Final report for OS18-117
Project Information
Alabama has some of the best fields for agriculture in the country due to ample rainfall, long growing season, and proximity to major urban markets. Considering the long-term drought in California, urban development and high land cost in central and south Florida, vegetable acreage in Alabama is projected to rise significantly in the next decade due to low production costs and long growing season for crops. However, one of the biggest problems with expanding vegetable production in Alabama and the Southeast is limited weed control options and tremendous weed pressure as compared to Midwest and northern U.S. Southern crabgrass, goosegrass, pigweed species, lambs quarter and nutsedges can outcompete plant growth early in the season, and reduce yield and harvest efficiency. Moreover, sensitive vegetable varieties can be easily injured by herbicides, and herbicides registered for vegetable production are generally limited as compared to agronomic crops. Considering limited herbicide options, strong market demands, high weed pressure and long growing season, weed control in vegetable production has been challenging in the Southeast, particularly in organic production.
To suppress weeds, increase soil temperature, retain moisture and prevent nutrient leaching, many vegetable farmers utilize plastic mulch in their production. However, initial installation costs, irrigation equipment and annual material costs are high. In some cases, direct seeding without plastic mulch may be easier to operate and more cost-effective as plastic mulch disposal and recycling are both financially and environmentally costly. To increase sustainability, biodegradable mulches have been developed since the 1980s but adoption rate is low due to high cost, inconsistent breakdown time, and lack of knowledge among farmers about the performance of biodegradable mulches. So far, little research and extension work has been done in the Southeast to evaluate the efficacy and economic viability of newer biodegradable mulches and to promote this option to vegetable farmers.
The proposed solutions to address the problems stated above include evaluating high-residue cover crops and biodegradable mulches for weed control in sustainable vegetable production.
- Evaluating high-residue cover crop systems plus reduced tillage for weed suppression and reduction of herbicide usage as compared to bare ground system.
- Assessing the potential of reducing polyethylene mulch usage with adopting high-residue cover crop systems plus biodegradable mulches in organic production.
Cooperators
Research
Field studies were conducted in Fall 2018 and Spring/Summer 2019 in Henry and Lee counties in Alabama (Hornsby farm and Wiregrass research and extension center). Challenges faced in the previous year of research were addressed through modification of cover crop seeding method, reduction of row middle size, evaluation of living versus terminated mulch systems, and addition of preemergence herbicides for further weed suppression. The study had a randomized complete block design with 4 replications. Plot was 3.6 by 6 m long bed, with beds formed on 1.8m row spacing (typical grower spacing). Beds were formed and plastic mulch was laid in Fall 2018. White clover, cereal rye, and a mixture of cereal rye plus crimson clover were broadcast seeded at rates of 16, 224, and 224 + 28 kg ha-1 (high seeding rates). Both seedless melons of the ‘Crunchy Red’ variety and bell peppers of the ‘Aristotle’ variety were included in individual plots. Every other row was planted to reduce cover crop interference and allow herbicide applications on an individual plot basis. Plots were either rolled before termination, terminated with glyphosate at 1.5 kg ha-1, glyphosate at 1.5 kg ha-1 + paraquat at 560 g ha-1, or glyphosate at 1.5 kg ha-1 + flumioxazin at 143 g ha-1 (Table 3). Plots that received glyphosate only were either rolled before or after applications to determine if residues from chemically terminated plots degrade faster than those rolled green. Vegetables were planted on 46 cm plant spacing and watermelons were planted at a 3:1 seedless melon to pollinator ratio. Herbicide treatments consisted of preemergence application of flumioxazin at 143 g ai ha-1 + trifluralin at 841 g ha-1 and/or postemergence applications of halosulfuron at 39 g ha-1 + clethodim at 136 g ha-1 5 WAP. Some plots only received a pre or a post application. Treatments are listed in table 3. Plant heights or vine lengths were recorded at 4 and 8 WAP followed by yield at maturity. Data from Henry County past 4 WAP is unavailable due to deer damages and crop failure. Data were subjected to an analysis of variance and means separations were generated from Fisher’s protected LSD.
