Summer 1999: Aphid trapping data.

Results reported in this issue of Aphid Alert are total captures of winged aphids and species identifications for the following locations and sampling interval end-dates. At some locations the potato crop has been harvested. If additional data is received for locations not reported on this page (no data) that data be incorporated into this week's issue of the newsletter once the samples have been received and sorted.

In addition to our summary of this weeks results we report results from our Aphid Alert subscriber survey and present an guest report by Debbie McLaren, Crop Production Pathologist with Agriculture and Agri-Food Canada, on aphid monitoring in Manitoba.

Figure 1 (below). Mean number of winged green peach aphid captured per trap across all locations reported, 1998 data (blue line) and 1999 data (maroon line). These data are also available in table format (Table 1).

Figure 2 (below). Mean number of winged aphids of species known to be capable of transmitting PVY (exclusive of green peach aphid) captured per trap across all locations reported, 1998 data (blue line) and 1999 data (maroon line). These data are also available in table format (Table 1).

Summary of Observations for Week Ending 2 September

Green peach aphids per trap declined from 3.19 per trap last week to 2.44 per trap this week. This is the first time this summer that green peach aphid captures per trap were less than in the corresponding week of 1998. Captures of other potential PVY vectors increased slightly, from 8.50 per trap last week to 11.73 this week. Turnip aphid has consistently been the most abundant of the potential PVY vectors. Turnip aphid is not as efficient a vector of PVY as is the green peach aphid, but it is a capable PVY vector and, therefore, cause for some concern. Like green peach aphid, we have found turnip aphid to be abundant this year on canola.

All winged green peach aphids captured in traps of the Aphid Alert network to this year (18 June through 25 August) have tested negative for potato leafroll virus and potato virus Y. Last week, 272 green peach aphids were tested and all were negative (Table 2).

Table 2

These results have surprised us, but are encouraging. These results suggest that, at most, a very small percentage of the winged green peach aphids migrating to potato prior to 25 August were infected with PVY or PLRV. Last summer, the first PLRV-positive green peach aphids were collected 14 July. In August of 1998, 59% of the winged green peach aphids captured in our traps tested positive for PLRV and in September, 86%. Results of the PCR testing of green peach aphids captured this past week will be reported next week.

The absence of any positives for either PLRV or PVY in the aphids collected this year is consistent with our interpretation that these are migrants moving into the potato crop from hosts other than potato.

As noted last week, winged aphids are now being produced in potato fields (i.e., the immature stages on potato are developing winged pads and will be able to fly as adults). Aphids developing on potatoes are much more likely to acquire and transmit potato viruses. Much current season transmission has already occurred. We believe that to date this has mostly been secondary transmission, i.e., within field transmission from plants grown from infected tubers.

Aphid Alert Subscriber Survey

Last week we mailed a survey to Aphid Alert subscribers. The survey was mailed to 123 who receive Aphid Alert by U.S. mail and to 78 who receive the Aphid Alert by e-mail. There is some overlap of these two lists and some recipients are not directly involved in the potato industry. To date, we have received 48 responses (we consider that a very impressive return), 19 by e-mail, 29 by U.S. Mail. Responses were received from 28 growers and 6 consultants. Here is what you had to say. Thirty seven said that you find Aphid Alert "very useful", 34 said that you read it "cover to cover", and 29 said that you use the information presented to "aid in management decisions." We are somewhat awed by the credibility (and responsibility) we appear to have, but we sincerely thank you for the huge vote of confidence and for having taken the time to complete this survey.

Detection of Potato Viruses in Manitoba

by D. L. McLaren
Crop Production Pathologist
Agriculture and Agri-Food Canada
Brandon Research Centre
P.O. Box 1000A
Brandon, MB R7A 5Y3 

The potato virology project was initiated in 1998 as a collaborative study involving Agriculture and Agri-Food Canada, Manitoba Agriculture, Manitoba Crop Diversification Centre, a number of industry partners and a number of commercial and seed potato growers. In 1998, 34 seed potato fields were surveyed for potato leaf roll virus and potato virus Y. This preliminary survey included a visual assessment of the field and evaluation of leaf and tuber samples. Virus levels in the leaf tissue were low but levels in the tubers were higher as was expected due to the influx of aphids occurring in August. In 1999, the study was expanded to include both commercial and seed potato fields to determine the presence and prevalence of these viruses, to evaluate the spread of viruses from different sources and to monitor aphid movement and detect the presence of aphids carrying virus.

In 1999, five suctions traps as well as 30 pan traps were located throughout potato production areas of Manitoba. A number of traps have been set up in a "cluster" which involve both seed potato fields and commercial fields. Fields are being monitored using traps, or have been assessed visually in areas including Shilo, Portage, Winkler, Holland, Carberry, Carman and Minto. Leaf samples are being collected from all fields where traps are located. Tubers will be collected from all 35 fields and assessed for viral infection. 

Webmasters note: next summer we plan to coordinate our activities and reporting with those of our Canadian colleagues to make this a truly regional, and indeed international project.