Effect of fumigants and non-fumigants on nematode and weed control, crop yield, and soil microbial diversity and predicted functionality in a strawberry production system.

Fumigants are commonly used to control soil-borne pathogens of high-value crops, but they may also impact non-target soil microorganisms. Increasing interest in the use of sustainable management practices to control plant- and root-parasitic nematodes has resulted in the formulation of non-fumigant nematicides (chemicals or bionematicides) which are considered environmentally friendly alternatives to fumigants. However, the impact of these new products compared to standard fumigants on soil-borne pathogens, plant production, and the diversity and composition of non-target microbial communities in all crops remains unclear. To begin to address this knowledge gap, we examined the effect of fumigants commonly used in Florida (United States) strawberry production and newly formulated non-fumigant nematicides on nematode and weed control, plant growth, crop yield, and bacterial and fungal community diversity and predicted functionality. We found the standard fumigants increased crop yields and reduced weed pressure more than non-fumigants. Both fumigants and non-fumigants were an efficient management strategy to control sting nematodes. Treatments also impacted the abundance of specific beneficial and antagonistic taxa. Both fumigants and non-fumigants reduced soil bacterial and fungal diversity, an effect that remained for six months, thus suggesting a potential residual impact of these products on soil microorganisms. However, only fumigants altered soil microbial community composition and reduced network complexity, inducing a decrease or even a loss of some predicted bacterial and fungal functions, particularly during the first weeks after fumigation. Nevertheless, soil collected at the end of the season showed significant levels of root-knot nematode suppression in a growth chamber experiment, irrespective of the previous treatment. By linking the effect of fumigants and non-fumigants on soil-borne pests, plant and production, and the soil microbiome, this study increases our knowledge regarding the environmental impact of these products.

A reassessment of the fungicidal efficacy of 1,3-dichloropropene, chloropicrin, and metam potassium against Macrophomina phaseolina in strawberry.

BACKGROUND: The effectiveness of metam potassium, 1,3-dichloropropene, chloropicrin, and different ratios of 1,3-dichloropropene and chloropicrin on the reduction of natural and artificial inoculum of Macrophomina phaseolina were investigated in laboratory and field experiments. Additionally, a multivariate meta-analysis with data from six field trials conducted in Florida from 2012 to 2018 was performed. RESULTS: In small-plot field experiments using drip stakes, the highest rate (468 L ha-1 ) of metam potassium was most effective in controlling M. phaseolina in infected crowns buried at 15.2 cm from the point of fumigant injection, whereas none of the rates was able to reduce inoculum buried at 30.5 cm. In closed-container experiments, use of the highest rate of 1,3-dichloropropene (168 kg ha-1 ) resulted in the highest level of pathogen control. Different rates of chloropicrin also reduced inoculum when compared to the non-treated control. 1,3-dichloropropene + chloropicrin at different ratios were also highly effective in controlling M. phaseolina. Results from the meta-analysis of open-field experiments indicated that metam potassium and 1,3-dichloropropene + chloropicrin (63:35, v:v) treatments were significantly more effective in reducing M. phaseolina than the 1,3-dichloropropene + chloropicrin (39:60, v:v) treatment; however, metam potassium was not as effective at the side of the beds. CONCLUSION: 1,3-dichloropropene alone and in mixture with chloropicrin were more effective in reducing inoculum of M. phaseolina than chloropicrin alone, indicating the fungicidal efficacy of 1,3-dichloropropene. Formulation with higher 1,3-dichloropropene concentration performed better than the formulation with higher chloropicrin concentration in field trials. Metam potassium was effective when applied at the highest rate, but with limited lateral movement perpendicular to the drip irrigation line. © 2022 Society of Chemical Industry.

Cultivar Selection Is an Effective and Economic Strategy for Managing Charcoal Rot of Strawberry in Florida.

