Spring-Seeded Grass Cover Crops in Watermelon Production
Commercially acceptable weed control is difficult to achieve in plasticulture vegetables even with pre- and post-emergent herbicide applications. These applications often do not provide season long weed control between rows. Moreover, several weed species have become resistant to commonly used postemergence herbicides, including common ragweed and pigweed species. Cover crops are an additional tool that could be successfully integrated into a weed management program.
Objectives
- Evaluate the use of cover crop management tactics on weed suppression
- Evaluate the utility of cover crops for reducing herbicide applications and environmental impact in plasticulture systems.
- Demonstrate the utility of cover crops for weed management in plasticulture production.
Methods
This study was conducted at the Wye Research and Education Center in Queenstown, MD. The design was a two-factor factorial arranged in a split-plot design consisting of cover crop management and factorial subplots of cover crop species and residual herbicide treatment (Table 1). Cereal rye (240 lb a⁻¹), spring oats (277 lb a⁻¹), or cereal rye (120 lb a⁻¹) + spring oats (138 lb a⁻¹) were seeded in between plastic rows at least 4 weeks prior to transplanting watermelon. No cover crop treatments were also included for comparison. Cover crops were managed by terminating with Gramoxone (1.25 pt a⁻¹), Select Max (16 oz a⁻¹), or no herbicide (rolled-only). Residual herbicide treatments consisted of Reflex (24 oz a⁻¹) + Dual Magnum (1.67 pt a⁻¹) or no residual herbicide.
Cover crops were terminated 3 weeks after transplanting (WATr) using a tractor-mounted shielded sprayer (Figure 1). However, additional crimping was required and achieved with a second tractor pass without an herbicide application. Residual herbicides were applied using a hooded backpack sprayer 24 hours after cover crop termination. All plots were evaluated for weed density and crop response.
| Cover Crop Managment | Cover Crop Species | Residual Herbicide |
|---|---|---|
| 1. Gramoxone (1.2 pt a⁻¹) |
1. cereal rye (240 lb a⁻¹) 2. spring oats (277 lb a⁻¹) 3. cereal rye (120 lb a⁻¹) + spring oats (138 lb a⁻¹) 4. no cover crop |
1. Reflex (1.5 pt a⁻¹) + Dual Magnum (1.67 pt a⁻¹) |
| 2. Select Max (1 pt a⁻¹) | 2. No residual herbicide | |
| 3. No herbicide (rolled) |
Results
The presence of a cover crop, as well as termination method, influenced broadleaf weed density and watermelon yield. Cover crop treatments, regardless of species, reduced overall broadleaf weed density 90%, 92%, 75% compared to no cover treatments 4, 6, and 8 WATr, respectively (Figure 2). At 4 WATr, plots terminated with Gramoxone showed a 100% decrease in broadleaf weed density compared to rolled plots and plots terminated with Select Max (Figure 3). At 6 WATr, plots terminated with Gramoxone showed a 100% reduction in broadleaf weed density compared to plots treated with Select Max, but there were no significant differences among rolled-only plots. At 8 WATr, plots terminated with Gramoxone showed a 60% reduction in broadleaf weed density compared to plots terminated with Select Max and rolled-only plots.
