The use of Bacillus subtilis qst 713 and bacillus pumilus qst 2808 as protectant fungicides in conventional application programs for black leaf streak control

The protectant fungicides Sonata, based on the patented Bacillus pumilus strain QST 2808 (Agraquest, Davis - CA), and Serenade (Agraquest), based on the proprietary Bacillus subtilis strain QST 713, have been both successfully used in rotational and tank-mix programs with single-site fungicides for the control of black leaf streak (Mycosphaerella fijiensis) in banana. The main mode of action of Sonata is based on the production of aminosugars and that of Serenade on the production of lipopeptides. Aminosugars interfere with new cell wall production of fungal pathogens such as M. fijiensis, while lipopeptides disrupt pathogen cell membranes. These modes of action are different from other fungicides and therefore represent an opportunity for resistance management and synergy with single-site fungicides. In 2010, in the Province of Guayas, Ecuador, a trial was setup in order to demonstrate the efficacy of Sonata for black leaf streak control. The following treatments were tested: 1) Sonata - 1.3 L/ha + adjuvant Ecuafix 2%; 2) Sonata - 1.0 L/ha + mineral oil - 7 L/ha; 3) Sonata - 0.8 L/ha + mineral oil - 7,0 L/ha, alternately mixed with the single-site fungicides difenoconazole - 0.4 L/ha, spiroxamine - 0.5 L/ha, pyraclostrobin - 0.4 L/ha and fenpropimorph - 1.0 L/ha; and 4) a commercial program of applications. All the treatments with Sonata reduced the severity of black leaf streak and had higher efficacy than the chemical standards in the last evaluation at 14 days after the last application. Based on the results, treatments 1 and 2 are recommended for conditions of low disease pressure with shorter applications intervals and treatment 3 is recommended for mid to high disease pressures with an application interval of 16 days. A large field trial was conducted over 3 years in Guápiles, Costa Rica, where Serenade 1 L/ha + adjuvant 1% + emulsifier 1% + oil - 7 L/ha was applied every 14 days in the first 6 months and monthly over the next 2,5 years of trial duration, replacing single applications of mancozeb (Dithane 60 OF) + emulsifier 1% + oil - 7 L/ha. The data show that Serenade had an efficacy equal to mancozeb as a protectant fungicide in an integrated program in which triazoles, amines, anilinopyrimidines, strobilurins and protectant fungicides were used. In addition to their high efficacy when used in black leaf streak control programs, both products also have an excellent toxicology profile for both worker safety as well as non-target beneficial organisms and the environment at large, supporting their use as protectant fungicides for sustainable production.