When disc mowers came spinning onto the scene about 20 years ago, they were faster and tougher than sickle mowers. But they were also more expensive, both to buy and to repair.

Design refinements have solved many of the repair and maintenance problems, and the addition of conditioning rolls has made disc mower-conditioners the cutting machine of choice in many areas.

They're now more popular than sickle models, points out John Deere's Steve Mayberry.

"In the 12-month period ending Jan. 31, 1998, U.S. farmers bought more than 6,800 disc mower-conditioners, compared with just under 6,100 sickle machines," says Mayberry. "That's the first time disc mower-conditioners have outsold sickle machines."

Sales of disc cutters (without conditioners) are fast-approaching those of straight sicklebar mowers, too.

In less-than-ideal cutting conditions, sicklebar mower-conditioners can't match the cutting speed of a disc machine. And today's disc mower-conditioners are much easier to maintain than were earlier models.

A quick daily service routine will keep the machine performing up to expectations and extend its useful life, says Cliff Addison at Krone Niemeyer, West Memphis, AR. The routine should include checking lubricant levels, knives for sharpness and damage, and discs for wrapped twine or wire, says Addison.

Cutting blades on the discs can be changed quickly with no special tools or skills, says New Holland's Chuck Hoffman.

Even major maintenance takes less time than it used to, points out Randy Hoffman of White New Idea products at AGCO.

Early disc cutters used one drive shaft to power three cutting heads. Repairing one head meant removing the entire drive shaft. Now, most disc machines sold in the U.S. are designed so that's not necessary, says Randy Hoffman.

While disc mowers will handle tougher conditions, work in wetter hay and allow faster mowing, there are drawbacks.

The higher initial cost is one. Disc mowers have more moving parts and require more manufacturing precision. Expect to spend at least 10%, and maybe as much as 30%, more for the same-size cutterbar. And if you want the ultimate in a self-propelled disc mower-conditioner, it's probably going to have a number at least 50% higher on the sticker than a comparable sickle model.

If field appearance is important to you, your landlords or your custom clients, go slow in the switch to a disc mower.

"It leaves the field looking different," admits New Holland's Hoffman.

"Some people think it's more ragged looking. It really doesn't leave any more hay in the field than a sickle mower, but it looks like more to people who are used to a sickle."

Hoffman says hay growers and custom operators who harvest pure stands of alfalfa in uniform fields may be more satisfied staying with sickle mowers.

"It takes tough conditions, with down or matted hay, to really appreciate the superior performance of a disc machine," Hoffman says.