ABSTRACT
Symptoms associated with summer decline in creeping bentgrass are nondescript and normally appear as a loss of green color, vigor, and stand density. Root systems often are shallow and brown in color with few white roots visible. On golf greens it is not unusual to see circular yellow or darker-green clones. Some clones may be dense while others are thin or dying. Clonal thinning or dying in discreet circular patches is often confused with disease activity (Figure 2.1). This is because many creeping bentgrass diseases are associated with distinctive color changes and often appear in a spot or circular pattern. When the application of fungicides does not reverse observed symptoms, golf course superintendents usually turn to plant diagnostic clinics to help sort out the potential causes of turf decline or loss on greens. Foliar diseases are relatively easy to diagnose by turfgrass pathologists. Plant parasitic nematode and root pathogen (e.g., Pythium species in roots) interactions, however, are more complicated and time consuming to identify. The latter two types of disease-causing agents are almost always found in association with turfgrass roots. The difœcult question to answer is are they there as secondary pathogens because the turf is in decline due to some other stress or are they the actual cause of the problem? Problems also arise for diagnosticians when populations of primary pathogens are in the low to moderate range and are mixed with less virulent pathogens or senectophytes (i.e., saprophytes or weak pathogens). To determine the relative importance of these microbes, pathologists need to gather information on cultural and potential stress factors (i.e., golf green location, shade, mowing height, soil moisture level, recent coring or grooming practices, recent fertilizer and pesticide applications, and cultivar grown). Many times, root pathogen activity may be superœcial, but in concert with other abiotic stress factors, may become the proverbial “straw that breaks the camel’s back” and the grass declines. In most situations, a pathologist will discuss or recommend on a green-bygreen basis the potential beneœts of applying a plant protection chemical, nutrient, biostimulant, or combination of products. Invariably, pathologists and agronomists will recommend that increasing height of cut, reducing mowing frequency, roll to replace mowing periodically, solid tine aeration to vent wet surfaces, less grooming, and judicious water management must accompany any chemical inputs to alleviate the overall summer stress complex. Simply applying biostimulants, fungicides, and other plant protection
chemicals, however, seldom solves or cures more basic cultural problems. In this section, cultural practices are reviewed, and their potential negative effects in summer are described.
