Perennial Weed Control Programs in Succession Planted and Fallowed Sugarcane (Saccharum Spp.) Fields.

Studies were conducted over two years to compare weed control programs in succession planted sugarcane and in fallowed sugarcane fields. Glyphosate combined with tillage during the summer fallow period was more effective in controlling bermudagrass than tillage alone. Bermudagrass ground cover 240 days after planting ranged from 7 to 47% when glyphosate plus tillage was followed by atrazine after planting and pendimethalin plus atrazine in February. Bermudagrass ground cover was no more than 5% with applications of terbacil after planting and metribuzin in February. Cane and sugar yields were equivalent for the herbicide/tillage treatments even though bermudagrass control differed. In simulated rainfall studies, plots received either no rainfall or rainfall 15 or 60 minutes after herbicide application using a simulator delivering 1.3 cm of water in 15 minutes. Glyphosate at 2100 g/ha was applied in combination with Kinetic HV at 0.25%, Break-thru at 0.125%, or Induce at 1.0%. Johnsongrass control 14 days after application at the reproductive stage was at least 89% with no rainfall, but no more than 65% with rainfall. Johnsongrass regrowth was not observed regardless of rainfall timing or adjuvant. When applications were made to vegetative johnsongrass, responses were inconsistent. Sulfometuron applied preemergence after planting reduced shoot population of succession planted sugarcane the first year 33, 58, and 68% at 53, 105 and 158 g/ha, respectively. In the second year, however, shoot population ranged from 6740 to 8620 shoots/ha, with no differences observed among treatments. Johnsongrass control with sulfometuron 180 days after planting ranged 79 to 93%, but was no more than 37% with metribuzin. Sugarcane stalk population for the sulfometuron treatments was either equivalent to or greater than that for metribuzin followed by asulam. In other studies, sulfometuron applied preemergence after planting did not adversely affect emergence, early growth, or yield of succession planted sugarcane infested with bermudagrass. Additionally, sulfometuron applied at 131 g/ha to the soil surface or at 8 g/ha in furrow did not adversely affect sugarcane emergence in the fall or spring. For the in-furrow sulfometuron application of 17 g/ha, shoot population in fall and spring was reduced at least 18% compared with the no herbicide treatment. Application of sulfometuron in furrow reduced sugar yields 13 to 48% compared with metribuzin