26th Southern Conservation Tillage Conference
purple nutsedge in unmulched row middles and under mulch showed no significant differences for root-knot and stubby-root nematodes, but more ring nematodes were observed in soil collected from row middles than under the mulch (Table 2).
PSREU. The nematodes most frequently encountered at this site were the same as those in Rosie’s Organic Farm. Ring nematode was the most abundant, with highest population means on pigweed and crabgrass, and lowest on hairy indigo (Table 2).
Hammock Hollow Farm. Root-knot, ring, lance, and sting (Belonolaimus sp.) nematodes were frequently encountered at this site. However, only sting nematode population means were significantly (P ≤ 0.05) different between pigweed and the millet cover crop at this site (Table 2). Ring nematodes were the most common nematodes found at this site (Table 2). Root-knot nematode population levels were moderate (36.0/100 cm3 soil) on pigweed soil samples from one of three blocks with the counts remaining very low to zero in the other two blocks.
Other weeds not equally represented among blocks and therefore not included in the analysis were purple nutsedge, crabgrass, and Florida pusley, with low root-knot nematode population means of 1.5, 3.0, and 8.0 per 100 cm3, respectively. Ring nematode means on these weeds were 20.0, 13.7, and 8.5 per 100 cm3, respectively. Population means for lance nematode were 35.5, 27.7, and 7.0 per 100 cm3 on Florida pusley, crabgrass, and nutsedge, respectively. Sting nematode population means for crabgrass and nutsedge were 2.0 per 100 cm3.
Most weeds showed no signs of nematode attack and were growing vigorously while supporting high root-knot nematode populations. Purple nutsedge in particular had no visible root galls but root-knot nematode egg masses and females became visible after staining and teasing of the root in the vicinity of the egg masses. However, root galls were observed on pigweed and lambsquarters where root-knot nematode associations were found.
Greenhouse experiment: Pepper was heavily galled by root-knot nematodes, American black nightshade was intermediate, and the other plants showed only sparse or no galling (Table 3). However, while the nutsedges showed no visible galling, staining of their roots revealed a mean (standard deviation) of 27.5 (50.4) egg masses per 3 g of roots on yellow nutsedge and 48.2 (62.4) egg masses per 3 g on purple nutsedge. Root-knot nematodes reproduced well on pepper, which harbored higher numbers of hatched J2 per g (fresh weight) of root than any of the other plant species tested (Table 3). Among the weed species tested, American black nightshade had higher (P ≤ 0.05)) numbers of J2 per g than five other plant species. While numbers of nematodes per g of root were low in several cases, some weeds, such as purple nutsedge, bermudagrass, and johnsongrass, had large root systems, so that total numbers of nematodes per root system were relatively high (Table 3). Four of the weed species had higher (P<0.05) numbers of nematodes per root system than did cowpea and Virginia pepperweed, which showed the highest levels of resistance among the plants tested (Table 3). Nematode numbers in soil around the weed species tested were sparse and not particularly informative (Table 3).
Pigweed (annual dicot), lambsquarters (annual dicot), purple nutsedge (perennial monocot), crabgrass (annual monocot), signalgrass (annual monocot), Florida pusley (annual dicot), and hairy indigo (perennial dicot) are weeds commonly encountered in north Florida cropping systems. Pigweed, lambsquarters, purple nutsedge, and crabgrass are considered to be among the worst weeds in the world, as well as the USA (Bendixen, 1988c). According to Bendixen (1988c), the factors that define this category as worst weeds may not be limited to their level of competition in cultivated