Organic cucurbit production involves using a variety of management strategies for the many pests and diseases that attack cucurbit crops, while maintaining healthy soils. Plasticulture systems, the use of polyethylene mulch on raised beds with drip irrigation, are commonly used for the production of many cucurbit crops. While plasticulture systems have many benefits, disadvantages include plastic disposal issues and costs and the intensive tillage required for installation. Strip-till systems have been shown to decrease soil erosion, increase soil moisture retention and increase soil microbial communities.

Striped cucumber beetles (Acalymma vittatum) and bacterial wilt (Erwinia tracheiphila) are two of the most damaging problems in cucurbits. Bacterial wilt is vectored by the striped (and spotted (Diabrotica undecimpunctata)) cucumber beetles. Infected beetles spread the bacteria by feeding and excreting frass on plants. Bacterial wilt can reduce cucurbit stands by up to 60% (Leib et al., 2000). Installing row covers is a management strategy commonly used for the cucumber beetle/ bacterial wilt complex.

Research at Penn State's Russell E. Larson Research and Education Center in Rock Springs, PA was conducted in 2013-14 to evaluated producing muskmelon (Cucumis melo ‘Athena’) or summer squash (Cucurbita pepo ‘Lioness’) in a strip-till system compared to a plasticulture system. Within these production systems the effectiveness of spunbonded polypropylene row covers was also tested.

Crops were managed following the National Organic Standards. A cover crop seeding mix of 75% winter rye (Secale cereal) and 25% hairy vetch (Vicia villosa) at a rate of 90 lb/A was planted in early September, the fall before both growing seasons.

cereal rye hairy vetch cover crop
Cover crop mix of winter rye (75% of seed weight) and hairy vetch (25% seed weight) in early June 2014.

A roller crimper was used to terminate the cover crop at flowering of the winter rye, and again when the hairy vetch had formed 2 pods per vine.

roller crimper
This water filled front mounted roller crimper kinks the stems of the cover crop every 8” along the stem, interfering the flow of nutrients and killing the plant. This is most effective when the plant is developing seeds, yet before the seeds mature.

Strip-till plots were prepared by making two passes with a Hiniker 6000 strip-tiller on 7 foot center-to-center row spacing.

Strip Tiller
Hiniker 6000 single row strip-tiller with cleaning coulters (above) that remove crop residue from planting zone, a cutting disk to cut through the remaining crop residue and soil surface, opening a zone for the cultivation shank that lifts soil from 8-9 inches deep, creating a one foot wide planting strip. This is all followed by a beater basket that breaks up soil clods. Two passes over the same row were needed for sufficient planting zone preparation.

Plastic mulch plots were prepared using a chisel plow, rototiller, and a bed shaper and plastic layer to form 2.5 foot wide and six inch high raised beds covered with 1.25 mL embossed black polyethylene mulch. Drip irrigation was used in both the plastic mulch and strip tillage systems.

Plasticulture and Strip Tillage sytems
A 2.5 foot wide and six inch high raised bed covered with 1.25 mL embossed black polyethylene mulch, with drip irrigation (above left).One foot wide strip tillage row with drip irrigation. Note the cover crop residue remaining between rows. (above right).

At transplanting row covers were installed immediately after transplanting over half of the test plants, while the other half were left uncovered. Agribond AG-30 was used for the summer squash experiment while Agribond AG-19 was used for the muskmelon experiment.

Row Covers
Row covers installed over one row within each plot (plasticulture and strip-till). One row in each plot was left uncovered.

Row covers were left on until 50% of the summer squash plants in strip-till plots had at least one blossom. Row covers were removed from the muskmelons 10 days after blossoms were observed in the strip-till plots.

Strip-till plots were weeded by hand after row covers were removed and once more mid-harvest. Four to 6 inches of wheat straw was placed between rows in the plasticulture plots and they were not weeded in the row.

Due to waiting for the appropriate stage of cover crop development to effectively kill it with the roller crimper, planting muskmelon and summer squash transplants was not achieved until relatively late in the season (June 26, 2013 and July 10, 2014). This late planting date is of smaller consequence for summer squash because there is a short time to harvest (50 days for ‘Lioness’), showing potential to be used in this system as a second or late season planting. For a heat loving long season crop such as muskmelon (‘Athena’ melons takes 75 days to harvest), this late planting proved risky as colder temperatures set in before harvest was completed in 2014.

Row covers had a significant effect on plant size at row cover removal. Row covers significantly increased average air and soil temperatures compared to plots without row covers, significantly increasing plant size at row cover removal. Row covers also served to protect the young plants from pests at a time when they were most susceptible to insect damage and disease. The combination of the increased rate of plant development and the extended time without pest damage greatly decreased the incidence of bacterial with in other studies (Hernandez, 2013; Rojas et al., 2011). Bacterial wilt incidence was low in all treatments evaluated in these experiments.

Row covers increased yields for summer squash in strip-till, but had negative impacts on yields from plasticulture plots due to mechanical damage to the leaf petioles by the row cover. Intense plant damage was observed in 2013 with moderate amounts in 2014 as a result of late row cover removal. Row covers were anticipated to increase yields of plasticulture plots had this damage not occurred. 

Row covers generally had little impact muskmelons. Yield increases as a result of row cover use were only observed in the 2013 plasticulture plots, and in the 2013 strip-till plots where the non-row cover plot produced no marketable fruit due to a late planting date.

Plants grown in the strip-till system had significantly lower yields than in the plasticulture system in both seasons, with one exception. In 2013, muskmelon yields from plants grown in the strip tillage system were only 37% of yields from plants grown the plasticulture system. The decreased yield from plants grown in the strip-till system compared to the plasticulture system was even lower in 2014. In 2013, summer squash grown in the strip-till system with row covers produced only 62% of the yields from plants grown in the plasticulture system.
Yet, in 2014 this treatment resulted in yields that were equal to those observed in the plasticulture system. The overall trend of lower yields in the strip-till plots follows a trend of equal or lower early season nitrate levels in strip-till plots followed by dramatically lower nitrate levels at season’s end. Soil temperatures were also significantly higher in plasticulture plots.

This research showed that the use of row cover creates increased air and soil temperatures, and therefore increased rates of plant growth, while decreasing pest pressure during the early stages of crop development. Other studies have shown row cover use to be beneficial for cucurbit growers in regions and years of high pest pressure, primarily due their ability to significantly reduce incidence of bacterial wilt and increase yields (Hernandez, 2013; Rojas et al., 2011). The potential for increased summer squash yields observed in this research along with early season pest management in both crops makes row cover use an important tool for cucurbit growers.

The use of the plasticulture system resulted in higher soil nitrate levels and elevated soil temperatures and higher yields than the strip tillage system in most comparisons. The high temperature requirements of muskmelons, along with the long growing season makes muskmelon production following the above described strip-till field preparation not an economically viable option.

While some yield losses are acceptable in this system due to decreased time needed to prepare the field and decreased input costs, the lower yields observed in the muskmelon trials were beyond an acceptable level. While the summer squash grown in the strip-till system with row cover matched the productivity of the plasticulture system in the 2014 season, it resulted in significantly lower squash yields in 2013.

The need for specialized tillage equipment, and the lateness of planting, and increased weed pressure are all obstacles to the successful use of this production technique for these crops. Further research should be conducted on the use of earlier maturing cover crops for earlier planting in strip-till systems. An investigation of alternatives to plastic mulch may also unveil new methods for seeing the benefits of plastic mulch without the environmental consequences associated with its use.