Abstract
ABSTRACT: Herbicides of the imidazolinone group have been used in irrigated rice and presented a long persistence in the soil, especially in floodplain areas with a low drainage, and could cause environmental contamination. This study aims to evaluate the leaching and residual of herbicides belonging to the imidazolinone group in sprinkler and flood irrigation systems. The experiment was carried out under greenhouse conditions, with the application of the herbicides imazethapyr, imazethapyr + imazapic, and imazapyr + imazapic in soil irrigated by flooding and sprinkling. Subsequently, the soil was collected from the layers of 0-5, 5-10, 10-15, 15-20, and 20-25 cm and packed in 500 mL capacity plastic pots in order to sow tomato as a bioindicator plant of the presence of the herbicides belonging to the imidazolinones. Phytotoxicity, length, and shoot dry matter mass of tomato plants were evaluated at 10 and 20 days after emergence. The herbicides of the imidazolinone chemical group presented a high potential for leaching and persistence with effects for more than 180 days after application. Based on the symptoms presented by the sensitive crop, the degradation of imazethapyr, imazethapyr + imazapic, and imazapyr + imazapic in the 0-15 cm layers was higher in soil with sprinkler irrigation when compared to flood irrigation. Thus, non-flooded soils present a greater capacity to degrade the herbicides belonging to the imidazolinone chemical group.
Highlights
To control the rice weed in cultivated rice fields, herbicide-tolerant cultivars of the imidazolinone chemical group were developed (SOSBAI, 2012)
The herbicides belonging to the imidazolinone group are generally absorbed by roots and leaves and transported by the phloem and xylem, being accumulated in the meristems, where their mechanism of action occurs, with a reduction of the branched-chain aliphatic amino acid levels valine, leucine, and isoleucine through the inhibition of the enzyme acetolactate synthase (ALS) or acetohydroxyacid synthase (AHAS) (Kraemer et al, 2009)
A difference was observed between irrigation systems, in which the herbicides had the highest effect on tomato plants in the flooded system in the surface layers of the soil profile
Summary
To control the rice weed (red and black rice) in cultivated rice fields, herbicide-tolerant cultivars of the imidazolinone chemical group were developed (SOSBAI, 2012). Some herbicides in the imidazolinone chemical group are selective to important crops, such as soybean and rice, and are broad-spectrum on weeds in these two cultivated species. These herbicides are usually applied in pre- or post-emergence, controlling magnoliopsid and liliopsid species (Steele et al, 2002), but can be used as non-selective herbicides in non-agricultural areas because of their high persistence in the soil (Masters et al (1996), which is very important for this herbicide group (Villa et al, 2006). The symptoms of the action of these herbicides are visible, such as the decrease of plant growth, elongation, and chlorosis between the ribs of the leaves (Tan et al, 2006)
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