David M. Kopec, Extension Turfgrass Specialist
May is the time to think about plans for the spring transition back to bermudagrass. We want our overseed to die nicely, without any loss of turf. This is the "tough" part. How do you nicely get rid of the overseed grass, but keep the golf course looking great? Nice kids don't want to leave! Can you blame them?
As always, the transition is affected by two major factors. Fall overseed practices and spring weather early conditions.
Minimal disruption of the bermuda during fall overseeding, should result in quicker spring transition. This is because the bermudagrass has more growing points and more stored energy to grow back from. Other things equal, Tifway grows back more aggressively at transition than common and probably other seeded types of bermudagrass, as well.
And now for the rest to the story. Spring and early summer conditions can be unpredictable. Today's perennial ryegrass generally are much more heat tolerant then those of fifteen years ago. They are less reluctant to die out in the heat. Note that the night temperature is critical for the survival of ryegrass in the early summer and late spring. Cool nights of 60 or less, favor the ryegrass, even when the day time temperatures are 80, or higher. This condition can allow ryegrass to hold on aggressively until June. After this, the "daytime" heat tolerance of ryegrass extends its life into early July. This is what causes panic, since you'll be overseeding again in 60-90 days! A long story short -- late springs cause a much delayed transition. After being in Tucson for thirteen years, I have more unanswered questions about transition than ever before. By conventional wisdom and observation, here's my suggestion for spring transition -- back to bermudagrass.
Slowly decrease the mowing height. Do not heavily verticut the greens and tees until you see 80% or more bermudagrass. Instead, lightly verticut periodically just to "lift" up the ryegrass plants. Grooming is also good, since it can cut leaves and slice the crowns, but not necessarily lift them up. I have tried various combinations of these practices. "Deep grooming" also dings up the bermudagrass, but once you have 70% bermudagrass, you can stop grooming. Follow with quick release nitrogen and light topdressings. Basically, if you don't see any bermuda, it's not their yet! Cultivation to bring it back may only injure the overseed, but not allow a quick and desirable regrowth of the bermudagrass. For greens and tees, lower mowing heights should be the least disruptive for transition. Once you are in the first week of June, hammer the grass with nitrate fertilizer. Weekly applications, combined with lower mowing should help the rye burn out. Don't deeply verticut till mid-summer when you have 85% or more bermudagrass. You need foliage first to make food for new growing points to gain the most benefit from verticutting.
Higher mowed ryegrass has it easier than when its on a green or tee. This makes it worse for the bermudagrass. For transition here, try the following, after the night time low temperature is 60 or above for five nights in a row. Decrease the mowing heights by 35% and mow more often. Add 1/4 lb. - 3/8 lb. of water soluble -N- per week (nitrate form) in June. After the fertilizer is watered in, try decreasing the water application amounts by 20% for a four day stretch out of the week. Than after fertilizing, irrigate normally for 2-3 days, then decrease the amount for four days again. This cycling may cause the ryegrass to be less competitive with the bermudagrass. The idea is to give the grass enough water to grow bermudagrass (in the four day cycle) while stressing the ryegrass.
There are herbicides and PGR's that are stressful on ryegrass. SURFLAN will ding perennial ryegrass. IMAGE (imazaquin) will get rid of it in a hurry. KERB will as well, but it may ding up the bermuda as well. PRIMO is more active on bermudagrass than cool season grasses at the same rates. EMBARK is more active on cool season grasses than bermudagrass at the same rates.
Rule of thumb: If you don't see a lot bermudagrass, then there isn't a lot of bermuda! You can be aggressive, but not early in the season. Heavily shaded areas will hold ryegrass till mid-August.
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.