Vulnerability of St. Augustinegrass to the southern chinch bug

The southern chinch bug, Blissus insularis Barber, is a serious pest of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. Both pesticidal and genetic resistance strategies have been overcome by this resilient pest. In 1973, 'Floratam' St. Augustinegrass was released because of its re sistance to the southern chinch bug. In 1985 Floratam was killed in some places by a population of the southern chinch bug adapted to feed on this host. The objective of this study was to assess the status of the southern chinch bug as a pest of St. Augustinegrass in Florida. A survey was conducted in volving 23 sod producers and the 67 county extension offices in Florida. County extension agents indicated that the chinch bug was the most serious insect pest of St. Augustinegrass turf, followed by mole crickets, caterpillars, and white grubs. Sod producers indicated that the chinch bug was slightly less serious than caterpillars. Most (37 out of 67) county agents and most (14 out of 23) sod producers indicated that they knew of chinch bug damage to Floratam. Chinch bugs (Blissus spp.) have periodically exerted sudden and widespread damage to grass crops. In 1785 Elissus leucopterus (Say) threatened lo destroy the entire North Carolina grain crop (7). In 1864, the same species also destroyed 75% of the wheat and 50% of the maize in much of the Mississippi Valley, "with an estimated loss of more than one hundred million of dollars in the currency that then prevailed" (11). This spawned some of the earFlorida Agricultural Experiment Stations Journal Series No. 9499. Supported in part by a grant from the Florida Turfgrass Research Foun dation, cooperative with the Turfgrass Producers Association of Florida. We thank Cooperative Extension Service Faculty in all Florida counties, and Turfgrass Producers statewide, for participating. 132 liest attempts at biological control. In 1888, the Kansas state legislature established an experiment station to pro duce large quantities of the chinch-bug pathogenic fungus, Beauveria sp. (3). To control the chinch bug, 50,000 pack ages of fungus were distributed to farmers. Following sea sonally variable results, the project was abandoned. In Florida, the southern chinch bug, Blissus insularis Barber, has long been recognized as a serious pest and the "chief weakness" of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze turf (4). The annual cost of chinch bug control and losses in Florida has been estimated at $5 million (5). Despite the importance of the southern chinch bug and the extensive applied research done on it, rela tively little is known of its biology (7). Chemical control strategies for the southern chinch bug have included numerous products, from Snuff No. 2, i.e., nicotine (14), to synthetic pesticides. Chinch bugs have progressively developed resistance to synthetic pesticides developed for their control, including DDT, parathion, diazinon, and chlorpyrifos (10). Considerable amounts of bahiagrass (Paspalum notatum Fluegge) were planted in the 1960's because it is not a host for chinch bugs (15). St. Augustinegrass resistance to chinch bugs has been documented (9) and was the basis for releasing a chinch bug-resistant cultivar, 'Floratam' (6). This resistant, polyploid grass was an environmentally safe alternative to pes ticides which had so often failed. In 1985, turfgrass pro ducers reported chinch bugs killing large patches of Flora tam. Laboratory studies implicated a new kind of southern chinch bug which was adapted to Floratam (2). Because of the past association of host resistance and polyploidy in St. Augustinegrass germplasm (8) and the ability of the new population to overcome polyploids, it was dubbed PDP (Polyploid Damaging Population). The PDP chinch bug was an ominous sign, because of commercial reliance on Floratam as the only resistant cultivar. For example, in a 1980-81 survey, Floratam represented 77% of commercial sod sampled in southern Florida (1). The geographic range and damage potential of the PDP southern chinch bug are unknown, but should be monitored. Other aspects of chinch bug distribution and Proc. Fla. State Hort. Soc. 101: 1988. host relationships need to be studied. In 1988, we con ducted a survey to assess the status of the southern chinch bug as a pest of St. Augustinegrass turf in Florida. Materials and Methods Comparable survey questionnaires were mailed to ex tension agents in all 67 Florida counties and 50 sod pro ducers, which was the complete population of all known St. Augustinegrass producers. Responses were obtained from all county agents and 23 of the St. Augustinegrass sod producers. County extension agents were asked to con sider all turfgrass except for sod. Both strata, county agents and sod producers, were asked to report: (A) presence of chinch bug damage (if any) in Floratam and size of dam aged areas; (B) the need for pesticidal treatment (if any) against chinch bugs in Floratam; (C) the main chemical used or recommended; (D) the main problem (if any) with chinch bugs in St. Augustinegrass; (E) the relative serious ness of four groups of insects as pests of St. Augustineg rass; and (F) comments. Comments were solicited in two chinch-bug related subjects: best recommendations for dealing with chinch bugs and experience with chinch bugs on grasses other than St. Augustinegrass. County agents were also asked to report the presence of chinch bug dam age to any, hence various, St. Augustinegrass(es), and the size of areas affected. Three classes were provided for re spondents to describe the size of damaged areas: small, < 1 ft diam; medium, < 10 ft diam; and large, > 10 ft diam. The intention in asking for this information in this way was to obtain an index of insect damage severity, based on the fact that chinch bugs damage turf in distinctive, enlarg ing patches, which are initially circular. A highly suscepti ble cultivar, e.g., 'Florida Common', would frequently dis play killed patches > 10 ft diam, which would be unaccept able. Smaller diameter damaged patches would indicate partial susceptibility and, in some cases, acceptable damage levels. County extension agents were also asked to estimate the percent of turf areas in their counties which consisted of St. Augustinegrass. To develop a meaningful statewide estimate, county St. Augustinegrass percentages were weight-averaged. The weighting factor, county population, was multiplied by county St. Augustinegrass percentages, and the sum of products was divided by the total statewide population estimate. The population estimate was the aver age of the 1986 population estimate and a 1990 mediumgrowth population projection (12). Results and Discussion The average reported St. Augustinegrass area was 41 % of all turf areas, on a county basis. Densely populated urban counties were reported to have a higher proportion of St. Augustinegrass than were less populated rural coun ties. St. Augustinegrass area estimates, weight-averaged for population, were 64% of established turf areas in Florida. This was consistent with an early report which stated, "St. Augustine grass is the most common lawn grass in Florida" (4). Most county agents (85%) reported chinch bug damage to St. Augustinegrass (Fig. 1). County agents considered chinch bugs as the major insect pest of St. Augustinegrass, Proc. Fla. State HorL Soc. 101: 1988. Various