Integrated effects of anaerobic soil disinfestation and beneficial microbes in strawberry production

Abstract

Fruit rot diseases, including anthracnose fruit rot and Botrytis fruit rot caused by Colletotrichum acutatum and Botrytis cinerea, respectively, pose major challenges to sustainable strawberry production in the United States. Organic and small-scale growers require non-chemical alternatives to soil fumigation due to health, regulatory, or technical constraints. This study evaluated anaerobic soil disinfestation (ASD), beneficial bacteria (Bacillus velezensis IALR619 and TerraGrow-a commercial product), and their combinations as integrated strategies to manage fruit rot, suppress weeds, and enhance fruit quality. A split-plot field trial was conducted over two growing seasons (2022/23-2023/24) at the Hampton Roads AREC in Virginia Beach, VA. ASD significantly reduced AFR, BFR, and overall fruit rot incidence compared to non-fumigated and Pic-Clor 60-fumigated controls. Post-plant inoculation with B. velezensis IALR619, TerraGrow, or TerraGrow + Oxidate 5.0 further decreased AFR incidence. ASD also reduced weed density and improved postharvest fruit firmness, total soluble solids, and juice pH. B. velezensis IALR619 inoculation enhanced fruit firmness compared to uninoculated controls. The beneficial microbes with ASD offer a promising alternative to synthetic fumigation, reducing fungicide usage by organic growers, small farms, and resource-limited growers, while also improving strawberry fruit quality.

Fig 1. The mean daily soil redox potential (Eh) was influenced by anaerobic soil disinfestation (ASD) during the three-week treatment period.

Value is the mean of n = 4 replicates for each treatment during for two growing seasons 2022/23 and 2023/24. The dotted line indicates the critical redox potential value of 200 mV. ASD_2022: ASD with brewer’s spent grain in the 2022/23 growing season. UTC_2022: Untreated control during the 2022/23 growing season. ASD_2023: ASD during the 2023/24 growing season. UTC_2023: non-fumigated control during the 2023/24 growing season.

Fig 2. Effect of preplant treatments (a) and post-plant treatments (b) on anthracnose fruit rot (AFR) fruit biomass during the 2022/23 and 2023/24 growing seasons.

UTC: non-fumigated control; Pic-Clor 60: [1,3-dichloropropene plus chloropicrin (40:60, w/w)] shank fumigated at 196 kg ha^-1; ASD: anaerobic soil disinfestation using brewer’s spent grain (4.5 tons/ ha^-1) as nitrogen source and paper mulch (4.8 tons/ ha^-1) as a carbon source. The post-plant treatments: N: non-inoculated control; BV: inoculated with B. velezensis IALR619,  OD₆₀₀ = 1.0; TG: inoculated with TerraGrow; OTG: inculcated with Oxidate 5.0 + TerraGrow. The means in the bar graphs with the same letters indicate no statistically significant differences (P < 0.05) using Fisher’s Least Significant Difference (LSD). Error bars indicate the standard error of the mean.

Fig 3. Effect of preplant treatments on botrytis fruit rot (BFR) diseases during the 2022/23 and 2023/24 growing seasons.

UTC: non-fumigated control; Pic-Clor 60: [1,3-dichloropropene plus chloropicrin (40:60, w/w)] shank fumigated at 196 kg ha^-1; ASD: anaerobic soil disinfestation using brewer’s spent grain (4.5 tons/ ha^-1) as nitrogen source and paper mulch (4.8 tons/ ha^-1) as a carbon source. The means with the same letters indicate no statistically significant differences (P < 0.05) using Fisher’s Least Significant Difference (LSD). Error bars indicate standard error of the mean.

Fig 4. Effect of preplant treatments on the biomass of infected fruits by other diseases during the 2022/23 and 2023/24 growing seasons.

UTC: non-fumigated control; Pic-Clor 60: [1,3-dichloropropene plus chloropicrin (40:60, w/w)] shank fumigated at 196 kg ha^-1; ASD: anaerobic soil disinfestation using brewer’s spent grain (4.5 tons/ ha^-1) as nitrogen source and paper mulch (4.8 tons/ ha^-1) as a carbon source. Means are represented by bars with the same letters, indicating no statistically significant differences (P < 0.05) using Fisher’s Least Significant Difference (LSD). Error bars indicate the standard error of the mean.

Fig 5. Effect of preplant treatments and post-plant treatments on fruit firmness.

UTC: non-fumigated control; Pic-Clor 60: [1,3-dichloropropene plus chloropicrin (40:60, w/w)] shank fumigated at 196 kg ha^-1; ASD: anaerobic soil disinfestation using brewer’s spent grain (4.5 tons/ ha^-1) as nitrogen source and paper mulch (4.8 tons/ ha^-1) as a carbon source. The post-plant treatments: N: uninoculated control; BV: inoculated with B. velezensis IALR619,  OD₆₀₀ = 1.0; TG: inoculated with TerraGrow; OTG: inculcated with Oxidate 5.0 + TerraGrow. Means are represented by bars with the same letters, indicating no statistically significant differences (P < 0.05) using Fisher’s Least Significant Difference (LSD). Error bars indicate the standard error of the mean.

Fig 6. Effect of preplant treatments on the total soluble solids (TSS) during the 2022/23 and 2023/24 growing seasons.

UTC: non-fumigated control; Pic-Clor 60: [1,3-dichloropropene plus chloropicrin (40:60, w/w)] shank fumigated at 196 kg ha^-1; ASD: anaerobic soil disinfestation using brewer’s spent grain (4.5 tons/ ha^-1) as nitrogen source and paper mulch (4.8 tons/ ha^-1) as a carbon source. Means are represented by bars with the same letters, indicating no statistically significant differences (P < 0.05) using Fisher’s Least Significant Difference (LSD). Error bars indicate the standard error of the mean.

Fig 7. Effect of preplant treatments on the pH of the fruit juice during the 2022/23 and 2023/24 growing seasons.

UTC: non-fumigated control; Pic-Clor 60: [1,3-dichloropropene plus chloropicrin (40:60, w/w)] shank fumigated at 196 kg ha^-1; ASD: anaerobic soil disinfestation using brewer’s spent grain (4.5 tons/ ha^-1) as nitrogen source and paper mulch (4.8 tons/ ha^-1) as a carbon source. Means are represented by bars with the same letters, indicating no statistically significant differences (P < 0.05) using Fisher’s Least Significant Difference (LSD). Error bars indicate the standard error of the mean.