Summer stress of Poa annua, Poa trivialis on Golf Courses – Turfgrass Science at Purdue University

Summer stress of Poa annua, Poa trivialis on Golf Courses

Persistent air tempertatures of 90F and soil temperatures greater than 80F combine with high humidity and adequate rainfall (in some areas) is doing in the Poa annua (annual bluegrass)and Poa trivialis (rough bluegrass)on golf courses. After a week or two of these conditions, Poa annua greens and fairways will start to thin and die in small patches. Patches of Poa trivialis in fairways will also start to brown, probably get infected with dollar spot and eventually go dormant. Poa annua is primarily an annual species whereas Poa trivialis is a perennial but with extremely poor heat tolerance. Many golf course superintendents can prolong Poa survival through the heat by careful management, but unfortunately the death of these two grasses is almost inevitable. As with all cool season turfgrass plants, they perform best when temperatures are near 70F. If hot weather continues for an extended period, the weakened plants will be extremely susceptible to damage from pressures such as heat, drought, traffic, disease, and insects. 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 a slight drought stress, a weekend day when the grass didn’t receive irrigation, a dusting of topdressing, etc. may be just enough to put the Poa over the edge. To help these survive the longest, minimize the stress on it now (even though it may be too late in many situations). Raising the mowing heights slightly (combine with rolling to maintain speed), 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 minimizing 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 and many are quick to blame a disease as the primary factor in the decline of these grasses, especially Poa annua. However, though fungicides may help to extend the life of these grasses during the heat of July and August, these grasses will probably still weaken and die with extended heat regardless of the fungicide program. On the large majority of Poa annua samples that we receive at Purdue, there are few or no disease organisms present even though the plants appear weakened or dying. This is because many of the commercially available fungicides will control the organisms, but they still cannot keep the plant alive beyond its normal life cycle.

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