Purdue University
Agricultural Extension Service
Department of Botany and Plant Pathology

Mimeo BP 10-4 March 1957

Weed Control in Soybeans
Oliver C. Lee

Both broadleaved and grass type weeds are troublesome in soybean fields.
Some of the most common in the broadleaved group are:	Smartweed, Jimson, pig-weed giant and common ragweed, butter print or mallow, lambs quarter, morning glory and flower-of-an-hour. Grasses include:	Yellow, green, and giant fox-
tails, barnyard grass, crabgrass, and several species of panicum or panic grass. Sedges, sometimes called nut grasses, are also troublesome in a few areas.

Cultural Control Practices

There are several cultural practices that are useful in controlling weeds in soybeans. The following suggestions are listed:

1.	Begin seed bed preparation early with several diskings at frequent intervals before planting,
2.	Delay planting until growing conditions are favorable for rapid germination and growth of soybeans,
3. Use the rotary hoe if weeds emerge before the soybeans. Avoid hoeing unless necessary just at time soybeans emerge. It may injure the plants at this time,
4. Use rotary hoe when beans are 3 to 8 inches tall.
5. Use properly adjusted shovel cultivator in row planted soybeans.
Shallow cultivation with sweep-type shovels is preferred.

Chemical Control Practices

Chemical weed control in soybeans has not been fully dependable. There are no post-emergence sprays recommended. Pre-emergence treatments offer some possibilities. They are, however, expensive and results are unpredictable because of behavior of the chemicals under different soil, moisture and temperate conditions. Dinitros, Chloro-IPC and Alanap are used as pre-emergency applications to a limited extent for weed control in soybeans, but they are generally practical to use, however, because results have been erratic.
CDAA, also known as "Randox", is recommended for annual grass control. It appears to be practical for use on fields heavily infested with giant foxtail. Four quarts of CDAA in 20 gallons of water is recommended for overall spraying.
To reduce cost, it may be applied in a band over the row. For band treatments, 1 1/2 quarts in 6 gallons of water per acre is used. It should be applied at planting time or after planting but before the soybeans emerge. It is most elective on loam or heavier soils. Should not be used on sandy soil. Read directions for use and caution on label before using CDAA.

Cooperative Extension Work in Agriculture and Home Economics State of Indiana, Purdue University and the United States Department of Agriculture Cooperating H. J. Reed, Director, Lafayette, Indiana Issued in furtherance of the Acts of May 8 and June 30, 1914.