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 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.
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
- 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.