26th Southern Conservation Tillage Conference
to health and environmental concerns, the continued availability and use of methyl bromide are uncertain, and the search for alternative control measures has become increasingly important (Noling and Gilreath, 2002b). Non-conventional systems such as organic farming are presently prohibited from using synthetic chemicals and rely on nonchemical methods, particularly cultural practices, for the management of plant-parasitic nematodes and weeds. The development of an integrated approach to weed and nematode management will require pertinent information in order to make informed management decisions. Despite our anthropocentric views and compartmentalization of pest management practices, the interrelationships among organisms in the field has continued, and hence knowledge regarding these relationships will serve us in developing sustainable management practices.
The objectives of this study were to 1) illustrate the role of weeds as reservoirs of plant-parasitic nematodes in Florida agricultural fields, 2) compare the nematode host status of major weeds encountered in agricultural fields, 3) examine the host status of several common weeds to the root- knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood in the greenhouse.
MATERIALS AND METHODS Field visits were made to four agricultural fields, including two certified organic farms: Rosie’s Organic Farm, Gainesville, FL (located near 29° 32’ N, 86° 26’ W), Hammock Hollow Farm, Cross Creek, FL (located near 29° 30’ N, 82° 11’ W), the University of Florida’s Plant Science Research and Education Unit, Citra, FL (located near 29° 25’ N, 82° 10’ W), and the University of Florida Plant Science Field Teaching Laboratory, Gainesville, FL (located near 29° 39’ N, 82° 21’ W). At each location, the types and distribution of major weed species were noted. The field was divided into three blocks, each containing representatives of the predominant weed species. Weeds that could not be easily identified in the field were collected and taken to the Weed Science Laboratory in the Horticultural Sciences Department at the University of Florida for identification. Representatives from each weed species were randomly selected and soil samples taken from the root zones. Each composite nematode sample consisted of five soil cores (2.5 cm diameter × 20 cm deep) collected from five plants per weed species per block. Composite samples were placed in a plastic bag and stored in a cooler to protect samples from sunlight. Samples were taken to the University of Florida in Gainesville where they were stored in a cold room at 10oC until processed. Soil subsamples of 100-cm3 were taken for nematode extraction using a modified sieving and centrifugal flotation procedure (Jenkins, 1964). An inverted microscope was used to identify and count extracted nematodes.
Plant Science Field Teaching Lab (PSFTL). Sampling was done on 21 May 2003. Soil type was Arredondo fine sand. This site had experienced little or no rainfall within the week prior to sampling. Soil samples were taken from a 50-m2 weedy fallow area. The area was previously cropped in sesame (Sesamum indicum L.) and cowpea (Vigna unguiculata (L.) Walp.). Blocking was done according to the major weed types present. The predominant weeds at this site were Virginia pepperweed (Lepidium virginicum L.), volunteer cowpea, Florida pusley (Richardia scabra L.), johnsongrass (Sorghum halepense (L.) Pers.), and purple nutsedge (Cyperus rotundus L.). However, only Virginia pepperweed and volunteer cowpea were consistently present in each block, so only soil at the root zone of these weeds were sampled. A total of six composite samples were collected.
Rosie’s Organic Farm. Sampling was done on 9 June 2003. Soils were of the Jonesville Cadillac Bonneau complex with good organic matter content. Rainfall had occurred three days prior to sampling. Soil samples for nematode analysis were taken from an experimental site of 480 m2 that had been used by the grower to compare the effectiveness of various types of mulch in suppressing