Weed control is critical for potatoes as weeds in the planted row and furrow compete with the crop before the plants are large enough to shade out weeds. Weeds in and between the rows are typically controlled with cultivation, herbicides, or a combination of approaches. An effective weed control program identifies the weeds common to the farm, assesses cultivation practices used, reviews available herbicides, and determines the competitive ability of the potato varieties grown. If herbicides are used, they should be tailored to the weeds present in the field.
In organic production systems, mulches (such as straw, cardboard, etc.) can provide good weed control if applied in a thick mat. There are OMRI approved organic herbicides that can assist in weed management in organic operations. Most organic herbicides have limited residual activity so use a combination of controls like tillage, hoeing, and mulches in addition to herbicides.
Many herbicides are manufactured by different companies under different trade names. The use of chemical names (active ingredient) along with one representative trade name is listed at the end of this section. Herbicide and pesticide labels change so growers must always consult a current label to determine 1) if the crop is listed for herbicide use; 2) what precautions in use are required; and 3) what rates and application methods are allowed. Off-label applications are hazardous to the environment, to people using the product, and can severely injure the crop.
Use herbicides only for those crops for which they are approved and recommended. Use the recommended amount of product and apply it as stated. Pay attention to re-entry intervals (REI) and pre-harvest intervals (PHI). The EPA has the authority to seize any agricultural commodity that carries a pesticide residue in excess of the established tolerance. In addition, if residues of unlabeled chemicals are detected on fresh produce, they could be traced back to your farm.
Don’t spray in high wind conditions so drift injury to susceptible crops is minimized. Work with your neighbors as many herbicides are toxic to other crops that are growing nearby. Finally, herbicides are just one tool available for weed control and their use should supplement other good weed-management practices.
Herbicides are applied in the following ways:
- Before planting: incorporated into the soil prior to seeding or transplanting the crop.
- Pre-emergence: applied to the soil after planting but before the crop or weeds emerge.
- At/after hilling: applied to the soil after the crop is transplanted either before weeds emerge or after clean cultivation. In some cases, sprays are directed to row middles and shielded from application to the crop.
- Directed / Shielded: applied as a directed or shielded spray post-emergence on small weeds in rows of taller crops or in row middles. When using a post-emergence herbicide, the entire weed must be covered for maximum control.
- Post-emergence: applied to weeds after both weeds and the crop have emerged.