Poa
Annua ControlBy Mike Plummer
My article is on the ever familiar and often written about subject of Poa annua control on bentgrass putting greens. Hopefully, my article has somewhat of a new twist to it. Actually, I’m not writing about controlling it, but rather the subject of preventing the weed from becoming a serious infestation on bentgrass putting greens. I receive a newsletter titled Turfcomms put out by Douglas T. Hawes, Ph.D. that has a purpose statement that I hope I’m following. His purpose is “to pass on what we learn willingly and happily to others in the profession so as to improve turf conditions around the country.” I don’t think that I can help improve turf conditions around the country, but maybe I can pass on a couple of ideas that might help fellow superintendents in North Texas.
I have had the opportunity to be at Lakewood Country Club for over ten years now. During this time, I have had the experience of managing some bentgrass greens that were heavily infested with Poa annua or annual bluegrass (I think we had some perennial types, also). Thanks to our clubs leaders and members, I am now managing “bentgrass only” greens due to our greens being rebuilt. Just for the record, our greens were not rebuilt just due to annual bluegrass infestation even though that was a huge factor. Our greens were rebuilt in phases over several years dating from 1989 through 1995. During this time of rebuilding, I had the experience or challenge of keeping annual bluegrass out of our new greens while still maintaining our old greens which were infested, Well, now I actually feel even more challenged than I did several years ago to keep out annual bluegrass since we are still free of it!
Not to be a pessimist, but the rest of this article which contains some practices or ideas to prevent the weed from becoming a serious infestation, is not really going to help if you already have a serious infestation on all greens at your course. I know that I have not tried all the control products that are available, but I think about all that can be hoped for is to hold the annual bluegrass in check. My experience was that we held the weed in check by suppressing or eliminating the unsightly seedhead formation. So, to move on with the subject of keeping annual bluegrass out of bentgrass greens, here is my list of ten ideas, practices, or thoughts that I would like to pass on:
- 1) We use Bensulide for our pre-emerge weed control on our putting
greens. If you have new greens that are free of annual bluegrass, then
now is the time to start the program. Don’t wait until you have the problem.
I promise, I’m not promoting any company, but I think this is the best
program. I have used many different formulations of Bensulide and I don’t
really have a preference. I do think that it is best to make applications
in September, again in December, and once again in February or March for
any late season germination. I just advise you to follow label directions
and not exceed the maximum rate applied per given area per year. Remember
that the bentgrass doesn’t understand our calender year, so please realize
that my recommended three applications come in about a six month period.
What this means, if I understand the label correctly, is that you are going
to need to give up that application for goosegrass control.
2) Try to remain free of annual bluegrass in any adjacent cool season turfgrass area. For example, we have several areas of tall fescue located between the cart path and putting green that most players walk through, and I consider these critical areas. If it is infested with annual bluegrass, I think that seed is easily tracked onto the green, We always try re-seeding into these existing fescue areas in early fall at high seeding rates to produce such a dense stand that annual bluegrass can’t compete. Most seeding guidelines that I have seen recommended two to five pounds per one-thousand square feet for seeding into existing stands and seven to ten pounds per one thousand square feet for new areas. I like to treat our existing stands similar to new areas that are being seeded for the first time. I think this method of seeding at high rates is also applicable in overseeding fairways and approaches.
3) We try to schedule our fall pre-emergent herbicide application for the bermudagrass areas that are not being overseeded, as early as possible. I like to set our target date between the middle of August to first of September. Hopefully you don’t have to overseed your green surrounds and can make this important application
4) Maintain good quality control when making your fall pre-emergent application, The green surrounds are the most important area on the golf course to try to keep clean due to the close distance to the putting greens. Our product of choice is usually a granular or combination material. Like most courses we normally use a tractor driven spreader for the fairways and roughs. However, to maintain good quality control on green surrounds, we use walk-behind spreaders with flagmen to mark the spread or swath width. By using flagmen to mark the spread of the material on green surrounds, it’s also easier then to match up with the tractor driven spreader.
5) We plug out any visible annual bluegrass on our greens and replace them with plugs from our nursery to try and reduce any seeds from being spread for a new crop. It seems like we normally do this in March, April, and May when it is easy to see due to the unsightly seedheads. I think that this has to be done every spring or the condition will be worse by next spring.
6) Even with fall pre-emergent applications being made on the course, we always have to do some post-emergent herbicide work on dormant bermudagrass in the winter. I still prefer the use of Roundup herbicide on dormant bermudagrass to clean up annual bluegrass and many other weeds. During a mild winter when bermudagrass doesn’t go dormant and it appears that Roundup might not be a wise choice due to turf safety, we still try to clean up our bermudagrass. I think there are other herbicide choices such as Reward and Princep.
7) As I mentioned in one of my above ideas about staying free of annual bluegrass in cool season turfgrass areas that are adjacent to putting greens, I realized that sometimes it’s better to try something else. There have been some areas of tall fescue that had about as much annual bluegrass as fescue that we have converted to zoysiagrass. We are trying this due to the thinking that the zoysiagrass goes somewhat dormant in the winter and we can do our post-emergent herbicide work to clean up the winter weeds.
8) We try to keep our putting greens on the dry side especially during fall, winter, and spring, I think we all know that it is best to water deep and infrequent. If greens are watered light and frequent, which is very similar to getting seed to germinate on new greens, then we are probably providing perfect conditions to germinate annual bluegrass.
9) If the bermudagrass has broken dormancy, and it’s unsafe for any herbicide control of annual bluegrass due to possible injury to the bermudagrass, we go ahead and pull it. Around the putting greens it is so important, that I would use all available labor to hand pull annual bluegrass on collars and green surrounds to keep it clean.
10) Several years ago when we had some greens that were infested with annual bluegrass and some greens that had been rebuilt and were clean, we performed all cultural practices to the clean ones first. I really think this helped reduced the spread of annual bluegrass seed onto the clean greens. For whatever reason, if you have to track equipment over an infested green and then over a clean green, I would recommend washing the piece of equipment prior to tracking it across the clean green. One way to make this practice easier is to install ten inch round valve boxes over quick coupling valves with a short piece of hose rolled up inside. If these are at several locations on the course it makes it much easier to wash off the contaminated piece of equipment prior to tracking it across the clean green.