In southern Manitoba, the conditions and farming inputs necessary to produce high yields and good quality also favour vigorous weed growth. Corn, owing to its erect habit of growth, competes poorly with weeds until mid-July when the leaf canopy has closed over the inter-row area. For this reason, the control program for May and June must be well planned. Weeds in corn may be controlled by two basic methods - cultural or chemical - or by combination of both.

 

Cultural, or mechanical weed control has been the age-old method since the beginning of domestic corn production. At present, cultural weed control mainly involves removing weeds from the inter-row area with various types of tillage equipment. However, this leaves weeds in the rows, and the number of entries into the field must be limited to reduce root pruning to the corn and the cost of the fuel, and to avoid numerous tillage operations on light soils. Mechanical weed control will be restricted by weather, the height of the crop and the spread of the corn root system.

 

Chemical control of weeds in corn involves the use of various registered herbicides singly or in combination.

 

Herbicides are divided into two broad classes: pre-emergence and post-emergence.

 

The need to choose a product from these two classes is governed by many considerations, including:

 

 

For information regarding identification and specific weed control measures, consult the Field Scouting Guide and Guide to Crop Protection, available from Manitoba Agriculture, Food and Rural Development.

This method involves the use of inter-row tillage equipment combined with herbicide application only to the rows. In parts of Europe and North America, this method of controlling weeds in corn has gained some acceptance but, with the rising costs of fuel, a change to a chemical program rather than this integrated form is probable. The practice results in a clean field until wet weather make infield machinery use impossible. The only advantage of this system is that less herbicide is used, with a resulting cost saving, but this has to be balanced against the farmer's time, the number of entries that must be made to maintain mechanical weed control, and yield potential of the field.