Volunteer cereals

Volunteer cereals are plants of grain crops, such as wheat, barley, or oats, that grow from seeds left in the field after harvesting. Botanically, they belong to the Poaceae family. While these are desirable crops in their primary season, they behave as problematic weeds in subsequent rotations.

These volunteers are common in fields previously cropped with small grains. They cause the most significant economic damage when they emerge in fields planted with broad-leaved crops like canola, sunflowers, or pulses. Because they share similar nutrient requirements as the main crop, they aggressively compete for water, sunlight, and soil fertility.

The biology of volunteer cereals is defined by their rapid germination once soil moisture is adequate. If seeds remain on the surface after harvest, they often sprout quickly. Those that survive the winter as seedlings (winter-type volunteers) can gain a significant competitive advantage over spring-sown crops, significantly reducing the final yield potential.

Beyond resource competition, volunteer cereals serve as a major disease and pest reservoir. They act as "green bridges," harboring insects like aphids and cereal flies, and pathogens like rusts and powdery mildew. These pests move from the volunteers onto the new crop, leading to widespread infections that require additional pesticide applications.

Management strategies focus on reducing the seed bank and controlling existing seedlings:

• Tillage practices, such as stubble cultivation immediately after harvest, encourage rapid germination so that subsequent crops can kill the seedlings.
• Crop rotation that alternates between grass and broad-leaved species.
• Optimizing harvester settings to minimize grain loss at the field level.
• Application of selective graminicides (grass-specific herbicides) when volunteer densities exceed the economic threshold in broad-leaved crops.