July/August 2024
Butte County Walnut Variety Trial update on efforts to improve crop performance, yield
In May of 2023, the 10-acre Butte County Walnut Variety Trial was planted at the Chico State Farm in Chico, California, with a goal to identify new varieties that would perform well in the region.
The project is a joint venture between Chico State, UC Davis Walnut Improvement Program and the University of California Cooperative Extension (UCCE). The orchard includes 18 new selections developed by the UC Walnut Improvement Program, all planted on RX1 rootstock on a 26’ X 26’ spacing with micro-sprinklers.
“The goal of the trial is to use farming techniques as close as possible to what a typical grower in this area would be doing,” said Becky Wheeler- Dykes, a UCCE orchard systems/ weed ecology farm advisor. “Ideally, we want to identify a variety that can be put straight into our conventional farming model and thrive; we don’t want growers to have to change much to accommodate a new variety.”
A little over a year later, things are looking promising.
“My co-PI’s, Dr. Richard Rosecrance at CSU Chico and Clarissa Reyes, another farm advisor with UCANR, are absolutely amazed at how great the trees are looking,” Wheeler-Dykes said.
And while it’s a little too early to tell if there are any standouts — typically, in variety trials, they weed out the really poor performers before identifying the top performers — the team did make some observations last year that indicate there is one variety that might be really precocious.
“This means the tree will start bearing early in its lifespan,” Wheeler- Dykes said. “We evaluate precocity because the sooner an orchard can start yielding, the earlier a grower can start recouping the capital investment into orchard establishment.”
The main quality characteristics that the team will be emphasizing are the kernel color and the percentage of edible yield.
“The high-quality product coming out of California really sets us apart on the world stage, and that’s a non- negotiable for any new variety to be a viable contender commercially,” Wheeler-Dykes said. “All of the varieties selected for the trial have good nut quality, but the sample size has been pretty small. Since we haven’t had a harvest yet, we don’t have any data on that. We’ll likely get a few nuts off the trees this year; by the third year we think we’ll have enough to get good data from.”
Pest and disease scouting
Because of the necessary layout of a variety trial, some of the harvest looks a little different so that the team can keep the nuts separate for evaluation.
“We also do intensive data collection periodically, which is where we go through the orchard tree by tree and make detailed observations, including what beneficial insects we see, any unusual morphological features, any indication of variable pest or disease pressure, etc.,” Wheeler-Dykes said.
In the orchards, pest and disease evaluation is done periodically by a student researcher whose focus is this trial and a master’s student who will be writing her thesis on the walnut blight findings in the trial.
“We’ll be using a scoring system of disease severity and incidence that’s been used to evaluate walnut blight in the past,” Wheeler-Dykes said. “Last year the trees were planted after the risk of blight had largely passed, and the crop was removed the first year to allow the trees to focus energy on canopy development. This year we’ll start blight evaluations pretty soon, probably in the next couple of weeks.”
A key difference in managing walnuts in the North Sacramento Valley compared to areas farther south is the susceptibility to blight. The bacteria that causes walnut blight is spread by splashing raindrops and infects young tissues like new shoots and blooms/young fruit.
“Down south, most of the rain for the season has ended before these tissues start growing,” Wheeler- Dykes said. “For us up here, we often continue to get rain into May, sometimes even early June. Growers typically manage blight by applying copper-based materials. Having a variety that is avoidant or resistant to blight, either because it leafs out and blooms later or because of an inherent actual resistance, would be a huge benefit.”
Not only would growers save money on material and labor, but they would also potentially produce a higher quality product without blight damage and would drastically reduce the potential for environmental effects of heavy copper use.
Overcoming challenges
One big challenge early on was that, since these are experimental varieties, there wasn’t enough material to have all the trees budded and ready when the team initially planted the orchard.
“We had to come through later in the season to field bud the remaining trees,” Wheeler-Dykes said. “This was a challenge logistically, but ended up being a great opportunity for us and students to learn field budding techniques.”
She credits the staff and students at the Chico State farm with being proactive in their practices, making things run smoothly.
Wildlife management
In the trial orchard, most of the vertebrate pest management is focused on gophers and tree squirrels, and the management used is predominantly trapping.
“There have been increasing restrictions on chemical/bait management of vertebrate pests,” Wheeler-Dykes said. “The tree squirrels have been particularly challenging in the neighboring almond orchard here, so we will have to see if they migrate over and put pressure on the walnuts.”
Important for the future
Joe Grant, production research director for the California Walnut Board, noted California walnut growers support the development of new walnut varieties and rootstocks through their assessment dollars, so this is an important mission.
“One measure of success is for growers to be confident that new varieties and rootstocks are going to perform well under their local conditions,” he said. “Regional trials like this one provide invaluable data for assessing a new variety’s or rootstock’s potential under local conditions and allow local growers to get a ‘sneak peek’ at up-and-coming new materials in a commercial orchard setting.”
Additionally, the walnut board provided funds for a state-the-art irrigation system that supports the trial and is designed to allow for the study on the impacts of differential irrigation on new varieties and rootstocks.
Working with CSU Chico to conduct the trial will provide opportunities for future research projects and become a place where students can gain hands-on learning experience with walnuts as a part of their academic training, Grant said.
Wheeler-Dykes added the team is really optimistic about what will be discovered with the variety trial.
“The industry is going through some incredibly challenging times right now,” she said. “Prices have been low, forcing growers to make really hard choices that span from limiting inputs to pulling orchards. In a way, this makes it a good time for us to be gathering this data for growers. We’re hoping we’ll have good results and options available when growers are ready to plant walnuts again. We’re all looking ahead at the future of walnut production and hoping to contribute to California growers’ success.”
