Features Agronomy
Dollar spot, greens moss, drainage are issues brought to forefront at ‘turf academy’ series

By Dr. Joe Vargas

IT was nice to visit with all of you and exchange ideas about growing
turf. Best wishes to all of you in the up coming years. Below is a
summary of the things we saw or discussed.

Dollar spot

The most prevalent disease on most of the golf courses visited was
dollar spot in the fairways. It is so common it is usually not
considered a serious disease. However, when it comes to dollars spent
trying to control this disease, it is probably the most economically
important disease.

One way of reducing the cost of dollar spot applications is to make early season applications. The dollar spot fungus, Rutstroemia floccosum, does not produce any spores. It survives as a stroma which is a tiny mass of mycelium wound tightly around itself.  This stroma is very small in the spring and needs to gain size before it can cause disease. If early fungicide applications are made when the stroma is small, it sets it back and delays the time before it can gain size and become a pathogen again. It is kind of like a preemergence herbicide application.
There are many different models on when to make the application. We like to make our application within two weeks after the second actual mowing of the turf is made. This is different than the first mowing to remove the desiccated tissue from the winter. It is the second mowing when the grass is actually growing. The DMI chemistry like Banner works well and carboximide chemistry like Cadence also works well.

Poa trivialis

There is quite a bit of Poa trivialis in most of the fairways we observed. The Poa trivialis was turning brown with the arrival of the warm weather from a disease called bacterial wilt caused by a bacterium called Xanthomonas campestris. The bacterium, unfortunately, does not completely kill the Poa trivialis but it causes it to go into dormancy. The Poa trivialis appears to have died but it actually goes dormant and will begin to grow again when the cool weather of the late summer and fall returns. 

Because it produces such vigorous stolons each year, it will consume more and more area. Also, the stolons will be spread throughout the fairways by the mowers. Unfortunately, there are no selective controls available for Poa trivialis in creeping bentgrass fairways. It will either have to be plugged out or killed with Roundup and the area reseeded or sodded to creeping bentgrass.

Moss in the greens

Some courses had moss in some of the greens. The best product for the control of moss in the U.S. is carfentrazone. It is best applied in the cool weather of the spring and fall. When it is applied in warm weather, carfentrazone tends to turn the turf yellow. It will take about three applications to completely kill the moss. There is a rate for annual bluegrass and another for creeping bentgrass greens. If the creeping bentgrass rate is used on annual bluegrass, it will injure it and may even kill it.

Since most of the greens we observed have both species in them, the annual bluegrass rate should be used. Carfentrazone is available in Canada, but is not labeled for turf. If it does become labeled for turf in Canada, the annual bluegrass rate of 1.75 ounces per acre of the Canadian product should be used when both species are present on the green. 

Velocity

Many of you have tried Velocity to control annual bluegrass with mixed results. Here is the latest thinking at MSU on controlling annual bluegrass using Velocity. For greens, 16 applications of Velocity should be applied at 12 gms ai per HA at seven-day intervals. For fairways, six to eight applications of Velocity should be applied at 25 gms ai per HA at seven-day intervals. From what I recall, most of you had the correct rates but had not made enough applications. 

Drainage

In a wet summer like that which occurred in Ontario this year, you can see the importance of proper drainage. Fairways are normally drained using French drains over underlying drain tiles.  For French drains to work properly, the pea stone must be brought to the surface. This, of course, causes problems with mowing and often bothers the players. But if you are going to put in a drain tile and cover it with pea stone, it needs to be brought to the surface. If you only bring the pea stone part way to the surface and then cover it with five to 10 centimetres of soil, it will not function properly and you will have wasted your time. Putting five to 10 centimetres of soil over the pea gravel creates a perched water table, and the water will remain in the soil and not go into the pea gravel.

Crown rot anthracnose

There was some crown rot anthracnose on some greens which is not surprising considering all the wet weather you had this season. However, because of the cool weather there was little damage to most of the greens we saw.
 
Crown hydration

It was pointed out to me that both annual bluegrass and creeping bentgrass greens had suffered losses over the winter. I had always believed only annual bluegrass dies from winter injury. It proves you are never too old to learn new things. Normally when crown hydration injury occurs, it is on annual bluegrass greens and fairways. The problem occurs in late winter, when daytime temperatures become warm enough that the annual bluegrass plant begins to take up water (hydrate) and then there is a rapid freeze. Winterkill associated with crown hydration and refreezing is often during the late winter and early spring when there is snow melt or rainfall and then refreezing of the water that has not drained away.

The reason crown hydration is a problem is because during these events, ice crystal formation can occur in the crown of the plant. Ice crystal formation will rupture the plant cells and ultimately cause the plant to die.    
Annual bluegrass is more susceptible to crown hydration injury because it loses it cold-temperature-hardy proteins very quickly in the spring. It emerges from dormancy and begins taking up water earlier than creeping bentgrass. Creeping bentgrass remains in the dormant state longer, and therefore does not take up water and become susceptible to crown hydration injury during the late winter period.

Many golf course superintendents in the Quebec area use covers to prevent crown hydration. They typically place a perforated cover on the green and then place 30 centimetres of straw on top of this cover. Some also use bubble wrap in place of the straw. Then a solid cover is placed on top of the straw or bubble wrap. The perforated cover makes the cleanup easier if straw is used, and the straw or bubble wrap provides insulation so the annual bluegrass does not lose its cold-temperature-hardy proteins, and the solid cover prevents rain from going on to the green and forming ice.  

Ice sheets

Ice sheets on top of the turf can also cause turf to be lost, especially on greens in low areas. This is believed to be due to the depletion of oxygen (anoxia) or the reduction of oxygen (hypoxia) followed by the buildup of toxic gases—principally butanol and ethyl butyrate. This may be what was responsible for the killing of the creeping bentgrass. Other than covers, the only other solution to this problem is to break up the ice as soon as possible.

Collars

The creeping bentgrass collars are susceptible to scalping. They tend to produce a transitional thatch in the summer time as a survival mechanism. Collars are normally mowed less frequently than greens—usually three times a week.

Mowing them every other day causes them to be scalped because the transitional thatch has a chance to grow between mowing, resulting in scalping. Creeping bentgrass collars need to be mowed every day just like creeping bentgrass greens.