We had an uncharacteristically hot and dry summer here in Ontario and although disease activity as a whole was not high, many superintendents lost a great deal of Poa annua on their greens this season.  Much of the annual bluegrass started to suffer in mid to late July and by August a number of courses had numerous areas that failed.  When samples came into our diagnostic clinic, more often than not, there were no visible signs of pathogens.  However, each sample had similar characteristics: extremely short to non-existent root systems and a significant thatch or mat layer in the upper rootzone.

Annual bluegrass decline on a golf green. Photo courtesy Tim Steen

This year was especially difficult as we had a cool, wet spring followed by a very long, hot, dry summer. That led to Poa annua that was unable to recover from winter damage, did not have the opportunity to form deep roots and was stressed for an extended period of time.  After June and July, the annual ecotypes had used all the reserves they had and just started to give out.  In addition, diseases like anthracnose were rather prevalent with the temperatures and stress, making it more difficult for Poa to survive.  To make matters worse, the water quality on a number of golf courses in Ontario is quite poor, with high salt and often sodium levels.  A summer like the one we had leads to more frequent irrigation events and the addition of poor quality water to the soil only adds to the stress. Even cool-season turf that is ideally managed can die off after a season such as this past one simply because it has given all it has to give.  Remember, after all, that annual bluegrass is just that – a grass with annual characteristics.  It has not evolved to survive in the vegetative state season after season and although there are a number of different ecotypes with varying characteristics throughout a golf course or even on the same green, in general, most annual bluegrass turf will put its energy into seeding and then wait to come back in the next season.

The key to getting through a season like this one we just had is to start out with a healthy stand of turf. Thanks to the wet spring and then the heat wave, most Poa annua plants didn’t really get the chance to develop sufficient roots heading into the playing season.  After weeks and weeks of heat and drought, a lot of annual bluegrass in the region died off quickly.  We are finally at the end of our summer season and just as quickly as the heat came in, it seems to have left Ontario.  Much of the damaged turf that we saw through July and August has recovered but some supers are still trying to get back on track.  The cooler weather combined with the periodic rainfall is allowing managers to back off of irrigation which will hopefully lead to deeper root formation heading into the winter.  Anything that can be done to encourage deeper root growth at this stage is highly recommended.  Both thatch layers and compacted soils can hinder deep root formation, so deep vertical mowing and/or core aerification are two ways to reduce those potential issues.  Increasing your nitrogen will also speed up recovery while staving off diseases such as dollar spot and basal rot anthracnose.  If you have the ability to increase mowing heights as play decreases, this will also encourage more growth and subsequently more root development.  The healthier your plants are going into the winter, the better they should come out in the spring.  Then we just need to hope for a more “normal” season to encourage healthy turf going into next summer.