Figure 1. Terminating the cover crop with a shielded herbicide application.
Using Spring-Seeded Cover Crops to Complement Weed Management in Cucurbits
Weed management in plasticulture vegetable systems can be challenging. Control can be achieved with herbicides, but fewer options are available due to lack of registered products and loss of efficacy due to the presence of herbicide resistance weeds. Cover crops are an alternative tool that has successfully been used for weed management in multiple cropping systems. Cover crops help to suppress weeds through direct competition with and physical suppression of emerging weeds. However, unlike herbicides, cover crops alone do not kill weeds, and weed escapes can still be a problem. Therefore, we examined how spring-seeded grass cover crops could be used in conjunction with herbicide programs to manage weeds in cucurbits.
| Cover crop | Termination | Residual Herbicide |
|---|---|---|
| cereal rye | clethodim | Yes |
| spring oat | paraquat | No |
| spring oat + cereal rye | rolled | |
| no cover |
ᵃ Cover crop seeding rates consisted of cereal rye (240 lb/A), spring oats (277 lb/A), and cereal rye (120 lb/A) + spring oats (138 lb/A)
ᵇ Cover crop termination methods consisted of clethodim (Select Max, 16 oz/A), paraquat (Gramoxone SL 2.0, 2 pt/A), and rolled via one pass of a tractor followed by shielded spray.
ᶜ Residual herbicide treatment consisted of applying fomesafen (Reflex, 24 oz/A) plus S-metolachlor (Dual Magnum, 1.67 pt/A). Dual Magnum and Reflex are not currently labeled for cucumber and watermelon production in Maryland.
In 2021 and 2022 watermelon trials were conducted at the University of Maryland Wye Research and Education Center in Queenstown, MD and cucumber trials at the Rutgers Agricultural Research and Extension Center in Bridgeton, NJ. These trials evaluated different methods to manage both cover crops and weeds (Table 1). Three different cover crop treatments were seeded immediately after laying plastic (approximately 4 weeks before seeding/transplanting the cash crop. A no cover treatment was also included for comparison. Cover crops were terminated either with a shielded sprayer application of clethodim or paraquat, or by rolling with a tractor at least 4 weeks after seeding/transplanting (Figure 1). To evaluate whether or not a residual herbicide was needed in addition to the cover crop residue, Dual Magnum + Reflex was applied to select plots.
Results
Spring-seeded grass cover crops alone caused a significant reduction in weed density several weeks after planting in both cucumber and watermelon trials. Overall cover crops reduced cucumber weed density 42% and watermelon weed density 68% (Figure 2). This trend continued up to harvest. Overall, the presence of cover crop residues on the soil surface provided good weed control (Figure 3). In the cucumber study, terminating a cover crop with paraquat provided better weed control than having no cover crop or terminating the other cover crops with clethodim or by rolling (Figure 4). Similar results were observed in the watermelon study when oats and rye were terminated with paraquat. Both cucumber and watermelon yields were generally higher when a cover crop was included; however, the oat + rye treatment had similar watermelon yields to the no cover treatment (Figure 5). In addition, cucumber yields were 35% greater when the cover crop was terminated with paraquat.
* Values for the same treatment with the same letter are not significantly different according to Student’s T-test (α = 0.05).
Summary
These results show that the inclusion of a spring-seeded grass cover crop can complement weed control programs in plasticulture vegetables such as cucumber and watermelon.
- Seeding a cover crop such as spring oats early allows it to compete with weeds prior to seeding/transplant.
- Allowing the cover to grow after seeding/transplant allows for additional biomass production, which allows for more weed-suppressing residue following termination.
- Applying paraquat allows for both cover crop termination and effective control of emerged weeds.
Acknowledgements
Funding for this study was provided by National Institute of Food and Agriculture, Crop Protection and Pest Management, Applied Research and Development Program through award #2020-70006-33016. The authors would like to than the farm and weed science crews and the UMD Wye Research and Education Center and the Rutgers Agricultural Research and Extension Center.
This article appears in October 2023, Volume 14, Issue 8 of the Vegetable and Fruit News
Vegetable & Fruit News, October 2023, Volume 14, Issue 8
Vegetable and Fruit News is a statewide publication for the commercial vegetable and fruit industries and is published monthly during the growing season (April through October). Subscribers will receive an email with the latest edition.
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