Sugarcane (Saccharum officinarum L.) was planted in the fall; the seed cane was healthy or infected either with sugarcane mosaic virus (strain H) or with ratoon stunting disease (RSD) (Clavibacter xyli). Herbicide treatments were applied the following spring and each subsequent spring during the 3-yr crop cycle. Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at 1.1 kg ai/ha was applied as a soil foliage treatment when sugarcane was about 30 cm tall. The methyl ester of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} at 1.1 kg ai/ha and the sodium salt of asulam {methyl [(4-aminophenyl)sulfonyl] carbamate} at 3.4 or 3.8 kg ai/ha were applied as foliage treatments when sugarcane was about 90 cm tall. Both mosaic and RSD reduced yield of sugar/ha by 16% for the 3-yr crop, primarily by causing a decrease in stalk population. Hexazinone reduced yield of sugar/ha by 24% primarily by causing a decrease in both stalk population and sugar content of stalks. Diclofop reduced yield by 7% and asulam caused no significant yield loss. Combinations of disease and herbicide treatment reduced yields in an additive manner, with the combination of hexazinone and either mosaic or RSD causing a 38% reduction.