Suction traps

Flight patterns for aphid vectors of the main viruses in Potatoes are presented for:

Canterbury

• Courtenay trap - this trap has been turned off for the winter
• Lincoln trap
• Rokeby trap - this trap has been turned off for the winter
• Hilton trap - previous flights

North Island

• Hawkes Bay trap
• Pukekohe trap

The graphs show the number of potential virus-vector winged aphids that colonise potatoes, caught per week in the 7.5 m high suction traps ( Figure 1 ).

These aphids are:

For each graph, the single thick violet line represents the total number of these aphids caught in each trap for this current growing season, between October-July.

For comparisons of current aphid flights with previous flights, historic aphid flights are presented to give some idea of the relative abundance of aphid flights compared to other years. The shaded areas represent historical data of the total numbers of the four aphids (mean ±S.E.). For the sites in Canterbury, the aphid numbers trapped at Lincoln from 1988 until last growing season (October to June) in seasons of high aphid flights are represented by the dark-green shaded area, and in seasons of low aphid flights by a purple shaded area. For Hawke's Bay, the dark-green shaded area represents mean (±) totals of the four aphids caught in the trap from 1998 to the last season.

Growers are advised to monitor their potato crops during aphid flights by counting the aphids on the top, middle and bottom leaves of 50 plants within a paddock. Potato crops are at risk from virus infection by aphids if any aphids are present. The current threshold for when the crop should be sprayed with an insecticide registered for use on potatoes is of 10 wingless aphids per 150 leaves. However, a lower threshold could be used.

Figure 1 : Suction trap, 7.5 m in height (left), with a weekly aphid catch (right top) separated from the total trap catch which include all flying insects.

Local aphid flights

Yellow pan traps are being trialed this year (2004-05) on selected potato grower properties to evaluate their use for monitoring local aphid flights onto potato crops ( Figure 2 ). The aphid catch in these traps is being related to the catch in the suction traps.

Last year's evaluation showed that the traps could catch aphids that colonised potatoes and transmitted viruses. Of the total aphid catch, 10% in spring and 20% in autumn comprised green peach, melon or potato aphids. The traps were weekly by counting aphids in the traps, and re-setting them with fresh water that contained detergent.

Figure 2 : Yellow pan boxes (left) or bowls (right) can alert growers as to when to inspect the potato plants for aphids to time appropriate times to spray insecticides.