Control of powdery mildew on glasshousegrown roses and tomatoes in the Netherlands using anhydrous milk fat and soybean oil emulsions

Abstract

Powdery mildew (PM) is a very serious disease affecting glasshouse-grown roses and tomatoes in the Netherlands. Control is limited because of resistance to existing fungicides. Anhydrous milk fat (AMF) and soybean oil (SBO) emulsions were evaluated for control of PM in roses and tomatoes. Both AMF (14 g/litre) and SBO (14 g/litre) provided powdery mildew control on rose leaves and blooms that was significantly better (P<0.001) than that achieved using formulated dodemorph acetate (2.5 ml/litre), a systemic fungicide commonly used by Dutch rose growers. Powdery mildew control with SBO was as good as that provided by dodemorph acetate on tomato fruit and flowers, while AMF was slightly less effective. Combination of SBO (3.5 g/litre) and AMF (3.5 g/litre) mostly provided PM control rivalling that of SBO (14 g/litre). Spraying roses with whole milk (20% v/v) left white residues. No evidence of phytotoxicity with the use of natural product emulsions was found on floral and fruit tissues.

Fungicidal Activity of Soybean Oil against Powdery Mildew on Wheat

“…In addition, pathogens do not tend to develop resistance to agricultural sprays containing oils [30,31,42], because membrane transport is such a fundamental life process. The combination of reduced amounts of SBO and AMF has been shown to be as effective as greater concentrations of each biofungicide on its own [10]. Non-toxic (physical) rather than toxic (chemical/antibiotic) MoAs are also advantageous when it comes to product registration, since the latter higher-risk product group requires expensive and time consuming toxicology testing.…”

“…SBO has also been demonstrated to have a much less adverse effect on plant health than AMF [32]. Another effective option is that SBO can be tank mixed with AMF at much lower concentrations than either product on its own [10]. This offers the dual advantages of reduced cost of goods and greater durability, due to differing modes of action as described in the preceding SEM section.…”

“…This offers the dual advantages of reduced cost of goods and greater durability, due to differing modes of action as described in the preceding SEM section. Other recommendations include not spraying below 4°C (40°F), because the emulsion breaks down, and avoiding sprays on newly emerged foliage or floral tissue, although we have treated rose blooms without any toxic effects [10].…”

“…Soybean oil is a vegetable oil that is solvent-extracted from pressed seeds of soybean, followed by refinement, blending and optional hydrogenation, and is one of the world's most widely consumed edible plant oils [3,4]. While plant-derived oils, such as SBO, are predominantly used in agriculture as an adjuvant to aid the spread of pesticides over plant surfaces and also to help the pesticide to stick to the plant surface [5,6], SBO is also directly antimicrobial against a range of powdery mildew fungi [7][8][9][10], Botrytis cinerea [11] and bacteria such as Staphylococcus aureus and Escherichia coli [12]. In addition, SBO has insecticidal activity against mites [13], whitefly and aphids [14,15] and insects associated with stored grain products [16] .…”

Product formulation is crucial to the success of lipid-based bio-fungicides

“…Anhydrous milk fat (AMF) and soybean oil (SBO) formulations have been identified in field and glasshouse trials as natural, environmentallybenign bio-fungicides for control of PM and other pathogens, with efficacy rivalling that of synthetic pesticides currently on the market (Ah Wurms & Hofland-Zijlstra 2015). The three main components of these bio-fungicide formulations are: (i) the lipid active ingredient; (ii) an emulsifier that prevents the lipids from separating out from the water diluent; and (iii) an antioxidant, which minimises the breakdown of the fatty acid chains and associated development of rancid odours (Wurms & Ah Chee 2007).…”