volunteer

A volunteer is any plant that establishes itself in a field without deliberate sowing. It germinates from seed left in the soil from a previous crop, or from seed that has blown or washed in from elsewhere. The term applies equally to the desired species appearing where it was not planted and to genuinely unwanted plants, though context usually makes the distinction clear.

Volunteers most commonly arise from the previous season's harvest residue. Corn volunteers frequently appear in soybean fields the following year; canola volunteers persist in cereal rotations; and wheat volunteers germinate in spring fields prepared for other crops. In perennial cropping systems, fruit and nut volunteers can emerge years after the original trees were removed. The persistence depends on seed dormancy characteristics, soil disturbance patterns, and whether the seed has been exposed to conditions that break dormancy.

Management and agronomic significance

When volunteers match the intended crop, they can supplement stand density at no cost, though they may germinate unevenly or at inconvenient times. More often they compete with the cash crop for water, nutrients, and light, reducing yields measurably. Herbicide-resistant volunteers pose particular problems: glyphosate-resistant volunteers in glyphosate-tolerant fields can only be controlled by mechanical removal or alternative chemistry. Some volunteers carry disease; volunteer potatoes are a serious vector for potato viruses and late blight.

Controlling volunteers requires timing and consistency. Mechanical cultivation, flame weeding, or well-timed herbicide applications before the cash crop emerges work best. The term "volunteer" itself reflects the plant's independent action, as if it has chosen to grow without being asked, in contrast to the deliberate seeding and management that defines cultivated crops.