Previous research suggests that certain inorganic salts can be useful for enhancing the toxicity of various herbicides. This increased activity has been shown with such herbicides such as MSMA, imazaquin, and imazethapyr by adding ammonium sulfate (AMS) to the spray solutions. Environmental conditions at the time of application have been shown to influence the effect of AMS on the activity of these herbicides.

Preliminary greenhouse studies were conducted to determine the influence of 0.1M AMS on the toxicity of 0.25, 0.5, and 1 lb ai/A fluometuron in several weed species. These studies indicated that the addition of AMS to fluometuron enhanced the activity at some rates with some weed species but the results were inconsistent. Another study was conducted to determine the effects of environment and 0.1M AMS on the toxicity of 0.5 and 1 lb ai/A of fluometuron in pitted morningglory (Ipomoea lacunosa L.) and prickly sida (Sida spinosa L.). Plants were grown in the greenhouse to the 2- to 3-leaf stage. All treatment solutions contained 1% v/v Agridex^® and were foliar applied in water at 20 GPA. Prior to application, the surface of the soil was covered with vermiculite and removed following treatment to prevent any soil activity of fluometuron. Treated plants were placed immediately into growth chambers maintained at 35 C and 40 or 100% relative humidity (RH). After 48 h in controlled conditions, plants were returned to the greenhouse for 14 days. Visual ratings were made at 7, 10, and 14 days after treatment (DAT) with pitted morningglory and 10 and 14 DAT with prickly sida. Control was expressed as 5 injury compared to the untreated control with 0% = no injury and 100% = complete kill. The experiment was a split plot with a factorial arrangement of treatments, replicated four times and was repeated.

At 10 and 14 DAT, there were no significant increases in % control of pitted morningglory at 0.5 or 1 lb/A fluometuron at either 40 or 100% RH among treatments with or without AMS added. At 7 DAT only, an increase in control occurred with AMS added when the treatments were averaged over rate. However, this increase was not present at 1 and 14 DAT. A rate response was shown at 7, 10, and 14 DAT with the greater control provided by the higher rate of fluometuron.

Similar results were shown with prickly sida. At 14 DAT, no increases in control were found at either rate by the addition of AMS at either 40 to 100% RH. However, at 10 DAT, there was a slight decrease in % control when AMS was added to the 1 lb fluometuron rate and compared to that with fluometuron alone and averaged over RH. No differences were found among treatments at the 0.5 lb/A rate.

In conclusion, the addition of AMS to fluometuron for postemergence broadleaf weed control had little effect on weed control when evaluated under these environmental conditions. The inconsistency of control over environment, rate, and AMS indicates little reliability in the use of AMS in enhancing weed control with fluometuron.