David M. Kopec, Extension Turfgrass Specialist
There seems to be more than ever to do on the golf course after a successful overseeding. The overseeded greens should be looking nice, if the mowing height reduction program was carried out successfully. November is creeping up so it's time to start thinking about winter nutrition for the greens and Poa annua control.
When the soil temperature decreases and the soil is moist, phosphorous and iron deficiencies can show up on overseeded greens. These problems can first show up in late October to early November, but are usually most severe in December.
A phosphorous deficiency shows up on overseeded greens and on bentgrass greens usually with the following conditions:
1. reduction in clippings
2. darker color on the underside of the leaves which eventually turns the leaves purple in color. When ryegrass plants first emerge, the base of the plant is naturally reddish at the base. The purple cast from a phosphorous deficiency is more "bronzed" in appearance and travels upward from the base of the tillers towards the leaf tips.
3. On bentgrass, a phosphorous deficiency is harder to identify. The leaves are sometimes "limp" and show only a light discoloration on the underside of the leaf base.
Nitrogen deficiencies show up as 1) poor color turf, 2) lower leaves (closest to the ground) turn brown, and 3) decreased density.
When the soil is cold, spoon feed with nitrate forms of nitrogen. Ammonium sources will not be as available in the cold weather. Potassium nitrate ( Kno3), ammonium nitrate (NH4 No3) and calcium nitrate (Ca (No3)2) are options. An application of 1/4 lb. N every 10-14 days is usually satisfactory. Check your fertilizer bag to see what form(s) of nitrogen are contained in the bag.
Iron deficiencies can readily occur in late fall and winter on tee's and greens. Generally the turf is light green in color. The key difference between iron and nitrogen deficiencies is that with an iron problem the newer leaves (closest to the bedknife) are off color, while the older leaves (closest to the soil) are still green. Iron deficiencies usually effect most areas of the greens. On fairways, the deficiencies appear randomly, due to soil and drainage conditions.
A safe way to stay on top of these conditions is to pick two or three greens on the golf course for "subliminal strip fertilization". Using a small drop spreader, apply a single pass of the fertilizer in question going east to west, and another single pass going north to south. The point where the two fertilizers intersect will get twice the rate. Since you are "spoon feeding", the double rate which occurs where the drop spreader overlaps, should not cause injury due to the low rate application.
For phosphorous you can make a fertilizer strip once every three weeks by applying 1/2 lb/1000 ft2 of phosphorous only. If the grass has a visual response or more growth, it means that a complete application may be warranted. Iron and nitrogen will almost always show up with a positive effect, so apply these in strips first if you see any symptoms as described. If you apply strips again later, choose another area of the green to apply the strips. This avoids responses from accumulated effects.
Potassium deficiencies can show up on greens, especially in late fall. The overseeded bermuda (ryegrass) shows a stunting in growth and pale color along the edges of the leaves. The edges of the leaves may shred, nick or tear easily. The pale color is usually yellow to light tan in color. However, the leaf will still remain alive. If you suspect a potassium deficiency apply a strip on the green at the rate of 1/2 lb./1000 ft2 of potassium . Use potassium sulphate as the source, since it has no N or P in it.
When deficiencies are recognized and favorable responses result from the fertilizer "strip tests", you can either apply fertilizers that contain multiple nutrients, or make single applications of a product for each nutrient. Make sure you check the availability of the nitrogen source.
Poa control on overseeded greens is possible by using PROGRASS. The greens must be seeded with perennial ryegrass. PROGRASS will damage Poatrivialis and bentgrass at label rates on greens. PROGRASS eliminates Poaannua when the plants are young (and perhaps not readily visible). Therefore, the best time to treat is around November 15. The bermuda will be damaged, if it is not dormant. Read the label carefully.
Bensulide (betasan) is registered for pre-emergence control of Poaannua on bentgrass greens. As a pre-emergence herbicide, it works by stopping cell division in roots. The herbicide can cause "root pruning" if repeat applications are made and/or label rates are exceeded.
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.