Use of Crop Rotations, Cover Crops and Green Manures for Disease Suppression in Potato Cropping Systems

Crop rotations and the inclusion of cover crops and green manures are primary tools in the sustainable management of soil-borne diseases in crop production systems. Crop rotations can reduce soil-borne disease through three general mechanisms: (1) serving as a break in the host-pathogen cycle; (2) by altering the soil physical, chemical, or biological characteristics to stimulate microbial activity and diversity; or (3) directly inhibiting pathogens through the release of suppressive or toxic compounds or the enhancement of specific antagonists. Brassicas, sudangrass, and related plant types are disease-suppressive crops well-known for their biofumigation potential but also have other effects on soil microbiology that are important in disease suppression. The efficacy of rotations for reducing soil-borne diseases is dependent on several factors, including crop type, rotation length, rotation sequence, and use of the crop (as full-season rotation, cover crop, or green manure). Years of field research with Brassica and non-Brassica rotation crops in potato cropping systems in Maine have documented the efficacy of Brassica green manures for the reduction of multiple soil-borne diseases. However, they have also indicated that these crops can provide disease control even when not incorporated as green manures and that other non-biofumigant crops (such as barley, ryegrass, and buckwheat) can also be effective in disease suppression. In general, all crops provided better disease control when used as green manure vs. as a cover crop, but the addition of a cover crop can improve control provided by most rotation crops. In long-term cropping system trials, rotations incorporating multiple soil health management practices, such as longer rotations, disease-suppressive rotation crops, cover crops, and green manures, and/or organic amendments have resulted in greater yield and microbial activity and fewer disease problems than standard rotations. These results indicate that improved cropping systems may enhance productivity, sustainability, and economic viability.

Biofumigation Experiences in Argentina

Short Report

Biofumigation for the Control of Vegetables Soilborne Pathogens in Some non-Temperate Climate Countries

Soil-borne pathogens (SBPs) significantly reduce the yield and quality of crops worldwide. In the past, their control was principally accomplished by using soil fumigants such as methyl bromide (MB). However, this fumigant which is a powerful ozone-depleting substance, has completely been phased out under the Montreal Protocol (MP). New chemicals and non-chemical alternatives to MB, including biofumigation, have been actively researched, developed, and commercially adopted worldwide. This review seeks to provide the status of biofumigation for the control of SBPs in some non-temperate climate zones referred to in this paper as Article 5 countries or developing countries according to the Montreal Protocol (MP) classification. The review will first define “the non-temperate climate zone,” list the countries belonging to this zone, focus on the role and importance of the MP in phasing-out MB, and in searching and commercially adopting alternatives including biofumigation to this fumigant. It also describes the biofumigation techniques reported and used, reports its efficacy/inefficacy to manage SBPs in some non-climate temperate countries, insists on the place it must have in an IPM program to increase its efficacy, and finally, lists the collaboration and the research needed to further develop and commercially adopt this technology in non-temperate climate countries.

Plant-Derived Carbon Sources for Anaerobic Soil Disinfestation in Southern California

Anaerobic soil disinfestation (ASD) has been optimized and adopted as an organic alternative to chemical fumigation by strawberry growers in California. The ASD process relies on mixing labile carbon sources into the soil to generate chemical, physical, and microbiological changes aiding suppression of the soil-borne pathogens and enhancing fruit production. Continued ASD adoption is hindered by the increasing cost of rice bran, currently the most widely used carbon source. To address this need and to find suitable and economical alternative carbon sources, we conducted field evaluations of locally produced or sourced plant-based products. ASD with incorporated grass-sod clippings spent grain and coffee grounds from one supplier provided a 47% to 83% increase in fruit yields compared to untreated soil, but coffee grounds from a different supplier decreased strawberry yields. Carbon, nitrogen, and their ratios had important impacts on the efficacy of ASD with coffee grounds and grape pomace. ASD with wheat midds at 20 t/ha provided strawberry yields similar to chloropicrin-fumigated soil while substituting 30% of rice bran carbon rate with on-site grown cereal cover crop biomass resulted in yields similar to the full rate of rice bran but at a reduced cost. As we continue exploring cost-effective methods of soil disinfestation, we utilize ASD integrated with other pest management tools, such as the use of resistant cultivars and crop rotation for sustainable production.

