With the trees still dormant at the end of February, things were quiet in the northern Sacramento Valley walnut orchards of Tehama County. “We’ve had pretty good weather for the bloom, and the trees look good,” reports Rick Buchner, University of California Cooperative Extension county director and farm advisor. “But, who knows what that means as to when the walnuts will start leafing out?”
Typically, with the late-leafing varieties like Chandler, Howard and Hartley, buds begin unfurling towards the end of March or the first week of April. That’s as much as three weeks later than such early-leafing varieties, such as Ashley and Payne, which are popular farther south in the San Joaquin Valley.
As the county’s walnut growers await the start of the new season, they are facing three concerns, notes Buchner. The most pressing has been the low rainfall this winter. Growers have seen little, if any rain, since the first of the year. A system that passed through the area in the third week of February, brought only some scattered showers and a little hail, he says. The forecast through the first week of March called for more dry weather.
“If we don’t get some free water pretty soon, growers will have to start irrigating,” Buchner says.
Timing hinges on the amount of vegetation on the orchard floor and soil water reserves. “Weeds or a cover crop could deplete a great deal of water from the root zone of the trees fairly quickly,” he says. “Once the tree canopy forms, the trees will need a full load of water.”
Increasing pressure from walnut blight is another concern. The disease is creeping into more orchards and infestations are becoming more severe, Buchner says. The more blight damage last year, the more inoculum levels this year to threaten the crop, he notes.
Managing this disease requires applying protective sprays to buds, flowers and developing nuts. “Unless you intervene with a good spray program, you’ll have problems,” he says. “If you had a higher than tolerable level of walnut blight last year, you need to be spot-on perfect with your spray program this year,”
In fact, he attributes much of the increased incidence of walnut blight on improper spraying. This has allowed inoculum levels to build up, increasing the difficulty of controlling the disease. Success depends on applying the proper chemicals at the correct rate at the right time and achieving good coverage of the canopy, Bucher notes.
“All four components have to be right,” he says.
A Section 18 for Manzate on walnuts has been approved again for this year, Buchner notes. This allows growers to tank mix this product with copper.
Resistance to copper is common in Sacramento Valley orchards and has been found in a few San Joaquin Valley orchards. However, no walnut blight resistance to Manzate had been documented, Buchner reports. If Manzate is used, it must be added to every copper treatment for the greatest benefit.
“This chemistry works well to control the disease,” he says.
“Depending on the weather, once disease infests about 2 percent to 3 percent of the crop, you have a problem,” Buchner says.