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Botrytis Resources

Botrytis is one of the most serious post-harvest problems facing the floral industry. It is extremely difficult to control and causes significant losses and reduced profits.

Botrytis blight, also known as gray mold, causes brown spots on petals and leaves that renders the plant unmarketable. In less severe cases, Botrytis-infected flowers have reduced vase life. Interestingly, Botrytis damage has been shown to result in ethylene production within flowers. Botrytis spores germinate at a wide range of temperatures, including temperatures typically used for shipping and storage and at humidity levels of 93% or higher. Spores will germinate in 4 – 8 hours if water is present. In other words, the conditions used for production, shipping, and storage are also ideal for Botrytis growth. 

Additionally, the spores survive on living or decayed plant material for up to one year and may be spread by water, wind or on the hands and clothes of workers. Then, when moisture is present, the spores germinate and invade the petals and leaves. The germinated spores inject a toxin in the petal and leaf cells that leads to the damage we see on Botrytis-infected petals and leaves. The worst cases of Botrytis damage occur when production areas experience rain and high humidity conditions, water is present on leaves and stems in the shipping boxes, and temperature fluctuations cause condensation on the flowers and inside the sleeves.

Find more resources and solutions by clicking the topics below or watch webinars on top issues facing growers by clicking on the image below.

Topics Index:

Scouting
Management in the Greenhouse
Postharvest Management
Fungicide Info
Biological Control and IPM
Identifying New Biological Control Agents
Calcium Applications
Chitosan


Scouting 

Key Takeaways:

  • Lesions in flower petals can be caused by both abiotic and biotic factors.
  • At the early stages of infection, Botrytis isn’t easily distinguished from other fungal pathogens.
  • Botrytis causes small necrotic or discolored lesions that expand as the fungus invades the tissue.
  • Infected tissue can be placed into a sealed plastic bag or humid chamber. The fungus will produce spores in 3-7 days, which will aid in identification. Spores are the best way to identify fungi!
  • Frequently walk through your greenhouse and remove symptomatic tissue.

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Webinars:

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Management in the Greenhouse

Key Takeaways:

  • The optimal temperatures for Botrytis development and growth are very similar to the optimal conditions for plant growth and development.
  • Relative humidity >94% or continuous periods of leaf wetness for over 12 hours promote Botrytis spore germination.
  • Cultural practices to manage Botrytis should focus on reducing greenhouse moisture, humidity, and condensation.
  • Remove humidity from the plant canopy with horizontal airflow fans.
  • Remove humid air from the greenhouse with exhaust fans.
  • Keep air temperature above the dewpoint to prevent water condensation on plant surfaces.
  • Frequently remove decaying plant material.
  • Strengthen plant tissue with calcium applications. (See Calcium Applications for more information)

Resources:

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Postharvest Management

Key Takeaways:

  • The temperature and relative humidity within shipping boxes are mostly within the range that promotes Botrytis germination and growth.
  • Susceptibility to Botrytis and ethylene damage varies greatly among different rose cultivars.
  • Botrytis susceptibility and ethylene sensitivity do not correlate. The presence of one does not predict the presence of the other.
  • Laboratory testing of Botrytis susceptibility and ethylene sensitivity do not always align with observations made during commercial production and postharvest handling.
  • Sensitivity to ethylene was not influenced by Botrytis inoculation in any of the four cut rose cultivars used in this research.
  • Exposure to ethylene often results in a significant increase in Botrytis damage, regardless of the cultivar’s innate susceptibility to Botrytis or ethylene.
  • Precooling the packed boxes before placement into coolers enhances the vase life, slows down bud opening, minimizes Botrytis damage to the flowers, and reduces the frequency of Botrytis on leaves.
  • Regardless of a cultivar’s seeming response to ethylene, exposure to ethylene at the Botrytis establishment and/or development stage could amplify Botrytis damage.

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Fungicide Info

Key Takeaways:

  • Botrytis fungicide resistance can develop rapidly.
  • Botrytis spore isolates from roses imported from Colombia, Ecuador, Guatemala, Kenya, and Mexico consistently exhibited a high degree of resistance to FRAC 1 (thiophanate-methyl; the oldest fungicide with single mode of action registered in the early 1970s) and FRAC 9 (cyprodinil).
  • Resistance to FRAC 1 and FRAC 2 (another fungicide class developed many decades ago) was consistently observed over time, while the resistance patterns changed dramatically for most of the other fungicides on a week to week basis likely due to weekly fungicide use. 
  • Botrytis exhibited no resistance to some FRAC 7s (pydiflumetofen) or FRAC 19 (polyoxin-D) over the course of six shipments in our studies. 
  • Our research shows that the fungus has mutated in key genes that allows it to survive the chemical treatments.

Best practices for fungicide use:

  • Reduce inoculum through sanitation.
  • Use fungicides preventatively.
  • Apply appropriate chemical rates (high rates during periods of high disease pressure).
  • Rotate fungicides of different FRAC codes.
  • Use multi-site fungicides alone or in combination with single-site fungicides when Botrytis pressure is high.
  • Reserve an effective FRAC code for postharvest applications to ensure maximum fungicide efficacy. (See Postharvest Management for more information)
  • Fewer targeted fungicide applications instead of calendar applications will lower selection pressure and allow the fungicide efficacy to remain high for a longer period of time.

