26th Southern Conservation Tillage Conference
pigweed, and millet. Of the three weeds, only nutsedge and crabgrass have been reported as suitable weed hosts of sting nematode (Bendixen, 1988c).
Lesion and lance nematodes are considered of economic importance on some crops in Florida such as sweet corn and turfgrass. Relatively low numbers of lance nematode were associated with purple nutsedge at Rosie’s Organic Farm and moderate levels on Florida pusley at Hammock Hollow Farm. Purple nutsedge and Florida pusley have previously been reported as hosts of lance nematode (Bendixen, 1979; Bendixen, 1988c). The association of lesion nematode with Virginia pepperweed in this study is supported by a study by Hogger and Bird (1976).
Ring nematodes usually are not considered of economic importance unless present in very high numbers. Ring nematodes are very common on numerous hosts and usually associated with grasses and trees. Ring nematode populations in this survey ranged from low to moderate, depending on the weed species.
Some weed hosts showed no effects of nematode damage, such as purple nutsedge infected with root-knot nematode. Casual inspection of roots may not reveal galls, and could lead to the erroneous conclusion that the roots were free of nematodes.
Current results suggest that economically important plant-parasitic nematodes cannot be effectively managed unless weeds are managed. These are important implications for cover crop use, in that, a cover crop may be a non-host for plant-parasitic nematodes but infestations of weed hosts may cause a build up of nematodes capable of attacking subsequent crops. Weeds that are allowed to grow and increase in numbers, particularly in areas between rows, covered with polyethylene mulch, can serve to increase nematode population densities. This is of considerable importance in organic farming systems where synthetic herbicides are prohibited and nonsynthetic herbicides are limited, and their use is often restricted.
Further research on weeds as nematode reservoirs is critical to emphasize and understand the role of weeds and the importance of weed control in crop production. Research could be conducted to
monitor nematode populations on major understand weed-nematode interactions.
weeds in various The information
growers and even to conventional growers in the advent of (1988c) even suggested the probability that weeds provide a isolate development in nematode species. Race development of resistance bred into crops to withstand specific infection.
cropping systems over time to better generated will be critical to organic methyl bromide withdrawal. Bendixen very favorable environment for race or in nematodes reduces the effectiveness Consequently, the cost of breeding for
crop resistance and the costs of sustained yield unclear whether the nematodes in this study have this study were growing vigorously in spite of the
losses are increased (Bendixen, 1988c). any effect on their weed hosts, since most infestation.
It is still weeds in
CONCLUSIONS In the field, plant-parasitic nematodes, including root-knot nematodes, were found associated with many common weed species in northern Florida. A greenhouse test confirmed that American black nightshade, yellow nutsedge, purple nutsedge, and bermudagrass supported relatively high levels of M. incognita, whereas Florida pusley and johnsongrass supported intermediate to low levels, and Virginia pepperweed was nearly immune. It is clear that weed management is critical if plant- parasitic nematodes are to be successfully managed in cropping systems in northern Florida.