Cucurbit crops, such as cucumbers and watermelons, are staple produce in the United States, covering over 74,000 hectares and generating more than $1 billion annually. These crops are primarily grown using plasticulture, a system where plastic mulch is laid over raised beds to control weeds, retain soil moisture, and boost crop yields. However, plasticulture has its limitations. While the plastic mulch effectively suppresses weeds directly under it, the wide spaces between the rows, often left bare, become prime areas for weed growth. These weeds not only compete with crops for nutrients, sunlight, and water but can also harbor pests and diseases, complicating crop management and reducing yields.

Traditionally, farmers have relied on a combination of herbicides and manual labor to manage these weeds. However, the evolving resistance of weeds to herbicides and the rising costs of labor make these methods increasingly unsustainable. In this context, cover crops offer a promising alternative. Cover crops are plants grown primarily to protect and enrich the soil rather than for harvest. By planting cover crops between the rows of plastic mulch, farmers can suppress weed growth, reduce soil erosion, and improve soil health.

To explore the potential of cover crops in cucurbit production, Dr. Vollmer and his team conducted field trials in Maryland and New Jersey over two growing seasons in 2021 and 2022. They tested three types of cover crop treatments: cereal rye, spring oats, and a mix of both. These cover crops were hand-sown between the rows after the plastic mulch was laid, and different methods were used to terminate the cover crops approximately three weeks after planting the cucurbits. Termination methods included applying herbicides such as paraquat, a non-selective herbicide that kills a wide range of plants, and clethodim, which targets only grasses, as well as mechanical rolling, which flattens the cover crops to form a natural mulch.

The results of the study were compelling. Cover crops significantly reduced weed density before and after their termination. For instance, the presence of cover crops reduced broadleaf weed density by 73% before termination and by 83% two weeks after termination compared with areas without cover crops. The study also found that the method of cover crop termination influenced weed control effectiveness. When the cover crops were terminated using paraquat, weed control was particularly high, 90% for cereal rye and 91% for a mix of spring oats and cereal rye, compared with less effective outcomes after rolling.

One of the most problematic weeds in cucurbit production is smooth pigweed, a species known for its resistance to multiple herbicides. In the study, smooth pigweed density was reduced by over 70% in plots with cover crops compared with those without. Notably, terminating oats using paraquat completely suppressed smooth pigweed two weeks after termination. This is a significant finding, as it suggests that cover crops, combined with targeted herbicides, can be highly effective in managing even the most stubborn weeds.

While weed suppression is a critical benefit of cover crops, Dr. Vollmer and his colleagues also discovered that these crops could boost cucurbit yields. In their trials, cucumber yields increased by 63%, and watermelon yields by 52% in plots with cover crops compared to those without. This yield boost can be attributed to the reduced competition from weeds and the improved soil conditions created by the cover crops.

Cover crops such as cereal rye and spring oats help improve soil structure, increase organic matter, and enhance soil moisture retention. These factors contribute to a healthier growing environment for the cucurbit crops, leading to larger and more plentiful fruits. For instance, the study found that the average weight of marketable watermelon fruits was 21% higher in plots with cover crops than in those without.

The benefits extended to both the quantity and quality of the harvested fruits. In cucumber plots, cover crops led to a 65% increase in the number of marketable fruits, and in watermelon plots, marketable yields were 65% greater. This suggests that integrating cover crops into plasticulture systems not only addresses the problem of weed control but also enhances overall crop productivity, making it a win-win solution for farmers.

To fully appreciate the significance of this research, it’s important to understand what cover crops are and why they are beneficial. Cover crops are not grown for sale or consumption but are planted primarily to improve soil health, manage water, and control pests and weeds. Common cover crops include grasses like rye and oats, legumes like clover, and brassicas like radishes.

These crops play several critical roles in sustainable agriculture. First, they protect the soil from erosion by wind and water, especially during the off-season when fields might otherwise be bare. Second, they add organic matter to the soil as they decompose, improving soil fertility and structure. This organic matter enhances the soil’s ability to retain water, reducing the need for irrigation. Third, cover crops can suppress weeds by competing with them for light, water, and nutrients. Their dense growth creates a physical barrier that makes it difficult for weeds to establish themselves.

While the results of Dr. Vollmer and his colleagues’ research are promising, they also highlight the need for further investigation. For instance, determining the optimal timing for cover crop termination is essential to maximize their benefits without competing with the main crops. The study suggests that terminating cover crops around three weeks after planting the main crop is effective, but this timing may vary depending on factors like climate, soil type, and the specific crops being grown.

Moreover, the study raises questions about the long-term impact of using different termination methods and herbicides. While paraquat was effective in this study, its high toxicity and potential environmental impact make it less desirable. Future research could explore alternative herbicides or mechanical methods that might offer similar benefits with fewer drawbacks.

Finally, expanding the use of cover crops beyond cucurbit production to other types of crops and farming systems could help generalize these findings and promote wider adoption of sustainable practices.

As farmers continue to face the dual pressures of maintaining productivity and reducing environmental impact, the adoption of cover crops represents a practical and effective strategy. By harnessing the natural benefits of cover crops, farmers can build more resilient agricultural systems that are better equipped to meet the demands of a changing world.

In the pursuit of a sustainable future for agriculture, the work of Dr. Vollmer and his colleagues stands as a testament to the power of innovation and the promise of practices that work in harmony with nature.