Features Agronomy
Hot, humid summer of 2010 made turf maintenance difficult

Prepared by J. M. Vargas Jr.
Professor, Michigan State University

There has not been a hot, humid summer like the summer of 2010 in
Canada for a long time. It has caused many problems not normally seen
in Canada. The combined hot, humid weather makes it difficult to
maintain healthy turf.

 What have been especially bad are the high nighttime temperatures. When the nighttime temperatures stay above 20 degrees Celsius, the plants continue to respire at a high rate, burning up stored carbohydrates. During the daytime, when the temperatures go above 30 degrees, photorespiration exceeds photosynthesis, meaning there is a net loss of carbohydrates. So basically the plants are photosynthesizing for a few hours every morning, producing the products they need to survive and the rest of the day and night burning up the carbohydrates through respiration. In spite of all this, the courses we visited were able to maintain fairly healthy turf. 

Brown patch, dollar spot and pythium blight

On our tours, we were able to see brown patch and pythium blight. The brown patch was more prevalent in creeping bentgrass in the roughs, and pythium blight was more prevalent in the poa annua in the fairways. This is the most brown patch I have seen in a long time. Although dollar spot normally occurs in most years, it was especially bad in both fairways and rough due to the heat and humidity.

The small patches of pythium blight are typical of the way the disease occurs on golf course fairways, not the overnight killing entire fairways that folklore suggests happens. The overnight killing of fairways was due to calcium arsenate applications that were made to try and eliminate the poa annua. The calcium arsenate was supposed to slowly kill the poa annua, allowing the creeping bentgrass to take over. But what happened in hot summers like this one, the calcium arsenates quickly killed the poa annua, and the few patches of pythium blight that occurred were blamed for the problem. 

The reason the poa annua, and even the creeping bentgrass, died was because the calcium arsenate limited the roots to the thatch where they were susceptible to wilting. The calcium arsenate that accumulated in the soil was toxic to the roots. It was also toxic to the young creeping bentgrass seedlings so they never became established.  Knowing that large areas of your turf will not die overnight allows you to treat for pythium blight on a curative basis rather than on a preventative basis in hot, humid summers like this.

Localized dry spot and fairy rings

Localized dry spots were present in some greens and fairways. There were also some fairy rings in the greens and fairways. The same fungi that cause fairy rings are also responsible for localized dry spots. The localized dry spots and fairy rings in the greens need to be eliminated or at least prevented from killing the turf in the greens. 

Fairy rings are common when turf is growing in high sand-content soils. They thrive in high sand-content soils because there is very little competition from bacteria. They produce organic acids as they grow which eventually lead to localized dry spots or rings. These organic acids have structure when the soil temperatures are cool, but as the soil temperatures warm up these organic acids lose their structure and become hydrophobic which results in localized dry spots. The fairy rings, in addition, produce compounds that cause the turf to grow faster and turn dark green in colour. 

There are two approaches to managing fairy rings—one is to kill them with a fungicide. Two of the best fungicides are Heritage and Endorse. They need to be drenched into the top two centimetres of soil which is where the mycelium of the fairy ring fungus is located. It usually takes two to three years of fungicide applications to completely eliminate them from an area. 

The other approach is to leave them alone because even though they are unsightly, they do little harm to the turf as long as the area they are growing in does not become hydrophobic from the organic acids they are producing. If this approach is taken, a wetting agent should be applied to insure the soil around the fairy ring does not become hydrophobic. The wetting agent will also eliminate the localized dry spots. 

Moss

Moss was a problem on some of the courses we visited. We were able to see how the rhizoids of the moss plant were able to eliminate the soil to make room for their rhizoids. In my studies, the best treatment has been Quick Silver. I realize this product is not registered for use on turf in Canada, but, hopefully, it will be registered some day. When it is registered, it will take monthly applications to control the moss. It can cause some yellowing of the turf when applied during warm weather.

The secret to success in removing moss is repeated applications of whatever product you use. This is because moss has no true roots, only rhizoids, so products to control moss cannot be transported to the rhizoids since there is no xylem or phloem. Therefore it takes repeated applications to kill the rhizoids. My experience with moss is that even though you think you have killed it all, some of it returns the following season. It usually takes three to four years to completely remove it from a green.

Snow mold control

Although we did not talk about snow mold control a lot, this year will be the last year that quintozene can be used for snow mold control in Canada. In my studies in northern Michigan, three-way fungicide combinations worked the best with a similar climate to the Toronto area of Canada where snow covers the ground for more than three months. This is probably because there are at least three different species of fungi that cause snow mold under these conditions—typhula blight caused by typhula incarnata, and typhula ishikariensis and microdochium patch, caused by microdochium nivale. In order to control all the species, different fungicides are needed. This would be a good year to try some three-way fungicide combinations like Instrata on significant acreage so you can see how the fungicides you are going to have to use in the future are going to work in your situation.

Bacterial wilt

We saw many greens that had bacterial wilt in both the poa annua and the creeping bentgrass. The bacterium that is attacking poa annua is called xanthomonas translucence, and the bacterium that attacks creeping bentgrass is called acidovorax avenae. 
It was only attacking certain biotypes of poa annua and creeping bentgrass as evidenced by the fact that disease was occurring in patches. The bacterium plugs up the xylem vessels of the turfgrass plant, making it difficult for the plant to transfer water from the roots up to the foliage. Plants cool themselves on warm days by a process called transpiration where water vapors escape through the stomates and, as it evaporates, the plant is cooled. If the xylem vessels are plugged up with bacteria, the plant cannot properly cool itself which may result in high internal temperatures in the plant.

Unfortunately there is no registered chemical control for bacterial wilt. The best you can do is to not let the infected plants go under stress, particularly drought stress. It will require syringing to foliar feed the infected plants’ water and to cool them off during the day.