Echinochloa crus-galli is the main weed in direct dry-seeded rice systems worldwide and is the target of most herbicide applications. Numerous cases of E. crus-galli biotypes with resistance to herbicides have been reported in different regions of the world; however, to date, no cases have been reported in Uruguay. The purpose of this research is to assess the presence of herbicide-resistant E. crus-galli in the rice fields of Uruguay. More than 40 E. crus-galli biotypes were sampled from eastern to northern regions in different years and assessed following the Herbicide Resistance Action Committee (HRAC) protocols of confirmation, using the herbicides propanil, quinclorac, clomazone, bispyribac–sodium, penoxsulam, imazapyr + imazapic, profoxidim and cyhalofop. Herbicides rates included 0, 0.125, 0.25, 0.50, 1, 2, 4 and 8 times the label rate. Most E. crus-galli biotypes (35) resulted as resistant to quinclorac. Furthermore, resistance was confirmed to propanil in at least seven biotypes, 12 to imazapyr + imazapic, and three to penoxsulam. Five biotypes showed multiple resistance to propanil and quinclorac, and one biotype was resistant to quinclorac, penoxsulam and imazapyr + imazapic. No biotype showed confirmed resistance to clomazone, bispyribac-sodium, cyhalofop or profoxidim—herbicides that ensure satisfactory control. The presence of E. crus-galli herbicide resistant-biotypes reduces herbicide options, threatening rice production in Uruguay. In this context, a redesign of the productive systems would represent an opportunity to complement the chemical control, integrating larger-scale cultural and management practices.

The rice sector is facing the challenge of increasing rice yields while maintaining or improving input use efficiency. The purpose of this study was to determine the most effective vegetation indices for monitoring nitrogen uptake (N uptake) under different irrigation techniques. The study was conducted in Uruguay over two rice-growing seasons. A split plot experimental design featured two irrigation treatments (main plots): continuous flooding (C) and alternate wetting and drying (AWD). The nitrogen-rate (N-rate) treatments (split plots) included no nitrogen, the recommended N-rate based on soil analyses, and two additional doses (±50% of the recommendation). The plant N uptake relationships with selected drone-based vegetation indices (VIs) were assessed at panicle initiation. The presence or absence of standing water during image collection affected the VIs and their relationships with N uptake. The relationships estimated for traditional irrigation may not be applicable for AWD. The SCCCI was the top index with a significantly stronger relationship with N uptake under the C (R² = 0.84) and AWD (R² = 0.71) irrigation techniques in relation to all evaluated vegetation indices. The Clre, NDRE², NDRE, and CLg also had a significant relationship with N uptake under both irrigation treatments in both seasons, though their average R² values of 0.75, 0.74, 0.73, and 0.71, respectively, were lower than the SCCCI (average R² = 0.78). The findings would assist rice growers for selecting effective VIs for remote crop monitoring.

The intensification of rice–livestock systems has encouraged the integration of forage species into rice cultivation. However, the use of imidazolinone-tolerant rice cultivars (imazapyr + imazapic, IMIs), essential for weedy rice control, may hinder the establishment of sensitive forages due to herbicide residues. This study evaluated the emergence and early growth of six forage species through bioassays in soils with different IMI use histories. Over three years (2021–2023), soils were collected from three rice-growing regions in Uruguay with contrasting soil properties, at depths of 0–15 and 16–30 cm, under three IMI conditions: Control (no prior use), IMI-1 (applied one season before sampling), and IMI-2 (applied in the season before sampling). Emergence, plant height, and shoot and root biomass were analyzed using linear mixed models and principal component analysis. Shoot biomass was reduced by up to 60% in IMI-2 soils. Poaceae species and T. pratense were the most affected, while T. repens and L. corniculatus exhibited higher tolerance. Multivariate analysis indicated stronger residual effects on sandy loam soils. These findings highlight that imidazolinone persistence varies with forage species and soil properties, underscoring the need for careful planning in rice–pasture rotations to prevent adverse effects on forage establishment and system sustainability.