Offseason Management for Organic High Tunnels for Improved Pest Suppression and Soil Health

Project Overview

Project Type: On-Farm Research
Funds awarded in 2012: $14,967.00
Projected End Date: 12/31/2013
Region: Southern
State: Florida
Principal Investigator:
Dr. Carlene Chase
University of Florida


  • Vegetables: cucurbits, tomatoes


  • Crop Production: crop rotation, cover crops
  • Education and Training: on-farm/ranch research, participatory research
  • Pest Management: cultural control, physical control, mulching - plastic, soil solarization


    An on-farm study was conducted to address weed and root-knot nematode (RKN) infestations in an organic high tunnel in central Florida. A randomized complete block design with four replications was used to assess the effect of off-season management with four cover crop treatments: Iron Clay (IC), US-1136, US-1137, and US-1138 cowpeas (Vigna unguiculata (L.) Walp.), a soil solarization treatment (SS), and US-1137 cowpea followed by soil solarization (US-1137+SS) in comparison with a weedy control (W), a weed-free (WF) treatment. A fall cucumber (Cucumis sativus L.) crop was followed by a winter fallow, then a romaine lettuce crop (Lactuca sativa L.). The cowpea treatments did not differ in the amount of biomass produced. The dominant weed group by mass consisted of grasses and all off-season fallow treatments resulted in lower grass and total weed biomass than the weedy control. Although the quantities of marketable cucumbers with the W and WF treatments were lower than with the summer fallow treatments, no difference in marketable cucumber weight was apparent. Both the W and the WF treatments had the highest marketable lettuce weights compared to the other treatments. The US-1137+SS treatment did not improve cucumber or lettuce yields over SS alone. Root-knot nematode populations in December after cucumber and in April after lettuce averaged over treatments were 5 per 100 cc and 7 per 100 cc, respectively, compared to the baseline 82 per 100 cc obtained in July prior to the off-season treatments. Root-knot nematode galling indices in cucumber and lettuce plants also were not different from those with the weedy control. Therefore, decreases in root-knot nematode occurrence were not the result of suppression of weeds with summer or winter fallow treatments.


    Earliness, extended production season, increased productivity, and reduced pest and disease problems are some of the advantages of using high tunnels for crop production over open field production (Lamont et al., 2003; Wells and Loy, 1993; Wells, 1996). Because of the season extension capability, high tunnels allow growers to offer a wider range of produce and obtain premium prices for produce that is in scarce supply during the winter. Although estimated to be only about 100 acres in 2009, high tunnel acreage in Florida has been growing rapidly and is currently estimated to be 1500 acres (Burfield, 2013).

    Despite the many benefits, weed and root-knot nematode (Meloidogyne spp.) management have proven to be challenging for high tunnel growers (Larson, 2009; Oloo et al., 2009; Sanchez, 2008; Santos et al., 2008). Whereas herbicides and soil fumigants can be used in conventional high tunnels, organic growers have fewer available options. Therefore, ensuring that organic growers have effective pest management measures is a priority. Nonchemical alternatives to soil fumigants designed for managing soil borne pests in organic high tunnels can also be applicable to conventional high tunnels in urban and peri-urban areas where buffer zones preclude the use of soil fumigants. In considering nonchemical approaches with applicability for organic high tunnels, we hypothesized that a root-knot nematode-resistant cover crop and soil solarization could be effective tools for suppressing weeds and root-knot nematodes during the summer off-season.

    Cowpea (Vigna unguiculata (L.) Walp.) is a legume that is widely recognized for its ability to serve as a cover crop and green manure and is well adapted to high temperatures and sandy soil. In addition to these attributes, some cowpea cultivars exhibit vigorous growth and rapid canopy closure that are effective for suppressing weeds. Iron Clay cowpea has also shown potential for allelopathic inhibition of weeds (Adler and Chase, 2007) and for effectively suppressing root-knot nematodes (McSorley et al., 1999).

    Whereas soil solarization has been shown to be an effective means of suppressing weeds, the control of root-knot nematodes has been less consistent. Unlike nematode control, excellent weed suppression has been reported in high tunnels with soil solarization (Larson, 2009; Medina et al., 2009; Santos et al., 2008). In open-field studies, after an initial reduction in soil infestation by root-knot nematodes with soil solarization, populations may recover when subsequent susceptible crops are planted (Wang and McSorley, 2008). These authors proposed that improved soil heating at greater soil depths may extend the suppressive effects of soil solarization. Although Larson (2009) demonstrated enhanced soil heating and more hours of lethal soil temperatures when soil solarization is performed in tunnels than in adjacent uncovered fields, Santos et al. (2008) reported that root-knot nematodes in a hot pepper crop had not been effectively controlled by soil solarization conducted in the high tunnel prior to the crop. A combination of measures can sometimes be more effective than either measure used by itself. Wang et al. (2006) found that persistence of control with a cowpea cover crop followed by soil solarization was equivalent to that obtained with methyl bromide soil fumigation.

    Project objectives:

    The objective of this on-farm study was to evaluate cover cropping and soil solarization for the suppression of weeds and root-knot nematodes during the off-season in an organically managed high tunnel.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.