Submitted to: Weed Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/11/2005
Publication Date: 12/1/2005
Citation: Ulbrich, A., Souza, J., Shaner, D.L. 2005. Persistence and carry over effect of imazapic and imazapyr in brazilian cropping systems. Weed Technology. 19:986-991 Interpretive Summary: Imidazolinone resistant corn is planted in Brazil and is treated with a combination of imazapic plus imazapyr for weed control. This paper examined the rate of dissipation of both of these herbicides and the time required after planting before rotational crops can be used in two different sites in Brazil. The results show that imazapic and imazapyr dissipate much more rapidly under the subtropical conditions in Brazil compared to reported values from temperate regions. We also found that soybeans was the most tolerant rotational crops, and corn was the most sensitive. The results of this work will give guidance to Brazilian farmers as to which crops they can safely plant after applying a combination of imazapic plus imazapyr with appropriate time intervals after treatment.
Technical Abstract: In Londrina and Palmeira, PR, Brazil, four field studies were conducted on clay soil and sandy-loam soil from 1999 to 2000 to determine the persistence and carryover effect of a mixture of imazapic and imazapyr, applied to imidazolinone tolerant corn, on rotational crops as soybean, edible bean, wheat and corn, to estimate the level of soil residues under tropical conditions, in two different planting systems (no-till and tillage). Main plots were herbicide treatments (0, 52.5+17.5 and 105+35 g ai/ha) and subplots were five intervals (0, 30, 60, 90 and 120 d) between the herbicide application and the rotational crop planting date. Soil samples were collected for a cucumber bioassay and also for a chemical residues analysis. The dissipation time (DT50) of the herbicides in the soil was greater in Londrina than Palmeira, both for imazapic (54 d vs. 27 d, respectively) and for imazapyr (40 d vs. 33 d, respectively), probably due to the lower pH and greater clay content in the soil in Londrina compared to Palmeira. Soybean was the least sensitive rotational crop with a period for no yield drag (PINYD) of 87d in Londrina and 88d in Palmeira. Wheat and edible bean showed intermediate sensitivity ' 99d and 98d for Londrina and 91d and 97d for Palmeira, respectively. Corn was the most sensitive crop, 117d in Londrina and 97d in Palmeira. Cucumber was more sensitive to the herbicide residues than the rotational crops showing damage at 28 DAP between 6% and 20% in the same periods in which the crops no longer had yield reduction.