Progress 06/01/04 to 11/30/05
Outputs
In the early to mid-1990s, we found that surrounding early-generation seed potato fields with 3-4 m borders of soybean protected against spread of Potato virus Y (PVY), an aphid-transmitted Potyviridae. Subsequently, use of crop borders to protect seed potatoes from PVY spread was widely adopted in MN and ND. Emergence of soybean aphid as a major pest throughout the Midwest in 2003 and discovery that this insect is a capable vector of PVY caused some growers to question the advisability of continuing to use soybean as a crop border. To address that concern, large-scale, replicated field plot research was undertaken at Rosemount, MN (in 2004 and 2005) and Grand Forks, ND (2004 only) to compare the efficacy of soybean and three alternative borders (fallow, potato, and spring planted winter wheat) in preventing PVY spread, and to determine the benefit of applying aphidicides (pymetrozene on potato, lambda-cyhalothrin on soybean and wheat) to prevent aphid colonization of
the crop borders. At harvest, 100 random tubers are taken from each treatment, (total of 3000 tubers per location per year). These tubers are planted in Oahu, HI in November and in January each plant is visually scored for PVY and PLRV infection. Leaf samples from each plant are indexed for PVY, PVS, and PLRV infection by ELISA and 100 random leaf samples are indexed for PVY infections by RT-PCR. Results presented are for 2004 as the 2005 winter grow out will not be completed until mid-January 2006. Data are analyzed using multinomial logistic regression and the statistical software R and significance is tested using the likelihood ratio test (LRT). Visual differences in PVY spread between using a border (soybean, wheat, or potato) and no border (fallow) were highly significant (Chi2 = 30.36, P-value = 1.160e-06), but serological results (which detected showed many infections not detected visually) showed no significant differences in PVY infection between border and no border. Crop
borders significantly reduced PVS transmission (LRT P-value: 0.016), but did not significantly reduce PLRV transmission. Using categorical data analysis, we were able to distinguish the effects between crop borders and the effects between spraying and not spraying with an insecticide. Wheat borders significantly increased % PVY positives (LRT P-value: 0.029). Seed potatoes with insecticide-treated borders had significantly more PVY than untreated borders (LRT P-value: 0.015). We believe that the crop borders failed to reduce PVY spread in 2004 (unlike in previous research) because the seed tubers used to establish the plots although certified to have zero PVY actually had 8% infection. Roguing was ineffective because many of the infected plants were visually asymptomatic. Crop borders were effective in limiting PVS spread because the seed tubers used to establish the plots were free of that virus. PLRV infection was not reduced since crop borders are only effective against
non-persistently transmitted virus and PLRV is persistently transmitted. Results suggest that borders should not be sprayed, as spraying may increase aphid movement and thus, increase virus spread.
Impacts
We have shown that crop borders of soybean, potato, or winter wheat can reduce spread of PVY by 50-70%. Crop borders provide better control of PVY than is usually achieved with insecticides or crop oils and accordingly many growers have adopted this technology. The recent establishment of soybean aphid in North America and our demonstration that this aphid is a efficient vector of PVY has called into question the effectiveness of using soybean as a crop border to protect seed potatoes, therefore, it is important reassess this technology.
Publications
- Davis, J.A., Radcliffe, E. B. and Ragsdale, D. W. 2005. Soybean aphid, Aphis glycines Matsumura, a new vector of Potato virus Y in potato. Am. J. Potato Res. 82:197-201.
- Davis, J.A., E.B. Radcliffe and D.W. Ragsdale. 2005. Crop borders revisited. Potato Assoc. Am., Annual meeting Potato Assoc. Am., Abstr. G74, http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/opp8616/$FIL E/generalabstracts05.pdf.
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Progress 01/01/04 to 12/31/04
Outputs
PVY has, over the past 20 years, become a very serious problem throughout most major seed potato producing states, e.g., seed lot rejections due to PVY in Minnesota Department of Agriculture Seed Potato Certification Program winter tests have averaged 42.1% annually since 1998. Since the early 1990's we have promoted use of crop borders to protect seed potatoes, especially high value, early generation seed lots, from PVY spread. This technology has been widely adopted by Minnesota and North Dakota growers. Recent emergence of soybean aphid as a major pest throughout the Midwest and discovery that this insect is a capable vector of PVY has caused some growers to question advisability of continuing to use soybean as a crop border. This research project, initiated in 2004, addresses that concern. We are comparing efficacy of soybean and two possible alternative crop borders (potato and spring planted winter wheat) in preventing PVY spread, and testing whether there is
benefit to applying aphicides to prevent aphid colonization of the crop borders. Field research in 2004 was done at UMore Park, Rosemount, MN and the Northern Plains Potato Growers Association Research Farm, Grand Forks, ND. Both experiment stations hosted grower field days providing a demonstration for growers of proper deployment of this technology. Objectives of this research include measuring PVY spread to potatoes grown from virus-free tubers in field plots bordered on their sides by 4-m widths of soybean, potato, spring planted winter wheat, or fallow. The protection provided will be measured by comparing the incidence of PVY in tubers harvested from plots bordered by crop borders, with and without insecticidal treatment, to the incidence of PVY in tubers harvested from control plots bordered by fallow. Tubers have been harvested from the field plots for winter grow-out in Hawaii. All visual positives will be confirmed by monoclonal DAS-ELISA and RT-PCR. Laboratory research will
compare PVY-transmission efficiency of green peach aphid, bird cherry-oat aphid and soybean aphid. Three strains of PVY, PVYo, PVYn, and PVYntn, all known to occur in Minnesota were used as inoculum sources. The aphid species we have chosen are the most important PVY-vector species associated with the three species of crop borders used in this research. Seed potato growers will be interviewed to collect data on their crop management practices. This will permit an economic analysis of potential savings in active ingredients and control costs from using crop borders to manage PVY. We will use mailed surveys and personal interviews of seed potato growers to assess their perception of the profitability and risks associated with this technology and the probability that they will continue to use crop borders or plan to do so in the future. We plan to promote the use of crop borders through various outreach activities, e.g., presentations at field days and grower meetings, and by preparing
an article for the Valley Potato Grower. Our goal will be to have the VPG article appear before the 2005 planting season in the hope of influencing more growers to use crop borders.
Impacts
We have previously shown that the use of crop borders of as little as 3 m width can reduce spread of PVY to small plantings (0.08 acre) of seed potato by up to 64%. Crop borders of soybean, sorghum, spring planted winter wheat and potato appeared equally effective. Use of crop borders to protect seed potatoes, especially high value, early generation seed, from PVY spread has since been adopted by many Minnesota and North Dakota growers. Anecdotal evidence suggests the use of crop borders has worked well for the growers who have used them. However, the recent emergence of soybean aphid as a major pest throughout the Midwest and our discovery that this insect is a capable vector of PVY has caused growers to question the advisability of continuing to soybean as a crop border. This research will answer that concern. Preliminary evidence (2004) suggests that for crop borders to be effective it is essential that the seed lot being protected not have missing stand, e.g.,
planting misses, plants rogued for virus, or plant otherwise damaged). We measured the spread of PVY to healthy potato plants adjacent to planting skips or gaps created by the death of plants infected with PVYntn. Thirty-six gaps were measured, ranging in area from 0 to 42 ft2 . At harvest, 28 of the 36 gaps had at least one adjacent plant that tested positive for PVY. Linear regression of gap area and percentage of adjacent plants testing positive for PVY (Y = 0.1443 + 0.2951*gap area) was highly significant (P = 0.0001).
Publications
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