June 1998

"Knee High by the Fourth"
Growing a Good Crop of Summer Golf Greens

David M. Kopec, Extension Turfgrass Specialist

Remember the old saying that corn should be "knee high by the fourth" (of July), if a farmer was going to have a good corn crop? Well luckily, we don't have that in turf, but there are some benchmarks that you may want to consider for your turf in July.

Bermudagrass Greens:
Hopefully, the overseed is finally going out quickly by the first two weeks in July. Sometimes the Poa trivialis will last longer than anticipated, but there are some techniques you can use to hasten the transition of ryegrass and Poa trivialis. The first thing to do is to take one or two cups out of the green and look for how much bermuda is underneath the overseed. Pluck out the overseed. Then look for (a) bermudagrass stolons­the above ground runners and (b) rhizomes­the underground runners. If at this time, you have many more rhizomes than stolons, then you can induce a "gentle transition". If you have lots of stolons, you can start a more "aggressive" transition.

Gentle Transition: (more rhizomes/few stolons)
The idea here is to maintain a good putting surface without a "loss of turf" during a "sudden" or "forced" transition. The objective is to force growth of the rhizomes to reach the surface, establish new roots, and then make stolons.

1. Drop the moving height to promote stress on the remaining overseed and expose the canopy to more light.

  1. Groom to uplift the ryegrass crowns, and to cut the stolons on Poa trivialis.
  2. Lightly verticut in one direction, and lightly topdress, roll, and fertilize with 1 lb-N-/M
  3. Decrease the irrigation two days after you have fertilized. Keep it on the dry side, but don't damage the new bermudagrass plants. Keep it dry enough so the overseed is stressed.
  4. Fertilize each week with ¼ - ½ lb -N-/M from a highly soluble source. Include P-K and iron as well. Water three days "normal", and four days "dry"during the week..
  5. Do not regularly verticut at this time, because you do not have lots of stolons yet. Save your deep verticut (Tifgreen only) and aerification for the second week in August.
  6. Once you have 50-65% bermuda level, keep fertilizing and water to avoid stress.
Aggressive Transition: (Lots of stolons present)
In this case, we want to increase the shoot density (stolons), so they become independent from the mother plants. When this occurs, the green becomes dense, as the shoots become vertical. This makes for a good bermudagrass green, since it better approximates a table top from the vertical shoots, rather than a green surface of long stringy stolons.
  1. Fertilize the green with 1 lb-N-/M.
  2. Drop the mowing height for one week to stress the remaining overseed grasses.
  3. Water as usual.
  4. Verticut moderately deep in one direction. This cuts, both the stolons and rhizomes from the mother plant, and forces them to regrow on their own and make "new" plants.
  5. You may summer aerify now if wish also.
  6. Topdress.
  7. Add ¼ - lb-N-/M week for the next three weeks. Add P-K as well.
  8. Provide adequate irrigation for maximum growth of bermudagrass.
  9. Topdress the "new growth" accordingly so the new stolons from the new plants re-root and grow up vertically.
Bentgrass Greens:
Mid July is the beginning of the uphill summer stress period. For "Penncross" greens, provide maybe 1/10th lb-N-/M month if needed. Substitute with iron applications on a regular basis. Lightly topdress, early in the morning or last thing at night, when necessary. On more aggressive and denser varieties (A series, G series, SR1020, Crenshaw), you have to topdress more often. If the bentgrass is very dense and spongy, then decide if a deep groom or light verticut in one direction is possible (to open up the canopy slightly). Then topdress lightly. In high traffic greens, this may not be a problem, or it may not be possible to do at all. Tread carefully. Some of the "summer aggressive" varieties will actively grow when fed nitrogen, but this can cause real problems. Start with the regular iron application programs to maintain color.

High traffic spots will start to show thinning at this time. Move pins accordingly and promote exit schemes with the golf professional so he can pass those on to the players. Clean up passes from the tri-plexes are a summer bummer. Either aerify with ¼" solid tines, or use water injection aerification. You don't have to do the entire green. If possible, make the clean up pass with a walk-behind mower, two passes wide, while still mowing the green with the tri-plex. This is a good compromise.

Persistent dry spots are either from poor irrigation, or from localized dry spots (soil condition). You can apply a wetting agent selectively with a hand pump sprayer on chronic problem acres, and aerify just these spots as well. There is no substitute for proper hand watering. 

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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.

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