WENATCHEE, Wash. — Mark Mazzola has been investigating replant disease in apple orchards for 20 years and says he’s found a solution that may work better than soil fumigation.
A combination of yellow and white mustard seed meals combats replant disease longer than fumigants by addressing the whole ecosystem of soil rather than just its chemistry, says Mazzola, a research plant pathologist at USDA’s Agriculture Research Service Tree Fruit Research Laboratory in Wenatchee.
Mustard seed meal also results in better tree growth and fruit yields than fumigation, he said.
Replant disease is pervasive when replanting an orchard and is a “major impediment to the establishment of an economically viable orchard,” Mazzola said.
Replant disease is a build-up of micro-organisms in soil from old tree roots that hampers the growth and productivity of new trees. It wasn’t much known before a disastrous freeze in 1968 and 1969 killed a lot of orchards in Central Washington.
Growers tore out dead trees and replanted new ones and began having more problems with diseases, Tom Auvil, research horticulturist at the Washington Tree Fruit Research Commission in Wenatchee, has said.
The industry turned to fumigation but it doesn’t always work because temperature, soil texture and soil moisture all can hinder its effectiveness, Auvil said.
Mazzola, now 54, was hired at the ARS in Wenatchee in 1995, primarily to investigate replant disease. He has focused on apples but looked at pears and cherries, which are susceptible to the same pathogens.
He believes his undergraduate work in forest biology and strong foundation in ecology gives him a broad perspective in looking at replant disease and soils.
“Most people in this research come from agricultural programs like plant and soil science. It’s relatively rare to find people with an ecology background in plant pathology. I try to understand how soils function from a biological and ecological perspective,” he said.
Many diverse organisms are at work in soils, he said.
He has managed a nematode diagnostics lab, worked on rust fungi, soil bore fungi and bacteria and then studied the molecular genetics of bacteria that are pathogens of rice.
“You don’t find a lot of people who have worked on trees, beans, rice, wheat and now apples. We get pigeon-holed quickly,” he said.
In looking at replant disease, Mazzola first identified four fungal organisms and the lesion nematode as the main problems. He tested several cover crops to control the pathogens on the ground before it was replanted as orchard but without the results he was looking for. He left ground fallow for up to three years without a reduction in disease development.
About 15 years ago, there was a lot of interest in using mustards, canola, broccoli and other brassica plants as green manure in soil for their biologically active chemistries.
“But you can’t produce enough biomass to obtain the chemistry needed to suppress plant pathogens. Seed meal possesses higher quantities of these chemistries,” Mazzola said.
He began experimenting with seed meal from various brassica crops and found none of them alone controlled replant organisms. Then he tested various combinations and ratios. He landed on a 50-50 mix of yellow and white mustard seed meal applied in the fall before a spring planting.
The mix produces chemicals that kill the pathogens but also changes the microbiology of the soil to make it more resistant to re-infestation.
A field trial of Jonagold trees on Geneva 11 rootstock, planted in 2010, resulted in a 45 percent increase in fruit yield. Gala on Malling 9 and Geneva 11, also planted in 2010, in the mustard seed meal treated soil yielded 25 percent more fruit cumulatively in the first two years.
Mazzola used metagenome analysis, generating and sifting through millions of DNA sequences, to study roots and attached soil and found microbes in fumigated soil reverted back to their original state after two seasons while microbes in seed meal treatment were distinct and still suppressing disease after the fourth season.
“We’re able to identify all the bacteria and fungi colonizing the apple tree root system and improve the root-soil ecosystem to manage the pathogens of this disease,” he said.
Auvil has said Mazzola has done a great job of showing a wide array of organisms at work in tree fruit soil, but that the seed meal solution takes too much meal from too far away to be practical beyond test plots.
“Growers apply 20 tons per acre of compost in the fall to orchards,” Mazzola said, noting he applies mustard seed meal at 3 tons per acre and has successfully reduced that by one-third.
Mustard seed meal is mainly a biodiesel byproduct produced in the Midwest but mustard seed is grown in Washington and can be increased, he said.
“Growers will make this work,” he said, adding meal flakes have been turned into pellets commercially in California for easier application.
Interaction between Geneva rootstock and the seed meal are likely to allow further reductions in the quantities required, he said. And seed meal may not be the only solution. Mazzola continues to research other potential solutions.
“The Geneva rootstock was developed for precocity, dwarfing and fire blight resistance, not replant disease,” he said. “That’s a side benefit. It has a tolerance for replant disease. It handles it.”
Mazzola and Yanmin Zhu, an ARS geneticist in Wenatchee, and Gennaro Fazio, an ARS rootstock breeder in Geneva, N.Y., who developed the Geneva rootstock, are collaborating to investigate differences in gene expression with an eye toward developing a rootstock truly resistant to replant disease.
This article was first published on March 27, 2015.
Born and raised: Boston, Mass.
Family: Wife, Michelle Mazzola, a funding consultant.
Education: Bachelor’s in forest biology, University of Vermont, 1983; master’s in forest pathology, University of Vermont, 1985; doctorate in plant pathology, Washington State University, 1990.
Occupation: Research plant pathologist, USDA ARS Tree Fruit Research Laboratory, Wenatchee, since 1995.
Previous work: Research plant pathologist, USDA ARS, Pullman, Wash., 1993-1995; post-doctorate research associate, Kansas State University, 1990-1993; manager, Nematode Diagnostic Laboratory, University of Vermont, 1985-1986.
Quote: “My interests were in natural resources and that related to my first hiking trip in the White Mountains of New Hampshire.”