In strawberry (Fragaria X ananassa) annual plasticulture production system, weeds and other pests can be a major problem. Early season weed competition is detrimental to strawberry production if not controlled. Preemergence herbicide choice is limited in strawberry production; alternative fumigants currently being used after the methyl bromide (MB) phase out do not provide complete control of pests, have regulatory constraints, and require maintenance of buffer zones. Many growers choose to no longer fumigate their land. With challenges in using herbicides and fumigants, it is necessary to look at alternative strategies to facilitate well establishment of strawberry plants. A field study was done in 2015-16 growing season at Hampton Roads Agricultural Research and Extension Center with the objective to evaluate the effect of soil solarization (SS) integrated with corn gluten meal (CGM), mustard seed meal (MSM), and paper pellet mulch (PPM) on crop health, weed control, and crop yield. The study was set up as a randomized complete block design with four replications or plots. Treatments were untreated control, CGM at 1710 kg/ha, MSM at 1121 kg/ha, and PPM 3662 kg/ha with and without SS. SS was done for a 3 week preplant period. Treatment products were broadcast on the respective strawberry plots and rototilled up to 15 cm depth. Plots were covered either with a 1.25 mil. black polyethylene tarp in case of non SS treatments, or with 1 mil. clear polyethylene tarp in SS treatments. When the same study was done in 2014-15 growing season, the SS + CGM plots were damaged by raccoons soon after treatment application, and that particular treatment evaluation was discontinued, and not included in the 2015-16 growing season. Each plot was 3.1 m of bed length by 0.8 wide at bed top, of which 0.9 m length of the bed was replaced with clear tarp in case of non-solarization plots, and that “window area” was used for weed data collection. For the SS plots, no tarp replacement was needed, and 0.9 m length of bed top was marked to collect weed data in 0.9 m long by 0.8 m wide area. Strawberry ‘Chandler’ were transplanted on 30 September, 2015. Plant stand count and health rating for each plot was done on a monthly basis. Weed density data was collected periodically through the season from October to April. Yield data was collected by picking berries twice a week during bearing season, and sorting them into marketable and non-marketable fruits. Weed density count was lower in plots treated with SS, SS+MSM, and SS+PPM as compared to the untreated control, but there were no significant differences in marketable or total yields among the different treatments.
The purpose of this project was to evaluate pelleted products with soil solarization (SS) for weed control in strawberry annual plasticulture production system. Weeds once emerged, can establish very fast. With the absence of MB, control of soil borne diseases and other pests is a problem. Though alternative fumigants are available, they are not as effective as MB. Use of fumigants comes with mandatory requirements such as maintaining buffer zones, writing a fumigant management plan, and dose restrictions. With lack of interest from chemical companies to register herbicides for many specialty crops, weed control remains a challenge in annual strawberry production. Currently registered herbicides such as oxyfluorfen and flumioxazin, have a 30 day –pre-plant application period, while others such as flumioxazin and napropamide have potential to cause phytotoxicity to strawberry plants (Southeast Regional Strawberry IPM Guide, 2015). Due to shortage of labor, weeds are often unattended at grower sites, and sometimes weeds are hand pulled as they come out of planting holes. In SS process, a clear tarp allows radiation to pass and trap heat; and can be used to increase soil temperature to the extent that it is lethal to pathogens, insects and weeds. SS is also more effective when used with other soil amendments (Ajwa et al., 2003). Paper mulch helps by preventing weed emergence. Paper mulch also helps to control nutsedge, which is not controlled by solarization. One of the advantages of using paper pellet mulch (PPM) is that it does not have weed seeds, does not blow away like shredded newspaper; the pellets expand upon absorbing water and releases water back to soil, keeping root zone moist. The paper pellets used in the study releases a starter fertilizer that promotes root development. The justification of using mustard seed pellets was that the allellopathic property of some plants in Brassicaceae inhibit growth, emergence and germination of weeds (Rice et al., 2007). Corn gluten meal is a minimum risk pesticide and also provides 10% nitrogen by weight and is a natural fertilizer. It controls weeds by preventing normal root development under dry conditions. In Virginia, a high percentage of strawberry is grown for fresh consumption and in summer, consumers with their families and friends pick strawberries at pick-your-own farms where they are in close contact with plants. Increased awareness among consumers about the use of pesticides in farms make them more at ease when minimum risk herbicides or non- chemical approaches are being adopted.
