By The Certis Team
Weather forecasts from mid-April through early May are predicting conditions pointing to low to moderate fire blight infections. However, in mid-April rising daily average temperatures in the mid 60’s and potential rainfall will create a moderate to high-risk window for fire blight. This heightened risk and increasing resistance to some antibiotic treatments could put apple growers in a tough spot.
There are two products from Certis Biologicals that protect your apple trees from
fire blight.
Theia® fungicide contains a Bacillus subtilis strain that produces two lipopeptides that work together to control fire blight. Research has shown Bacillus strains that contain multiple lipopeptides are more effective than a single lipopeptide in helping to control bacterial diseases. Among lipopeptides, fengycin and surfactin are the most effective against fire blight and is the lipopeptide in the highest concentration in Theia.
The lipopeptides in Theia work together against fire blight and other disease with multiple modes of action to:
Disrupt the bacteria's cell membrane, allowing leakage of cell content resulting in collapse and death.
Destroy existing biofilm on blossoms that the fire blight pathogen requires for infection.
Trigger Systemic Acquired Resistance (SAR) in the plant.
Theia should be a component of any fire blight spray program concerned with resistance to antibiotics. Including Theia as one blossom spray treatment can help slow down resistance to antibiotic treatments.
Theia will be widely available for the 2026 season through your Certis distributor.
If you are using a copper product in your pre-bloom/bloom spray programs you need to consider Cueva® bactericide/fungicide. It is a 10% Cu formulation containing a fatty acid soap that performs better than older Cu formulations.
Cueva is an important part of a fire blight spray program because:
A 10% soluble copper + fatty acid results in better control with less residue versus other copper products.
Less Cu translates into better crop safety for early dormant/green tissue sprays
Spraying early knocks down existing pathogens reducing the level of in-season infection.
As a bloom spray it gives the same level of control as an antibiotic treatment while helping manage antibiotic resistance.
Scott Ockey, Certis PNW Senior Field Development Manager, on using adjuvants,
“Using a high-quality non-ionic surfactant is a smart decision with biologicals.
This is especially true with Theia when used as a bloom spray. So much of a biological product’s performance is dependent on getting good coverage so the minimal cost of an adjuvant can pay off with less disease or insect damage.”
Additional Product Resources:
For additional information on Theia® and Cueva® , including technical specifications and labeled use directions, please refer to the resources below.
Always read and follow label directions. For a full list of protected crops and controlled diseases, visit the product pages and refer to the product labels.