The Science of Overseeding Bermudagrass with Perennial Ryegrass
One of the highest performing grass species is bermudagrass. With over 50 actively grown varieties around the world, bermudagrass is a favorite in hot, sunny locations from home lawns, fairways, even golf greens. All varieties of Bermudagrass can excel in the sun and heat where other grass types fail. The number of months it stays actively growing is determined by where in the country it is planted. Bermudagrass has a wide growth range that extends from the deep south to the top of the Transition Zone.
In Southern states, the DOT (Department of Transportation) plants bermudagrass along roadsides since it is a low maintenance turf that does extremely well, even in hot, dry locations. Mowing is performed as the only maintenance. However, on the high end of the spectrum, high maintenance sports turf with improved or hybrid varieties have been used due to their beauty and ability to endure heavy traffic.
Like most warm-season grasses, as winter approaches and soil temperatures drop, bermudagrass goes dormant. In the northern reaches of its range, the active growing time may be no more than half the year. The tan-colored dormant grass will remain unchanged until spring when the weather and soil temperatures warm again. The problem is that dormant bermudagrass does not provide a quality playing surface for golf or on sports fields. To fix the problem, some sports turf managers will begin overseeding the dormant grass with Ryegrass.
Of all the species of warm-season grass, only bermudagrass can survive unharmed when overseeded in the fall. Overseeded bermudagrass allows for a better appearance and play on golf courses and better turf quality for team sports than playing on dormant bermudagrass alone. Bermudagrass is the primary grass here and it is the one that a turf manager is primarily concerned about. The overseeded grass, while well cared for, is always temporary but needed.
Seed of Choice for Overseeding
The grass of choice for overseeding was Annual Ryegrass in years past. However, the current choice is Perennial Ryegrass. Dormant bermudagrass can easily revive after a winter of fertilization, irrigation, and other maintenance requirements needed to maintain the ryegrass. The same winter treatment can weaken or injure centipede, zoysia, or other warm-weather species. It has become a common practice for many golf courses and even some homeowners to overseed the bermudagrass in the fall with perennial ryegrass or annual ryegrass to provide a green color in winter.
Why Perennial Ryegrass is Preferred
You may wonder why Perennial Ryegrass is preferred, especially since it is a perennial and not an annual. Perennial Ryegrass is used as a stand-alone year-round grass but is mostly restricted to the transition zone. It can't handle the high heat of the southern summers or the extreme winter cold of the most northern states. It is used in the south as a winter grass.
To be fair, in years past, annual ryegrass was used on sports fields and golf courses, but the problem was annual ryegrass (i.e. Italian ryegrass) was not as developed as a turfgrass. It didn't possess the qualities needed to make a fine home turf or sports turf. Sports managers moved to Perennial Ryegrass due to its better turfgrass qualities. Managers had to factor in the grass being a perennial and how it would increase the time and effort in maintaining and removing it. The payoff was how Perennial Ryegrass was undeniably better in every way. Compared to Annual Ryegrass, Perennial Ryegrass is a much darker green and is less coarse than Annual Ryegrass. Plus it can endure traffic better, grows quicker, and will last longer into the spring. Annual Ryegrass often begins to die back before the manager desires it to, leaving behind a less than desirable lawn full of clumps of pale and dying grass and a lower quality playing surface. While Perennial Ryegrass is not an annual grass, in this case, it is being managed as an annual.
In many areas of the country, Annual Ryegrass is still what is planted, especially by non-professionals. It doesn't require the knowledge of turf management compared to Perennial Ryegrass. In southeast Texas, I did a search of all the farm and landscape stores in a 20-mile radius and most of them had Annual Ryegrass. In fact, I found it was the only cool-season grass any store sold. While planting Annual Rye is far easier, it can't come close to the beauty or quality of Perennial Ryegrass.
While planting Perennial Ryegrass will provide a much better quality turf, it also requires more skill and knowledge of both bermudagrass and Perennial Ryegrass growth habits. Turf managers understand the goal is to encourage the bermudagrass to recover in the spring while at the same time ensuring the Perennial Ryegrass is dying back. The window is short and timing is crucial. Southern states use a combination of cultural practices and specialized herbicides at just the right time that will eliminate the ryegrass without harm to the bermudagrass just as the bermudagrass is recovering from dormancy. Northern states most often use specialized herbicide almost exclusively.
