Information is limited concerning the impact of delaying applications of pesticides after solution preparation on efficacy. Experiments were conducted to determine weed control when diclosulam, dimethenamid-P, flumioxazin, fomesafen, imazethapyr, pendimethalin, and S-metolachlor were applied preemergence the day of solution preparation or 3, 6, and 9 days after solution preparation. Herbicide solutions were applied on the same day regardless of when prepared. Control of broadleaf signalgrass, common lambsquarters, entireleaf morningglory, and Palmer amaranth by these herbicides was not reduced regardless of when herbicide solutions were prepared. Surprisingly entireleaf morningglory control by all herbicides increased when herbicide application was delayed by 9 days. In separate experiments, control of broadleaf signalgrass by clethodim, common ragweed by glyphosate and lactofen, entireleaf morningglory by lactofen, Italian rye grass by glyphosate and paraquat, and Palmer amaranth by atrazine, dicamba, glufosinate, glyphosate, imazethapyr, lactofen, and 2,4-D was affected more by increase in weed size due to delayed application than the time between solution preparation and application. 1. Introduction Unforeseen circumstances such as high wind speed, excessive rain, and equipment failure may prevent timely application of spray solutions. Spray water quality has been shown to reduce efficacy of glyphosate and other herbicides applied postemergence [1–6]. The greater the length of time the herbicide is in solution the greater the possibility of interactions among constituents in the aqueous carrier [7, 8]. Ammonium sulfate as a spray conditioner prior to adding glyphosate or other herbicides to the solution can minimize adverse effects of polyvalent compounds on herbicide absorption and subsequent efficacy [9–13]. The amount of time between solution preparation and application may increase the time herbicides and polyvalent cations can interact and possibly affect weed control [8]. Efficacy may be affected when pesticides remain in spray solutions for extended periods of time. Permethrin left in municipality ultra-low volume spray tanks for 4 months averaged 55.5% degradation of the product when analyzed by gas chromatography [14]. In cotton (Gossypium hirsutum L.), performance of ethephon, indoxacarb, methomyl, spinosad, and thidiazuron was influenced when spray solution application was delayed 1 or more days, whereas efficacy of acephate, carfentrazone, diuron plus thidiazuron, ethephon plus cyclanilide, indoxacarb, lambda-cyhalothrin,
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