When it comes to cool-season putting greens, there is often a focus on promoting creeping bentgrass and suppressing Poa annua. The dominance of poa annua in greens that were originally seeded with bentgrass is nothing new and happens frequently, especially in historical Clubs where the original seeding occurred many years ago. Thanks to its capacity to produce an extraordinary number of seeds, and its capacity to adapt to very diverse climate conditions, the poa annua is able to invade, establish and become dominant on greens even with good bentgrass density. In general, poa annua can provide with great playing conditions, even for tournament standards.
Factors that make poa annua the wrong option
However, there are 3 main factors that make poa annua the wrong option, especially in certain latitudes:
- The irregular growth rate during the year due to a complex growing cycle. This includes the emergence of seedheads.
- Susceptibility to diseases and particularly to dollar spot, waitea and rhizoctonia.
- Sensitive to high temperatures, suffering with temperatures over 27ºC, when photorespiration occurs and goes through a serious decline.
In order to revert this situation, and taking into account restrictions with chemical control, an obvious option is Interseeding. The main difference between this and overseeding (where the seed is applied over the existing sward), is that the seed is sown into “grooves” in an established grass sward, leaving the seeds in contact with the soil. In this case, La Peñaza, acquired a specific seeder for this purpose (Vredo), that can seed very small seeds (such as bentgrass) at low doses (5,5 g/m2). Prior to Interseeding, growth regulators were applied, and a double verticut and a lowering of the mowing height performed (3mm), to weaken the poa annua. Also, irrigation did not take place the night before to work with dry conditions.
In this case, it was important to not Interseed outside the green, and to not contaminate other areas where bentgrass is not present. Once all this process is completed, greens were rolled to improve seed-soil contact, and topdressed to fill the “grooves” that were produced when verticutting and Interseeding. Finally, an irrigation event was applied to moisturize the surface.
Germination and seedling establishment
Regarding the germination and the establishment of the new seed, it is essential to perform daily irrigation to keep the surface moist during the day. Also, to increase the mowing height to 3.5-4mm, as well as, to make sure that the mower cage do not pick sand. In addition to these, it is very important to supress verticuts and hollow-tining, and carry out weekly light top-dressing to avoid the accumulation of organic matter. Last, but not least, it is vital to carry out a preventive fungicide treatment against Pythium.
The results will not be evident during the first year, but if the plan is carefully followed, after the second Interseeding process, bentgrass will become dominant over the poa annua, and other parallel means of control can be implemented. There is only one more factor to consider: the patience of the members during the process. The results are well worth and overcome the effort taken.