The breeding of crop varieties that are resistant to pest organisms is often touted as an effective means of replacing pesticide use. And yet, pest organisms mutate and overcome the plant’s resistance. According to the California Department of Pesticide Regulation, fungicide use in California spinach fields has doubled in the last decade. The reason for the increase has been the breakdown of the plant’s resistance to mildew (Peronospora farinosa f. sp. spinaciae).

“Downy mildew disease is the most important disease problem facing the extensive spinach industry in California. … While downy mildew has been around California spinach fields for decades, the last few years have seen the development of four or five new races. Each new race potentially overcomes the resistance factors in the cultivars being planted at that time, leaving the crop susceptible to severe damage.”

“Integrated management steps must be used. … Resistant cultivars will remain a foundational piece of such a program. Judicious use of effective fungicides will remain important.”

Authors: Steven Koike and Jim Correll
Affiliation: University of California and University of Arkansas, respectively
Title: Spinach Downy Mildew: Outlining the Challenges.
Publication: Crop Notes (University of California Cooperative Extension)