when you stop making ineffective fungicide applications for a nematode problem. Until new nematicides come along, the best you can do is increase irrigation frequency and foliar feed the turf with its severely damaged root systems.

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Controlling Turfgrass Diseases: Snow mould control

A microdochium patch on a fairway following snow melt. Photo courtesy Nancy Dykema


By Joseph M. Vargas Jr.

Years ago, controlling snow mould was easy and simply involved applying mercury fungicide in the fall. Then, mercury fungicides were banned and controlling snow mould became a little more difficult. There were still quintozine products for control, which made things a bit easier; however, this author did not like to see them used on greens because of their root-pruning properties.

Quintozine was a good fairway product and was inexpensive, but it has now been banned. Fortunately, many researchers felt this restriction was coming and began testing existing products as replacements. What they found was to get adequate snow mould control of the three dominant pathogens—Typhula incarnata, Typhula ishikariensis, and Microdochium nivale—three-way fungicide combinations were needed. Many different combinations were found to work, but the reliable tank mix is generally chlorothalonil and a DMI fungicide, which work well on the Typhula species, and then QoI or iprodione fungicide added to assist with control of Microdochium nivale.

There is a three-way product with a different combination of fungicides (i.e. propiconazole-fludioxonil-chlorothalonil). All three are necessary to control the snow mould complex. Additionally, it only requires one annual application. Resistance develops quickly when repeated applications are made throughout the season against a single fungal pathogen. We are dealing with multiple pathogens requiring different chemistries for control.

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Controlling Turfgrass Diseases: Crown-rot anthracnose

Crown-rot anthracnose (CRA) on a putting green. Photo courtesy Joseph M. Vargas Jr.
By Joseph M. Vargas Jr.

Crown-rot anthracnose, caused by Colletotrichum cereale, remains the most important disease of the past decade on golf course greens. This is because of the demand by golfers for ‘fast greens,’ which is accomplished by lowering the mowing height and reducing the nitrogen fertility. These two factors exacerbate CRA and have helped make it a significant disease on annual bluegrass (i.e. Poa annua) in the past decade.

Controlling CRA is also becoming a problem because of C. cereale becoming resistant to thiophanate-methyl and quinone outside inhibitor (QoI) fungicides. For years, this author has tried to convince golf course superintendents to use one class of fungicides until resistance develops, but this recommendation has mostly been drowned out by many voices urging superintendents not to forget to practice good fungicide resistance management by rotating different chemistries. This idea was supposed to work by one class of chemistry “getting rid of resistant strains that developed to a different class of chemistry,” and it might have worked if the fungus could have only become resistant to one class of chemistry at a time.

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Controlling Turfgrass Diseases: Dollar spot

Dollar spot mycelium on a tee early in the morning while the dew (i.e. guttation water) is still present. Photo courtesy Joseph M. Vargas Jr.


By Joseph M. Vargas Jr.

Dollar spot, caused by Sclerotinia homoeocarpa (this is technically not the correct fungal name, but hopefully the fungus’ true identity will be known soon), is arguably the most important disease on golf courses in Canada. While not spectacular and relatively easy to control, it consumes the largest portion of most fungicide budgets, making it important.

S. homoeocarpa is also becoming resistant to many classes of fungicides, including benzimidazoles (i.e. thiophanate-methyl) and dicarboximides (i.e. iprodione). Further, it has become resistant to Dimethyl-2-imidazolidinone (DMI) chemistry, but fortunately, this is in the form of shortening the control interval. Golf course superintendents used to get 21 to 28 days of control, but once resistance develops to the DMI chemistry, the control interval is reduced to around 14 days, assuming the fungicide is applied before disease development.

Curative applications may only last around seven days once resistance develops. Fortunately, boscalid and chlorothalonil are still available for dollar spot control, although both work best when applied before the disease is present. Dollar spot can also be suppressed by rolling greens at least three times a week, and new research has demonstrated light daily irrigation (i.e. 3 to 4 mL [0.1 oz]) shortly after dark also reduces the amount of dollar spot.

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Controlling Turfgrass Diseases

Photo courtesy Joseph M. Vargas Jr.


By Joseph M. Vargas Jr.

Turfgrass diseases are a major concern on golf courses throughout Canada. The fungicides used to control them are the largest part of chemical and fertility budgets. However, managing them is becoming more difficult as turfgrass pathogens are becoming resistant to many traditional fungicides.

Read the full article: Controlling Turfgrass Diseases