Macrophomina phaseolina, the causal agent of charcoal rot, is a soilborne pathogen that affects strawberry crowns leading to plant wilt and collapse. Disease management involves a combination of physical, cultural, and chemical methods. Field trials were conducted for 10 consecutive Florida seasons (2010-11 to 2019-20) to determine the susceptibility of strawberry cultivars to charcoal rot and the effect of cultivar selection on disease and to estimate the economic impact of cultivar selection on disease management. Six cultivars grown commercially in Florida were chosen and grouped as highly susceptible (HS) ('Strawberry Festival' and 'Treasure'), susceptible (S) ('Florida Radiance' and 'Florida Beauty'), and moderately resistant (MR) (Sensation 'Florida127' and Winterstar 'FL05-107') according to their susceptibility levels. After a primary analysis of the individual trials, a network meta-analysis was conducted to estimate and compare the final disease incidence and the disease progress rate of each susceptibility group. The economic impact of charcoal rot on strawberry production and gross revenue was estimated based on plant production functions, weekly fruit prices, and disease progress over time with parameters obtained via the meta-analytical models. Disease incidence was reduced by 91.5 and 77.3%, respectively, when the MR and S cultivar groups were adopted instead of the HS group. There was a 62.5% reduction in the disease incidence when the MR group was used instead of the S group. Significant differences in disease progress rates were also observed when the MR and S groups were adopted instead of the HS group. Therefore, the adoption of more resistant cultivars is an effective strategy when incorporated into a charcoal rot integrated management program and can significantly impact growers' revenue by reducing disease incidence, preventing yield loss, and, consequently, minimizing economic losses.

Physical, Cultural, and Chemical Alternatives for Integrated Management of Charcoal Rot of Strawberry.

Macrophomina phaseolina, the causal agent of charcoal rot in strawberry, induces plant wilting and collapse. The pathogen survives through the production of microsclerotia in the soil and in strawberry debris. However, its management is difficult, and the disease has become an increasing problem for the strawberry industry. Physical, cultural, and chemical alternatives for integrated management of charcoal rot were evaluated in laboratory and field trials during the 2017-18 and 2018-19 strawberry seasons. In a laboratory trial, M. phaseolina microsclerotia were subjected to heat treatment and germination was inhibited at 52, 56, 80, and 95°C after 30, 10, 1, and 0.5 min of exposure, respectively. In infected strawberry crowns, microsclerotial viability was reduced after 5 min, regardless of temperature, whereas in the field, reduction was observed after 1 min. In field trials, charcoal rot incidence of inoculated strawberry plants transplanted into white-striped plastic-mulched beds was reduced to 20.8%, compared with 60.8% for plants grown in the black plastic mulch. On commercial farms, crop residue removal from infested areas reduced the M. phaseolina population in the soil but did not decrease charcoal rot incidence. Moreover, M. phaseolina propagule densities in the soil and in strawberry debris was reduced by fumigant application at crop termination but surviving propagules allowed the population to increase over the summer. Furthermore, preplant fumigation with metam potassium reduced soil population and charcoal rot incidence. Overall, the adoption of integrated approaches such as physical, chemical, and/or cultural methods played a significant role in reducing M. phaseolina inoculum and contributed to control of the disease in areas with high disease pressure.

Fluensulfone and 1,3-dichloroprene for plant-parasitic nematode management in potato production.

