Suppression of weeds and other pests in fresh market vegetables using wild radish cover crop

Suppression of weeds and other pests in fresh market vegetables using wild radish cover crop

Summary

Field experiments were conducted near Blackville to evaluate the effect of wild radish and rye cover crops on weed, insect, and soilborne pathogen suppression and sweet corn yield when used in conjunction with lower than recommended herbicide rates. An additional test site was located near Tifton, GA where weed suppression and sweet corn yields were assessed. Cover crop treatments included wild radish, rye, and no cover crop alone and in conjunction with one-half and full recommended rates of atrazine at 1.68 kg ai/ha plus S-metolachlor at 0.87 kg ai/ha applied prior to sweet corn emergence. Florida pusley, large crabgrass, spreading dayflower, Texas panicum, smallflower morningglory and ivyleaf morningglory were the predominant weeds infesting the test sites at Blackville or Tifton. In the absence of a cover crop, weed control with atrazine plus S-metolachlor ranged from 54 to 98% at both locations. Wild radish or rye in conjunction with a one-half or full rate of atrazine and S-metolachlor provided >95% weed control at Tifton. Wild radish or rye cover crops had no negative effect on corn earworm populations. Pythium populations increased more in rye and wild radish plots than in fallow plots. Populations of Fusarium spp. and F. oxysporum also increased significantly after incorporating cover crops in fallow plots and in wild radish or rye plots, respectively, compared to the initial sampling. Sweet corn in wild radish or rye cover crop plots produced 21,000 to 48,000 and 28,000 to 35,000 marketable ears/ha, respectively, in herbicide treated and handweeded plots; however, marketable ear production was 39 to 83% lower than total ear production across all treatments at Blackville. Sweet corn in wild radish or rye cover crop plots in the absence of herbicides produced less marketable ears than herbicide treated plots, indicating a combination of cover crops and herbicides are required to optimize yields and obtain desirable weed control. Wild radish or rye cover crop in conjunction with one-half rates of atrazine plus S-metolachlor can provide adequate early season weed control and optimize yields. Results from these experiments were shared with Extension weed scientists at the Southeastern Extension Vegetable Workshop, presented to students at Clemson University enrolled in Integrated Pest Management (IPM 401/601), and presented to attendees of the Horticulture section at the Southern Weed Science Meeting.

Objectives/Performance Targets

1) Determine if a wild radish extract negatively affects insect pests.

2)Evaluate the effect of wild radish on growth and yield of sweet corn in field studies along with mycorrhizal colonization and weed, pathogen, and insect populations.

3) Disseminate results to vegetable producers and other clientele.

Accomplishments/Milestones

Aqueous extracts of wild radish roots, stems, and leaves were examined for antibiotic effect on hatching and larval development of the southern corn rootworm, [Diabrotica balteata Le Conte (Coleoptera: Chrysomelidae)] and black cutworm [Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae)]. There appears to be an antibiotic effect on the eggs of D. balteata, and in some trials the percentage hatching increased to similar levels as other treatments by the third and final day of hatching; in others, the percentage hatching remained significantly less in eggs exposed to aqueous wild radish extract for the duration of the study. The highest mortality rate of D. balteata larvae was detected in 100% extract, followed by 50%, and then the control sample, although these data were inconsistent from trial to trial. Hatching of A. ipsilon was delayed significantly by the 18-hour exposure to the aqueous extract 4 days after treatment in only one of the six trials. In that trial, all results of treatments were homogenous by the next day. In A. ipsilon bioassays, both of the treatments (water and wild radish) that consisted of 18 h exposure resulted in decreased hatching. Therefore, the effect on hatching of A. ipsilon eggs in the aqueous wild radish extract was very similar to the effect on hatching in the water treatment.

Field experiments were conducted near Blackville, SC and Tifton, GA in 2005 to evaluate the effect of wild radish and rye cover crops on weed suppression and sweet corn yield when used in conjunction with lower than recommended herbicide rates. Insect and pathogen populations were also monitored in field plots in SC. Cover crop treatments included wild radish, rye, and no cover crop alone and in conjunction with one-half and full recommended rates of atrazine at 1.68 kg ai/ha plus S-metolachlor at 0.87 kg ai/ha applied prior to sweet corn emergence. Florida pusley, large crabgrass, spreading dayflower, Texas panicum, smallflower morningglory and ivyleaf morningglory were the predominant weeds infesting the test sites at Blackville or Tifton. Wild radish or rye in conjunction with one-half and full recommended rates of atrazine plus S-metolachlor provided 64 to 97% and 78 to 100% weed control, respectively, 4 wk after planting (WAP) across both locations. In the absence of a cover crop, weed control with atrazine plus S-metolachlor ranged from 54 to 98% at both locations. Weed control in wild radish cover crop plots alone was not different from rye. Wild radish or rye in conjunction with a one-half or full rate of atrazine and S-metolachlor provided >95% weed control at Tifton. Soil samples were collected from the control (non-sprayed, hand-weeded) subplots in all main plots on April 18, 2005. Soilborne pathogens were assayed from soil samples collected from the control and 1X herbicide subplots in all main plots on May 10, 2005, ca. 2 weeks after seeding sweet corn. Soils were assayed using dilution plating on media selective for Pythium and Fusarium. The population level and activity of Rhizoctonia were measured using a beet-seed colonization assay. Prior to incorporating cover crops, colonization of beet seed by Rhizoctonia was significantly lower with fallow (61%) than with wild radish (79%). Neither cover crops nor herbicide use had a significant effect on levels of soilborne pathogens at the second sampling. There also were no significant cover crop-by-herbicide interactions. Pythium populations increased more in rye (P=0.005) and wild radish (P<0.05) plots than in fallow plots. Populations of Fusarium spp. and F. oxysporum also increased significantly (P<0.03) after incorporating cover crops in fallow plots and in wild radish or rye plots, respectively, compared to the initial sampling. For insect evaluations, there were no differences in populations of corn earworm, the major pest of sweet corn, in corn ears at harvest. Data from the small plots were inconsistent with corn earworm populations from 2004 to 2005 in the various cover crops, indicating that a long term study with larger plots is essential when studying the effects of cover crops on pest insects. Sweet corn in wild radish or rye cover crop plots produced 21,000 to 48,000 and 28,000 to 35,000 marketable ears/ha, respectively, in herbicide treated and handweeded plots; however, marketable ear production was 39 to 83% lower than total ear production across all treatments at Blackville. Sweet corn in wild radish or rye cover crop plots in the absence of herbicides produced less marketable ears than herbicide treated plots, indicating a combination of cover crops and herbicides are required to optimize yields and obtain desirable weed control.

Impacts and Contributions/Outcomes

This research shows that wild radish can aid early season weed suppression in systems where herbicides are excluded or their use is substantially reduced. Furthermore, a wild radish or rye cover crop in conjunction with one-half rates of atrazine plus S-metolachlor will provide sufficient early season weed control to optimize sweet corn yields.