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Eucalyptus are trees sensitive to interference imposed by weeds mainly during the early growth phase. The repetitive use of herbicides with the same mechanism of action has led to the selection of resistant weeds, and Digitaria insularis stands out for its resistance to glyphosate. Due to its occurrence in eucalyptus plantations, knowledge regarding D. insularis interference in eucalyptus early growth is needed to develop management strategies. This study aimed to confirm D. insularis glyphosate-resistence; and also to evaluate the effect of densities and distances of glyphosate-resistant D. insularis, seeded and in regrowth, on the early growth of Eucalyptus urophylla × E. grandis (Clone AEC-144). Prior to eucalyptus' experiments, D. insularis glyphosate-resistance was confirmed through a dose–response curve experiment. After that, two experiments [one for weed's first growth (seeded) and other for second growth (regrowth)] were carried out in an open area, in 700 L pots, for 105 days after planting eucalyptus seedlings. The treatments consisted of increasing densities of D. insularis (0, 1, 2 and 3 plants m−2) planted at 10, 20 or 30 cm from the eucalyptus seedlings. Eucalyptus height, stem diameter, leaf area and dry matter were evaluated. The eucalyptus variables most sensitive to interference were leaf and stem dry matter, with reductions of 45% and 88.4%, respectively for weeds seeded and regrowth. Weed second growth (regrowth) interfered more aggressively in eucalyptus growth. The coexistence with D. insularis, regardless of density and distance, negatively interfered early tree growth. [ABSTRACT FROM AUTHOR]

Previous studies have reported that phosphorus transporters are involved in glyphosate uptake by plants, so phosphorus fertilization might act as an attenuator of glyphosate effects on a possible drift. The objective of this study was to evaluate the influence of phosphorus fertilization on the initial growth of Pinus taeda genotypes submitted to glyphosate subdoses applied during two growing seasons, warm and cold. Four experiments were conducted in an open area using 10-L pots, two in the warm season (during 180 days after application on Genotypes 1 and 2) and two in the cold season (during 81 days after application on Genotypes 3 and 4). The treatments consisted of a 2 × 4 factorial scheme, with presence or absence of phosphorus fertilization (25.2 kg ha−1 P2O5) and four subdoses of glyphosate (0, 72, 144 and 288 g ha−1 acid equivalente), using five replicates. For warm season, glyphosate subdoses provided a stimulatory effect on the plant growth of both P. taeda genotypes independently of the fertilization condition. The supplementary phosphorus fertilization increased plant growth characteristic in both warm and cold season, regardless of the exposure to glyphosate subdoses. However, the plant response is dependent on the genotype. Glyphosate subdoses did not negatively affect P. taeda genotypes growth at both experimental seasons, regardless of phosphorus fertilization. [ABSTRACT FROM AUTHOR]