Deere & Co, the world's largest maker of farm equipment, said it would indefinitely lay off more than 600 employees at plants in Illinois, Iowa and Kansas as falling grain prices hurt demand for tractors, harvesters and other agricultural machinery.

The company reported a 5% drop in third-quarter sales on Wednesday and cut its full-year profit forecast.

Deere had about 67,000 full-time employees as of Oct. 31, 2013, of which about 33,900 were in the United States and Canada.

The layoffs are at plants in Moline and East Moline, Illinois; Ankeny, Iowa; and Coffeyville, Kansas.

Deere, whose shares were little changed at $84.90 in early trading on Friday, said it would also implement seasonal and inventory-adjustment shutdowns at the affected plants that would result in temporary layoffs.

The company operated 26 plants in the United States and Canada as of Oct. 31, of which 17 primarily make agriculture and turf equipment. Deere also makes construction and forestry equipment.

The U.S. Department of Agriculture has forecast record U.S. corn and soybean crops this year - a prospect that has sent prices plummeting and discouraged farmers from buying equipment.

Up to Thursday's close, Deere's stock had fallen 6 percent this year. It fell about 2% on Wednesday.