Walnut Blight Spraying

For 20 years, California walnut growers had to convince the EPA to grant a temporary emergency registration for a fungicide to control annual outbreaks of walnut blight. At the same time, the growers assembled the data necessary to make a full registration possible. After 20 years, the EPA granted the full registration and the walnut growers can rest easy.

“Depending on variety, walnut blight can take a heavy toll on walnut production, particularly when inoculum is high and spring weather is warm and wet.

However, with the federal EPA granting Manzate (flowable or dry flowable formulations) a Section 3 registration last year, walnut growers throughout California now have a reliable option for controlling the disease. For the previous two decades, growers in the state could use this and other ethylene bis-dithio-carbamates (EBDCs) products to treat for walnut blight only in selected counties under a Section 18 (emergency exemption) registration. Applying for Section 18 registration required submitting extensive environmental, health and safety data each year.

The walnut blight bacterium (Xanthomonas arboricola pv juglandis) over-winters in dormant buds primarily under the outer bud scales or cataphylls. When buds break in the spring, cataphylls open and young shoots extend past them. Rain drops spread the disease by splashing bacteria onto any green tissue, infecting them.

The disease appears as black lesions on green tissue. As bacteria spread inside the walnut, they grow toward the center of the nut early in the season, destroying the developing kernel.

In orchards with histories of walnut blight damage, protective treatments at seven to 10-day intervals during prolonged wet springs are necessary for adequate disease control.”

Author: Northcutt, G.
Affiliation: Reporter.
Title: Tips for better control of walnut blight.
Source: Western Farm Press. 2014-04-09. Available: http://westernfarmpress.com/tree-nuts/tips-better-control-walnut-blight