No late blight reported in Maine, North Dakota or Minnesota

While late blight has been found on potatoes in Dufferin County, Ontario, no cases have yet been reported in Maine, and spore counts continue to decline.

The July 18 Potato Pest Alert from the University of Maine Cooperative Extension recommends maintaining regular fungicide applications with a stretch of favorable weather expected.

Growing conditions have been very good overall, with many fields in full bloom, according to the report.

Colorado potato beetles, both adults and larvae, remain active across the report’s scouting area, with several fields exceeding treatment thresholds for larvae. Aphid pressure is still generally low to moderate, with a few hotspots of higher activity.

As grass and grain crops are harvested in central Maine, non-colonizing aphid numbers are rising. Many of these grain aphids are capable of transmitting PVY.

The Extension will continue monitoring traps for any significant increases in aphid activity.

The news is also good in other potato-producing states. No late blight has been reported in North Dakota or Minnesota, according to Andy Robinson, North Dakota State/University of Minnesota Extension potato agronomist.

Severity values continue to increase in the late blight model, with the p-values increasing in the early blight model. Aphid populations are similar to the average, but the PVY Vector Risk Index are about three times higher than average, according to Robinson.

Aphid numbers are expected to increase over the next four weeks.

Late blight has also not been confirmed in the Columbia Basin, according to Washington State University Extension, which recommends monitoring crops for symptoms.

Editor’s note: Article updated with North Dakota, Minnesota and Washington information.