IPM Protects Macadamia Nut Production on Hawaii
Visitors to Hawaii often return home with three things: a sun tan, a pineapple, and a box (or six) of chocolate-covered macadamia nuts.
Macadamia nuts are an identity crop for the state, like chile in New Mexico or potatoes in Idaho. They are also the third-largest economic crop in the islands, behind seed corn and coffee. Macadamia orchards cover some 18,000 acres on Hawaii and generate $53 million annually.
But since the arrival of the macadamia felted coccid in 2005, maintaining that production and profitability has become more difficult. Native to Australia like the macadamia nut itself, the macadamia felted coccid is a tiny scale insect that is difficult to detect before it causes branch dieback and damages trees.
“When you see it, it means you have to do something,” said Dan Springer, the orchard manager of the 4,000-acre MacFarms operation on Hawaii’s Big Island. “Actually, when you see it, it means you should have done something two months ago.”
It’s the only insect pest macadamia growers have to deal with, and research funded in part by the Western Integrated Pest Management Center has helped show how.
Unique Crop, Unique Challenges
Offer most orchard growers the opportunity to only have one insect to control and they’d jump at the chance. But that’s where Hawaii is different.
“There are other insect problems in macadamia, but because of the costs of control and the other challenges in Hawaii, they're not worth any type of management to address them,” explained Alyssa Cho, a researcher at the University of Hawaii. “Macadamia felted coccid is a new management need for growers and it adds a lot of costs. For some growers, it could be a make-or-break in terms of their ability to continue farming.”
Macadamia trees are tall and densely canopied. Old orchards in Hawaii were planted with tight spacing between the trees and on rocky, volcanic hillsides. There are areas of the MacFarms orchards, Springer said, that only his most experienced equipment operators can navigate. The rough terrain makes scouting difficult, spraying difficult and even driving down the farm roads a suspension-breaking, bone-rattle chore. Tractor tires last one year. Equipment breaks. Everything is slow.
“We can spray a maximum of 100 acres a week,” Springer said. “This year, we sprayed 400 acres and it took us four months.”
An IPM Solution
In 2016, Cho received a Western IPM Center grant to study integrated pest management approaches to managing the coccid. Specifically, she wanted to know if thinning the orchard canopy would reduce infestation levels and encourage natural enemies.
The answer was yes, it absolutely does.
“We've found that by pruning we can not only reduce the macadamia felted coccid, but we also see an increase in predation and parasitism of naturally occurring beneficial insects in the orchards,” she said. “We found that this, in combination with a reduced spray application, can provide effective control for our growers.”
It’s good news, but it wasn’t necessarily the answer the state’s growers hoped to hear. Many worried that the pruning and thinning Cho recommended would cut into their yields more than the insect itself. She has data that show just the opposite.
“Over a two-year trial period, we actually showed that there was no effect on yield when growers were pruning,” she said. “And that's primarily because pruning actually can be beneficial for production yield. It instigates new growth on the trees and by opening up the canopy you're actually allowing more light in which helps with yield and production.”
Pruning can also help maximize spray efficiency when growers do need to apply insecticides, and the increased light encourages some weed growth, which is habitat for predator insects that feed on the coccid.
Springer is following Cho’s recommendations, both pruning and removing trees in tightly planted areas of the farm to open up more room for the ones that remain. He also most aggressively removes a specific variety of tree which has proven more susceptible to coccid damage than others.
Keeping Land in Production
By developing an effective IPM strategy, Cho has alleviated one challenge for growers. Others remain.
“One of the biggest challenges across all of our crops is the limited availability of labor and the high cost of labor,” Cho explained. “Macadamia in particular is challenging. When a macadamia nut is mature it falls off the tree, so they have to be hand-harvested and picked up off the orchard floor. That’s difficult, back-breaking work.”
Springer, for example, has 80 pickers in his permanent crew but work for 120.
For Cho, the biggest challenge is finding research funding to support the industry. While important on Hawaii, macadamia nuts are a small-acreage specialty crop that not many programs prioritize.
“An additional challenge is that Hawaii is tropical,” she said. “We are the main state that produces tropical fruits and we have a limited ability to translate our research to other major macadamia-producing areas in the U.S., for instance, because there aren't any other major macadamia-producing areas in the U.S.”
But supporting the industry is vital, she believes, if not for the production itself, but for the benefits the state gains by keeping land in production.
“A lot of agricultural land in our state after it's no longer in production will either be broken up into smaller parcels and sometimes it'll be developed or abandoned,” she said. “These orchards are rain irrigated and there are a lot of benefits from growing orchard crops and having tree like these in the ground for 50 or 60 years. It would be pretty devastating to see someone take out these trees and put in apartment complexes.”