Hybrids: The Next Generation

Published online: Nov 10, 2021 Articles, Fungicide, New Products Moshe Reuveni
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This article appears in the November 2021 issue of Potato Grower.

The global search for plant protection solutions that are both environmentally safe and efficacious is driven by the need to supply food to an ever-growing world population. The call for chemical load reduction is an important aspect of sustainable agriculture. In addition, years of farming and inbreeding have led to crops losing their natural immunity or resistance to fungal and bacterial pathogens. Despite the application of traditional chemical pesticides aimed to combat this resistance—either by chemical rotation or mixtures of different chemicals—the result is highly toxic environments that are mostly effective in the short term.

New effective alternatives to existing products are required to increase options for the control of plant diseases. These need to provide different and multiple modes of action with a lower risk for fungicide resistance and place a smaller chemical load on the environment simultaneously with consistent disease control.

Biopesticides are naturally occurring products derived from materials such as plants, bacteria, viruses and minerals. Among them, botanical biopesticides are considered attractive for plant protection.

Tea tree oil is a valuable essential oil extracted by steam distillation of Melaleuca alternifolia leaves. It contains many components, mostly terpenes and their alcohols, has been shown to be an effective antiseptic, fungicide and bactericide. STK Bio-Ag Technologies has recognized tea tree oil’s uniquely powerful potential for plant protection and has developed it for a broad spectrum of plant-pathogenic fungi with strong prophylactic and curative activities in numerous crops, including vegetables, herbs, grapevines, bananas, rice, coffee and fruit trees.

This photomicroscopy shows the rupture of a diseased cell caused by Regev hybrid fungicide.

New hybrid solutions are now proving a “best-of-both-worlds” opportunity by combining biological and chemical crop protection active ingredients to provide an effective solution for long-term protection. A hybrid solution approaches crop control differently than traditional pesticides by creating a long-lasting and highly effective solution.

Regev EC by STK Bio-Ag (exclusively distributed in the U.S. by SummitAgro) is the first potent hybrid fungicide in the market. Its unique activity presents a very low probability for the development of resistance or cross-resistance in plant pathogens. Regev’s hybrid formulation of difenoconazole and tea tree oil provides various modes of action against plant pathogens and plant defense mechanisms for improved efficacy in plant disease control and the cultivation of successful crop yields.

Activity and MOA

At suitable concentrations, Regev significantly inhibited spore germination or lesion development on treated leaves, and limited the expansion of lesions caused by various fungi. Diseases effectively controlled by Regev include powdery mildews (caused by fungi in the order Erysiphales), apple scab (Venturia inaequlis), black Sigatoka in banana (Mycosphaerella fijiensis), species of Alternaria, Cercospora, Botrytis, Rhizoctonia, Pyricularia, Helminthosporium, Sclerothium and more.

The fungicidal and antimicrobial activities of tea tree oil against fungal pathogens are derived from its ability to inhibit respiration and disrupt the permeability barrier presented by the membrane structures of living organisms. Tea tree oil was found to disrupt the fungal cell membrane and cell wall in plant tissue infected with phytopathogenic fungi. This explains why it exhibited outstanding curative activity against fungal pathogens, making it a unique product and enabling growers to use it even when the disease is already visible on the tissue.

Difenoconazole affects the fungal cell membrane by inhibiting ergosterol biosynthesis. The mode of action of sterol biosynthesis inhibitors, including difenoconazole, has been investigated extensively. The different modes of action of tea tree oil and difenoconazole makes Regev an effective and unique tool for resistance management which is suitable for integrated pest management programs. This combination results in a reduced synthetic chemical load on the environment compared to other mixtures based on two traditional chemicals.

Resistance Management

Because Regev has a unique multiple functional activity and presents a very low probability for development of resistance or cross-resistance in plant pathogens, it could be an important tool in preventing the development of resistance during the growing season. Its application can be rotated with products that exhibit different modes of action and to which fungal pathogen populations have shown a loss of sensitivity, so that the population of individuals that are less sensitive to chemical products can be reduced. Studies have also shown that a combination of tea tree oil and difenoconazole improved the efficacy of difenoconazole, including against fungal populations that had exhibited a lower sensitivity to difenoconazole.

Field tests have shown very small doses of Regev hybrid fungicide to result in a significant reduction in brown spot in potatoes. Courtesy GLC Consulting, Quitman, Georgia


Historically, biopesticides have been used largely on high-value crops, such as fruits and vegetables, but hybrids like Regev are not only being used on fruits and vegetables, but have proven to be a cost-effective approach for row crops like soybeans, and field and broad-acre crops like corn.

Regev is expected to prove an important component in plant disease control thanks to its preventive and curative activities; the indirect activity via the host plant either by systemic resistance or enhancing plant growth and yield; and the fact that it is reliable, leaves little residue and provides significant added value to growers. Its activity has been shown on a wide range of plant diseases. Regev promises successful yields without risking profit margins while simultaneously upholding regulations and responding to growing consumer demands. It represents a new generation in the future of crop protection

Moshe Reuveni is chief scientist at STK Bio-Ag Technologies in Israel, where he has been involved for nearly two decades in developing new, plant-based biopesticides.