Vegetable Trial Summary 2017 & 2018 Cover Crop Integration into Vegetable Production
Cover crop biomass for cereal rye and cereal rye plus crimson clover mixtures were 4,642 and 5,253 kg ha-1 for Henry County and 6,841 and 5,497 kg ha-1 for Lee County (Table 4). A location by treatment interaction was observed for weed densities 4 WAP (P = 0.05). Weed densities for all cover crops tested were significantly lower than the nontreated control 4 WAP in Henry and Lee counties with reductions of 65 to 96% in Henry County and 76 to 90% in Lee County (Table 5). Weed densities in Lee County were also significantly reduced for plots with cover crops compared to the nontreated control 8 WAP. However, cover crops did not differ from one another regardless of herbicide regime or termination method. In general, addition of a preemergence herbicide did not increase weed suppression.
A location by treatment interaction did not exist for watermelon vine lengths 4 WAP. Therefore, data were combined. No significant differences were observed for watermelon vine lengths 4 WAP for any treatment compared to the nontreated control (Figure 3). A location by treatment interaction was observed for bell pepper heights 4 WAP (P = 0.04). Regardless of termination method, bell peppers planted in cereal rye + crimson clover plots that received preemergence and postemergence applications and the chemical control had significantly reduced heights of 27 to 42% as compared to the nontreated control in Henry County (Figure 4). Bell peppers grown in the chemical control plots in Lee County also had significantly lower heights than the nontreated control by 33%. The results for the chemical control are likely due to drift of flumioxazin onto plastic during termination of winter weeds prior to planting, which grower should be aware of in their production. Data collection from Henry County was not taken following after 4 WAP due to plot destruction therefore the remainder of the discussion pertains to Lee County only.
Bell pepper heights in Lee County 8 WAP for all cereal rye and cereal rye plus crimson clover mixtures (PRE + POST, rolled) were significantly higher as compared to the nontreated control with increases of 19 to 47% (Figure 5). Bell pepper yields followed similar trends and the treatments listed above yielded more than the nontreated control by at least 4-fold (Figure 6). Watermelon vinelengths recovered from injury observed in the chemical control plots by 8 WAP and were 48% longer than the NTC (Figure 5). Additionally, vinelengths of watermelons grown with cereal rye and cereal rye cover crop residues were 19 to 47% longer than the NTC with the exception of the cereal rye and crimson clover mixture that did not receive a preemergence herbicide application. Compared to the nontreated control, watermelons grown with terminated mulch had increased yields at least 3-fold. Living mulch of white clover did not increase yields as compared to the nontreated control and a large amount of disease was observed on watermelon plants in those plots. Watermelons grown in plots with cereal rye residues that received a pre and post herbicide application and cereal rye + crimson clover mixtures with all herbicide regimes produced yields that were not significantly different from the chemical control. Similar to bell peppers, watermelons in the chemical control were injured early in the season from flumioxazin drift onto plastic while terminating winter weeds before planting. However, the growing season for watermelons is much longer in comparison to bell peppers and plants were able to recover. The data suggest terminated cover crop residues in combination with herbicide applications can produce similar yields as the chemical control, however, there is concern with PRE herbicide drift on plastic causing crop seedling injury. Furthermore, watermelons grown with cereal rye + crimson clover residues that only received a post herbicide application in row middles produced yields similar to the chemical control, indicating a preemergence herbicide application could be removed from programs in the presence of cover crop mixtures. Additional research may be warranted to further explore the practicality of using cover crop residues for weed suppression in vegetable production. Cover crop residues in combination with herbicide regimes could provide an additional platform for weed suppression in vegetable row middles.
