Diverse and integrated weed management (IWM) strategies based on the practices of crop rotation, competitive crop cultivars, cover crops, and prudent use of tillage and herbicides are needed to confront herbicide resistance. Agronomic strategies aimed at reducing the time to crop canopy closure represent the foundation of cultural weed control. Numerous factors may influence crop canopy development including soil management strategy (i.e., tillage, no-till), planting date, row spacing, seeding rate, soil fertility, herbicide program, and environmental conditions. Earlier canopy closure can limit the amount of light reaching the soil surface which impacts weed seed germination, establishment, and growth.
Soybean is generally a poor competitor during earlier stages of development, however, early planting and narrow row spacing can improve its competitiveness. The use of an effective
pre-emergence herbicide program represents the foundation for chemical weed control in soybeans. Early-season soybean injury leading to slower canopy closure and potential for yield reduction is a concern of soybean growers adopting effective pre-emergence herbicides with multiple sites of action.
In 2019 and 2020 the UW-Madison Cropping Systems Weed Science Lab conducted field experiments evaluating the impact of integrated agronomic and weed management practices on soybean canopy development and yield. According to their results, all practices investigated (planting time, row spacing, tillage practice, and pre-emergence herbicide application) influenced when soybean canopy closure occurred but only planting time and tillage impacted yield. Canopy closure occurred earlier for early planted soybeans and narrow row spacing. The potential delay in canopy development and yield loss if soybeans are allowed to compete with weeds early in the season likely outweigh the slight delay in canopy development caused by an effective pre-emergence herbicide.
For complete study information, check their Research Report: www.wiscweeds.info/img/Update%20Series%20Articles/WWRUS%20Article%208_Canopy%20Closure.pdf
and this paper: doi.org/10.1017/wet.2021.92
Author: Nikola Arsenijevic, UW-Madison
Picture credits: Nikola Arsenijevic