Mesotrione typically requires multiple applications to control emerged weeds in turfgrass. As it is absorbed by both foliage and roots, a controlled-release (CR) formulation could eliminate the need for multiple applications. Research was conducted to evaluate simulated-release scenarios that mimic a potential CR mesotrione formulation. A soluble-concentrate formulation of mesotrione was titrated to produce a stepwise change in mesotrione rates, which were applied daily to mimic predetermined release scenarios over a 3-wk period. CR scenarios were compared to a broadcast treatment of mesotrione at 280 g ai ha–1 applied twice at 3-wk intervals, and a nontreated. Mesotrione applied in three temporal-release scenarios controlled creeping bentgrass, goosegrass, nimblewill, smooth crabgrass, and white clover equivalent to the standard sprayed mesotrione treatment in every comparison. However, each CR scenario injured tall fescue two to seven times more than the standard treatment. Soil- and foliar-initiated repeat treatments were equivalent in most comparisons. Our data indicate that mesotrione applied in a temporal range to simulate controlled-release scenarios can deliver desired weed control efficacy comparable to sequential broadcast applications. More research is needed to elucidate proper timings and release scenarios to minimize turfgrass injury.

Three microcapsule formulations, two starch xanthate formulations, and one commercial formulation of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were evaluated in the greenhouse and field for their relative herbicidal efficacy and persistence. Biological assays with Italian ryegrass (Lolium multiflorum Lam.) revealed significant differences among the formulations in phytotoxicity and persistence. The commercial formulation of trifluralin was generally more phytotoxic than the others to Italian ryegrass sown the week of herbicide application. The two starch xanthate formulations and one microcapsule formulation of trifluralin were generally more phytotoxic and more persistent than the commercial formulation to Italian ryegrass sown from 1 through 19 weeks after herbicide application.

Scanning electron micrographs that depict the surface and internal structure of several starch-encapsulated granular formulations of EPTC (S-ethyl dipropylthiocarbamate) and butylate (S-ethyl diisobutylthiocarbamate) relate well with herbicidal release rates previously reported. Fast-release formulations appear to have a porous surface with little distinctive internal structure. Diffusion would be expected to be more rapid as fewer diffusion barriers are present. Slow-release formulations have a smooth, hard surface with irregular surface pores and a honeycombed internal structure. The slower release characteristics are associated with stronger oxidants used for crosslinking xanthate in the entrapment of herbicides. The scanning electron microscope would be an excellent quality control technique in the preparation of starch-encapsulated herbicides.

Experimental controlled release starch granules (CRSG) containing 5.3% a.i. (w/w) norflurazon or 6% a.i. (w/w) simazine retarded the leaching of both herbicides in loamy sand soil columns when compared to commercial formulations of norflurazon [80% (w/w) dry flowable] or simazine [90% (w/w) water dispersible granule]. Barley bioassays indicated norflurazon and simazine remained in the surface 0 to 2.5 cm of soil when applied as CRSG formulations and moved to a depth of 15 cm when applied as commercial dry formulations and leached with 6 cm of water. CRSG placed on pre-wetted soil columns began to release norflurazon by 7 d at 25 C or 14 d at 15 C, and subsequent leaching moved norflurazon beyond the top 2.5 cm of the soil column.

Four starch-encapsulated formulations of EPTC (S-ethyl dipropylthiocarbamate) and of butylate (S-ethyl diisobutylthiocarbamate) were prepared and evaluated by comparison with their respective emulsifiable concentrate formulations for their slow-release capabilities and efficacies. Chemical and biological evaluation indicated that difference in controlled-release could be achieved by the selection of the starch xanthate and oxidant used in the formualtion process. EPTC and butylate released slower when formulated as starch-encapsulated granules than when formulated as emulsifiable concentrates under soil conditions that favored rapid release. The initial release was adequate for weed control and slow enough for desired residual activity. Repeated seeding and harvesting the treated soils and bioassays of treated soils generally produced release rate anticipated from short term dry and wet chemical tests.

Field studies were conducted in 1977 and 1978 to compare the efficacy of the starch xanthate and activated-sludge polymer controlled-release herbicide formulations with the emulsifiable-concentrate formulations. As incorporation was delayed from immediately to never incorporated, starch xanthate and sludge polymer thiocarbamate herbicide formulations had activity equal to that of the emulsifiable concentrates at our initial and final rating dates. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-starch xanthate in 1977 had increased activity over that of the emulsifiable concentrate as incorporation was delayed, as indicated by initial and final visual rating. Starch xanthate did not greatly increase the residual activity of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], or several thiocarbamate herbicides. Starch xanthate formulations of EPTC (S-ethyl dipropylthiocarbamate) and vernolate (S-propyl dipropylthiocarbamate) provided significantly less protection to corn than did addition of the protectant R-29148 [3-(dichloroacetyl)-2,2,5-trimethyloxazolidine]. The sludge polymer formulation had no controlled-release properties.

The formulation of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) encapsulated within a starch granule can reduce the loss in activity associated with the delayed incorporation of the emulsifiable concentrate formulation of trifluralin. Good weed control and high soybean [Glycine max (L.) Merr. ‘Wells II’] yields were obtained when a starch formulation of trifluralin was applied in the fall and incorporated at planting time the following spring. The cultural practices of shallow incorporation, delayed incorporation, and/or midseason cultivation intensified the weed control provided by a starch formulation of trifluralin. The adsorption of additional trifluralin onto the granule surface, cross-linking starch xanthate with a weak oxidant, and mixing granules with different release rates also increased initial control. Granules produced by the starch-calcium and starch-borate processes exhibited many of the same characteristics of granules produced by the older starch xanthate process, but are much less expensive to produce and do not require the use of the toxic carbon disulfide in the encapsulation process. The combination of an appropriate starch formulation of trifluralin with proper cultural practices provided good weed control from fall and spring applications of trifluralin.