Bulb crops are a crop grouping that includes all of the Allium species except chives. Bulb crops include onions (dry and green), leeks, garlic, and shallots. Very few shallots or garlic crops are grown in Florida. Dry bulb onions, green and bunching onions, and leeks are the main crops of this group grown in the state. Where herbicides are limited, the culture of these crops must accommodate cultivation. Bulb crops do not shade out weeds that emerge in the rows. Also, many of the crops, such as dry bulb onions and leeks, require a long growing season. Therefore, a plan for weed control must be made before planting.
Avoid fields that are infested with nutsedge, hard-seeded legumes, or other difficult-to-control weeds. Many weed problems can be reduced by preparing the land well ahead of planting and using Roundup in a "cropping systems" approach, and/or using paraquat in a "stale seed bed" approach. Preemergence and early postemergence herbicides may control many weeds for 4–6 weeks.
Onions and leeks are fairly shallow rooted, and care must be taken not to prune these roots with cultivation, especially when onions begin to bulb. Pulling or hoeing occasional large broadleaf weeds, while labor intensive, may be preferable when plants are older and bulbing.
Emerged grass weeds may be controlled either by Select®, Fusilade® or Poast®. Care should be taken not to apply any herbicide beyond the preharvest interval specified on the labels.
Herbicide performance depends on weather, irrigation, soil type, and proper selection for the weed species to be controlled. Obtain consistent results by reading the herbicide label and other information about proper application and timing of each herbicide.
Table 1 includes herbicides and directions for application before crop emergence or transplanting. Table 2 lists herbicides for use after crop emergence or transplanting.
Preplant/preemergence chemical weed control in onion, leek, garlic, and shallot.
Postemergence chemical weed control in onion, leek, garlic, and shallot.