Potato Grower

August Potato/IGSA 2010

Issue link: http://read.uberflip.com/i/14183

Contents of this Issue


Page 41 of 56

diggin’ in FUMIGATION by Fred Rehrman, CEO, Elysian Fields Tackling Nematodes WSU, OSU FLANK A GROWING PROBLEM NOT ALL PROBLEMS CAN BE FIXED IN the same way. With some problems, such as a seasonal drought, you have to tackle it short term—provided the drought doesn’t continue the next season. Other problems take a lot more effort and a lot more time. Nematodes are one such problem. Washington State University field trials suggest growers take a long-term approach to managing nematodes. Those trials, now in their sixth year, study “residual populations” of nematodes based on various nematode treatments. “Residual nematodes are, essentially, the nematodes left over at potato harvest,” says John Wilson, WSU research supervisor. “Those nematodes are important for their potential impact on future potato crops.” For many pests, crop rotation is an effective pest management strategy. The rotation concept is simple: plant a crop that is not a host for a certain pest and eventually pest populations will decrease. But for Pacific Northwest growers battling nematodes, it’s not that easy. “A common crop rotation in the Columbia Basin is potatoes to corn to wheat, then back to potatoes,” Wilson says. “Nematodes have a tremendous amount of host crops, including corn and wheat. At the end of that three-year rotation, 18 Potato Grower | AUGUST 2010 a grower could be left with a very high population of nematodes—so high that he may decide not to plant potatoes back into that field.” Wilson’s trials are conducted like many straight product efficacy trials, where multiple products are applied and pest population counts are registered before and after treatments. The 2009 trial included an untreated plot, plus plots for Telone II soil fumigant (20 gpa), Telone II + metam sodium (15 and 30 gpa), metam sodium (37.5 gpa) and Vydate (4.2 pt/A at-plant followed by six applications at 2.1 pt/A). Wilson rotates the ground to corn and wheat just like in a commercial growing situation. Nematode populations are measured three times: pre-treatment (in the fall), prior to planting and post harvest. Columbia root knot, stubby root and lesion nematode populations are counted at one- and two-foot depths. “What you would expect to find are nematode populations dropping after treatment, then increasing throughout the season,” Wilson says. “The question is always, ‘How much are they increasing?’” In the untreated plot, Columbia root knot populations increased three-fold by the end of the 2009 season, leaving a post- harvest, or residual, population of nearly 300 nematodes per 250 cc of soil. The lowest post-harvest population was found in the Telone + metam sodium plot where a pre-treatment level near 500 nematodes per 250 cc of soil dropped to less than 10 at post-harvest (see Figure 1). When stubby root populations were measured at two feet deep, the untreated plot had 24 nematodes at post-harvest. Zero stubby root nematodes were found in the Telone + metam sodium plot at post- harvest. A low population at harvest will hopefully lead to a manageable population when potatoes are planted to the same field a few years later. “The options open up to a grower with low nematode populations,” Wilson says. “First off, you can plant the field to potatoes rather than holding out until populations come down. Then, you can opt for short- or long-season varieties and can decide whether to store or process right away at harvest. You can also consider fresh market and export markets. All these options are much more risky when pre-plant sampling shows high nematode populations.” A high residual nematode population may or may not be consistent with actual nematode damage to the tubers within a given year. “Generally, there

Articles in this issue

Archives of this issue

view archives of Potato Grower - August Potato/IGSA 2010