Susceptibility of Urochloa species subjected to pre-emergence application of [imazapyr + imazapic] herbicide

Intercropping imidazolinone resistance crops, resistant to herbicides imazapyr + imazapic, with forage species may be a viable alternative to recover degraded pasture areas. This practice requires herbicides to slow down development of the forage and avoid reduced rice yield. However, as it is a relatively new technology, the proper management of this herbicide to control forage is not known. The objective of this study was to determine the susceptibility of forages Urochloa ruziziensis, U. brizantha cv. Paiaguás, and U. brizantha cv. Marandu, submitted to the pre-emergence application of the herbicides [imazapyr + imazapic]. The experimental design was completely randomized in a 3×5+3 factorial scheme with five replications. Treatments consisted of the combination of the three species (Urochloa ruziziensis, U. brizantha cv. Paiaguás, and U. brizantha cv. Marandu) and five intervals between herbicide application in the soil and forage sowing (0; 5; 10; 15; and 20 days after its application), in addition to three control treatments, without herbicide application. This study found that application of herbicide on the day of forage sowing for intercropping with imidazolinone resistance crops is not feasible. Increasing the time interval between herbicide application and forage sowing provides increased development of U. brizantha cvs. Marandu and Paiaguás. The species U. ruziziensis is more susceptible to pre-emergence application imazapyr + imazapic. According to the results, U. brizantha cvs. Marandu and Paiaguás are more suitable to be managed by imidazolinone herbicides to recover degraded pasture areas