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Table 3. Cover crops, termination methods, and herbicide timing |
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Cover Crop |
Termination Method |
Herbicides (row middles)AB |
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White clover |
Glyphosate (1.5 kg ai ha-1) + paraquat (560 g ai ha-1) |
PRE |
|
Cereal rye |
rolled |
PRE + POST |
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Cereal rye |
rolled |
POST |
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Cereal rye + crimson clover |
Glyphosate (3.1 kg ai ha-1), rolled |
PRE + POST |
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Cereal rye + crimson clover |
rolled |
PRE + POST |
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Cereal rye + crimson clover |
rolled |
POST |
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Chemical control |
Glyphosate (1.5 kg ai ha-1) + flumioxazin (143 g ai ha-1) |
PRE + POST |
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NTC |
N/A |
N/A |
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A PRE application: flumioxazin (143 g ai ha-1) + trifluralin (841 g ai ha-1) B POST application: halosulfuron (39 g ai ha-1) + clethodim (136 g ai ha-1) at 5 WAP |
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Table 4. Cover crop seeding rates and biomass at termination in Henry and Lee counties in 2019. |
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Cover Crop |
Seeding rate (kg ha-1) |
Biomass at Termination (kg ha-1) |
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Henry Co. |
Lee Co. |
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White clover |
16 |
N/A |
N/A |
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Cereal rye |
224 |
4642 |
6841 |
|
Cereal rye + Crimson clover |
224 + 28 |
5253 |
5497 |
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Table 5. Weed densities 4 and 8 weeks after planting |
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Cover Crop |
Weed Density 4 WAP C (plants per 10 m2) |
Weed Density 8 WAP (plants per 10 m2) |
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Henry Co. |
Lee Co. |
Lee Co. |
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White clover |
1.68 c |
6.05 bc |
1.68 b |
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Cereal rye (PRE + POST, rolled) |
1.61 c |
4.10 bc |
3.29 b |
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Cereal rye (POST, rolled) |
3.49 bc |
5.78 bc |
6.05 b |
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Cereal rye + crimson Clover (PRE + POST, glyphosate) |
14.06 b |
2.35 c |
19.10 b |
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Cereal rye + crimson clover (PRE + POST, rolled) |
1.54 c |
3.22 bc |
2.35 b |
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Cereal rye + crimson clover (POST, rolled) |
2.35 c |
6.79 b |
3.90 b |
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Chemical control (PRE + POST) |
9.88 bc |
4.17 bc |
10.96 b |
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NTC |
41.17 a |
26.03 a |
101.45 a |
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A Weed densities were combined for Amaranthus spp., Cyperus spp., Oenothera sp. and Digitaria spp. B Means followed by the same letter in a column are not significantly different at P = 0.05 C Location x cover crop interaction observed 4 WAP (P = 0.0029) |
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Educational & Outreach Activities
Participation Summary:
This study has been shown in Wiregrass cover crop field day back in Mar 2019, and was presented in the Southern Cover Crop Conference in Auburn AL in July of 2019 to 80 vegetable growers, agricultural professionals and researchers which has generated large amount of interest due to low requirement on equipment, easy implementation, effective results to suppress weeds with less herbicides, and very visual results for weed suppression. An extension article has been developed to promote this method to vegetable growers in AL and the southeast. A presentation developed from this study will be conducted through ACES online webinar and AL fruit and vegetable conference later this year. Continuation of this study on farm and on agricultural research stations will be carried out in future when more funding is secured.
Learning Outcomes
Establishing cover crop in plasticulture vegetable system without special equipment other than tractor and fertilizer spreader.
Terminate cereal grain cover crop with using chemicals
Effectively suppress weeds in row middles with less chemicals
Increase crop yield with less herbicide input and higher profit margin
Project Outcomes
Weed densities for all cover crops tested were significantly lower than the non-treated control 4 weeks after planting in Henry and Lee counties with reductions of 65 to 96% in Henry County and 76 to 90% in Lee County. Bell pepper yields followed similar trends and several cover crop treatments yielded more than the non-treated control by at least 4-fold. Compared to the non-treated control, watermelons grown with terminated mulch had increased yields at least 3-fold. The data suggest terminated cover crop residues in combination with PRE herbicide applications can produce similar yields as the chemical control, however, there is concern with PRE herbicide drift on plastic causing crop seedling injury. Furthermore, watermelons grown with cereal rye + crimson clover residues that only received a post herbicide application in row middles produced yields similar to the chemical control, indicating a PRE herbicide application could be removed from programs in the presence of cover crop mixtures.
Through research studies in this project, we successfully eliminated the glyphosate application to terminate cover crops, and proved addition of a PRE herbicide application at transplanting is not necessary. Cover crop treatments produced statistically similar amount of vegetables as conventional chemical weed control check. This means much less chemicals are needed after eliminating two applications of herbicide for vegetable production without sacrificing yield, and system sustainability has been increased. The estimated saving for these two applications was $5 (glyphosate cost) + $15 (PRE herbicide cost) + $5 (labor, surfactant, equipment wear, and fuel cost) =$25 per acre, in addition to the benefits that cover crop bring to producers such as improve soil texture, promote soil microbial activities, increase nutrient and soil OM level, conserve soil moisture, etc. Clover is also beneficial for pollinators and we have observed large amount of bees and pollinators in Mar and April before cover crop termination. Vegetable producers and researchers also showed sufficient interest in alternative mulch which will certainly increase system sustainability. More research is needed in this area to further evaluate these alternative mulches made by cellulose and starch regarding their persistence and surface integrity.
We will need to apply additional funding to continue this project since we saw amazing results of suppressing weeds with two fewer applications of herbicides. System sustainability has been elevated significantly.