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Lisa Myers1, Koon-Hui Wang2*, Robert McSorley2, and Carlene Chase3 - page 3 / 10





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26th Southern Conservation Tillage Conference

weed populations under pepper (Capsicum annuum L.), muskmelon (Cucumis melo L.), or no crop. This site was blocked according to crop planted. The predominant weeds present in each block that were sampled at this site were smooth pigweed (Amaranthus viridis L.), lambsquarters (Chenopodium album L.), purple nutsedge, and signalgrass (Brachiaria platyphylla (Griseb.) Nash). Crabgrass (Digitaria sp.) was also present, but in only two of three blocks. Soil samples were taken from the unmulched row middles around the root zone of the above mentioned weeds. In addition, soil samples were also taken from purple nutsedge in a mulch treatment. A total of 18 composite samples were collected.

Plant Science Research and Education Unit (PSREU). Sampling was done on 16 June 2003. Soil type was Candler sand. This site had been in weedy fallow for 20 years prior to cultivation to establish an experiment consisting of plots with ‘Iron Clay’ cowpea cover or fallow with weeds. Soil samples were taken from weedy fallow plots in each of three blocks over a 260-m2 area. The predominant weeds at this site were spiny amaranth (Amaranthus spinosus L.), purple nutsedge, hairy indigo (Indigofera hirsuta L.), and crabgrass. Thus, 12 composite soil samples were taken from root zones of these 4 weeds.

Hammock Hollow Farm. Sampling was done on 11 July 2003 at the end of the growing season. Soil type was Pomona sand. This site has been in organic vegetable and herb production for 17 years. The grower used crop rotation and cover crops such as browntop millet (Brachiaria sp.) and sunn hemp (Crotalaria juncea L.) to suppress weeds and nematodes. At the time of sampling, three areas each about 200 m2 had been planted with a browntop millet cover crop. The predominant weeds at this site were redroot pigweed (Amaranthus retroflexus), spiny amaranth, Florida pusley, purple nutsedge, and crabgrass (Digitaria sp.). Weeds at this site were localized in a few areas including red-rooted pigweed that was frequently observed within the millet cover crop. Due to the irregular distribution of weeds, only soil samples taken from the root zones of pigweed and millet in the millet cover crop were included in data analysis, although other weeds previously mentioned were also sampled.

Greenhouse Experiment. This experiment was carried out in a greenhouse on the University of Florida campus in Gainesville, FL. Seeds, tubers, or nematode-free cuttings of several common weed species were obtained and germinated in early summer, 2003. Weed species included yellow nutsedge (C. esculentus L.), purple nutsedge, Florida pusley, bermudagrass (Cynodon dactylon (L. Pers.), johnsongrass (Sorghum halepense (L.) Pers.), American black nightshade (Solanum americanum Mill.), and Virginia pepperweed. ‘California Wonder’ pepper, an excellent host of M. incognita (Taylor and Sasser, 1978), and two cover crops, velvetbean (Mucuna deeringiana (Bort.) Merr.) and ‘Iron Clay’ cowpea, known to have a high level of resistance to M. incognita (McSorley, 2001) were also included. In July 2003, seedlings were transplanted into plastic pots (12.5-cm-diam) containing approximately 1100 cm3 of soil. The soil used was a nematode-free 4:1 (v:v) mixture of sand:potting soil (Greenleaf Products, Inc., Haines City, FL), providing a final mix containing 97.0% sand, 0.5% silt, and 2.5% clay, with 3.0% organic matter.

On 4 August 2003, each pot was inoculated with 1000 second-stage juveniles (J2) of M. incognita race 1. The nematodes used for inoculation had been maintained in a greenhouse on ‘California Wonder’ pepper. One week before inoculation, nematode eggs were extracted from pepper roots in 0.394% NaOCl using the method of Hussey and Barker (1973). Eggs were incubated at room temperature for seven days on modified Baermann trays (Rodriguez-Kabana and Pope, 1981) containing two pieces of tissue paper (Kimwipes, Kimberly Clark Corp., Roswell, GA) for collection of J2. Nematode inoculum was delivered into holes (2 cm deep) near the base of the seedlings.


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