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Turfgrass Science

Renovating Bermudagrass Following Winterkill

Gregg Munshaw and David Williams

University of Kentucky

Reports have surfaced from all over Kentucky about winter-damaged bermudagrass. Low lying and wet areas, north facing slopes, and high traffic areas have resulted in the greatest loss of bermudagrass, but it has certainly been found in almost all situations. Regardless of how the bermudagrass was lost, the important factor now is how to fix the problem.

Thin bermudagrass will recover if 1 live plant per square can be found. Fertilizer and cultivation will likely speed recovery.

The first consideration is to determine how wide spread was bermudagrass winterkill on your property? If only sporadic patches were killed, it may be best to work with what you have and fertilize to promote recovery. Small areas may also be plugged or sodded from out-of-the-way areas or nurseries. Dr. Mike Goatley at Virginia Tech wrote a very informative article titled “How much bermudagrass is enough bermudagrass for adequate spring recovery”. You can find it here. Briefly, Dr. Goatley explains that if you have at least 1 live plant per square foot, you should be able to regrow your entire stand. This is especially true of aggressive cultivars.

A bermudagrass soccer pitch in Bowling Green exhibiting excessive winterkill. Photo by Tony Whitmer.

For sports fields that may not need to be fully grassed until mid-August, regrowing surviving bermudagrass is certainly an option. Bermudagrass responds very well to nitrogen fertilization and will spread more quickly with higher levels of nitrogen. The UK and WKU turf programs performed bermudagrass grow-in studies in 2013 and found when planted on July 15, vegetative and seeded cultivars can reach full cover by late-August with adequate nitrogen. Rates of 1, 2, and 4 lbs of N/1000 ft2/month were applied and the higher rates resulted in quicker establishment than the low rate. Interestingly though, the highest rate of summer nitrogen resulted in the greatest amount of winterkill this spring.

Bermudagrass winter survival following various summer nitrogen regimes. From left to right: 4 lbs N/1000 sq ft/month; 2 lbs N/1000 sq ft/month; 1 lb N/1000 sq ft/month. Final nitrogen application was made Sept. 1, 2013.

For areas such as golf fairways, 1 plant per square foot is likely going to be a concern for golfers and owners. In this type of situation, it may be best to sprig or seed to ensure timely recovery of large areas. You will always have the greatest success creating a seedbed prior to planting rather than seeding or sprigging into un-worked earth. If some sort of tillage is not practical, aggressive vertical mowing or running a verti-seeder in several directions is better than not doing anything. For a detailed account of renovating with vegetative cultivars, click here. For a detailed description of seeding bermudagrass click here.  A current list of recommended bermudagrass varieties can be found here. If possible, it is best to plant cold tolerant varieties that will be less likely to winterkill in coming years. Cold tolerant vegetative varieties include Latitude 36, Midiron/Midlawn, Northbridge, Patriot, and Quickstand. Cold tolerant seeded varieties include Riviera and Yukon.

Seeded and vegetative varieties will be in great demand across the transition zone this spring so you may have to do a little legwork to find the variety you are looking for. Several sod producers that serve Kentucky have also lost bermudagrass this winter so may have trouble meeting the demand for their grasses.

If a pre-emergent herbicide was applied this spring, activated charcoal will help to deactivate the herbicide to increase your chances of success with seeding. Sprigging can be successful without applying charcoal into areas that were treated with Ronstar this spring, but not with any other pre-emergent herbicide. Ronstar has the same effect on bermudagrass seed as it does on summer annual weeds. If seeding areas that have been treated with Ronstar, then applying charcoal first would be necessary. Regardless of vegetative or seeded planting, you will likely need to control weeds. Golf courses still have the option for spot treating summer annual grassy weeds with MSMA, but this is not an option for sports turf. Quinclorac and carfentrazone have shown to be safe on seedling bermudagrass and will provide adequate control of immature crabgrass and broadleaf weeds, respectively.

It is important to educate your superiors on the causes of winterkill and the fact that it is widespread across Kentucky and beyond. It is also important to educate them on the fact that recovery will not be completed over night. Depending on the severity of bermudagrass winterkill at your location, it may be as much as two months before the stand approaches 100% recovery.