As listed in the proposal: 1. Evaluate pelleted products of mustard seed meal, paper, corn gluten meal integrated with soil solarization for weed control in annual strawberry plasticulture system. 2. Evaluate the effect of using pelleted products on crop yield of strawberries. 3. Evaluate the nutritional status of plants as a result of using pelleted products. 4. Evaluate crop growth through taking canopy growth data, and estimate growth of roots using a software. 5. Evaluate fruit quality of fruits as fruit firmness, sweetness and size. 6. Evaluate disease of plants in field. 7. Perform a cost analysis of using the pelleted products with soil solarization in a practical scenario at a grower’s farm.
The study was set up as a randomized complete block design with four replications at Hampton Road AREC, Virginia Beach, in the 2015-16 growing season. Treatments were soil solarization (SS) for a three week period, MSM (1121 kg/ha, MPT Mustard Products & Technologies Inc., Saskatoon), CGM (1710 kg/ha, Grain Processing Corporation, IA), PPM (3662 kg/ha, Lebanon Seaboard Corporation, PA) alone and in combination with SS and an untreated control. Treatment plots were pre-bedded and fertilizer was applied after pre-bedding. Fertilizer rates were adjusted according to each treatment as CGM (10%N), MSM (5:1:1) and PPM (0.7:1:0.4) provided some fertilizer. No adjustments to treatments were made for phosphorus or potassium as the recommended fertilizer addition rate was 0, but adjustment was made for nitrogen using fertilizer of grade 10-0-20. MSM and CGM treatments were broadcast after pre-bedding and prior to final bed formation. PPM was surface applied after the bed was formed in the first running. In the second run of bed forming, the appropriate plastic was used, 1 mil clear embossed polyethylene tarp (Robert Marvel Plastic Mulch, LLC, Annville, PA, 17003) for SS plots and 1.25 mil. black polyethylene tarp (TriEst Ag Group, Inc, Greenville, NC, 27835). Temperature probes were inserted at 2 inch and 6 inch depths to record temperatures in solar and untreated plots. A 0.9 m long section on each plot was covered with clear plastic to evaluate weed density to form a 0.9 m long by 0.8 m wide bed area. Total of 16 ‘Chandler’ plug plants were planted in each plot, five plants being in the window, and remaining 11 outside the window- on which yield data was collected. In our study floating row covers of 1.2 oz per sq yd were employed each time there was a threat of air temperatures dropping to twenties or lower thirties °F, depending on phenological stages of strawberry plant flowers and fruits (Poling, 2005). Italian ryegrass (Lolium multiflorum Lam.) was seeded in furrows for improving draining in furrows, and to suppress weed species. SS period was initiated on 3 September and ended on 25 September 2015. ‘Chandler’ plugs were transplanted in two rows per bed in a staggered manner at 14 inch spacing on 30 September 2015. Row covers were used on 4 January and 11 January, 2016 as air temperatures were expected to be low. On the 6 April 2016 temperature was supposed to be around 37 F, but we saw about 40% damage of open blossoms the day after. The same weekend an additional row cover of 1.2 oz per sq yd was put to prevent frost damage, as there was a prediction of a cold weekend.
