AQ-10 as a Rose Fungicide

The future of pest and disease controls is in the discovery and sometimes rediscovery of environmentally friendly pesticides.Market availability of these products is increasing as consumers and producers alike have begun demanding controls which are lower in toxicity while having a lesser impact on nontarget organisms. Although some biological control insecticides like Bacillus thuringiensis have been around for decades, more are coming into the marketplace. Biological controls for fungi, however, have fallen short... until now.

As mentioned in past articles, for every pest and disease there is an equal and opposite counterpart, and powdery mildew is no exception. Growing amidst the leaves and fruit of grapevines is a "beneficial" fungus called Ampelomyces quisqualis, a naturally occurring parasitic fungus of powdery mildew. Although this "hyperparasite" has been studied for more than 50 years, only recently has it become commercially available.

Powdery mildew is, of course, arguably the most pervasive, most destructive of the plant-attacking fungi in food and ornamental crops - not the least of which is our roses. According to Dr. David Gadoury of Cornell University, various species of powdery mildews have attacked not less than 256 plant species around the world.

A. quisqualis overwinters as pycnidia (a kind of fungal version of fruit). When it rains, the conidia (we call them "spores") exude from the pycnidia and are splashed onto leaves and stems where mildew is actively growing. Within 24 hours, A. quisqualis penetrates the mildew's cell walls and uses it as a host to reproduce more A. quisqualis spores. It spends the next 7 to 10 days spreading throughout the mildew colony.  Within 2 to 4 days afterwards, the mildew colony is destroyed and the A. quisqualis goes back to "lying in wait" for another rainstorm. (Kind of a sinister little thing, isn't it?)

In the mid-90's, Ecogen Corporation isolated the A quisqualis fungus and received U.S. government approval to market it as a biological fungicide for control of powdery mildew in apples, cucurbits, grapes, strawberries, tomatoes, and (most important to us rosarians), ornamentals. Their product, called AQ-10 (from its A. quisqualis isolate M-10), is currently registered only for commercial users, but according to Kate Burroughs of Harmony Farms, an AQ-10 distributor, it should be available to the "lawn and garden" market very soon.

The problem appears to be one of formulation. AQ-10 is a "water dispersible granule" applied at a rate of 1 - 2 Tbsp. (15 - 30 ml)   per acre (0.4 ha) or 1 oz (30 ml) per 100 gal (378 l). For the homeowner, trying to measure 1/100 of an ounce for a 1-gallon sprayer is a bit difficult. So Ecogen is working on a formulation more appropriate in small usage applications... like your rose garden.  According to Ms. Burroughs, it should be available before next season.

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