Response of Three St. Augustinegrass Cultivars to Sting Nematodes.

St. Augustinegrass (Stenotapharum secundatum [Walt] Kuntze) is the predominant turfgrass in Florida and the predominant cultivar is ‘Floratam’. Although southern chinch bug (Blissus insularis Barbar) is thought to be the pest most limiting persistence and turf quality, sting nematode (Belonolaimus longicaudatus Rau) is also often identified as a major pest limiting persistence of St. Augustinegrass.  We evaluated the response of ‘Captiva’, ‘Floratam’, and ‘Palmetto’ St. Augustinegrass grown in 650 cm³ plastic tubes in a greenhouse to inoculation with 0, 50, or 300 sting nematodes.  Two stolons per tube, of the three grasses, were allowed to root for 3-wk prior to infestation of the soil with nematodes.  Plants were grown for 90-d in the GH clipped every two to three weeks to maintain approximately 7 to 10 cm length stolons.  At termination of the experiment, nematodes were extracted from the complete soil volume of the growth tubes and counted. Roots were washed clean of soil and scanned with WinRHIZO^® software to determine total root lengths, mean root diameters, and other root characteristics.  After completion of the root scans, roots were dried to determine total root dry weight per plant. The experiment was conducted from September to December 2010 and was repeated from March to June of 2011. There were no differences among the three cultivars in the number of sting nematodes supported, but all three cultivars supported relatively high numbers of nematodes.  There were differences in final nematode numbers among the inoculation rates, where the 50 nematode per tube initial rate increased to a mean of 90 per plant and the 300 nematode initial rate decreased to 160 per plant. These results suggest that in these 650 cm³ volume tubes sting nematode population densities of between approximately 100 and 150 per plant will be supported by these St. Augustine grass cultivars.  The non-infested treatment had higher root weights and root lengths for all cultivars demonstrating that sting nematodes are a significant pest on St. Augustinegrass.  Root diameter was higher for Floratam than for Palmetto and Captiva.  The recently released cultivar Captiva has smaller diameter roots than Floratam with Palmetto intermediate.