Weed density count by species was collected November 2015 and in January 2016. Weeds were hand weeded after each count. Health rating and stand count was taken once a month from October 2015 to March 2016 using the scale of 0 to 10, where 0 = dead plant and 10 = vigorous plant. Canopy measurements were taken once in December 2015, and again in March 2016 on 6 berry plants per replicate. Crop yield data was collected from 21 April, 2015 and ended on 24 June, 2016. Marketable fruit comprised of fruit 10 g and above, without blemishes and diseases. Once a week during the harvest season, three berries from each plot were measured with Vernier caliper scale (Neiko®01407A, Taiwan) for fruit size, and kept in the refrigerator freezer with calyx off, for total soluble solids (TSS) reading. Berries were thawed, crushed, juice sieved through a fine mesh, puree temperature collected and refractometer reading noted at around 20 0C. At the end of the growing season, three plants were uprooted from each plot of three blocks, washed to get rid of soil and debris, and biomass of roots noted, and also the length of roots noted through winrhizo software (Regent Instruments Inc., Canada). When uprooting plants, care was taken to see that plants were taken from the bed center, and that plants looked healthy and disease free. The average of the season was analyzed by ANOVA and mean separation done with lsd at alpha 0.1, and no differences were found among treatments.
Data were analyzed using SAS v.9.3 and checked for normality of residuals. Data were transformed using log transformation where needed, and mean separation was done using LSD at alpha = 0.05 as default, and 0.1 in case of root biomass data. For analysis of fruit size and total soluble solid content, three fruits were considered, and average calculated over the season.
There were no significant differences in health rating among different treatments. Early season canopy diameter data indicated that the PPM and SS+MSM treated plants had larger canopy than the MSM, CGM, untreated or MSM + CGM plots. In the late season however, there were no significant differences among canopy diameter of plants to different treatments. The total weed density, which was measured twice in the 2015-16 season, showed a significant difference in treatments, where SS, SS + MSM, SS+ PPM had lower weed density counts than untreated plots. Main weeds during the growing season were common chickweed (Stellaria media (L.) Vill., wild garlic (Allium vineale L.), cudweed (Gnaphalium spp. L.), swinecress (Coronopus Zinn), bittercress (Cardamine L.), and speedwell (Veronica L.). In 2015-16 there was no significant difference in treatment in total yield (p: 0.3, alpha: 0.05, after log transformation). For root biomass, a significant difference was seen at alpha = 0.1, with SS, and SS+ PPM had the maximum biomass, and the least was seen in the non-treated plots. There were no differences in fruit size or root length in strawberries from the different preplant treatments.
Educational & Outreach Activities
Findings of the study were presented at the preplant meetings in Charlottesville, Richmond and Virginia Beach held on July 18, July 19, and July 22, 2016, respectively. Meeting in Charlottesville was attended by 17 growers and 5 industry members. In Richmond, meeting was attended by 12 growers and 5 industry members. In Virginia Beach, meeting was attended by 16 growers and 4 industry members. A poster on the study was presented on 14 August, 2016 at 8th International Strawberry Symposium in Québec City, Canada. A mix of industry representatives, university scientists, and growers viewed the findings of this study. There were ~12 attendees who viewed the poster. The same poster was also presented to small-farm growers and extension personnel at the 7th National Small Farm Conference in Virginia Beach, on 21 and 22 September, 2016. There were about 18 people who viewed the poster.
Many of these amendments evaluated in the study are new to berry production. PPM and MSM merit further evaluation with a longer duration of SS treatment. Based on the findings from this study, we have disseminated to growers what not to adopt or repeat in farm production practices. For example, we do not recommend SS period of less than 6 weeks even when used with amendments. We also do not recommend use of CGM due to its ability attract animals to its plots. We anticipate adoption of certain treatments such as PPM and MSM, after further evaluation, and after their rates are optimized for strawberry plasticulture production.
Limited economic analysis was done on treatment application costs for MSM, estimated at $1150/A, and for PPM estimated at $1765/A. In order to use these treatments in strawberry production, we need to achieve reduced weed pressure and an increase in yield with amended treatments over untreated control.
We are conducting on-farm trials in 2016-17 season at two grower farms: one in the city of Virginia Beach, VA, and other in Moyock, NC with a longer duration of SS with PPM and MSM treatments, to see if any of the treatments show promise in comparison to fumigated plots and untreated plots.
Areas needing additional study
PPM requires further evaluation in regards to optimizing dose rate requirements for strawberry production, and to look at different strategies to reduce treatment costs.