This year's yield of wild blueberries could be the worst in 13 years, falling about one-third below average crops because of poor weather conditions this spring and summer, an industry forecaster predicted Tuesday. David Yarborough, a specialist at the University of Maine Cooperative Extension in Orono, said next month's statewide harvest might be no more than 50 million pounds. The last time the yield was below 50 million pounds was 1991, when the crop totaled 39.5 million pounds. Maine's average crop for the last five years has been approximately 80 million pounds, Yarborough said. "If we get 50 million, that's only two-thirds of a usual crop," Yarborough said. "We still may go over 50 million, but the word on the street is to expect no more than that." The projected drop in the crop is because of considerable winter injury to the plants as well as a good amount of mummyberry disease, which is caused by a fungus. Additionally, the cool, wet conditions of spring and summer curtailed the pollination of the fields. "It was a tough pollination period," Yarborough said. "The reasons are cool weather, rain, wind, winter damage, blight and bears." The resulting crop should produce "less, but larger fruit," he said. Midcoast growers will begin their harvest July 28, about a week behind schedule because cool temperatures "are slowing things down," Yarborough said. "That just means the harvest is coming a little later," he said. "That's not a bad thing in the sense that it gives the fruit more time to fill out."