26th Southern Conservation Tillage Conference
INVESTIGATIONS OF WEEDS AS RESERVOIRS OF PLANT-PARASITIC NEMATODES IN AGRICULTURAL SYSTEMS IN NORTHERN FLORIDA
Lisa Myers1, Koon-Hui Wang2*, Robert McSorley2, and Carlene Chase3
1Formerly Doctor of Plant Medicine Program, University of Florida, Gainesville, Florida. Currently Ministry of Agriculture, Bodles Research Station, Old Harbour, St. Catherine, Jamaica Entomology and Nematology Dept., University of Florida, Gainesville, FL 32611-0620 Hoticultural Sciences Dept., University of Florida, Gainesville, FL 32611-0690 *Corresponding author’s email: firstname.lastname@example.org 2 3
ABSTRACT In addition to their direct effects on crop production through competition and allelopathy, weeds can serve as reservoirs of other pests including plant-parasitic nematodes, resulting indirectly in yield loss. Weeds enable plant-parasitic nematodes to survive in the absence or even presence of the crop, thus providing a source of nematode infection for the following season. The purpose of this study was to conduct a survey of common weeds and associated plant-parasitic nematodes at four agricultural sites, thereby demonstrating the importance of weeds as reservoirs of these pests. Two organic farms and two conventional farming systems were visited. Soil samples were taken from the root zones of predominant weed species at each site, and nematodes were extracted, identified, and counted. Purple nutsedge (Cyperus rotundus L.), pigweed (Amaranthus spp.), lambsquarters (Chenopodium album L.), and crabgrass (Digitaria spp.) were the weeds most frequently encountered. Root-knot nematodes (Meloidogyne spp.) were the major plant-parasitic nematodes frequently found in association with these weeds in relatively high numbers. A greenhouse experiment confirmed the susceptibility of American black nightshade (Solanum American Mill.), yellow nutsedge (Cyperus esculentus L.), purple nutsedge (C. rotundus L., Florida pusley (Richardia scabra L.), and bermudagrass (Cynodon dactylon (L.) Pers.) to M. incognita, but Virginia pepperweed (Lepidium virginicum L.) was relatively resistant to this nematode. The implications of these results and importance of weeds as hosts for plant-parasitic nematodes are discussed.
INTRODUCTION Weeds have long been recognized as a major constraint to agricultural production. Weeds can interfere with crops by competing for soil nutrients, water, and light, and by allelopathic inhibition of crop growth. They also affect crop production indirectly by providing food, shelter, and a reproductive site to maintain populations of pests (Bendixen et al., 1979). Many weeds associated with agricultural crops have been reported as hosts of plant-parasitic nematodes (Hogger and Bird, 1976; Bendixen et al., 1979,1988 a, b, c; Noling and Gilreath, 2002a).
In southeastern states such as Florida, the role of weeds as alternate hosts for plant-parasitic nematodes has become increasingly important (Hogger and Bird, 1976; Tedford and Fortnum, 1988; Noling and Gilreath, 2002a). Their importance is related to the dynamic nature of weed populations in fallow situations and their influence in crop rotations in shifting agriculture (Desaeger and Rao, 2000; McSorley and Parrado, 1983; Powell, 2001). Crops grown on the sandy soils of Florida are typically prone to nematode problems because of environmental conditions that favor nematode development and reproduction. As a result, there has been a heavy reliance on chemical control, especially soil fumigation with methyl bromide, as a “silver bullet” to control these pests. However, these organisms can never be eradicated and hence a focus on management is now warranted. Due