A fungal disease affecting white pines is growing worse in southern Maine, state forestry and entomology officials said Wednesday.

White pine needle disease, possibly exacerbated by above-average rainfall across the region, has reached epidemic proportions in Maine, mostly in southwestern and central western parts of the state, said William Ostrofsky, forest pathologist for the Maine Forest Service.

York, Cumberland and southern Oxford counties have shown a heavier concentration than some other areas, in part because white pines flourish in the sandy soils common to these areas, said Maine State Entomologist Dave Struble.

Forest landowners report it has spread through most of southern Maine, said Tom Doak, executive director of the Small Woodland Owner’s Association in Augusta, which represents about 5,000 woodlot operations in the state.

Maine has more than a million acres of white pine and white pine-mix forests that bring in at least $31 million a year to forest landowners, according to the forest service. That number does not include revenue from trees harvested for paper pulp or biomass, said Struble.

The total value of forest-related manufacturing, recreation and tourism to the Maine economy is more than $6.47 billion, according to the North East State Foresters Association.

Forest service officials say they haven’t yet come up with an estimate of the statewide damage to white pines. But a survey of damaged trees is underway, and results will be compared with defoliation estimates from previous years.

Early indications are that the severity of the disease is similar to past years, officials said. But several consecutive years of losing year-old needles has weakened some trees to the point that they cannot survive, they said.

The disease has not been much of an issue at garden centers in the Portland area, according to several randomly polled local nurseries and arborists.

But Struble said he believes commercial operations dealing with white pine should be concerned, because the disease “is everywhere.”

“I think people are gonna start watching and looking,” he said.

Commercial growers and woodlot owners “absolutely … should be concerned,” Doak said.

“The pine is a very valuable tree in Maine,” he said. “Maine is the Number One white pine-producing state. It is a significant tree and … it takes a very long time to grow.”

Used in paper-making and harvested for lumber, red and white pine together account for 8 percent of the state’s forests. It’s important to monitor any disease that can affect commercially valuable trees, Doak said.

But he and others say woodlot owners shouldn’t panic.

“It’s not like trees are dying all over the place,” Doak said.

For the first couple of years of the disease’s emergence, the problem seemed relatively minor. But in the last decade it has become more severe, foresters and growers said.

For the past eight years the disease has been spreading throughout New England and New York, and a decade of above-average spring and summer rainfall in the Northeast is believed to be a key factor. The infection can be caused by one or more of several pathogenic fungi, said Ostrofsky, the forest pathologist.

There is no effective treatment against the disease, Ostrofsky said, so the best measure is to safeguard the overall health of the tree with good management and appropriate care. Healthy trees fare better against the needle disease, which generally does not kill the tree but leaves it depleted. Weaker trees can be killed by the infection over a period of years, he said.

The fungus infects needles early in spring and moves through the tree during summer and fall, forestry officials said. The following year, in early to mid-June when the weather warms, one-year-old needles become discolored and drop off over the course of about three to four weeks.

“You’re always dealing with the infection of the previous year,” Struble said.