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Biological Control and IPM

Key Takeaways

  • Alternatives to conventional fungicides that can be used are biological control agents (BCAs), systemic acquired resistance (SAR) inducers, calcium, and ethylene-management products. (See Calcium Applications for more information)
    • BCAs
      • Howler® Pseudomonas chlororaphis
      • CeaseTM, Serenade® Bacillus subtilis
      • Revitalize® , Double Nickel Bacillus amyloliquefaciens
      • RootShield® Trichoderma harzianum
      • Guard® Trichoderma viridae
      • Botector® Aureobasidium pullulans
      • BotryStopTM Ulocladium oudemansii
      • RegaliaTM Reynoutria sachalinensis
    • SAR Inducers
      • Actigard® Acibenzolar-S-methyl
      • Aliette® Fosetyl-aluminum
      • AludeTM, BioPhos® Phosphorus acid
  • Some biological control agents may require multiple applications to become established.
  • Off-peak season and low disease risk conditions provide an opportunity to rely on alternative measures.

Resources

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Identifying New Biological Control Agents and Their Application

Key Takeaways

  • A study at The Ohio State University evaluated a collection of 60 bacterial strains and identified seven strains that reduced botrytis severity in greenhouse petunias. 
  • The study evaluated:
    • Evaluating beneficial bacteria application methods
    • Evaluating Botrytis biocontrol efficacy when beneficial bacteria are applied with and without additional calcium.
    • Comparing the biocontrol effects of individual bacteria to consortia (groups) of bacteria.
  • Combining both spray and drench application methods proved more effective in reducing disease severity than using either method alone for applications of Pseudomonas strains on Petunia ‘Carpet Red Bright.’
  • Different bacteria strains require different application methods for optimal control of Botrytis, with spray + drench method providing the most consistent results.
  • Calcium applications reduced Botrytis disease severity but didn’t always enhance the effect of beneficial bacteria.
  • The individual bacteria strain AP54 and the biopesticide Cease showed the best disease control among all treatments, with AP54 even outperforming or matching Cease at all time points.
  • Future research will continue to investigate the interplay and potential synergies between different bacteria strains in controlling Botrytis in Petunia.
    • Stay tuned for more results from this project!

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Calcium Applications
Key Takeaways:

  • Calcium (Ca) strengthens and stabilizes the cell wall, making the penetration of Botrytis cinerea more difficult.
  • Higher Ca concentration in petals, stems, leaves, and sepals makes them less susceptible to Botrytis infection.
  • Different application techniques are required for different plant tissues and flower forms. Fertigation solutions work best for leaves, additional spray applications are beneficial for stems, and for single flowers spray applications suffice. However, double-flower forms need a heavy shower or whole flower/stem dip for effective treatment. Surfactants can aid in enhancing calcium uptake through above-ground tissues.
  • Calcium chloride flower spray applications in greenhouse production can reduce Botrytis blight, despite the calcium concentration in rose petal tissue not significantly increasing. This suggests the reduction may be due to metabolic responses related to plant defense pathways triggered by calcium signaling.
  • The calcium flower spray doses that effectively decreased Botrytis blight severity in postharvest were 500 and 1000 ppm.
  • Natamycin and calcium showed an additive effect for reducing botrytis severity, i.e., the combined effect was higher than each product used alone; therefore, this combination is very promising for commercial use as a postharvest dip. Results rivaled the best performing commercial fungicide in the study.
  • Coadjuvant is not needed for natamycin and calcium dips on roses.
  • Postharvest calcium dips cause a series of metabolic changes in the plant, including increased activity in defense-related pathways such as phenylalanine, glucosinolate, and sphingolipid metabolism.
  • Postharvest calcium dips using calcium chloride have proven to be the most effective strategy to reduce Botrytis blight, with the 2000 ppm dose leading to an increase in calcium concentration in petals, and consequently enhancing petal physical strength.
  • The silicon-based adjuvant (CapSil®) did not improve disease severity, calcium assimilation, or petal strength when used in combination with calcium dips.

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Chitosan 

Key Takeaways

  • Chitosan, a derivative of chitin, is a seafood byproduct.
  • Chitin is a promising natural compound documented to have antifungal and disease suppressive properties. 
  • Chitin is one of the most abundant polymers on earth and is an important component of all insect and crustacean exoskeletons. 
  • Chitin is also a structural component in fungal cell walls. Some companies have begun utilizing waste from the seafood industry as a source of chitosan for use in agriculture as a new crop protection product. 
  • Chitosan has been used successfully in postharvest to prevent storage rot and extend the shelf life of perishable fruits and vegetables.
  • Chitosan was effective at reducing botrytis severity on the leaves of petunia and showed potential as a new tool to include in an IPM program.
  • Chitosan products were effective for preventing Botrytis blight on petunia leaves.
    • Stay tuned for more results from this project!

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To see resources for treating Thrips, click here.