Certified Crop Advisor Practice Exam

What is typically the most limiting factor for weed competition when crops outgrow them?

1. Soil quality

2. Moisture availability

3. Light

4. Nutrient levels

The correct answer is: Light

When crops achieve significant growth and canopy closure, light becomes the most limiting factor for weed competition. Agricultural crops often outgrow weeds by establishing a dense canopy that effectively shades the surrounding area. This reduced light availability hampers the photosynthesis process in the weeds, which can lead to their decline or stunted growth. While soil quality, moisture availability, and nutrient levels are also important factors that influence both crop and weed growth, they play less of a decisive role relative to the competitive advantage that crops gain when they can successfully outcompete weeds for light. When crops reach a certain height and density, they can efficiently block light from penetrating to the lighter-shade adapting weeds beneath them, which significantly hampers those weeds' growth and reproductive potential. In summary, the ability of crops to intercept sunlight effectively limits weed growth and competition as crops mature, making light the key factor in this dynamic.