Evaluation of various reduced-risk products for management of powdery mildew in greenhouse cucumber, tomato and pepper

Project Code : MUR06-110

Project Lead

Raymond Cerkauskas - Agriculture and Agri-Food Canada


To identify and assess new reduced-risk materials for control of powdery mildew on greenhouse vegetables

Summary of Results

Powdery mildew is a perennial problem of greenhouse cucumber, pepper, and tomato and can cause severe losses, if left unchecked. Environmental control of this disease is very limited and growers often depend on pesticides for control. Fungicides such as Sulphur, Nova (myclobutanil), and Milstop (potassium bicarbonate) are registered for control of powdery mildew on greenhouse vegetables. Sulphur is not often applied to the crop because of phytotoxicity, particularly during warm weather, and therefore growers have depended almost solely on Nova for control. However, since the registration of Nova several growers have reported decreased efficacy of this fungicide for control of powdery mildew.

In this project, a number of alternative reduced risk products were evaluated for their control of powdery mildew in greenhouse cucumber, pepper and tomato. Trials included water as well as Milstop and Nova as controls.

P. xanthii develops very quickly on cucumber leaf tissue in comparison to either pepper or tomato powdery mildew. Consequently, testing for efficacy of control of cucumber powdery mildew is a good indicator of likely success in control of pepper and tomato powdery mildews.

Lactosan, a fermented milk product, was not effective at 5% or 7.5% in controlling cucumber powdery mildew; however, the addition of surfactant (Agral 90) resulted in good control of powdery mildew. A somewhat similar observation was made with KBV when used with a surfactant. Yo-K-San, another milk product, with surfactant was somewhat effective, while Actinovate (Streptomyces lydicus) and Endofine (Clonostachys rosea) were not very effective in control of P. xanthii. The addition of a surfactant may contribute to enhanced efficacy of the latter two materials.

Quintec (quinoxyfen) was very effective at very low rates in our trials. Increasing rates of Quintec resulted in increasing the level of control of cucumber powdery mildew. Residual activity was considerably greater than 7 days.

Valent-10118, Procure (triflumizole fungicide), Pristine (pyraclostrobin + boscalid fungicide), and Prev-Am (citrus oil + borax) were effective in control of cucumber and pepper powdery mildew at the rates applied. Residual activity exceeded 7 days, the time by which a second application of Milstop (potassium bicarbonate) would need to be re-applied for control of cucumber powdery mildew.

Siliforce (SIO2, K2O: 2%, PEG 400: 46%) was intermediate in control of cucumber powdery mildew. CaCl2  + surfactant and K2HPO4 + surfactant, at the rates applied, were both only somewhat effective with CaCl2 + surfactant more effective than the latter. There was some phytotoxicity observed with K2HPO4 + surfactant after spray application. Residual activity of CaCl2 + surfactant and K2HPO4 + surfactant was less than that of the new fungicides such as Valent-10118, Procure, Pristine, and Prev-Am that were evaluated.

Results for control of pepper powdery mildew were similar to those for cucumber powdery mildew except CaCl2  + surfactant, K2HPO4 + surfactant, and lactosan + surfactant were only somewhat effective.

Results for control of tomato powdery mildew were less consistent than those for control of cucumber or pepper powdery mildew. Best control was achieved with Nova, Procure, Pristine, Quintec and Valent-10118. Some of the tomato powdery mildew trials need to be repeated.

Trials with Nova, Milstop, Sporodex (Pseudozyma flocculosa), ßitalicize Lactosan and Yo-K-San at several commercial greenhouse cucumber sites for control of powdery mildew were conducted. Milstop, Sporodex, Lactosan and Yo-K-San were as effective as Nova in control of cucumber powdery mildew over a 7 day period, however, more than double the number of spray applications were required to maintain similar control as that of the Nova treatment. Alternative reduced-risk materials, with a different chemistry and a different mode of action, are ideal and necessary to enable growers to practice rotation as a resistance management strategy.

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