Dollar spot tests yield tips Nutrient - turf

I B entgrasses are grown for golf purposes under conditions more severe and restrictive than for grasses grown under natural field conditions. As a result, prevention and control of disease becomes more difficult, particularly on greens. Bentgrass greens require large applications of nitrogen fertilizer each year. These high levels of nitrogen are needed to maintain the vigor of grass subjected to frequent mowings at heights of onequarter inch or less. Turf treated with high nitrogen and frequent mowing essentially never matures and remains soft and succulent. These conditions often lead to an increase in disease. However, one common disease of bentgrass greens, dollar spot, caused by the fungus Sclerotinia homoeocarpa is known to be worse on underfertilized turf than on well-fed turf. Bentgrass Resistance to Dollar SpotDollar spot resistance in bentgrasses may be divided into two categories. The first category may be referred to as genetic resistance. This involves the classification of strains of bentgrasses into groups which demonstrate a natural resistance to the disease. For example, at Ames, Iowa, Penncross bentgrass is less susceptible than Washington bentgrass to dollar spot. Various strains of Washington show differences in degree of susceptibility. The second category may be called managed resistance to dollar spot. Factors commonly associated with management include fungicide application to remove the disease organism, sanitation which helps prevent the entry of the disease, moisture regulation which may prevent infection, and finally fertilization which helps prevent spread of disease. Effect of Nitrogen Fertilization of Turf on Dollar Spot— Emphasis in this paper will be confined to nitrogen fertilization and its effect on dollar spot resistance in bentgrass. The important aspects are source, amount and frequency of application. Some nitrogen sources contain, in addition to nitrogen, potassium, phosphorus, and trace elements. Use of these fertilizers could lead to a more balanced nutrient status for the grass. This would increase growth and reduce dollar spot. Direct fungicidal effects could arise from the presence of copper, zinc, chromium, iron, etc. Increasing the total amount of nitrogen may stimulate the grass so that it simply outgrows the disease symptoms. The type of nitrogen may exert its influence by governing the rate of nitrogen release. Nitrogen sources most effective in disease control would supply nitrogen so as to maintain the grass in a vigorous, but not over-succulent state. Experimental Methods and Materials To investigate these nutrient-turf disease