Two previously identified triazine-resistant annual bluegrass (Poa annua) biotypes in Mississippi were evaluated to determine the level as well as the mode of resistance compared to a triazine-susceptible biotype. Annual bluegrass seeds were collected at two sites (Meridian and Tupelo, MS) from field plots previously treated with 11.2 kg ai/ha simazine. Seeds were planted on agar containing simazine (0, 0.001, 0.01, 0.1, 1, 10, or 100 mM) or diuron (0, 0.01, 0.1, 1, 10, 100, or 1,000 μM), placed in the growth chamber with an 8 h daylength and alternating temperatures of 15 and 20 C, and allowed to grow for 3 wk, after which fresh weight was determined. Data were subjected to regression analyses and the amount of simazine or diuron required to reduce fresh weight to 50% of the untreated plants was determined. These data indicated a greater than 1,000-fold level of resistance to simazine with either biotype. Diuron concentrations of 5.0, 3.0, and 3.2 μM were required to reduce fresh weight to 50% of the untreated for the triazine-susceptible, Meridian, and Tupelo biotypes, respectively. Sequencing a portion of the chloroplastpsbAgene revealed a serine 264 to glycine mutation, which reduced the affinity of the triazine herbicides for the QB-binding niche on the D1 protein in photosystem II.

Summary. The adsorption of diquat cation was found to be 0.3, 2.0–2.5 and 80–100 mg/g on a sandy loam soil, Grade Hydrite 10 Georgia kaolinite and National Standard Bentonite, respectively. Bentonite (113 lb/surface ac) applied to plastic pools previously treated with 1 ppm paraquat reduced the concentration of paraquat to less than 0–05 ppm within 24 hr of application. Only bentonite appeared to hold either diquat or paraquat in a form unavailable to wheat. Appreciable uptake by wheat from soil treated with diquat or paraquat (16 lb/ac pre‐emergence) occurred only in soil or sand in which the herbicide leached below the 05 in. zone. A 12 hr dark period following foliage application did not appear to enhance movement of either herbicide in wheat. Loss of radioactivity was observed when diquat or paraquat was exposed to ultraviolet light (2537 Å). Facteurs agissant sur la persistence et l'inactivation du diquat et du paraquat

Sicklepod control with one or two cultivations or postemergence (POE) directed-spray applications of linuron or metribuzin plus 2,4-DB was less than 50% in August evaluations when no soil-applied herbicide had been used. However, sicklepod control greater than 75% was noted through August when two cultivations or metribuzin plus 2,4-DB applied POE followed either metribuzin applied preplant incorporated (PPI) and preemergence (PRE) or metribuzin plus alachlor applied as a PRE treatment. One cultivation after these soil-applied herbicide treatments did not reduce sicklepod populations compared to the chemical treatments alone. Soybean yields more than doubled over yields in untreated plots when a combination of soil-applied herbicides and two cultivations or metribuzin plus 2,4-DB applied POE were used.

The influence of PRE herbicides on rooting characteristics of bermudagrass turfgrass was studied using sod plugs removed from the field. Greenhouse root fresh weight was reduced the greatest with dithiopyr or prodiamine. Pendimethalin caused fewer fresh weight reductions compared to dithiopyr or prodiamine and these reductions were usually for a short period. Root weight loss was due to lower root density and root malformation. Significant numbers of malformed roots were also observed for greater periods of time where dithiopyr or prodiamine had been applied.