Managing Bermudagrass Off-types on Sports Fields
Managing Bermudagrass Off-types on Sports Fields
Mike Goatley, Professor and Turfgrass Extension Specialist, and Jeff Derr, Professor of Weed Science
The following is a series of responses provided by Mike Goatley, PhD and Jeff Derr, PhD to an inquiry from a sports field manager in Norfolk, VA.
QUESTION (Sports Field Manager): "Our 'Tifway-419' soccer field in Norfolk has lighter green spots that become very noticeable in the summer through the fall. Is there anything you might recommend to help obtain a more consistent turf appearance? A soil test was done, and the results indicated that the phosphorus level might be a problem. We have made two applications of humic acid since then to try and help release the phosphorus. However, even after the humic acid applications, we are still noticing the lighter spots on the field. This spotting condition on the turf has been like this for numerous years, but we still haven't found a solution. We have had this field tested in the past for nematodes and the result was negative. Any help regarding this matter would be appreciated."
ANSWER (Dr. Goatley): Patches in bermudagrass fields are quite often due to some "off-type" of bermudagrass that has somehow infested the field and then has accidentally been moved around by standard maintenance practices, such as core-aeration, or possibly a genetic mutation that has occurred within the bermudagrass canopy, wherein those plants now exhibit slightly-different color, leaf texture, etc. (bermudagrass as a species is one that has fairly high-levels of genetic mutations).
You have taken the proper steps in soil testing, conducting nematode assays, and your other attempted treatments to remediate the discoloration; but if this is another form of bermudagrass, the genetics of the grass and its inherent color will overpower just about any chemical or cultural strategy. Neither supplemental applications of phosphorus (or enhanced release of P in the soil) will provide a noticeable color response. One way to temporarily 'mask' really obvious discoloration is by making foliar applications of iron. The circular patch will still be present, but the entire canopy should take on a more uniform and deeper green color. However, this effect is temporary at best as the darkening color response by the leaves is removed over the next 10-14 days due to regular mowing of the turf. Routine, foliar applications of iron must be applied every 2 weeks or so in order to keep the darkening effect in place. Turfgrass colorants can also help mask the color variability, but at significant cost and labor (and their effects are regularly mowed away each time the turf is cut).
ANSWER (Dr. Derr): The field is as Dr. Goatley discussed and evidenced in the photo. There is another bermudagrass variety/off-type bermudagrass, with a lighter green color, that has made it's way into the darker green variety. It is not common bermudagrass in these lighter green patches as the texture is similar between the lighter-green and darker-green areas. If the lighter-green type "greens up" sooner in spring, it could be more competitive than the darker-green cultivar, thus persisting/spreading in the area. We have spots like this in our bermudagrass area at the research station, where mowers, etc. probably moved some stems of the grasses around.
FOLLOW-UP QUESTION (Sports Field Manager): "Is it possible that this different variety of bermudagrass could have been in the initial sod that was laid at this site approximately 16 years ago and has continued to spread through the years? Other than re-sodding the field, do we have any other options which might make these spots less noticeable for an extended period of time?"
ANSWER (Dr. Derr): Dr. Goatley mentioned that foliar-iron applications might be used as a temporary masking treatment. Otherwise, you would be looking at killing out those sections of undesirable-colored grass with glyphosate and plugging in bermuda after the lighter-colored bermuda is controlled. It is possible there was some off-type bermuda in the sod initially, or the off-type could have moved in from other areas. It is very hard (if not impossible) to specifically identify the source of the contaminant.
ANSWER (Dr. Goatley): Dr. Derr’s answer matches mine. It is pretty much impossible to say how the off-types got there after this many years in the field. Remember, bermudagrass is a very genetically-unstable grass to begin with (highly mutable). Dr. Jim Beard (the author of the textbook generally considered to be the ‘Turfgrass Bible’, Turfgrass: Science and Culture) made a statement at a conference I attended many years ago that "... if a turfgrass manager can get 10 years of uniformity out of a vegetative bermudagrass stand without having off-types develop, they are very lucky!"
Spraying out those areas and plugging (or cutting them out and replacing with sod) are the only effective ways to eliminate most (not all) of the off-type (but remember that there still can be seed or stems in the soil). For the sod approach, you really would need a 'nursery' of your desired grass. If you have an area, well off the playing surface, with the desired variety, you might consider making this into a nursery for your replacement grass. There are two strategies for managing the nursery to ensure it is a perennial ‘crop’ for you: 1.) harvest a shallow cut sod, and this will leave plenty of stems for regrowth, OR 2.) you can leave some small strips of grass and periodically topdress to smooth as the bermuda grows back over.
Planting more Tifway 419 to fill in those spots is also a possibility, but it is highly doubtful that the new grass will precisely match the existing turf. I wish that we had easier answers for you, but remember that THE MOST IMPORTANT THING is the playability of the field. If it still plays great, focus on that as a strength, and educate your field users that playability and safety are the issues that matter most!