Tomato Crop Health, Yield, and Greenhouse Soil Conditions after 17 Years of Repeated Treatments of Biofumigation and Solarization

The combination of biofumigation and solarization is known as bio-solarization. An experiment was performed from 2003 to 2019 in a greenhouse at INTA San Pedro, Buenos Aires province, Argentina (33°44'12.7"S 59°47'58.2"W). Treatments (TRAT) were applied every two years. TRAT evaluated were: 1=Control; 2= Solarization, 3= Biorot, a succession of organic amendments (chicken manure, broccoli, chicken manure, broccoli, tomato, and pepper crop debris, mustard, tomato crop debris, broccoli, tomato crop debris), 4=Biobras based only on the use of brassicas (rapeseed, broccoli, mustard, and Brassica campestris). Treatments were carried out in spring or summer so that a late-season tomato crop could be grown after them. The tomato hybrid planted was Superman (Petoseed), except for the last season where the hybrid used was Rodeo (BHN). Fungal pathogens controlled were Pyrenochaeta lycopersici, Fusarium solani, Sclerotium rolfsii, and Sclerotinia sclerotiorum, and nematodes like Nacobbus aberrans, Helicotylenchus and Criconemella. Fungi of Aspergillus genera were observed growing on death sclerotia of Sclerotinia sclerotiorum and Sclerotium rolfsii in Biobras and Biorot. Tomato plants in control showed a higher percentage of dead plants, root rots, and lower root dry matter at the end of each crop. Solarization alone without adding organic matter reduced this parameter in the soil and showed more death plants and less yield than Biobras and Biorot. Tomato and pepper crop debris used as biofumigants produced high yield values and adequate pathogen control. Biofumigation in combination with solarization is an effective technique for managing soil-borne pathogens in greenhouses and is being adopted by horticultural growers in Argentina.

Biofumigation: A Cover Crop Option 12 Months of the Year to Manage Three Soilborne Pathogens Ailing the Australian Vegetable Industry

Brassica biofumigant cover crops are being increasingly considered in vegetable crop rotations as part of an integrated disease management strategy and simply as a cover cropping choice. Nine biofumigant varieties were assessed to see if they could be grown year-round in the Lockyer Valley South East Queensland region, for yield, days to incorporation and glucosinolate concentrations, as well as efficacy against 3 soilborne pathogens; Sclerotinia sclerotiorum, Sclerotium rolfsii and Macrophomina phaseolina. The fastest growing brassica biofumigant was BQ Mulch which reached 25% flowering in 36 and 59 days from planting to incorporation with a summer and winter planting respectively. Nemcon and Nemclear took the longest to incorporation when planted in summer, 101 days and failed to flower, while Caliente, Tillage Radish and Biofum reached 25% flowering and incorporation in 98 days when planted in winter. BQ Mulch produced the least amount of biomass, 30.93 t/ha fresh weight and 2.92 t/ha dry weight with a summer planting. Biofum producing the greatest amount of biomass, 185.76 t/ha fresh weight and 17.34 t/ha dry weight with a summer and winter planting respectively. Most varieties produced more total glucosinolates during summer compared to winter. Caliente produced the highest levels of Total GSLs with 53.47 µmol/g DW in summer compared to 23.78 µmol/g DW in winter. This was reflected in their efficacy against the soilborne pathogens. Caliente and Mustclean were more efficacious at controlling Macrophomina and Sclerotinia in summer compared to winter while all varieties were more efficacious at controlling Sclerotinia with a summer planting compared to a winter planting.

Efficacy of Different Forms of Green Manure Crops to Reduce Verticillium dahliae in Different Soils

The efficacy of green manure crops to reduce the number of Verticillium dahliae microsclerotia in different soils was investigated. Green manures tested were Indian mustard with a high glucosinolate content and sorghum-sudangrass as biocidal plants, and Indian mustard with a low glucosinolate content and rye as non-biocidal plants. The green manure plants were applied in fresh, dried, and ensilaged form. When applied as fresh plants, the glucosinolate content determining the biocidal activity of Indian mustard was only important in loam soil but not in sandy loam soil. In the latter soil, the non-biocidal rye had significantly higher efficacy than the Indian mustard. Volatiles released by fresh and dried, but not ensilaged, Indian mustard with a high glucosinolate content strongly decreased the number of living V. dahliae microsclerotia. When the same green manure crops were added to sandy loam and clay loam soil, the effect of the high glucosinolate content Indian mustard in fresh and dried form disappeared, whereas the ensilaged green manure crops had the highest efficacy. This effect was based on the increase of the soil microbial activity and the Streptomyces population size, which were negatively correlated with the number of living V. dahliae microsclerotia in the soil.

A Holistic Approach for Enhancing the Efficacy of Soil Microbial Inoculants in Agriculture:

Microbial inoculants can be an efficient tool to manage the soil and plant microbiomes providing direct beneficial effects, and for modulating native soil and plant-associated microbiota. However, the application of soil microbial inoculants as biofertilizers and biopesticides in agriculture is still limited by factors related to their formulation, application method, and the knowledge about the impact and interactions between microbial inoculants and native soil and plant host microbiomes. The review is thus describing and discussing three major aspects related to microbial-based product exploitation, namely: i) the discovery and screening of beneficial microbial strains; ii) the opportunities and challenges associated with strain multifunctional features; iii) the fermentation and formulation strategies also based on the use of wastes as growth substrates and the technical and regulatory challenges faced in their path to field application. All these issues are addressed in activities performed by the EXCALIBUR project (www.excaliburproject.eu), which aims to expand the current concept about microbiomes interactions, acknowledging their interactive network that can impact agricultural practices as well as on all living organisms within an ecosystem.