Weed Science
BP-10-3
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • DEPARTMENT OF BOTANY AND PLANT PATHOLOGY LILLY HALL OF LIFE SCIENCES • WEST LAFAYETTE, INDIANA 47907

FIGHTING JOHNSONGRASS Merrill A. Ross, Johnsongrass Specialist

Johnsongrass is a perennial sorghum spreading rapidly by seeds and rhizomes (underground stems). Originally introduced into Alabama about 1830 as a forage crop, it was reported in Indiana about 1900. John-songrass is Indiana's worst weed and is one of the world's ten worst. It is highly com -petitive and chokes out crops. In addition to lowering crop yields, it increases farming costs, limits cropping alternatives, harbors diseases of corn, reduces land values and decreases the market value of farm products.
Once considered a problem of river bot-toms, it has now spread to uplands and is a potential threat to more than 6 million acres of cropland in the southern half of Indiana.

FACTS CONCERNING JOHNSONGRASS

Nearly one million acres of Indiana corn and soybean land is infested with johnson-grass. Infested acreage doubles every 7 to 10 years.
Johnsongrass reproduces both by seed and rhizomes (underground stems).
Seed is the major means of spread and long-term survival.
Seeds buried in the soil can survive for years and serve as the major source of reinfestation.
Seed production on roadsides, utility rights-of-way, levees, waste lands,
stream banks, etc., is a major source of johnsongrass spread to adjacent uninfested areas.
-- A major reduction in seed production in crop and non-crop areas must be achieved annually if the spread of johnsongrass is to be slowed.
-- Even in stands of johnsongrass with
heavy infestations of established plants, seedlings are several times more prev-elant than plants emerging from rhizomes.
-- Several tons of rhizomes are produced per acre annually. Rhizomes have large quantities of stored food and have the potential of producing a new plant for every inch or so of length.
-- An individual rhizome rarely survives more than one winter. However, new rhizomes formed each summer perpetuate the perennial nature of this weedy pest.
-- Johnsongrass plants with six or more leaves produce new rhizomes.
-- Overwintering rhizomes harbor viruses responsible for two devastating com diseases, maize dwarf mosaic (MDM) and maize chlorotic dwarf virus (MCDV). These viruses are transmitted to corn by insects.
- - Rhizomes that have been mechanically disturbed are killed when exposed to
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture Cooperating. H.G. Diesslin, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30,1914. It is the policy of the Cooperative Extension Service of Purdue that all persons shall have equal opportunity and access to its programs and facilities without regard to race, religion, color, sex or national origin.