Fish Extract Products Can Control Foliar Diseases in Organic Blueberries

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Unsplash/Mario Mendez

Fish extract products have been found to suppress important foliar diseases in organic blueberries, based on the results of a University of Georgia study.

Harald Scherm, a UGA plant pathologist, received a two-year $119,000 Southern Sustainable Agriculture Research & Education (SARE) grant to study the effects of fish product formulations on suppressing leaf diseases and pests, and improving foliar nutrition in organic blueberry trials in Georgia.

“Before we initiated the study, we received anecdotal evidence from some growers that fish products (oils and emulsions) provide some benefits,” said Scherm. “So this study sought to kill three birds with one stone by developing an integrated system for disease, insect and nutrient management in organic blueberries using fish-derived products as a foliar spray.”

Researchers found that the four of the six fish extract products they evaluated significantly suppressed Septoria leaf spot and leaf rust, two common diseases of organic blueberries. However, the impacts on controlling the leaf beetle pest and boosting foliar fertility were less clear.

“The impact of the fish products on the leaf beetle was inconsistent, and the products did show some benefits in boosting foliar nutrition, but more so for plants growing in low-fertility sites than for plants growing in soils with higher fertility rates,” said Scherm. “With these results, we know that the products work in controlling disease pathogens.”

Scherm said that research literature supports the theory that fish extract products have an indirect effect in controlling the disease pathogens by boosting the defense responses in the plant.

Diseases, like Septoria spot, attack the blueberry bush in late summer, after the blueberries have been harvested, which may explain why many growers dismiss or overlook the disease during production. However, Scherm said that growers should pay closer attention to such diseases, since they can cause significant leaf defoliation, impacting yields the following season.

“That lack of photosynthesis from absent leaves impacts the number of flower buds that are formed and, therefore, the amount of berries that are produced,” said Scherm. “That premature defoliation and subsequent flower reduction further weakens the bushes and exposes them to more diseases and insect pests for the life of the plant.”

Scherm said that he is pleased with the outcomes of the SARE study because it provides growers with a product labeled for organic use that can be used after blueberry harvest, unlike other natural products, such as microbial biofungicides. “We estimate that about 50 percent of organic blueberry producers in Georgia, Florida, and South Carolina now use fish products as a foliar spray and a fertilizer,” said Scherm.

Scherm said that the next step in his research might be to trace the fish extract products back to their source and determine the sustainability of their production.

“It would be interesting to see what is actually used to make the products and where those ingredients are coming from,” said Scherm. “Getting a handle on the sustainability of their production practices would be a good thing to do.”

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