Managing vegetable disease in organic production

by Deborah Jeanne Sergeant
Managing plant diseases challenges many organic producers, but with the right products and techniques, farmers can improve yield, according to presenters at the recent eOrganic.info webinar, “Using biofungicides, biostimulants and biofertilizers to boost crop productivity and help manage vegetable diseases”, co-hosted by the Tomato Organic Management and Improvement Project.
Speakers included Mariateresa Cardarelli of CREA-RPS, Rome; Giuseppe Colla of University of Tuscia, Viterbo, Italy, and Dan Egel and Lori Hoagland, both of Purdue University.
Although commercial agricultural biological products offer wide diversity, “unlike a lot of more chemically-based products, they can have inconsistent results under field conditions and are labeled ‘snake oil’,” said Hoagland.
She added their reported benefits include increased productivity and ability to help plants tolerate drought, salinity and heat.
She further explained agricultural biological products are microorganisms — bacteria, fungi or viruses, microbial products, and plant and animal byproducts. Manufacturers develop them by isolating microbes from soil and plant surfaces, in a lab or from byproducts. They provide nutrients, aid in nutrient and water acquisition, regulate hormones, and control biological functions. The last of which can include competitive exclusion, parasitism, antimicrobial metabolite production, and induced systemic resistance.
“Depending upon where you’re at, these are classified in various categories,” Hoagland said.
She said in the United States, biological products are classified as follows:
Biofertilizers:

  • Microorganisms (bacteria, fungi)
  • Organic fertilizers
  • Compost tea

Application:

  • Nutrition
  • Nutrient availability

Biostimulants;

  • Microorganisms (bacteria, fungi)
  • Seaweed extracts
  • Humic and amino acids and other complex organics

Application:

  • Yield enhancers
  • Improve nutrient uptake
  • Tolerance to and recovery from abiotic stress

Bio-pesticides:

  • Microorganisms (bacteria, fungi, viruses)
  • Plant extracts (botanicals)
  • Plant growth regulators
  • Semiochemicals (pheromones)

Application:

