David M. Kopec, Extension Turfgrass Specialist
Normally, 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 current growing and environmental conditions.
The road back to bermudagrass is sometimes an inconsistent and troublesome one. Last year (Spring of 1995) we experienced the coolest mid April and month of May in at least 10 years. The amount of bermudagrass that was left alive by the middle of June was the deciding factor on how long the "late season transition" would be. This was a function of how many underground rhizomes were still alive under the soil. Last spring, too many superintendents found a low concentration of viable rhizomes underneath the ground. Dead rhizomes are hollow and rotten, and dark in appearance. Healthy rhizomes and shallow stolons should be firm when you roll them in your hand.
Overseeded bermudagrass actually has to green up in a different way than non-overseeded bermudagrass. Non-overseeded areas green up first due to heat absorption of the bermuda turf cover. They make a little food, but not much until it gets warmer. Overseeded bermudagrass is quite another story. Think about it! The light and heat is captured by the cool season grass, and the bermuda must send green leaves up to the surface, at the immediate expense of rhizome crown and stolon food reserves. If the soil is barely warm enough to stimulate rhizome growth of the bermuda, it's at the same temperatures that ryegrass can withstand for some period of time before it fades away. In cases like last year, there were clubs which did nothing in cultural management to aid transition (just waited for ryegrass to go out), and still they ended up with little or no bermudagrass until August. This is what happened last year. Hind-site is 20-20 ! So what about "when to start transition" and what can we do to help it along? If you want to mange in bermudagrass at the expense of the cool season overseed, here is what I think about "when". Wait until the night time low temperatures are 60 F for at least five consecutive nights. This is safer than going by the calendar. Tell this to the Greens chairman if a tournament schedule is in conflict. No one can schedule mother nature.
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 full sun and 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 for regrowth from mowing (burn-out). This should also open up the canopy for direct heat adsorption which would favor bermuda.
(2) 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). If its warm enough for the bermuda rhizomes and shallow stolons to become active, but cool enough to impede their active emergence and growth, then maybe fertilization may be bad for the bermuda. This has been demonstrated for St Augustinegrass.
(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 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 (419) 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 may stunt bermuda. Areas which receive IMAGE for nutsedge control 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. If you use a PGR for transition, a foliar absorbed PGR which has greater activity on the cool season grass (at the same application rate) should minimize the effect on the bermuda. For example, LIMIT, EMBARK and PRIMO are absorbed by the foliage, and LIMIT and EMBARK are more active on the cool season overseed ( at the same application rate).
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.
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.