Florida produces 35% of the spring potato (Solanum tuberosum) crop in the USA, but plant-parasitic nematodes suppress yield in the region. The stubby-root nematodes, Paratrichodorus (Nanidorus) spp. and Trichodorus spp., vectors for corky ringspot disease, and sting nematode (Belonolaimus longicaudatus) are among the most damaging nematodes in Florida potato production. Nematicide application is an important component of nematode management in this system, but relatively few nematicides are currently available. Therefore, pre-plant applications of fluensulfone nematicide at various rates (3, 4, 6, and 8 l/ha) and the commercial standard fumigant 1,3-dichloropropene (1,3-D) were tested for management of plant-parasitic nematodes in three field trials from 2016 to 2018. Both fluensulfone, at all rates, and 1,3-D consistently decreased sting nematode abundance relative to the untreated control at harvest. Neither fluensulfone nor 1,3-D affected stubby-root nematode abundances at harvest. Efficacy of fluensulfone and 1,3-D for lesion nematode (Pratylenchus sp.) management varied by year. In 2016 and 2018, fluensulfone at most rates and 1,3-D increased marketable potato yield relative to the untreated control with increases by 49 to 66% and 33 to 55% in 2016 and 2018, respectively. In 2017, fluensulfone at lower rates (3, 4, and 6 l/ha) increased marketable potato yield relative to the untreated control by 41 to 61%, but fluensulfone at 8 l/ha and 1,3-D had similar yields to the untreated control. Results suggest that nematicidal activity of fluensulfone and 1,3-D varies by target nematode with both products effective against sting nematode, ineffective against stubby-root nematodes, and inconsistent against lesion nematode. In conclusion, fluensulfone and 1,3-D are effective options for sting nematode management in Florida potato production.Florida produces 35% of the spring potato (Solanum tuberosum) crop in the USA, but plant-parasitic nematodes suppress yield in the region. The stubby-root nematodes, Paratrichodorus (Nanidorus) spp. and Trichodorus spp., vectors for corky ringspot disease, and sting nematode (Belonolaimus longicaudatus) are among the most damaging nematodes in Florida potato production. Nematicide application is an important component of nematode management in this system, but relatively few nematicides are currently available. Therefore, pre-plant applications of fluensulfone nematicide at various rates (3, 4, 6, and 8 l/ha) and the commercial standard fumigant 1,3-dichloropropene (1,3-D) were tested for management of plant-parasitic nematodes in three field trials from 2016 to 2018. Both fluensulfone, at all rates, and 1,3-D consistently decreased sting nematode abundance relative to the untreated control at harvest. Neither fluensulfone nor 1,3-D affected stubby-root nematode abundances at harvest. Efficacy of fluensulfone and 1,3-D for lesion nematode (Pratylenchus sp.) management varied by year. In 2016 and 2018, fluensulfone at most rates and 1,3-D increased marketable potato yield relative to the untreated control with increases by 49 to 66% and 33 to 55% in 2016 and 2018, respectively. In 2017, fluensulfone at lower rates (3, 4, and 6 l/ha) increased marketable potato yield relative to the untreated control by 41 to 61%, but fluensulfone at 8 l/ha and 1,3-D had similar yields to the untreated control. Results suggest that nematicidal activity of fluensulfone and 1,3-D varies by target nematode with both products effective against sting nematode, ineffective against stubby-root nematodes, and inconsistent against lesion nematode. In conclusion, fluensulfone and 1,3-D are effective options for sting nematode management in Florida potato production.

Effect of Formulations of Allyl Isothiocyanate on Survival of Macrophomina phaseolina from Strawberry.

Management of Macrophomina phaseolina, causal agent of charcoal rot in many crops worldwide, including strawberry, has become more challenging since the phase out of methyl bromide (MeBr). The search for a fumigant equally effective as MeBr to control soilborne pathogens has been extensive. Allyl isothiocyanate (AITC), a biofumigant recently registered in the United States, was evaluated at different rates, formulations, fumigant combinations, and application methods in the fall of 2014 and 2015 at two research facilities in Balm and Dover, FL. The efficacy of treatments was determined by evaluating the survival of M. phaseolina inoculum on infested corn-cob litter buried in bags 7.6 and 20.3 cm deep in the center, and 7.6 cm deep in the side, of plastic mulched raised beds. The biofumigant was shown to be more or as effective in reducing populations of M. phaseolina in the soil compared with standard fumigants, such as chloropicrin and 1,3-dichloropropene with chloropicrin. Thus, AITC is a promising biofumigant alternative for managing charcoal rot of strawberry, particularly in organic production systems, and should be evaluated for the management of other soilborne pathogens.