Dr. D talks the ups and downs of Poa annua

If there is a proverbial “shot across the bow” in the life of a golf course superintendent, it’s the arrival of annual bluegrass (Poa annua) in the spring. Poa is quick to initiate, not only does it start top growth sooner in the spring than creeping bentgrass, but it allocates up to 35 percent of the plant’s top growth for seed production.

Karl Danneberger, Ph.D

The appearance and number of Poa inflorescences soon after growth initiates is profuse. Approximately 88,000 to 265,000 tillers per sq. yd. each year.

The flowering that occurs from spring through early summer is especially disruptive on golf course greens. The inflorescences impact the uniformity and smoothness of the putting surface. Putts struck across a seeding Poa green are often bouncing and diverted offline.

The number of seeds produced from Poa flowering is consequential. It’s estimated that the amount of seed produced ranges from 177,000 to 767,000 seeds per sq. yd. per year. Poa seeds have characteristics similar to annual weeds that give them an advantage over cool-season turfgrass seeds like creeping bentgrass.

Poa seeds can lay dormant in the soil until a series of complex biochemical processes occur that allow for the seed to germinate. In other words, Poa seed is not only found at elevated numbers in the soil but remains dormant until conditions are desirable to germinate.

Know your Poa

A gradation of Poa types are found on a golf course. Under more stressful or extreme conditions, where moisture can fluctuate greatly — namely a golf course rough — a true annual type of Poa is common. On putting greens, where conditions like moisture are more moderated from irrigation practices, and mowing heights are lower a more perennial Poa will be dominant.

Based on research at Penn State University, when annual Poa types are subjected to continual low mowing heights the plants take on perennial-type characteristics. Researchers speculated the reason for this was that close mowing heights induce an epigenetic effect on gene regulation.

Simply stated the DNA functionality may be affected by mowing resulting in a perennial biotype, but the underlying DNA is not altered. Thus, if you were to remove mowing, the Poa would eventually revert to an annual type.

Friend or foe?

Since the hickory age of golf, management strategies have focused on controlling Poa. Taking just the adaptability of Poa to golf course conditions, and its reproductive potential described above makes for a formidable foe.

If I named every product or practice for controlling Poa, you would think it was an endangered species. In the quest for eradication, we occasionally forget Poa’s desirable golfing characteristics. It has an upright growth habit that, combined with its ability to tolerate low mowing heights, results in excellent putting green and fairway playing surfaces when managed properly.

Recently, I haven’t come across many articles or conference talks on the desirability of Poa as a golf course turf or how to manage it. Maybe it is due to the natural cycling of agronomic topics and its popularity will return. Positive reinforcement on managing Poa will enhance its desirability in those who maintain it.

Managing Poa or conversely controlling it requires knowing why it’s there in the first place. If you can’t change or modify the cause(s) for Poa being there in the first place, eradication is often short-lived. If Poa dies, what fills in? More Poa.