With furrow irrigation systems, maintaining deep furrows keeps the bed tops from becoming overly wet while maintaining adequate soil moisture for the crop. By keeping the bed tops drier, less weeds are likely to germinate in the soil surface. A continuation of cultivation, supplemented by in row hand-weeding plus irrigation management, will reduce weed competition. Herbicides may also be applied several weeks before planting, at the time of planting, after planting but before crop and weed emergence, after crop and weed emergence, or after thinning or transplanting. Postemergent herbicides are absorbed by leaves and stems of weeds.
Some herbicides have both preemergent and postemergent activity.
Herbicides and fumigants work best if soil moisture is adequate for plant growth. Preemergent herbicides are effective against germinating seeds, but not dry seeds. However, caution must be exercised not to apply these materials to wet soils as compaction can occur, particularly where power driven rotary tillers are used for soil incorporation. Postemergent herbicides work best on nonstressed plants. Fall Beds .