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Weed Management


The fruiting vegetables (eggplant, pepper, tomato) are almost exclusively started as transplants in Utah. These plants prefer warm weather conditions, where early establishment is necessary to ensure high productivity. Fruiting vegetables are often transplanted into bare soil and rely on furrow irrigation. Weed control is critical in the bare soil systems since weeds in the planted row and furrow are difficult to manage and compete with the desired crop. Weeds in and between the rows are typically controlled with cultivation, hand hoeing, herbicides, or some combination of the three approaches.

Planting through plastic mulches to improve early growth and reduce weed pressure associated with bare soil conditions may help manage weeds. Herbicides can be applied underneath the mulch, depending on the weed pressure and available labor. Weeds growing along the edge of the plastic mulch, however, are difficult to control with cultivation equipment. Use directed or shielded herbicide applications in these areas helps. Be cautious when using this method since spray drift and residual materials left on the plastic may affect the desired crop.

In organic systems, mulches (such as straw, cardboard, etc.) can provide good weed control in and between rows if applied in a thick mat before weeds emerge. There are OMRI approved organic herbicides that can assist in weed management in organic operations. These herbicides are primarily contact herbicides and must be applied to the green tissue of the weeds. Most organic herbicides have limited residual activity so weed control involves a combination of approaches like tillage, hoeing, and mulches in addition to the herbicides.

Most herbicides are now manufactured by many companies under different trade names. Herbicide and pesticide labels often change, so make sure to always consult the label to determine if the crop is listed on the label, what precautions are required, and what rates and application methods are allowed. It is critical to read the label before applying. Comparing the costs of different brands that may have the same active ingredient and percent of active ingredient is also a good idea.

Considerations for Herbicide Use

  • Carefully read and follow all label directions and precautions.
  • Use herbicides only on crops for which they are approved and recommended on the label.
  • Use the recommended amount of product and apply it as stated. (Too much material may damage the crop and make it unsafe for consumption.)
  • Apply herbicides only at times specified on the label and observe the recommended intervals of the time of planting and the time between treatments.
  • Follow re-entry intervals (REI) and pre-harvest intervals (PHI).
  • Don’t spray in high wind conditions.
  • It is a violation of the law to use herbicides other than directed on the label. The EPA has the authority to seize any agricultural commodity that carries a pesticide residue in excess of the established tolerance levels. In addition, if residues of unlabeled chemicals are detected on fresh produce, they could be traced back to your farm.

Herbicides are just one tool available for weed control and their use should supplement other good weedmanagement practices.

Herbicides for weed control are applied in the following ways:

  • Pre-plant incorporated: 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
  • Post-transplant: applied to the soil after crop is transplanted either before weeds have emerged or after clean cultivation
  • Post-emergence: applied to weeds after both weeds and the crop have emerged
  • Directed post-emergence: 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.