By GENE KEMMETER
of The Gazette
A potato late blight emergency has been declared for Portage County and the rest of central Wisconsin.
Walt Stevenson of the department of plant pathology at the University of Wisconsin-Madison says Integrated Pest Management (IPM) consultants recorded late blight in many fields throughout central and northcentral Wisconsin.
Late blight can have a devastating effect on potato fields if left unchecked.
"In most cases, the consultants are finding an occasional infected leaf," Stevenson said, "but in some fields late blight is spreading and there are hot spots to contend with. The cool nights, fog and long periods of dew, coupled with unwelcome rains are ideal for further spread."
Stevenson said there's a wide distribution of the blight due to the favorable conditions for the diseases and farmers need to take precautions to avoid its spread by killing the vines.
"If growers don't allow it to spread and growers protect storage, consumers won't notice anything," he said. "The consumer probably won't notice a difference in price but we hope to have the best quality possible."
All areas are considered at risk, he said, and "fungicide sprays should be applied at five to seven day intervals, with emphasis on coverage of all plants. We continue to observe effective control with mixtures of cymoxanil and chlorothalonil. Additional labeled late blight materials include Acrobat MZ and Tattoo-C."
Other protectant materials include chlorothalonil, mancozeb, maneb, metiram, triphenyl tin hydroxide and fixed coppers.
Regardless of the fungicides applied, coverage of all stems and leaves is essential for control of both early and late blight, he said. "This year with an ample supply of late blight inoculum, and the late blight fungus will find those mistakes and make them very visible."
He said those mistakes could be rows where a sprayer passes, edges of fields where an aerial applicator pulls ups or corners where ground equipment doesn't reach.
In many years there are minimal consequences with mistakes, he said, but this year farmers need to kill the hot spots in fields to reduce the supply of inoculum that can move to adjacent plants.
"Late blight inoculum can move from plant to plant and field to field via wind," he said. "During cool and foggy conditions, inoculum can move miles at a time. Inoculum can also move on equipment and people,"
Stevenson said. "The longer the vines are dead prior to the harvest, that greatly reduces the chance of infected tubers at harvest."
While fields in central and northcentral Wisconsin have late blight, no late blight has been detected in southern and northwestern Wisconsin, he said.