Decline of Poa annua on Golf Courses

Last updated 8/8/03

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8/8/03

Decline of Poa annua on Golf Courses

In spite of the relatively moderate summer, the annual decline of Poa annua (annual bluegrass) on golf courses is occurring now. We received samples from 5 golf courses of declining Poa annua in the lab in the last three days. Individual plants of Poa annua on greens and fairways are starting to yellow and even die in small patches. However, there have been almost no pathogens in the submitted samples other than occasional ectotrophic hyphae indicating summer patch. The areas sampled had been treated aggressively with fungicides so it’s not surprising that there were no disease organisms present. This does show that even though we can control pathogens, the Poa annua may still weaken and die.

Many golf course superintendents can prolong Poa survival through the heat by careful management, but unfortunately death is almost inevitable. As with all cool season turfgrass plants, Poa annua performs best when temperatures are near 65-70^oF. If temperatures above this persist for an extended period, the weakened plants will be extremely susceptible to damage from pressures such as heat, drought, traffic, disease, and submersion under water. Often a single event may be enough to put the Poa over the edge. A pass from a golf cart when the grass is under slight drought stress, a weekend day when the grass didn’t receive enough irrigation, a dusting of topdressing, etc. may be just enough to put the Poa over the edge. To help Poa survive the longest, minimize the stress on it now. Raising the mowing heights slightly, skipping maybe every fourth day of mowing, using smooth rollers instead of grooved rollers on the mowers, and walk mowing will help reduce stress on greens. Improve the oxygen levels in the soil by keeping the soil on the dry side and solid tine aerification, water injection aerification, and/or spiking. Consider syringing regularly during the afternoon to minimize heat stress. Avoid fertilization at rates greater than 0.25 lbs N/1000 ft² (quick release N) in a single application. Many pathogens will infect these species once they are weakened. Most of us would like to blame a disease like anthracnose as the primary factor in the decline of Poa annua, but this is the exception rather than the rule. Though fungicides may help to extend the life of Poa annua during July and August, it will still weaken and die with extended heat regardless of the fungicide program. Therefore, continue a preventative fungicide program on a 10-14 day schedule that includes systemic fungicides alternated with contacts, but aggressive applications every 7 days or less likely won’t help significantly.

Zac Reicher, Associate Professor/Turfgrass Extension Specialist