26th Southern Conservation Tillage Conference
fields, which limits crop productivity and yield, but might also be based on their indirect effects as hosts of nematodes in crop production. Effects from weeds could be complicated by a number of factors, such as the number of nematode species hosted, severity of damages by the nematodes, the number of crops involved, and the area occupied by those crops as well as weed distribution Bendixen (1988c). Weed populations are dynamic and the presence of certain weed types is often dependent on local weed seed banks, cropping and land history, and farming practices at any particular site.
The primary purpose of this preliminary investigation was to draw attention to the importance of weeds that can serve as hosts of nematodes and thus have an indirect effect on crop production. In this investigation, root-knot nematode was the nematode of greatest economic importance most frequently encountered. This nematode is considered the worst nematode worldwide and has an extensive host range, attacking many vegetable crops (Shurtleff and Averre, 2000).
In this survey, nematode population levels differed from one site to another, which could be explained in terms of varying local soil and weather conditions, weed types, cropping and land history, and farming practices. Of the two organic farms, root-knot nematode populations were higher at Rosie’s Organic Farm than at Hammock Hollow Farm. The Hammock Hollow site has a history of cover crop use and crop rotation that could have influenced nematode populations directly or indirectly by suppressing weed host species.
Root-knot nematodes were frequently associated with pigweed, purple nutsedge, and lambsquarters, indicating that these weeds were likely hosts for this nematode. Moderate to high levels of root-knot nematode populations were found associated with these weeds at Rosie’s Organic Farm. At this site, 1ow to moderate levels of root-knot nematodes were associated with signalgrass. According to Bendixen (1988c), purple nutsedge is by far the most serious weed in the world based on data supporting certain major weeds as nematode hosts. The list (Bendixen, 1988c) includes crabgrass, lambsquarters, and pigweed among the 10 most significant weed hosts of nematodes. Nutsedge, crabgrass, lambsquarters, and pigweed have been reported as major weed hosts of root-knot nematodes (Bendixen, 1979; Bendixen, 1988abc; Schroeder et al., 1993; Thomas et al., 1997). Although crabgrass has been reported as a host of root-knot nematodes, low nematode population means were reported here. Noling and Gilreath (2002a) reported that several species of crabgrass served as hosts of root-knot nematode but were relatively poor hosts. The greenhouse results reported here confirm the importance of yellow and purple nutsedge as hosts of M. incognita, but illustrate that American black nightshade and bermudagrass root systems can support similar high levels of this important nematode. In addition, common weeds like Florida pusley and johnsongrass may also support low to moderate levels of M. incognita. However, susceptibility of weed might vary according to species and races of root-knot nematode inoculated. For example, a pot test in North Carolina revealed that yellow nutsedge is a poor host to M. incognita race 3 and M. arenaria (Tedford and Fortnum, 1988).
Sting and stubby-root nematodes, although not as important as root-knot nematodes worldwide, are nematodes of economic importance in Florida. These nematodes occur in sandy soils (>85% sand) and sandy to sandy loam soils, respectively (Shurtleff and Averre, 2000). Both attack many vegetable crops and, like root-knot, have an extensive host range. Stubby-root nematode population means were low (<10 nematodes/100 cm3 soil) on weeds surveyed in the present study. Previous reports indicate that crabgrass, nutsedge, pigweed, and Florida pusley are suitable hosts for stubby- root nematodes (Bendixen, 1979). Sting nematode was only encountered at the Hammock Hollow site and was present at very low numbers (<5 nematodes/100 cm3 soil) on nutsedge, crabgrass,