Mid-September through mid- to late October is easily the best time to control weeds like dandelion, clover, and chickweed with an application of a broadleaf weed herbicide. Why?
Why are broadleaf herbicides more effective in the fall than spring?
Mid- September through mid- to late October is easily the best time to control weeds like dandelion, clover, and chickweed with an application of a broadleaf weed herbicide. Why? Broadleaf weed herbicides are systemic and move through the plant in the phloem, which also transports photosynthate. The effectiveness of control increases when the herbicide reaches as much of the plant as possible. In the fall, perennial plants are “preparing” for winter, translocating photosynthate and storage products to the crowns and roots. Herbicide applied in the fall will translocate with the photosythate throughout the plant, thus usually causing a complete kill. Conversely, in early Spring the weeds tends to be moving storage products from its roots and crowns to initiate leaves and flowers. Thus herbicide applied in the early spring tends to remain in the leaves, not translocating throughout the plant, and not providing nearly as effective long-term control as a fall application. Furthermore, fall applications have limited drift risks because most of the non-target susceptible plants have either lost their leaves, are dead or soon to be dead, or mature enough to withstand some limited drift. Plus fall applications will control weeds and allow turf to fill in this fall before crabgrass or other weeds germinate next spring. We normally will recommend treating well into late October, but more information on late applications is in last year’s Turf iNfo at http://turf.unl.edu/pdfctarticles/Oct_how_late_fall_bdlv.pdf- by Zac Reicher, Professor, Turfgrass Science, firstname.lastname@example.org