In the fall as Bermudagrass is transitioning from growth to dormancy is the time to overseed with a Perennial Ryegrass variety that grows best in your area. There are currently about 120 varieties being tested or grown as turfgrass.
The rate of seed spread recommended for golf courses is approximately 12-lbs per 1000-sq. ft. over thick, dormant bermudagrass. Determine the correct amount between 12-lbs and 15-lbs for thin bermudagrass or where bermudagrass and shade meet.
You will need to water the seeds lightly two to three times each day until it germinates. Keep in mind you are not watering the grass, but are just putting enough water down to keep the seeds moist. Ryegrass is a quickly germinating seed that can sprout as soon as 3-days after planting.
Every grass species has a temperature range and conditions in which it is said to reach maximum growth potential. For most cool-season grasses, the best growth temperature is 60 to 75-degrees. For warm season grasses, it is 85 to 95-degrees.
The timing of planting the seed is just as crucial as removing it. Planting ryegrass too early before dormancy is setting in or removing it too late in spring can cause serious harm to bermudagrass. If the Ryegrass is allowed to stay too long after bermudagrass should be greening up, you are risking injury because the ryegrass will shade the bermudagrass. Some managers will delay killing the ryegrass because in the spring it looks so good. But bermudagrass is the primary grass. Bermudagrass injury can start where the full sun is reduced by as little as 30-percent.
Here is one of the dilemmas that must be addressed. Emerging bermudagrass from dormancy to full recovery is a slow process. It can take as long as 120-days from emergence to full recovery. In Missouri, there are about 6 to 7-months of growth from emergence, dormancy, to full recovery and back to dormancy again. It depends a lot on how long into the spring the winter fights to stay around. Lately, that has been as late as May. Plus, the temperature when bermudagrass is emerging from dormancy is also the best temperature for ryegrass growth.
To help bermudagrass recover favorably in southern lawns, golf courses, and sports fields, just before emergence, managers perform low mowing below the height which is healthy for Perennial Ryegrass. You are performing practices that favor the bermudagrass over the Perennial Ryegrass and allow light to reach the bermudagrass. As standard cultural practices on golf courses for removing Perennial Ryegrass, you can perform vertical slicing to encourage bermudagrass growth, add Ammonium Nitrate at high rates to help burn the ryegrass, core aerate for increased bermudagrass root growth by allowing water and air increased access to the roots, and irrigate as needed.
Some Perennial Ryegrass varieties are more tolerant of cultural practices alone and not all will die back. If this is the case you will need to use specific herbicides that kill ryegrass without harm to bermudagrass.
Herbicides that kill Perennial Ryegrass are favored over cultural practices in northern locations. This is because the bermudagrass growth season is much shorter. The time allowed for full recovery must be completed before the end of the season or your bermudagrass will decline each year. Removing Perennial Ryegrass quickly is favored over cultural practices alone since the temperatures that favor ryegrass last much longer into the spring and the temperature that favors bermudagrass is equally short.
For chemical control of Perennial Ryegrass, there are several products that have been tested and used regularly. We will only look at three of them, but there are around half a dozen more. The tests found that of all the products that are labeled for removing ryegrass, some worked faster than others and some were more effective at removing ryegrass than others.
Kerb SC T&O Herbicide
Kerb SC T&O by Dow Agrosciences had the best results. It carries a “Caution Label” and is somewhat expensive. Two-and-a-half gallons can retail around $800. It is for use on all grass locations except home lawns (non-residential use).
Monument Herbicide 75WG
Among the top performers was Monument Herbicide 75WG. It is for professionals and sod farmers due to the way it must be sprayed. Your tank must have constant agitation from the moment it is mixed and continues even when not spraying at the time. The equipment in the label description is large equipment that is not generally used by homeowners. It comes in small boxes with packets of 5-grams each. The packet itself is dissolvable in water so you never touch the chemical.
This one is the most versatile herbicides for homeowners, sports fields, or commercial sites. It can be used on lawns or sports turf and can be mixed in containers as small as a gallon pump tank. It can remove most all cool-season grasses grown in warm-season grasses. It can also be used safely on bermudagrass, zoysiagrass, and buffalograss as a spot treatment only.
The cost of Revolver is less than $300 for a quart.
Read the entire label before using it. It is the law and regulates where and how it can be used, stored and the PPE that must be worn.
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AgriGro Turf Specialist
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