Issue link: https://read.dmtmag.com/i/418083
32 DECEMBER 2014 GOOD FRUIT GROWER www.goodfruit.com B efore replanting an orchard, apple growers are generally advised to fumigate the soil to prevent replant disease. Replant disease is caused by a build-up of microorganisms in the root zone of the trees, which negatively affects the growth and productivity of new trees planted into the same soil. But fumigation with a chemical, such as Telone C-17 (1,3 dichloropropene and chloropicrin) only provides short-lived control of harmful soil organisms, says U.S. Department of Agriculture plant pathologist Dr. Mark Mazzola. He has identifi ed an alternative treatment that has longer lasting effects and even greater benefi ts than fumigation in terms of both tree growth and fruit yields. He said growers probably aren't aware that trees in fumigated soil are still underperforming, even though they do better than trees with no replant disease control. That's because until now growers have had nothing else to compare to fumigation. Mazzola has found that a combination of yellow and white mustard seed meals incorporated into the soil as a preplant treatment controls all the organisms implicated in replant disease in Washington State orchards, including nematodes. And the treatment could be used by organic growers. Many currently drop their organic status while replanting their orchards so that they can chemically fumigate the ground to avoid having an underperforming orchard. Mazzola came to the Agricultural Research Laboratory in Wenatchee, Washington, in 1995 specifi cally to work on control of replant disease. His fi rst task was to identify the causes. The main culprits turned out to be the fungal organisms Pythium, Rhizoctonia, Ilyonectria, and Phytophthora, along with the lesion nematode. The relative importance of the various organisms varies from site to site. Mazzola fi rst tested the idea of growing a cover crop in the soil for a year before replanting, with the idea that this would change the soil microbiology. He tried a variety of crops, such as wheat, canola, and Sudan grass, but none provided the comprehensive benefi ts he was looking for. Leaving the ground fallow for as long as three years resulted in "not one iota of change in disease development," he reported. He then turned his attention to seed meal, which is a byproduct of biodiesel production. He tried canola, rape, white mustard, and yellow mustard seed Full meal DEAL I ncorporating mustard seed meal into the soil before planting trees is an effective way to control replant disease, research shows. But is it practical? The blend of white and yellow mustard seed that Dr. Mark Mazzola tested is available from Farm Fuels, Inc., of Watsonville, California. The company makes biofuels for use in trucks and tractors in California, and the seed meal is a byproduct, which it sells as a fertilizer. Stefanie Bourcier, chief executive offi cer and research director at Farm Fuels, said the company sells the mus- tard seed meal to California strawberry growers, who have to treat the soil annually before replanting and are using it as an alternative to fumigation. The treatment is effective for various crops, and the company has some customers in the Pacifi c Northwest. The seed meal costs about $1,500 to $1,600 a ton, depending on the quantity ordered. The rate that Mazzola, a U.S. Department of Agriculture plant pathol- ogist, found most effective in his trials was three tons per acre, but David Granatstein, Washington State University sustainable agriculture specialist, said only the soil in the tree row would need to be treated. Figuring a tree-row width of three feet and ten feet between rows, just under a third of each acre would be treated, meaning the actual rate would be less than a ton. Shipping costs vary, depending on the availability of trucks. Bourcier said a good time for Washington grow- ers to buy seed meal from California is during peak apple shipping periods, when trucks can backhaul the seed meal rather than return to Washington empty. Assuming a delivered cost of, say, $1,800 per ton, would that pencil out? Tim Smith, WSU extension specialist based in Wenatchee, estimates that treating replant disease with fumigation boosts fruit yields by a third over the life of an orchard compared with an untreated orchard. Mazzola, in his trials, found that seed meal-treated plots were even more productive. In comparison, broadcast fumigation with Telone C-17 (1,3-dichloropropene and chloropicrin) costs about $800 to $900 per acre. But Mazzola has found that the seed meal treatment provides longer-lasting protection against nematodes than does fumigation. Both fumiga- tion and the seed meal suppress nematodes initially, but in fumigated plots, the nematodes quickly repopulated the root zone. He also found that the Pythium fungus quickly reappeared in fumigated ground. Mazzola found that the seed meal treatment is most effective when the ground is covered with plastic for a week after it is incorporated into the soil. He noted that fumigation would also be more effective if the ground was covered, though that's not a standard practice in Washington. Bourcier said most of their agricultural customers, such as strawberry growers, use a black plastic mulch, though some use a biodegradable mulch. However, the seed meal still provides benefi ts, even if it is not eco- nomical to cover the ground after treatment. Granatstein said another benefi t of seed meal is that it supplies all the nitrogen the new orchard needs for the fi rst three years, so that represents a savings in fertilizer. It also helps suppress weeds, which could mean fewer herbicide applications. Seed meal qualifi es as an organic treatment, whereas fumigation does not. A common practice among organic growers is to drop the orchard's organic status when the old trees are removed so that the ground can be fumi- gated. It takes three years to transition back to certifi ed organic status, about the same length of time it takes the trees to produce their fi rst crop. With the seed meal treatment, the orchard could keep its organic certifi cation. Apart from not being organic, fumigation is subject to safety regulations and application buffers. Plant in Washington Most of the seeds that the company processes are grown in the Pacifi c Northwest—primarily in eastern Washington—and shipped to California, where most of the biodiesel customers are. However, the company is planning to build a processing facility in eastern Washington by 2015, which would greatly reduce ship- ping costs for Northwest growers. Bourcier also hopes to do more trials with the seed meal in the Northwest. The seed meal is labeled for use in Washington as a fertilizer, but the company is working with the U.S. Environmental Protection Agency to obtain a biopesticide label, which is also expected in 2015. —G.Warner Seed meal treatments outperform fumigation. by Geraldine Warner New replant disease TREATMENT PHOTO BY GERALDINE WARNER. In a greenhouse trial, Mark Mazzola is growing various rootstocks. After a time, he will plant them in soil in which other rootstocks have been growing and monitor WKHLUJURZWKWR¼QGRXWLIJURZWKGLIIHUHQFHVDUHUHODWHGWRWKHGLIIHUHQWFRPSOH[HV of microorganisms associated with the various rootstocks.