Effects of long-term organic amendments and soil sanitation on weed and nematode populations in pepper and watermelon crops in Florida

Abstract

Florida vegetable growers have relied on methyl bromide (MeBr) fumigation to manage soil pathogens, nematodes, and weeds. This system combined with raised beds, polyethylene mulch, and seepage and/or drip irrigation has been effective for producing high vegetable yields. Alternatives to MeBr such as solarization and organic amendments have given favorable results in small trials, but there are few large-scale studies. The objectives of this study were to evaluate the effects of long-term organic amendment applications and soil sanitation treatments on weed and nematode populations on pepper (Capsicum annuum L.) and watermelon (Citrullus lanatus [Thunb.] Manst.). During 1998 and 1999 fall vegetable seasons, main plots received a yearly organic amendment (biosolids) application or a non-amendment control, with sub-plots consisting of soil sanitation treatments with solarization, MeBr, Telone® (1,3-dichloropropene), or a non-fumigated control. Each sub-plot was further divided into two sub-sub-plots, one receiving additional weed and without control weed control. During the solarization period (60 d in 1998–1999; 90 d in 1999–2000), percent weed cover was higher in the non-biosolid plots than the biosolid plots for the first part of the solarization period, but there were no differences during the last 30 days in both seasons. Purple nutsedge was able to germinate on the north edge of the beds for a border effect; a point of vulnerability when beds run east–west. With the pepper crop, the number of weeds and percent weed cover were greater in the non-fumigated plots and Telone®-treated plots than in plots treated with MeBr or in solarized plots with and without biosolids. Nematode population densities from plot to plot within the site were highly variable, which likely accounted for the relatively few consistent effects from treatments observed during the experiment. The data do provide some indication of the importance of weeds in the recovery and buildup of nematode populations. During spring 1999, both root-knot and stubby-root nematodes were more abundant in the sub-sub-plots that had not received weed control. The results suggest that solarization and organic amendments can be viable alternatives to MeBr. However, MeBr produced the most consistent results.