Weed Management

Cucumber, Pumpkin, and Squash

The cucurbits prefer warm weather conditions to ensure high productivity. Many growers transplant early cucumbers and summer squash or seed cucumber, squash and pumpkins into bare soil and rely on furrow irrigation. Weed control is critical in bare soil systems as weeds in the planted row and furrow are difficult to manage and often 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, hand hoeing, herbicides, or a combination of approaches. More growers are planting through plastic mulches to improve early growth and reduce in-row weed pressure associated with bare soil conditions. Some herbicides can be applied underneath the mulch but it is those weeds growing along the edge of the plastic that are difficult to control, with cultivation equipment. Directed or shielded herbicide applications on bed edges helps with weed control but use caution as spray drift and residual herbicides left on the plastic may affect crop growth.

In organic production 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 non-selective, contact herbicides, and must be applied to green tissue. Most organic herbicides have limited residual activity so use a combination of controls like tillage, hoeing, and mulches in addition to herbicides.

Due to space limitations and the large list of chemicals available for weed management, it is not possible to include every comment and suggestion relative to a specific herbicide. It is the grower’s responsibility to have a current chemical applicators license, to obtain a copy of the label, and read it carefully. Many herbicides are manufactured by many companies under different trade names. We have provided the chemical name (active ingredient) along with one representative trade name in this publication. Growers should compare costs of different brands having the same active ingredient. Herbicide and pesticide labels change, so growers must always consult a current label to determine (1) is a crop listed for herbicide use, (2) what precautions in use are required, and (3) what rates and application methods are allowed. Follow the precautions stated on the label. It is a violation of federal law to use any herbicides for purposes other than those specified on the approved label. Off-label applications are hazardous to the environment, to people using the product, and can severely injure the crop.

Use herbicides only on the crops for which they are approved and recommended on the label. Some herbicides can be used only on specific cucurbits and off-label use will injure other crops. Use the recommended amount of product and apply it as stated. Pay attention to reentry intervals (REI) and preharvest intervals (PHI). Over-application wastes money and violates the law. Too much material may damage the crop and make it unsafe for consumption. 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.

Finally, apply herbicides only at times specified on the label and observe the recommended intervals between the time of treatment and time of planting or harvesting the crop. 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:

• Pretransplanting: incorporated into the soil prior to transplanting the crop.
• Preemergence: applied to the soil after planting but before the crop or weeds emerge.
• Direct post-transplant: 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.
• Postemergence: applied to weeds after both weeds and the crop have emerged.

Melons

Cucurbits prefer warm weather conditions to ensure high productivity. Many growers transplant early melons and then seed them into bare soil later in the year. Most growers also rely on furrow irrigation.

Weed control is critical in bare soil systems as weeds in the planted row and furrow are difficult to manage and often compete with the crop before the plants are large enough to shade them out. Weeds in and between the rows are controlled with cultivation, hand hoeing, herbicides, or a combination of approaches.

Plastic mulches improve early growth and reduce in-row weed pressure associated with bare soil conditions. Some herbicides can be applied underneath the mulch but it is those weeds growing along the edge of the plastic that are difficult to control with cultivation equipment. Directed or shielded herbicide applications on bed edges helps with weed control but use caution as spray drift and residual herbicides left on the plastic may affect crop growth.

In organic production systems, mulches can provide good weed control in and between rows if applied in a thick mat before weeds emerge. There are OMRI approved contact organic herbicides that are nonselective and must be applied to green tissue. Most organic herbicides have limited residual activity, so use a combination of controls like tillage, hoeing, and mulches in addition to herbicides.

There are many herbicides available for weed management. It is the grower’s responsibility to have a current chemical applicators license, and to read the product label carefully. Many herbicides are manufactured by many companies under different trade names. Be sure to compare costs of different brands having the same active ingredient. Herbicide and pesticide labels change, so always consult a current label to determine if the crop is listed, rate of application, and precautions. It is a violation of federal law to use any herbicides for purposes other than those specified on the approved label. Off-label applications are hazardous to the environment, to people using the product, and can severely injure the crop.

Some herbicides can be used only on specific cucurbits and off-label use will injure other crops. Pay attention to reentry intervals (REI) and preharvest 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. Finally, apply herbicides only at times specified on the label and observe the recommended intervals between the time of treatment and time of planting or harvesting the crop. Don’t spray in high wind conditions to avoid drift injury to susceptible crops.

Herbicides for weed control are applied in the following ways:

• Pre-plant incorporated: incorporated into the soil prior to seeding or transplanting the crop
• Preemergence: 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
• Postemergence: applied to weeds after both weeds and the crop have emerged
• Directed postemergence: applied as a directed or shielded spray post-emergence on small weeds in rows of taller crops or in row middles. When using a postemergence herbicide, the entire weed must be covered for maximum control.