Grass fertilized in fall instead of spring is less affected by the disease. This has been demonstrated in tests at the United States Department of Agriculture Experiment Station, Beltsville, Maryland, and other lawn research centers throughout the United States.
Our short springs are quickly followed by high temperatures, during which conditions are ideal for the multiplication of the spores of helminthosporium and septoria fungi—organisms that cause leaf spot diseases of grass.
When we apply a quickly available fertilizer in spring, we stimulate a lush, succulent growth readily attacked by these spores.
As a result, test plots at Baltaville of grasses fed in spring were turning brown by early May of last year; plots that had been fed in fall were still green.
Growth Stimulated By Fall Feeding
The type of growth stimulated by fall feeding is quite different. Two factors are at work to stimulate the growth of roots instead of tops.
For one thing, night temperature is lower, so soil temperature is lower even though day temperature may run in the 90s.
As the sun sinks lower and lower with the coming of fall, the quality of the light changes. The blue end of the spectrum is weaker, and the red end is stronger. Red light tends to stimulate root growth.
Another factor is day length, which is reduced. While we do not know too much about the effect of day length on grasses treated as mowed turf, there is reason to believe that in the shorter days of fall, the sod builds up in-depth so that it goes into the winter in better condition when adequately fed.
Applying Fertilizer in Fall
The type of fertilizer used for fall feeding is highly important. Organic plant foods are of little use unless dried blood or fish emulsions are used since their nitrogen is in the form of protein, which becomes available only when broken down by bacteria.
Fall soils are too cold for bacterial action to take place.
Organic fertilizers high in starches and sugars are bad because they feed the snow mold fungus, which grows best at temperatures below 42° degrees Fahrenheit. (Most severe cases of snow mold I examined last spring had been fertilized with sewage sludge.)
Ureaform Fertilizers For Fall Feeding
Straight chemical fertilizers can be used but should be applied quite late, say from mid-October on.
Much of the nitrogen they contain will be used for fall growth, but small amounts will be taken up on the clay and humus particles of the soil, leaving enough for the normal growth of grass in spring without overstimulation.
The ideal fertilizers for fall feeding are the new types of ureaform, which are made in mixed forms. They include phosphorus, potash, and other nutrient elements and nitrogen.
About 50% percent of the total nitrogen in the mixture should be reformed. The rest might well be a mixture of quickly available organic (dried blood), slowly available organic (tankage, etc.), and chemical (ammonium sulfate).
Such a fertilizer would release its chemical and organic nitrogen at once.
Since ureaform nitrogen would not be immediately available, such a fertilizer could be put on much earlier in the fall than other types.
In my tests, August and September applications have given excellent results, without a heavy flush of growth in spring, yet with a carry-over of available nitrogen for normal spring growth. The ureaform nitrogen fed the lawn through the entire summer until mid-August.
I applied 20 pounds of a 20-5-5 mixed urea form on my Illinois lawn to 1,000 square feet. This is four times the amount of nitrogen usually recommended but is in line with recommendations for maintaining the top growth of fine turf on golf courses.
Despite this high rate, spring growth was strong, and fungi did not hurt the turf.
44659 by R. Milton Carleton