Comparative Efficacy of Downy Mildew Fungicides on Spinach (April 1, 2015)

A downy mildew fungicide efficacy trial was conducted in conjunction with the International Spinach Conference held in Yuma during the last week of February. Eighteen different fungicides were evaluated, including biofungicide/organic products as well as conventional chemistries. Plots were planted with the cultivar Viroflay, which is susceptible to all known races of the downy mildew pathogen. Three applications of each fungicide were applied (Feb 6, 16, and 23). Disease severity was assessed by counting the number of leaves within two 1-square-foot areas within each plot. In plots sprayed only with water, 62% of spinach leaves were infected. Five conventional chemistries held spinach downy mildew to levels ranging from less than 0.5% to no downy mildew present. These products included Aliette, Revus, Blockade (also known as Actigard), Zampro, and Ranman. On the other hand, for the 10 biofungicides tested, disease severity ranged from 38 to 58% infected spinach leaves. Since the tolerance level for downy mildew on baby-leaf spinach is very low, none of the tested biological/organic products were effective on their own. The results of this fungicide trial provide good news for conventional spinach growers but are disappointing for organic spinach producers.

Click picture to listen to Mike's update

To contact Mike Matheron go to: matheron@ag.arizona.edu.