Clover Cover Crops, Weed Management and Consumer Tolerance to Insect Damage

Clover Cover Crops, Weed Management and Consumer Tolerance to Insect Damage

Summary

This project addressed three questions that arose naturally from a diversified family farm operation that sells to 50 regular customers and through a food co-op of 300 members.

1.) Can crimson and subterranean clover be used to replace synthetic fertilizers and reduce erosion? Which clover is better?

2.) How much insect damage will consumers tolerate when they purchase vegetables for home use?

3.) How effective are weed management alternatives to synthetic herbicides for vegetable production and sustainable farming practices?

Objectives
1.) Conduct a consumer survey to define potential market for the insect-damaged crops, and test different insect management practices that correspond to survey results.

2.) Compare crimson with subterranean clover as a cover crop and green manure crop for broccoli, crowder peas and sweet corn.

3.) Test alternative weed management strategies and compare the weed control efficacy and costs associated with the use of mulches, hand-weeding and herbicides.

Approach
As a cooperator in the project, a local food co-op surveyed their 300 members on willingness to buy sweet corn with earworms, crowder peas with stings from cowpea curculio and broccoli with worms. Information obtained from the surveys was used to determine the extent of insect management necessary for each crop. Concurrent cropping experiments were planned to compare the amount of insect damage on crops with no synthetic insecticide to the amount of damage on broccoli treated with Dipel, sweet corn treated with Sevin and peas treated with Thiodan.

The survey indicated that since most of the co-op members grew crowder peas they would not be purchasing them, so crowder peas were dropped from the cropping experiments. In other categories, 100 percent of the members indicated they would buy sweet corn damaged by ear worms. However, broccoli was viewed differently: 50 percent would buy their total broccoli supply without worm control by Dipel, 30 percent would buy half their broccoli without worm control by Dipel and 18 percent would not buy any of it without worm control by Dipel.

Since the survey indicated the food co-op members would purchase only about 25 percent of the grower’s broccoli crop, all of the broccoli was treated with Dipel to satisfy the conventional market outlet. In contrast, the demand for sweet corn by the food co-op members accounted for the total corn crop, which allowed the producer to comply with their wishes to have pesticide-free sweet corn. In an adjacent town, the produce market would not buy sweet corn with any earworm damage. The survey pointed out the need for a producer to know area market demands.

Results
Based on the survey answers, no Sevin was used on corn. In 1994, 80 percent of the corn was infested with earworms, and the members purchased it without major complaints. In 1995 corn earworm moths were less numerous and only about 16 percent was infested with earworms. Members purchased them without complaint.

For cover crop trials, subterranean and crimson clovers were planted in separate ¼-acre terraces in the fall and tilled under in the spring, two weeks prior to transplanting broccoli and planting sweet corn. As green manures, both clovers gave excellent yields for broccoli in 1994 and 1995 (1,100lbs/acre).

In 1994 sweet corn was destroyed by excess rain and three severe wind storms. At the time the sweet corn was blown down (silking stage), no major differences in growth of sweet corn were detected between crimson and subterranean clover.

In 1995, sweet corn yields with subterranean clover were 30 percent of yields with crimson clover. The growers discovered that crimson clover also was easier to rototill, produced more biomass and reseeded itself.

Based on three years experience, broccoli and sweet corn yields with crimson clover were equal to previous yields with synthetic fertilizers. These field trials indicated that for short season crops, such as broccoli, crimson and subterranean clovers as green manures provided adequate nutrients and could be substituted for synthetic fertilizers. For long season crops such as Silver Queen sweet corn, crimson clover was adequate as a green manure for nutrients but subterranean clover was not suitable.

The weed management tests compared 20-foot sections of 200-foot rows that were subjected to grass mulch, paper mulch, herbicide in reduced amounts, hand weeding or no weed control.

Grass clippings and paper mulch provided adequate weed control and crop yields. Based on that success, the participants expect that grass clippings and paper mulches could provide cost-effective weed control in communities where they present a waste disposal problem.

However, their use was found to be labor intensive. In these field trials, 726 hours per acre were required to gather and distribute grass clippings, and 363 hours were needed for paper mulch. The growers note that such time factors may not present a strong negative for home gardeners or for larger operations with mowers more efficient than an eight-horsepower riding mower to collect grass clippings.

Paper mulch revealed two potential drawbacks. A 20 percent early-season stunt in sweet corn in 1994 was attributed to a cooler soil temperature and less decomposition of soil organic matter, thus less available nitrogen than the grass-clippings, handweeded or herbicide treatments.

In 1995, paper mulch on broccoli increased the number of slugs to the point of crop damage. Paper provides cool damp conditions conducive to slug growth, and, perhaps offers more protection from predators as compared to mulches made from grass clippings.

Hand weeding required 100-200 hours per acre at $5 per hour, which would mean a labor cost of at least $500 per acre. This is less costly than the labor required to handle paper mulch (363 hours) or grass clippings (726 hours).

By using a band rather than broadcast application of herbicides, the amount used per acre was reduced by 67 percent. The labor cost to apply that herbicide with a backpack sprayer would be about $30 per acre.
The remaining treatment, no weed control, had no labor costs but crop yields were reduced by 40-70 percent due to weed competition for nutrients and water.

In conclusion, according to these on-farm tests, profitability after subtracting only labor costs for weed management treatments would be ranked high to low as follows:
1.) herbicide
2.) hand-weeded
3.) paper mulch
4.) none
5.) grass clippings.

For example, after deducting only the labor cost for weed management treatments, the profitability for sweet corn ranged from approximately $2,400/acre to a loss of $1,200/acre for the grass clippings.

Outreach
Field days were held in June and July, 1995, for a total attendance of about 50 people. A demonstration of insect sweeping was presented, and a sample sweep indicated significant insect diversity on the cooperator’s farm. A fact sheet on the 1994 broccoli results was distributed at both field days. The participants are available to present slides and talks to grower groups and other interested people.

December 1995.