With many North American no-tillers dealing with several years of serious drought, it’s critical to understand how weeds respond to low moisture conditions much better than most no-tilled crops.

While numerous studies have evaluated weed responses to drought, a global analysis at the University of Nebraska evaluated 1,196 paired observations from 86 scientific articles published over 30 years. In this analysis of studies from Asia, Australia, Europe and North America, graduate student Mandeep Singh looked at the water stress impact on weed germination, growth characteristics and seed production.

What Was Learned

Below-ground weed growth as measured by root biomass decreased by 39% at moderate water stress levels (30-60% of field capacity) and by 69% with severe water stress (less than 30% of field capacity).

With above-ground weed characteristics, plant height was reduced 24% with moderate water stress and by 37% with severe water stress. Leaf area decreased by 43% with moderate water stress and by 44% under severe water stress conditions. Weed shoot biomass decreased 39% with moderate water stress and by 61% under severe water stress conditions.

Weeds under water stress prioritize root growth to increase rooting depth, allowing them to extract water from deeper levels while providing more water to roots over longer periods of time. The analysis also showed grass weeds grew slightly better than broadleaf weeds under most drought conditions.

Even when water stressed, weeds continue to produce seeds. For example, the number of seeds produced per weed plant decreased by 50% under moderate water stress…