Tuesday, 22 September 2020

How to find success with overseeding new bentgrass varieties.


I think it's important to always continue to evaluate what you think you know in golf maintenance. I'm about to take a pretty hard turn with this blog post. It's because the new bentgrass varieties that we now have are completely different than those old varieties. With these drastic improvements come new ways that we can incorporate them into our courses to begin to enjoy the benefits that improved varieties offer golf course playing surfaces and your budget.

Bentgrass needs full sun. Bull shit. Some of the best establishment of bentgrass I have seen has been on my shady greens probably because the seedlings didn't dry out due to the shady conditions. Even under moderate to extreme shade it did just fine.

Bentgrass doesn't like disruption. Not from what I've seen. Don't get me wrong, I totally love the disturbance theory but in order for the bentgrass seedlings to have a hope in hell of making it to a mature plant you need to make space. Ideally you make that space but other times it's due to poa checking out from disease, too hot or too cold, weakening after going to seed or whatever else bullshit reason the poa decided to die this time. Good turf managers can kill poa in all 4 seasons.

Bentgrass is slow to wake up in the spring. Wrong. The only grass that I mow in the spring is bentgrass. The poa is sunken and feeling the hurt from almost no winter fertilization.

You can't overseed bentgrass into poa....wrong. I have never sodded any bentgrass and have greens that are now mostly bentgrass. I guess I'm doing it wrong?

How to successfully seed bentgrass into poa annua.

Don't limit water. Immature bentgrass plants don't have deep roots so don't let them dry out or throw seed when you can keep it wet. You'll need to wait for the bentgrass to mature before you can dial back the water.

Use fertilizer to put the hurt on poa. After years of working to optimize my fertilizer applications to provide just the right amount I have found that poa really doesn't like it when you back off fertilizer rates. Not just nitrogen, but everything. It loves fertilizer and maybe the main reason that poa is so widespread on golf courses is that we generally have been applying more fertilizer than is required because understanding how much is enough is really really hard to do. Use a standard fertilizer amount of 2 g nitrogen/m^2 to start. This will keep the poa alive but not as competitive as the bentgrass. If you go lower, the bentgrass will lose its competitive edge and moss will take over! Even bentgrass needs some fertilizer but it needs much much less than poa so this difference in needs can help you promote bentgrass over poa annua especially at the start.

When weather favors poa over bentgrass your only tool is soil fertility. If you have some cool wet weather, keep the fertilizer in the shed and watch the poa struggle. When conditions favor bentgrass, push that growth!

Maximize disruption when throwing down seed. BIG holes, and lots of them. When we seeded bentgrass last fall I poked millions of small, tightly spaced holes and put seed and sand into them. While we had a good germination in these holes, the plants the matured in many instances were in the deep tine holes that were much larger in diameter and spaced further apart. Give the plant room to mature, then let it do what it was designed to do. Spread out into the poa that is weak due to low fertilizer rates.

Bentgrass spreading to fill in the void (left) vs poa on the right. Bentgrass easily dominates these cup cutter sized holes.

Poa died in this dry fairway opening up space for bentgrass seedlings

It's hard to see in a picture but the 2cm diameter bentgrass plants are in old deep tine holes.

Be patient.
If you want instant results then buy some sod. Otherwise you need to be patient and throw seed at every opportunity. I've talked about overseeding and microdose applications already on this blog so go read those posts if you are thinking about overseeding . Generally it will take up to 2 seasons before you hard work starts to pay off. Don't let up, keep throwing that seed!

Let the improved plant do the dirty work. With pest control products that use systemic resistance etc you can give the bentgrass even more of an edge over the poa. As the newer bentgrass varieties have more disease resistance than unimproved poa annua you can boost is further with ISR products further giving the bentgrass the advantage. Of course, disease can quickly wipe out your poa especially with diseases like anthracnose but a small advantage over years can and will result in more bentgrass.

Once you get a good amount of plants to mature, get out of it's way. Let it do what it was designed to do. Dry it down every now and then, stretch those fungicide intervals, forget to fertilize them for a few months etc.

3 years after seeding into winter damage this green is now mostly bentgrass. With this much bentgrass coverage you can start to afford to seriously neglect the poa

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