Interactions of Tribenuron with Four Safeners and Piperonyl Butoxide on Corn (Zea mays)I

The efficacy of the safeners naphthalic anhydride (NA), R-29148, benoxacor, and dichlormid as protectants of corn against injury from the methyl ester of tribenuron was evaluated under greenhouse conditions. Tribenuron applied alone reduced the root length of both 'Pioneer 3180' and 'Northrup-King 9283' corn. The concentration of tribenuron causing 50% reduction of corn root length (GR50) was 1 ,uM. NA applied as a seed dressing at 0.5 and 1.0% (w/w) was the most effective of the four safeners tested and provided excel- lent protection to both corn hybrids against 1, 2, and 4 jM tribenuron. Soaking corn seeds in an aqueous solution of R-29148 containing 0.5, 1, or 2 mM protected 'Pioneer 3180' against 1 ,uM of tribenuron. The safening efficacy of R-29148 against tribenuron injury to 'Northrup-King 9283' corn was limited. Dichlormid and benoxacor, were less effective as tribenuron safeners and offered partial protection to both corn hybrids. Individual applications of the synergist piperonyl butoxide (PBO) at 0.1 and 0.2 mM did not affect the growth of corn seedlings. PBO synergized the activity of all concentrations of tribenuron, but only on the 'Northrup- King 9283' hybrid. These results demonstrate that the toler- ance of corn to tribenuron can be enhanced with the use of safeners such as NA and R-29148, and that oxidative reac- tions may be involved in the metabolism of tribenuron by corn. Nomenclature: Benoxacor, (4-dichloroacetyl)-3,1-dihy- dro-3-methyl-2H-1,4-benzoxazine; dichlormid, 2,2-di- chloro-N,N-di-2-propenylacetamide; NA, 1,8-naphthalic anhydride; piperonyl butoxide, a(2-(2-butoxyethoxy)- ethoxyl-4,5-methylenedioxy-2-propyltoluene; R-29148, 3- (dichloroacetyl)-2,2,5-trimethyl-1,3-oxazolidine; tri- benuron, 2-(((((1-methoxy-6-methyl-1,3,5-triazin-2- yl)methylamino)carbonyl)aminoJsulfonyl)benzoic acid; corn, Zea mays L. 'Pioneer 3180' and 'Northrup-King 9283.' Additional index words. Antagonism, antidotes, synergism, synergist.