Proper identification of the pest and proper timing of insecticide application is critical to successfully controlling insect pests. Aphids must be targeted at their most vulnerable life stage, and both the top and underside of the leaf surface must be inspected/treated. Sometimes spraying the leaves of the plant with water from the garden hose can knock the insects off the leaves. Another option is insecticidal soap. Aphids can develop resistance to pesticides. By improperly applying insecticide, beneficial insects that prey on aphids (e.g., lady beetles, lacewings, predator midges, minute pirate bugs) can also be killed, thereby reducing natural predators.
Although aphids can injure foliage by feeding on plant sap, extremely high numbers are required before tuber yield is affected. There are two economically important aphid species found in Minnesota which affect potatoes: green peach aphid and potato aphid.
Green peach aphid (Myzus persicae)
Green peach aphid is a serious pest of seed potato because it transmits potato leaf-roll virus (PLRV) and potato virus Y (PVY or mosaic). The same viruses are also transmitted to potatoes if there are high infestation levels.
Aphids are soft bodied, pear-shaped insects that are creamy white to light peach and somewhat translucent. Green peach aphids are unable to overwinter in the upper Midwest but arrive by migrating from southern states in the spring. They reproduce very rapidly but tend not to feed in large colonies like other aphids.
Control options: Although heavy rains/irrigation can wash aphids off plant foliage, there are few cultural control options growers can use to manage the pests. Aphids have many natural enemies, which should be conserved as much as possible.
Potato aphid (Macrosiphum euphorbiae)
Potato aphids range in color from pale/yellow-green to pink. Potato aphids also develop large populations quickly but do not transmit PLRV or PVY as efficiently as green peach aphids. Like the green peach aphid, large numbers of potato aphids can affect the yield of processing potatoes. They overwinter in the upper Midwest as eggs on cultivated and wild roses, raspberries, and shrubs and trees in the Rosaceae family.
As for control measures, here is a link to the Minnesota Department of Agriculture fact sheet on aphids:
Aphids
This fact sheet also gives instructions on an integrated management approach: targeting the insect at the right stage, reducing weeds, avoiding overfertilization, and using both physical and biological controls.
When using an insecticide (or any pesticide) be sure to read the label carefully and follow all directions. The label is the law.
