2.11. Determination of Herbicidal Activity Released from Microspheres

The weed growth test with metazachlor and pendimethalin as a soil-applied herbicide was performed using three widely occurring weeds, namely Galinsoga parviflora Cav., Rumex acetosa L., and Chenopodium album L. Herbicidal activity of herbicides for weeds was determined by visual assessment of plant growth, damage and drying out, and was documented by digital photographs. Herbicidal activity of microspheres loaded with metazachlor and pendimethalin was evaluated in two parallel tests. First, preliminary (screening) test was aimed to find the effective dose of herbicides to be immobilized in microspheres. For this purpose, to find the effective dose of herbicides loaded in microspheres, both were tested in 3 doses, namely the dose recommended by formulation user guide as well as half and double doses of the recommended one. For metazachlor, the recommended dose of Butisan^®400SC formulation user guide was 2.5 L/ha, which corresponds to 0.79 g/pot. In addition to the recommended dose, half and double doses were used as follows: 0.39 and 1.5 mg/pot, respectively. Pendimethalin dose recommended by the Activus^®400SC formulation user guide was 4.0 L/ha, which corresponds to 1.26 mg per pot. Similarly, half and double doses of the recommended one were as follows: 0.63 and 2.52 mg/pot, respectively. Herbicidal effectiveness of released herbicides was evaluated on weeds after 1 month of weed growth in the presence of microspheres with immobilized herbicides in soil. After selection of the effective dose of both immobilized herbicides among the doses mentioned above, the final test of these active substances after 2 and 3 months of incubation of microspheres in soil was conducted. The effectiveness of immobilized herbicides in microspheres against the tested weeds was compared to two control series: plants grown without any herbicides and plants grown in the presence of herbicides in non-immobilized form.

Ratings were assigned on the basis of the European Weed Research Council (EWRC) scale in terms of phytointoxication as follows: 1: total plant death (100%); 2: excellent (98.0% to 99.9%); 3: very good (95.0% to 97.9%); 4: good to acceptable (90% to 94.9%); 5: moderate (82.0% to 89.9%); 6: weak (70.0% to 81.9%); 7: bad (55.0% to 69.9%); 8: very bad (30% to 54.9%); and 9: none (0.0% to 29.9%).