Nursery and Landscape - Biological Fungicides

There are a number of biological fungicides on the market. The following is information on these products and their effectiveness.

Biological fungicides tend to have negligible toxicity to humans, and no history of carcinogenic or developmental effects on test animals. Data on the effectiveness of the biologicals in landscape use is often limited, but the labels are helpfully broad, encouraging product use for suppression of many different pathogens. Some of the pathogens named on the label may have been suppressed in laboratory plate tests rather than in field trials; time will tell whether they are also effectively treated for under the less controlled conditions in the outdoor environment. Rather than thinking of biofungicides as cures for diseases, think of them as biological tools for treating plants preventively, decreasing the odds that a pathogen will successfully attack to cause disease. Biological controls are thus used as health insurance, not in response to the appearance of disease symptoms. They are very compatible with overall integrated pest management (IPM) philosophy—but one should not wait for a disease threshold to be reached before deploying a biofungicide. In many instances, the best use of a biological may be occasional treatments in alternation with reduced-risk chemicals.

One of the best known of the biologicals for disease control is Rhapsody AS, which contains Bacillus subtilis strain QST 713, a bacterium. This protectant material is even approved by OMRI for use in organic production, as well as for use in a broad range of sites including landscapes and golf courses, plus sod and ornamental production. Using a surfactant to improve coverage is recommended, and the higher labeled rates may be needed under significant disease pressure. Rhapsody may be applied as a spray or as a drench. As a spray, its forté is powdery mildew, but a measurable benefit from Rhapsody has also been seen against some bacterial leaf spots, Cercospora leaf spot, Botrytis blight and downy mildew. Only copper treatments offer similar versatility, with effectiveness against bacteria as well as fungi. As a soil drench, the Rhapsody label offers suppression of Fusarium, Pythium, Phytophthora and Rhizoctonia.

Actinovate SP, a biofungicide labeled for production and landscape use, has Streptomyces lydicus WYEC 108, an actinomycete, as its active ingredient. Drenches and foliar sprays may be made in the landscape as new plants are being transplanted, or to established plants. Treatments are of benefit only when made preventively. Actinovate’s original use was for soilborne diseases—the label lists problems caused by Pythium, Rhizoctonia, Phytophthora, Verticillium and Fusarium. Some suppression of powdery mildew, downy mildew, Botrytis, Alternaria, and Sclerotinia is also claimed for foliar applications. Studies on ornamental crops have thus far shown powdery mildew and Botrytis to be measurably reduced by Actinovate treatment. The Actinovate AG label, which relates to agricultural uses, includes a mention of Monilinia control, which suggests that the Actinovate SP may help to keep ornamental cherries free from brown rot. This biocontrol is effective at temperatures above 45ºF. A non-ionic spreader-sticker such as Latron B1956 should be added for the best results. For landscape use, treatment can be at transplant or to established plants. Ornamental bulbs may also be dusted or soaked in a suspension of Actinovate SP prior to planting, or drenched subsequently. The material may also be used for pre-plant treatment of bare-root trees.

Information from "Exploring alternatives for disease control on trees and shrubs" by Margery Daughtrey, Cornell University Department of Plant Pathology and Plant-Microbe Biology in the May 23 edition of the Michigan State University Landscape Alert Newsletter.