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Aphid Alert: Apunte aquí para versión en Español [X]
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Article contents The Aphid Alert Initiative Potato viruses plague northern Midwest Green peach aphid outbreaks Factors contributing to perpetuation of present situation How Aphid Alert works Temporal trends in aphid flight activity Detecting virus in aphids Spatial aspects of managing virus epidemics Application of Global Information System technology |
The Aphid Alert Initiative The 1998 Minnesota State Legislature provided funding to the University of Minnesota College of Agricultural, Food, and Environmental Sciences to address urgent issues challenging the state's agricultural sector (Special Initiatives and Rapid Response Projects). One of the first projects selected for support addresses aphid transmitted viruses in seed potatoes. Additional support has been provided by a USDA, North Central IPM grant. Project leaders are entomologists Dave Ragsdale, Ted Radcliffe, Ian MacRae and plant virologist Ben Lockhart. Aphid identifications and on-site project management are the responsibility of post-doctoral fellow, entomologist Robert Suranyi. Potato viruses plague northern Midwest |
 Image: Wingless morph of green peach aphid.  Image: 'Aphid hole' caused by severe infestation of green peach aphid |
Green peach aphid outbreaks Concomitantly, with this most recent epidemic of virus diseases, many commercial potato growers have experienced exceptional green peach aphid outbreaks. Severe aphid pressure can cause premature senescence of plants ("aphid holes’) and yield losses up to 7 tons/acre. Green peach aphid is the most efficient vector of both PLRV and PVY, but this aphid is especially important in the epidemiology of PLRV because of its ability to colonize potato. As a consequence of severe green peach aphid pressure and resultant within field spread of PLRV, net necrosis (a tuber condition caused by PLRV) has become a common problem for the first time in this region. Since 1997, growers have had loads of potatoes downgraded or rejected by processors because of the presence of net necrosis. Similar problems have been experienced in Manitoba. Factors contributing to
perpetuation of present situation It has long been recognized that green peach aphid outbreaks can be induced by insecticides targeted against other pests, e.g., Colorado potato beetle or potato leafhopper. This occurs because green peach aphid tends to be highly resistant to most broad spectrum insecticides, but these insecticides are devastating to parasites and predators that otherwise hold this pest in check. |
More recently, we have demonstrated that intensive fungicide use can also contribute to increased green peach aphid pressure. The emergence and now predominance of a metalaxyl (Ridomil)-resistant strain (US8, A2 mating type) of Phytophtora infestans, causal agent of potato late blight, has precipitated major changes in fungicide use patterns in commercial and seed potato (both in chemistries used and frequency of application). Fungicides can be devastatingly disruptive to a group of beneficial fungi that are key mortality factors regulating the populations of green peach aphid (Lagnaoui and Radcliffe). Another factor that appears important in our region is the increase and southern expansion of canola production. Canola is a very favorable host for green peach aphid. Green peach aphid does not overwinter outdoors in our area so populations must be reestablished each spring. We suspect that the presence of large expanses of canola favors the survival and increase of spring migrants of this aphid from the south. Many of the best management tactics available to growers to prevent virus spread are
preventative or prophylactic, e.g., early planting, use of clean seed, isolation from
sources of inoculum, early season roguing, use of systemic insecticides at planting, and
use of crop borders (DiFonzo et al.).
However, once the growing season begins the only management tactics available to
growers are therapeutic , e.g., broadcast or border application of aphid-specific
insecticides, application of mineral oils, and early vine kill. Without
systematic biological monitoring, growers and their consultants cannot have sufficient
information to make informed decisions in using these therapeutic measures.
