Golf Course Management

JUL 2017

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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07.17 GOLF COURSE MANAGEMENT 61 billbug infestations are often overlooked: They spend most of their life cycle either in - side turfgrass plants or below ground. In the United States, at least nine species of billbugs attack turfgrass plants (8). Blue - grass billbug (S. parvulus Gyllenhal) is con- sidered the most widely distributed of these species and has received the most attention from turfgrass researchers. As their name in - dicates, the primary host plant for bluegrass billbugs is thought to be Kentucky bluegrass (Poa pratensis L.), although other turfgrass and non-turf species can be attacked as well (6). The hunting billbug, which can be found from Florida to New Jersey, is the species that damages warm-season grasses, including zoy - siagrasses (7). Accurately identifying a billbug to the species level is almost impossible at the larval stage without examining its genetic makeup. However, at the adult stage, billbugs can be diagnosed to species primarily based on the markings on the pronotum and elytra (Figure 2). Despite our belief that bluegrass billbug mainly attacks Kentucky bluegrass and hunt - ing billbug prefers warm-season turf, research studies have found complex populations that often feed on diverse turf species. For exam - ple, a study conducted in North Carolina re- ported abundant (>20,000) hunting billbug adults from mixed Kentucky bluegrass/ber - mudagrass (C. dactylon (L.) Pers.)/zoysiagrass turf, while only one bluegrass billbug adult Bluegrass and hunting billbug was found from the same sites over two years of sampling (1). This trend was also reported in Florida, where more than 15,000 hunting billbug adults were collected over two years of sampling from four golf course bermudagrass roughs, while only two bluegrass adults were found during the same period (5). In Kansas, natural infestation of bluegrass billbug on zoy - siagrass turf is responsible for up to 38% of plot damage (3). The complex nature of billbug compo - sition is suspected to be influenced by geo- graphic location and environmental condi- tions, which result in significant variations in microclimate conditions and in plant species that have adapted to and become established in different areas. Similarly, these variations also affect the biology of the billbugs. For ex - ample, bluegrass billbug is generally thought to go through one generation per year, al - though it has been reported that all develop- mental stages — including egg, larva, pupa and adult — can exist simultaneously dur - ing most of the year (8). Hunting billbug was thought to share a similar life cycle with bluegrass billbug, but research has shown that it likely exhibits one generation per year in northern states, and possibly two generations in Georgia and North Carolina (1,5). Such knowledge is essential for developing a man - agement plan — for example, for determin- ing the best insecticide application timing that targets larval and/or adult populations. Therefore, the objective of this research was to evaluate the billbug composition and biology on Missouri zoysiagrass turf. Materials and methods Beginning in spring 2015, the seventh fair- way at Columbia Country Club (CCC) and the 17th fairway at Country Club of Mis - souri (CCMO), both in Columbia, Mo., were monitored for billbug adult activity by using pitfall traps (Figure 3). Both fairways were Meyer zoysiagrass maintained under typical fairway conditions. Twenty pitfall traps were installed just below the soil surface and spaced 10 feet (3 meters) apart in two offset rows that were also 10 feet apart. A total of 40 pitfall traps were installed on each fairway. During the experi - mental periods in 2015 and 2016, the two fair- ways were maintained as usual, except that in- secticides were not applied within 20 feet (6.1 meters) of the pitfall traps. The traps were monitored weekly during the two growing seasons. Billbug specimens collected from the traps were transferred to the laboratory, where they were counted and identified to species. Billbug counts included total counts, counts according to species, sea - son-long cumulative counts, and counts made at each sampling during the two growing sea - sons. No statistical analysis was performed, because data collected reflected population dynamics at the two sites rather than the Figure 2. A bluegrass billbug (Sphenophorus parvulus, left) and a hunting billbug (S. venatus, right) collected in Columbia, Mo. The pronotum (area behind the head) of the bluegrass billbug is coarsely punctated (has numerous tiny holes), and the hunting billbug has a punctated pronotum with a smooth, non-punctated, Y-shaped median area. Photos by Robert Sites, Enns Entomology Museum, University of Missouri

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