Species that have seed that are wind disseminated and that can easily germinate at or near the soil surface tend to proliferate in reduced tillage systems. Volunteer peas, lentils, and sunflower posed less of a problem in zero than conventional tillage. Green foxtail would be the best example of a weed that has decreased dramatically with direct seeding on the Canadian prairies. Volunteer canola, flax, and wheat were equally prevalent across tillage systems. Species response to tillage intensity determined from 77 site-years of data in western Canada.
Growers then report that their herbicide use often declines in zero tillage systems.
This may be due to greater weed seed mortality when seeds remain on the soil surface due to predation by rodents, birds and insects, attack by fungi and bacteria, and dessication over the winter period. Timing of herbicide use may change with conservation tillage with reduced emphasis on in-crop herbicides and increased use of herbicides in fall or before crop seeding to control winter annuals and early germinating summer annuals. Preharvest glyphosate is an effective treatment for many perennial weeds. Crop selection and crop rotation sequence have been shown to have a greater impact on weed community composition than tillage system. Diversified rotations should include perennial, winter annual, and summer annual crops.