Apple Disease Management: Part 4 – Biofungicides

While biofungicide products are used most widely by organic producers, they can be a useful tool for conventional growers as well. Advantages of using these tools in conventional disease management could include:

• lower potential for pest resistance
• provide protection during times of lower infection risk, allowing more effective products to be saved for critical periods
• provide a rotational option to help manage resistance development to other conventional products
• shorter re-entry intervals helpful for times of significant orchard activity (eg., hand thinning, pruning)
• shorter preharvest intervals can provide disease suppression up to the day of harvest, helping to reduce potential storage issues
• potentially lower toxicity to non-target organisms

Biofungicides typically do not provide the same high level of control as conventional pesticides and are often labelled for suppression, or partial suppression, of pests. Control can be improved, however, when their use is combined with other control practices including cover crops, sanitation, promoting tree health and canopy management to name a few.

Although many biofungicide products are formulated, packaged and applied in a very similar fashion to conventional fungicides, the active ingredients are different. They have unique, specialized modes of action which make them more susceptible to numerous biological and environmental factors.

Some of the possible challenges associated with using these products are:

• more frequent applications needed to control pests
• slower action than conventional pesticides
• may provide suppression but not control of the pest
• more expensive than conventional pesticides
• fewer pests controlled

The following provides information on some registered biofungicides available for apples. Knowing the specific requirements for these products can improve the success of their use. See the label for more details.

Blossom Protect (Aureobasidium pullulans)

• Registered for the control of fire blight
  • Very effective product on West Coast, but tends to not be as effective in East Coast conditions
• Live strains of yeast Aureobasidium pullulans and citric acid buffer mixed prior to application
  • Citric acid buffer lowers pH in blossoms which inhibits growth and multiplication of fire blight bacteria
  • Lower pH also allows yeast strains to colonize same areas of blossoms, blocking infection site and utilizing same nutrients as fire blight bacteria
• Can be applied up to 5 times per season with the following exceptions
  • Only 2 applications should be applied to sensitive varieties including Golden Delicious, Idared and Jonagold.
  • Late applications can also result in enhanced russetting particularly with the onset of fruit set, so do not use this product after petal fall or to control rat tail blossoms.
  • During particularly wet conditions, use should be limited as russetting may occur.
• Yeast must colonize open blossoms before fire blight bacteria infect blossom, so early application is important
  • If available, use a forecast system (e.g., Cougar Blight or MaryBlyt) to target sprays 2-3 days before infection
  • If no forecast system is available, apply at 10%, 40%, 70% and 90% open blossoms
  • When used in a rotational program, ideal placement is early bloom so bacteria can become established and provide protection during lower infection risk times. In turn, this will save the use of antibiotics for critical infection periods that often occur later in the bloom period.
• Rate is dependent on tree height – for every 1m of tree height, mix 5.25 kg of Component A (yeast) in 500 L water and add 0.75 g Component B (buffer)
  • Apply 500 L spray solution per ha for every 1 m of tree height
• Do not tank-mix or apply within 2 days of streptomycin, kasugamycin (Kasumin), captan (Supra Captan, Maestro), dodine (Syllit), strobilurin (Flint, Sovran, Pristine) or copper fungicides as these are toxic to the yeast

Double Nickel (Bacillus amyloliquefaciens)

• Registered for suppression of fire blight
  • Effective on shoot blight as well for use during summer
• Active ingredient, Bacillus amyloliquefaciens, is a naturally occurring bacterium typically found in association with plant parts
• Multiple modes of action, including colonizing plant root hairs to prevent pathogen establishment (for soil pathogens), and by producing compounds that disrupt production of cell walls in plant pathogens
• Formulation of bacteria is safe to use with copper products
  • Some trials have found Double Nickel and Cueva work better together than when used alone (and with minimal risk of russetting)

Serenade OPTI (Bacillus subtilis)

• Registered for suppression of fire blight, apple scab and powdery mildew
  • Is 50% as effective as streptomycin, according to Dr. George Sundin, Michigan State University
• Active ingredient is a fermenting strain of Bacillus subtilis
• While the bacteria does colonize plant parts, the antibacterial and antifungal activity comes mainly from biochemical compounds produced by the bacterium during fermentation
  • Stops spore germination, disrupts cell membrane growth and inhibits attachment of pathogen to plant tissue
• For fire blight suppression, begin applications at early (1%–5%) bloom at the beginning of a warming trend, and follow with a streptomycin spray 2 or 3 days later if warm temperatures continue to favour blossom infection.
• For scab and powdery mildew suppression, begin application at green tip or when conditions favour disease development. Re-apply on 7-10 day intervals.
  • Use in a rotational program with other registered fungicides when disease pressure is heavy.
• Research findings consider Serenade to be most “fruit safe” biological for russet.

Buran (Garlic powder)

• Registered for suppression of apple scab and powdery mildew
• Active ingredient inhibits germination of fungal spores on plant surfaces, and interferes with the growth of the fungal mycelium
• Early post-infection activity
  • Time applications for after heavy rain or periods of prolonged leaf wetness when protectant fungicide activity may be reduced
• Repeated applications and thorough coverage required for efficacy
• Product is easily washed off by rain

Regalia Maxx (Reynoutria sachalinensis extract)

• Registered for suppression of powdery mildew, bitter rot, fly speck and sooty blotch
• Active ingredient is an extract of giant knotweed plant that triggers natural defense mechanisms of plants, inhibiting development of certain plant pathogens (induced systemic resistance)
• With the specific disease target range and 0-day preharvest interval, a good timing for this product is at the end of the season right before harvest
• Works best when applied prior to development of disease symptoms
• Use higher rate and shorter intervals when conditions conducive for disease development.
• Repeat applications may be required

Purespray Green Spray Oil (mineral oil)

• Registered for suppression of powdery mildew
• As a fungicide, acts as both eradicant and protectant, providing destruction of lightly established infections and providing modest protection for a short period of time
• Susceptible to wash-off and activity is significantly reduced by as little as 5 mm of rain
• Product must cover powdery mildew spores to be effective so thorough coverage is essential.
• Oils may cause plant injury – follow labels carefully for precautions.
  • Do not use within 48 hours of freezing temperatures or when temperatures are above 25⁰C.
  • Due to phytotoxicity concerns, there are many restrictions regarding the use of oil with products such as captan and sulphur products.