  • Weed control
  • Insect control
  • Disease control

“They’re usually classified by efficacy,” Hoagland said. “In many cases, these can fit into numerous categories and have many benefits.”
Trichoderma ssp., for example, has been widely cited for potential biocontrol activity and has other potential benefits, such as stimulating root growth and solubilize nutrients.
Hoagland referenced a tomato transplant study she performed in 2011 in which she used Rootshield plus Trichoderma harzianum T22 and Trichoderman virens G-41.
“They stimulated tomato seedling growth and reduced transplant stress,” Hoagland said.
She said challenges facing producers include regulations about classification and requirements for efficacy studies which vary by country and state. Also, some products lack independent, scientific and objective field trials.
“There are few recommendations on how and when to apply products to achieve best results,” Hoagland added. “Oftentimes, the plants where they’re applied are under stress.”
Producers must also consider storage conditions.
“These products are alive. If you put them in the car in 100-degree heat for the afternoon, you might kill those products,” Hoagland said.
To optimize application, she advised producers to “identify need and choose the appropriate product(s); ensure proper storage conditions; use the right dose; use the most appropriate application methods for product and goal; apply product(s) at the right time; consider soil and environmental conditions and conduct on-farm research.
Mariateresa Cardarelli presented the segment on biofertilizers, which she said have no legal definition in the U.S. She suggested Vessey’s definition, a “substance containing living microorganisms which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant.”
Cardarelli said biofertilizer actions include replacing soil nutrients, making nutrients more available to plants, and increasing plant access to nutrients. Biofertilizers include endophytic fungi and plant growth-promoting rhizobacteria. Mycorrhizal fungi are symbiotic fungi which colonize the plant’s host root system and form a large network of plant associated extraradical hyphae, greatly extending the volume of soil accessible to plant roots.
“Rhizobacteria are root-colonizing bacteria that form symbiotic relationships with many plants,” she said.
Rhizobacteria with PGP-activity include strains belonging to genera Bacillus, Pseudomonas, Azospirillum, Azotobacter, Alcaligens, Arthobacter, Agrobacterium, Burkholderia, Comamonas, Pantoea, Rhizobium.
“It’s important to consider that microrganizms are engaged in microbial interactions,” Cardarelli said.
Microbia interactions can be null, positive or negative.
“The greatest benefits are those with low nutrient uptake efficiency,” Cardarelli said.
She added that it’s useful to apply biofertilizers when a producer faces soil with low biological fertility, lack in the soil of specific nitrogen-fixing rhizobia, adverse soil chemical and physical characteristics, use of crops with low nutrient uptake efficiency, or reduced availability of nutrients for plant uptake.
A few factors affect biofertilizer efficacy, such as the crop’s cultivar and growth stage; environment, including climate, soil type and cultural practices; and microbial inoculum, including microbial strain(s) and propagule concentration.
Cardarelli said producers can apply biofertilizers in a variety of ways, including seed coating with liquid or powder inoculum, microgranule distribution via seed driller, or seedling spraying with liquid inoculum. Transplanted crops may be treated through mist irrigation after sowing, substrate application before sowing, root dipping, sprinkler irrigation in the nursery, drip irrigation after planting, or tablet application during transplanting.
Giuseppe Colla presented the segment on biostimulants. Like the previous speakers, he said biostimulants have no legal definition in the U.S.; however, “the Biostimulants Coalition agreed with Association of American Plant Food Control Officials to address ‘biostimulants’ as new subcategories of ‘Beneficial Substances’,” Colla said. “‘Beneficial Substance is any substance or compound other than primary, secondary, and micro plant nutrients that can be demonstrated by scientific research to be beneficial to one or more species of plants, when applied exogenously’,” he said, quoting the association.
Colla said biostimulant substances include organic plant biostimulants, including humic substances, protein hydrolysates, and seaweed extracts and other plant extracts, or inorganic biostimulants, like silicon.
“Humic substances are a mixture of complex organic compounds having yellow to black color formed by transformations — (humification — of organic residues of plants and animals by soil microorganisms,” Colla said.
Humins aren’t soluble in water at any pH value. Humic acids are not soluble in water under any acidic conditions where pH is less than two. Fulvic acids are soluble in water under all pH conditions.
Seaweed extracts are a mixture of organic and inorganic compounds from seaweed biomass using a different manufacturing systems such as alkaline or acid hydrolysis or cellular disruption under pressure or fermentation.
Protein hydrolisates are mixtures of polypeptides, oligopeptides and amino acids which are manufactured from protein sources using partial chemical and/or enzymatic hydrolysis.
Colla said biostimulant effects include growth stimulation, plant nutrition, abiotic stress tolerance and product quality.
“Root stimulation is quite common after application,” Colla added. “The number of fruits increase with repeated application of biostimulants.”
Plant nutrition is vital for growing healthy plants. Colla said soil nutrition availability, nutrient uptake and nutrient assimilation are necessary for adequate nutrition.
Dan Egel presented the next session on biofungicides, which he defined as “fungicides with active ingredients that are biological organisms or are derived from biological organisms.”
He divided biofungicides into three types: biological active ingredients — derived from microbe/plant, not necessarily living; place holders-microbes — which live on plant surface, slowing the disease; and hyper-parasites — parasites of a parasite.
Beyond selecting a biofungicide, calibrating the sprayer and using the right coverage makes a big difference in controlling fungi outbreaks.
“With small plots, it doesn’t make sense to bring a tractor in there,” Colla said. “A lot of people use garden sprayers. The backpack sprayer is much more appropriate for applying disease control products to a wide swath of area. You can constantly monitor the pressure going into the pump. It has a four to five-gallon capacity.”
He added garden sprayers are inexpensive and easy to use; however, their nozzle output is variable and the pressure and volume change over time. The backpack sprayer costs more; however, it’s maneuverable, and uses nozzles for pesticides. The boom arrangement and constant pressure make it more effective.
“The person doing the spraying does the calibration because we all act and walk differently,” Colla said. “If the person or equipment changes, new calibration is needed. Foliage should be thoroughly wet, not dripping. Keep speed constant, using a metronome, music or in some way keep that pace constant.”
To wrap up the webinar, Hoagland commented, “It takes a little more thought than some chemical products out there, so planning is important. If you have very fertile soil, some of these biostimulants may not be as effective.”

2017-05-05T11:00:22+00:00May 5th, 2017|Grower East, Grower Midwest, Grower West|0 Comments

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