Your trees are gone. In their place is a barren piece of ground. What should you do next? What questions should you be asking so that the new almond orchard you want to plant will thrive?
Experts at the Almond Board of California (ABC) suggest you start by finding out one piece of vital information: What’s in your soil?
Understanding your soil’s profile – its pH level, whether it’s heavy or sandy, the nutrients or potential toxins that exist in it, the amount and type of nematodes that are present, etc. – is critical to the success of your next orchard.
“An orchard is an ecosystem,” said Sebastian Saa, senior manager of Agricultural Affairs for the Almond Board. “For 20-plus years, the orchard is where your trees are living and growing, and if your orchard is well established with a deep, intricate root system then the trees can overcome potential threats such as nematodes and other pests.
“However, when you go to remove those older trees and replace them with new ones, those young trees are left to fend for themselves against those potential threats – and in the case of nematodes, in particular, a new, young tree is like a delicious snack.”
Start by assessing your soil
To get ahead of this issue, Saa recommends that growers conduct soil testing to best understand what factors they’re up against in their orchard’s soil. Testing will provide growers with critical data about their soil that will help them decide what varieties and rootstocks will work best with their specific soil types.
Saa said that even if a grower has conducted soil testing in the past, it’s important to do so again when looking to replant.
“A soil’s makeup can change over time,” he said. “Rootstocks, for example, that are available today may change one year from now, and companies and researchers are constantly discovering new ways to address soil problems. You want to ensure you’re staying ahead.”
For years, the Almond Board of California has funded research in the area of soil health, as well as conducting variety trials and evaluating rootstocks. One current research project is being led by Andreas Westphal, a University of California researcher based out of the Kearney Ag Center in Parlier. Westphal is currently working to optimize rootstocks to make them tolerant of crown and root infections and resistant to root-knot and root-lesion nematodes.
Saa said it is important that growers truly understand their soil analysis so they can choose the rootstock and variety that are most compatible. He recommends growers talk to their local UC ag advisor to begin the process of testing their soil.
To treat or not to treat?
Another key decision for growers to make before they replant is whether to treat their soil with a fumigant to combat nematodes or the risks associated with Prunus replant disease (PRD) or Phytophthora crown rot and root rot (PCRR). Both diseases are common, especially in situations when a new almond orchard is planted on the same land as an old one.
“There are threats in the soil, like nematodes and other pests, that are poised to damage young trees when they are young and more sensitive,” Jesse Roseman, ABC’s principal analyst for Environmental and Regulatory Affairs. “Once the trees grow larger, they can withstand some of those pressures.”
Fumigation is a typical treatment for these issues in the soil, but its toxicity and volatility has scientists searching for effective alternatives. Methyl bromide was used for years but has been banned internationally because of its effect on the Earth’s ozone layer. Telone and chloropicrin are currently still allowed, but Telone is under regulatory pressure.
ABC-funded researcher Greg Browne is working to identify natural ways to combat nematodes and prevent PRP and PCRR. He has studied anaerobic soil disinfestation (ASD), which spreads either rice hulls or an almond hull and shell meal mix into rows where new trees will be planted. The mix is then activated when water is applied. According to Roseman, Browne and his research team are looking to see if either mix can suppress PRP, PCCR and nematodes.
At the end of the day, when it comes to replanting an orchard, knowledge is power.
“If you make the wrong decision you may have higher operational costs for the following foreseeable years,” Saa said. “It could be a headache for the rest of your orchard’s life.”
Growers interested to learn more about Browne’s research in disease management may reference page 10 of the Almond Board’s 2019 Research Update, and those interested to learn more about Westphal’s work in rootstocks may see page 33.
