Optimal leaf crop production depends on successful weed control. Weeds reduce leaf crop yields by direct competition for nutrients, water, and light.
Weed control is especially important early in the growth of the crop. Competition from amaranth (spiney, common, or livid) weeds can cause 20%–40% yield reduction in lettuce if not controlled within 3–5 weeks of emergence. One spiney amaranth plant can reduce yield and quality of four lettuce plants in the row around it.
Effective weed control should include a combination of practices designed to suppress weeds during the entire year.
Management practices include crop rotation, cover cropping, cultivation flooding, and mulching. Crop rotation and flooding are routinely followed in Florida's more intensively cultivated organic soils. Care should be taken when leaf crops are rotated behind crops where more persistent herbicides were used. If carried out before planting, bioassays using indicator crops can save valuable time and problems by indicating if an herbicide persists in the soil.
Mulching should be considered for any lettuce grown in mineral soils. Colored mulches can increase or decrease soil temperature depending on the time of year. A labeled multipurpose fumigant may eliminate many soilborne insects, diseases, and weeds.
Cultivation in leaf crops is a necessity and is a detriment if not done properly.
In seeded lettuce, thinning and blocking usually are done at 21–28 days. Cultivation at this time is required to reduce any competition from weeds emerging in the row. Cultivation also prunes lettuce plant roots and in itself reduces subsequent quality and yield if special care is not exercised. Cultivation in older lettuce has also been shown to reduce quality if carried out improperly.
Pursuit® is a third-party registration. For legal use of the herbicide, the grower (applicator) must obtain the label from the third-party registrant (in this case TPR, Inc., Orlando). Use of the product without having a signed authorization and waiver and limitation of liability agreement is a misuse of the product.
To reduce confusion, the EPA has recently defined tolerance terminology in lettuce. If a label states head lettuce, the pesticide may only be applied to the crisp head varieties of lettuce. If leaf lettuce is stated, this may be applied to all leaf lettuce types, including leaf lettuce, cos (Romaine), and butterhead varieties. The term "lettuce" includes head and leaf lettuce (i.e., all types except endive and escarole). Endive is a separate tolerance crop and includes endive and escarole.
The leafy greens group includes lettuce (head and leaf), endive, and spinach, as well as amaranth, arugula (roquette), chervil, chrysanthemum, corn salad, garden and upland cress, dandelion, dock, orach, parsley, purslane (garden and winter), radicchio, New Zealand spinach, and vine spinach. A label for the "leafy greens" group includes all of these. If a label has the term "leafy vegetables," it is labeled for the leafy greens plus the leaf petiole (celery) group.
Preplant chemical weed control in leafy greens (lettuce, endive, escarole, and spinach).
Postemergence chemical weed control in leafy greens (lettuce, endive, escarole, and spinach).