Spinach Continued from Page 6
means of controlling spinach downy mil- dew.” The guidelines note that during the past 50 years in California, “each outbreak of a new downy mildew race was later matched by the development of resistant spinach lines.” Correll has screened spinach varieties for downy mildew resistance in Salinas, San Juan Bautista and Yuma, Arizona, for years. He said each new race of downy mil- dew is “identified and evaluated against a standard set of spinach differentials” to determine resistance or vulnerability. The International Working Group on Peronospora concluded that the 20th race of downy mildew “poses a significant threat to the spinach industry in all parts of the world.” Spinach varieties it can infect include Viroflay and Yakalo. The working group includes growers and pest control advisors in California and Arizona and representatives from seed and breeding companies. In the Salinas Valley, spinach is largely grown on 80-inch beds that are sprinkler irrigated. The dense canopy is moist and cool. The moist conditions are favorable to downy mildew, which makes itself known through unsightly spots that make the crop unfit to market. There has been limited research show- ing that drip irrigation decreases spinach downy mildew pressure. But because the
Spinach is infected by the plant disease downy mildew. Coastal breezes help carry disease spores to Salinas Valley fields. Farmers and researchers are working to develop new spinach varieties resistant to the disease.
crop is shallow rooted and densely packed, drip irrigation saves little on water or the energy to move it. Meanwhile, with spinach grown throughout Monterey County, the coastal breeze continues to spread downy mildew spores from field to field. Klosterman of USDA said researchers placing spore traps in the region have
worked with the Oakland pathogen man- agement firm Root Applied Sciences to de- velop enhanced monitoring to track the disease risks. In addition, seed companies have been adept at offering resistant varieties to man- age the newest races of the disease. For example, just two days after the working group designated spinach downy
mildew race 20, the vegetable breeding company Enza Zaden published a list of its spinach varieties that are resistant to the new race—providing spinach farmers with useful options, at least until the next threat drifts in with the coastal breeze. (Bob Johnson is a reporter in Monterey County. He may be contacted at bjohn11135@gmail.com.)
July 10, 2024 Ag Alert 7
Powered by FlippingBook