Consider fumigation an investment

Lynn Long discusses the fumigation in a new Regina cherry block at the Omeg orchard at The Dalles, Oregon.

Cherry growers may balk at the cost of fumigating land before planting, but the cost is soon recouped through higher productivity, Lynn Long, Oregon State University Extension educator, told growers during a summer orchard tour at The Dalles.

Growers visited an orchard that Mike Omeg replanted in 2008 that had been in agricultural production since 1900. At one time, it was a vineyard. It was most recently a cherry orchard, with tree trunks you could barely get your arms around, he told the group. “You could drive a freightliner between the rows.”

Omeg took the whole planting out in late summer of 2007, using an excavator to remove the trees and roots, rather than just pushing the trees over with a bulldozer. He then ripped the ground in three different directions so that the fumigant would penetrate deeply. In order to fumigate successfully, the soil must be moist, so he used aluminum hand lines to irrigate the ground and fumigated at the end of August 2007. He seeded winter wheat as a cover crop, irrigating it twice. A thick stand of wheat prevents soil erosion and provides a good green manure to till into the soil the following spring. He replanted in the spring of 2008 with Regina cherries on Gisela 12 rootstocks.

Omeg said on his old ground that has been replanted numerous times, he uses Telone C-35 (dichloropropene and 35 percent chloropicrin). That formulation contains twice as much of the fungicide chloropicrin as Telone C-17. Where the orchard has only been replanted a couple of times, he uses the more economical C-17.

Early yields

Omeg said he didn’t used to believe in fumigation, until he found out how well it worked.

Long said that in a trial at the neighboring orchard of Tim Dahle, fumigated trees had a trunk cross-sectional area of 128 square centimeter or 19.84 square inches in the fourth leaf compared with only 83.7 square centimeter or 12.97 square inches for the untreated trees. The yield in the fourth leaf in the fumigated plot was 8.25 pounds per tree, compared with only 3.75 pounds in the unfumigated plot. Multiplied by 340 trees per acre, that becomes a significant yield difference of more than 1,500 pounds per acre just in the one year. “That helps pay for the fumigation pretty quickly,” he commented. “I really think most growers who invest in fumigation are happy with the results. It’s not as expensive as you think it’s going to be because you get it back in early yields.”

Omeg said fumigation entails an up-front cost of about $750 per acre, and he spends an additional $1,000 on ripping and soil preparation. “But I do think you’re going to make that up in increased productivity,” he said.

Tim Smith, Washington State University Extension educator for north central Washington, told the Good Fruit Grower he has not conducted fumigation trials on cherries, but enough orchard ground has been fumigated before planting cherries to demonstrate how necessary it is.

“I have seen the effect, and the effect is evening out the health of the new planting,” he said. “The growth seems to be uniform down the row, rather than ragged,” he said. “By the time the trees are seven to eight years old, there’s a distinct visual difference between nonfumigated trees and fumigated ones.”

Smith said the difference is not in tree size, because cherry trees grow large and are generally pruned back to the same size. The differences are evident in the overall health of the tree, the size of the leaves, and the growth of secondary wood.

Verticillium

With the expansion of the cherry industry in the Pacific Northwest, cherry orchards have been planted in the Columbia Basin, sometimes on former potato or mint ground. In those situations, fumigation is mandatory because verticillium wilt, which is caused by a soilborne fungus, is a common disease of potatoes and mint and can affect cherries, Smith said. The fungus grows into the xylem of the tree, where it interferes with the transport of water up from the roots. Leaves turn yellow and drop, as if the trees haven’t been irrigated properly. The fungus produces toxins that cause wilting, according to information on OSU’s Plant Disease Control Web site, and plant-parasitic nematodes aggravate the disease.

Fumigation won’t eliminate the verticillium wilt pathogen, but it will slow it down, Smith said.

Asked whether there would be benefits from leaving the ground fallow for a year, Omeg said he did not think that would eliminate the need for fumigation. He thought it best to remove the old trees in late summer and plant the new ones the following spring.

Smith reports that leaving the ground fallow before replanting is not as beneficial as fumigation, as the complex of organisms in the ground that cause replant disease dissipate slowly. They will persist as long as there are living roots in the ground for them to live on. Root suckers are enough to keep the organisms thriving.

If the ground is not going to be replanted soon, fumigation should be delayed, Smith said. Typically, it is fumigated in the fall and replanted the following spring.

“You can’t fumigate now and plant two years later, because the fumigant begins to lose its effect right away,” he said. “If you fumigate a year ahead, it’s helpful, but you don’t have the full impact.”

For information about verticillium wilt, check the Web site at plant-disease.ippc.orst.edu.