WEST SALEM, WI (WKBT) -

They're at their busiest now, but Christmas free farmers put in long hours throughout the year to get ready for holiday season - so what happens when all that work is ruined by disease?

It takes years to grow a farm big enough to sustain the demand for trees - but the time spent building up a field of trees can sometimes be wiped out in one season with a plant disease or insect infestation. A big fear for Christmas tree farms across the country is root rot.

Outside West Salem, the Pederson Christmas Tree Farm has seen it in one susceptible species in particular.

"Our scotch pine have a problem with root rot," said co-owner Dan Pederson. "I end up cutting down and burning 2 of them for every one I sell."

Only about one-third of the Pedersons' scotch pines survive, and currently there's no sure cure for root rot - so they've cut down on their stock in favor of sturdier trees, like white pines and firs.

Even without scotch pines, the Petersons are doing well. Dan Pederson said the farm has served more than 500 families this year. The average trees sells for about $30 there.

Despite a late Thanksgiving that makes for a shorter season, farm owners said they've seen more families this year than in the past.

"It's been a good season so far this year," said co-owner Philip Pederson. "That weather last weekend was really nice for us and it's going out well today - people like getting out this time of year."

The farm has about 20,000 Christmas trees planted, but it might be closed for the season now - after two consecutive busy weekends, the owners say they likely won't stay open for next weekend.