David M. Kopec, Extension Turfgrass Specialist
Late spring means transition time for overseeded areas. At this time in Yuma, the transition is near completion and in Phoenix the cool season grasses are off color and the bermuda is showing up in patches. In Tucson the bermuda is about two weeks behind that of Phoenix and in Green Valley the overseed is still in its prime.
The transition back to bermuda is a major concern on tees and greens and of lesser importance on fairways and roughs. Transition is a combination of the condition of the underlying bermudagrass, the condition of the overseed and the ongoing growing and environmental conditions.
Think about how the bermuda was prepared and when the time the overseed was done.
A heavy verticutting done at overseeding can slow down spring transition. Why? Cut stolons and rhizomes do not grow back in the fall, and if they do, they don't store a lot of food for winter preparation and cold storage food reserves. This decreases the survival rate of the bermuda (more growing points are lost). The trick here is to control thatch on tees, fairways and greens during the summer, and lightly verticut/scalp accordingly at overseeding time. The same holds true for greens. Don't try to get rid of a spongy condition on Tifgreen putting surfaces by heavy verticutting and heavy topdressing at overseed time. Other summer greens management should have avoided such a condition.
Enhancing Transition in the Spring
On greens and tees that have good bermuda underneath, growing in predominately full sun, with good drainage, transition should occur normally. You can speed up transition in these areas by slightly antagonizing the cool season grasses to fade away while enhancing the bermudagrass below. Here are some options.
(1) Lower mowing. This decreases the leaf area of the overseed turf, which in turn enhances the use of food reserves (burn-out).
(2) Increases fertility. Light frequent applications of a water soluble quick release nitrogen fertilizer (1/4 lb. - 1000 ft2 every 10 days) will increase growth. The mowing will remove the new growth and enhance food reserve use (burn-out).
(3) Repeat grooming/light verticutting. This cuts into crowns of ryegrass and cuts stolons of poa trivialis. This forces regrowth and enhanced food reserve use (burn-out). Light verticutting can slice and lift crowns away from the roots. This disturbance disrupts the cool season grass, which should speed up transition. Don't verticut deeply if your not sure if you have ample numbers of bermuda rhizomes and stolons are underneath. If you verticut, it should be hot!
(4) Aerification and topdressing. This should do a real number on ryegrass, but I'm not so sure it will eliminate poa trivialis by this method alone.
(5) Shutting off the water. This is not good, especially on tees and greens. Maybe for 36 hours or so, but not for an extended period of time. This can damage the hydrated bermuda underneath, which is not "summer hardy" by any means.
Fairways and Roughs
Again, lower mowing and repeat applications of water soluble nitrogen fertilizers can help here. Keep the mowing pressure up. This enhances burn-out.
Some higher maintenance operations that have Tifway (408) will heavily dethatch and aerify in the spring to get rid of thatch and enhance transition. A moderate dethatching performed in two directions followed by aerification and a two day dry out should take a heavy toll on the ryegrass. It is important to fertilize and water right after the two day dry out process.
A two week drought is not a good idea. It is extremely rough on the bermuda, which has been irrigated along with the overseed for the last six months.
I have experimented with PGR's and herbicides for transition. IMAGE gets rid of cool season grasses, but does stunt bermuda. Areas which receive IMAGE on nutsedge end up with a loss of ryegrass or other cool season grasses. MSMA will burn ryegrass at the 2.0 lb. ai/a rate, especially when a surfactant is used. When using MSMA for transitions allow the turf to grow for 24 hours, then apply the MSMA (more leaf area for contact). KERB has yielded mixed results in my experimental tests and it can produce twisted leaves on the bermuda for up to five weeks.
Shaded areas will notoriously hold on to the overseed, even sometimes in the heat of midsummer. Often there is poor bermuda underneath (from shade). Low lying areas which are wet will hold onto the overseed, unless it keeps getting scalped from extra growth from fertilizer. The bermuda underneath is sparse at first, but then fills in quickly as the summer heat comes on.
Poor irrigation is a mixed blessing. Under irrigated areas (dry spots) often shed the ryegrass early in the spring. Then, the soil moisture reserves get used up and then the bermuda gets weak and thin. If the dry spot was "dry" all last summer and fall, then the bermuda underneath is often weak as well.
For good transition and bermuda, its basics. Mow close, mow often, lightly fertilize and water. Mother nature (should) do the rest.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.