Ending the present cycle of virus infection is essential to restore economic viability to
the northern Midwest seed potato production and to assure adequate supplies of
disease-free seed for a rapidly expanding regional potato processing industry. |
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  Images: Suction trap and pan trap |
How
Aphid Alert works The Aphid Alert program operates a trapping network to monitor aphid flight activity in seed potato production areas in Minnesota and North Dakota. In 1998, we monitored aphid flight activity at 12 locations (1998 summary). In 1999, we are operating 1 suction trap and 4 pan traps at each of 14 locations, 8 in Minnesota, 6 in North Dakota. The present Aphid Alert trap sites were selected to include all major seed potato producing regions of the two states. A similar program was initiated by Agriculture and Agri-Food Canada in Manitoba in 1999 (McLaren). |
We believe that a regional approach to monitoring is essential because the problem is shared and no respecter of state lines or international boundaries. We have agreed that future U.S. and Canadian aphid monitoring activities will be coordinated and a common advisory newsletter for growers/crop consultants developed. If sufficient funding can be generated, we intend to operate the region-wide, aphid-trapping network and continue associated research for 3 more years. We believe continuation of this project is
appropriate because the spatial and temporal dynamics of potato virus epidemiology are
extremely complex and variable across years and locations. This is evident from comparison
of 1998 and 1999 population trends of green peach aphid and the other aphid species that
are potential PVY vectors. Our research goals are longterm, but, there is immediate payoff
from data collected. Advisories and recommendations generated in the first 2 years of this
project have been closely followed by growers and crop consultants in Minnesota, North
Dakota and Manitoba, and are used in making management decisions. Indeed, more than 83% of
growers and crop consultants (n=42) responding to a recently conducted survey indicated
they read the advisories cover to cover and used the information in making management
decisions. |
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| Image: Captures of winged green peach aphids in 1998 (blue) and 1999 (red). |
Image: Captures of potential vectors of PVY other than green peach aphid in 1998 (blue) and 1999 (red). |
In future years, we plan to deploy two suction traps at each location. Until now, we have used 1 suction trap and 4 pan traps at each location. We have found no obvious differences in the selectivity of the two trap types. Suction traps are preferable because they are operated on timers and intake flow can be adjusted to only catch weak fliers. We now have strong evidence that for most of the season our traps are capturing winged adults originating from sources outside the potato field. This is exactly the information needed, since this provides warning of potential introduction of virus by in-coming aphids. Later in the season, as winged aphids begin to be produced on potatoes, trap captures may be of aphids that originated within that field. However, once winged aphids are developing on potatoes, immediate vine-kill is advisable since aphids from potato are likely to carry virus and inter-field movement is inevitable. The aphids captured in the traps are sorted and identified to species on a real-time, i.e., within 48 h of collection and results reported on our WWW website, Aphid Alert and by e-mail to Aphid Alert subscribers. Printed copy of Aphid Alert is mailed weekly to all seed potato growers in Minnesota and North Dakota and to other individuals who request it. To subscribe to the e-mail version of our newsletter write to us at RADCL001@umn.edu. Unfortunately, although electronic communication provides real-time communication, most of our growers must, or do, rely on printed copy. Detecting virus in
aphids Spatial aspects of
managing virus epidemics Effective geographic isolation of potato seed lots from potential virus inoculum is not possible in Minnesota and North Dakota; the distances required (estimated by some European workers to be approximately 80 km) are far greater than the physical separation feasible in this production region. However, our preliminary data indicate that immediate proximity to sources of inoculum and aphid pressure are actually the key determinants of risk. Aphid species that vector PVY and PLRV may increase in crop fields other than potato, resulting in a dispersal of these insects into adjacent potato fields. Dispersal of vectors from these alternative hosts tends to be associated with increased occurrence of the viral diseases in adjacent potato fields. Aphid populations are greatly influenced by their host plants, e.g., canola can support large populations of green peach aphid and turnip aphid. The recent southward expansion of canola production has provided vast tracts of an exceptionally suitable host to green peach aphid arriving from southern overwintering sites. Green peach aphid was not a significant factor in a previous PVY epidemic in the Red River Valley in the early 1990s when little canola was being grown. Rotational cropping systems present a landscape mosaic of different host plant species that impact aphid population dynamics. Crops in which aphid species readily increase favor dispersal into nearby potato fields. Flight ability and local weather conditions will determine dispersal capability. We propose to combine laboratory and field data to develop predictions of aphid vector population growth, and dispersal into and within potato fields. Selected potato fields and surrounding regional cropping systems will be mapped using Geographic Information Systems (GIS) and aphid movement into the potato fields monitored with a system of traps. Influence of wind, temperature and precipitation will be incorporated into the GIS models. Aphid populations in selected neighboring crops will be monitored and numbers and life stages recorded. This information will be combined with the trap catches to evaluate the influence of other crops on aphid populations immigrating into potato fields. The critical local distance over which aphid vectors can disperse will be established by combining laboratory wind tunnel experiments and mark/recapture field trials. Wind tunnel experiments will involve flying tethered aphids in a frictionless flight mill. Mark/recapture experiments will be conducted by marking aphids with fluorescent dust and monitoring dispersal between other crops and potato and within potato fields. These critical distances will be used to establish a threat radius within which seed potato lots would be subjected to unacceptable risk of high populations of the aphid vectors of PVY and PLRV. Application of
Global Information System technology |
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Image: Distribution of Green
Peach Aphid in potato field, Hoople, ND. Increasingly darker colors denote increasing aphid populations. A significant edge effect is shown with highest aphid populations being found at the edge of the field while populations at the center of the field are much lower. Map constructed with the GIS, ArcInfo©. |
Send comments or inquiries regarding this chapter to Ted Radcliffe. Return to top of page Visit the University of Minnesota's Aphid Alert Return to Radcliffe's IPM World Textbook Home Page. The University of Minnesota is an equal opportunity educator and employer.
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