Abstract The objective of this work was to evaluate the influence of herbicides 2,4-D and dicamba on the physiological response of chlorophyll a in olive (Olea europaea) seedlings. The following eight rates of the 2,4 D (670 g a.e. ha-1) and dicamba (720 g a.e. ha-1) herbicides were applied: 0, 1.56, 3.13, 6.25, 12, 25, 50, and 100% of the recommended for burndown. The herbicides were applied at 80 cm above the seedlings using a CO2 pressurized back sprayer with a 150 L ha-1 spray volume. Plant gas exchange was measured using a portable infrared gas analyzer. Chlorophyll a fluorescence was evaluated using a portable modulated light fluorometer. The application of both herbicides caused a decrease in the process of CO2 assimilation in the plants, reducing net photosynthesis and stomatal conductance. The 2,4-D herbicide caused the most severe effects on the variables related to chlorophyll a fluorescence. Low values of maximum quantic yield were observed after the application of the herbicides, of which dicamba was the most harmful. Both herbicides damage the photosynthetic apparatus of olive seedlings. 2,4D 24D 2 4 Olea europaea 24 2, 670 (67 ae e a.e ha1 ha 1 720 (72 0 156 56 1.56 313 3 13 3.13 625 6 25 6.25 12 50 100 burndown 8 CO 15 ha- volume analyzer fluorometer plants conductance harmful 4D 67 (6 72 (7 5 1.5 31 3.1 62 6.2 10 ( 7 1. 3. 6.

Resumo O objetivo deste trabalho foi avaliar a influência dos herbicidas 2,4-D e dicamba sobre a resposta fisiológica da clorofila a em mudas de oliveira (Olea europaea). As seguintes oito doses dos herbicidas 2,4-D (670 g a.e. ha-1) e dicamba (720 g a.e. ha-1) foram aplicadas: 0, 1,56, 3,13, 6,25, 12, 25, 50 e 100% das recomendadas para dessecação. Os herbicidas foram aplicados a 80 cm acima das mudas, por meio de um pulverizador costal pressurizado a CO2, com 150 L ha-1 de volume de calda. A troca gasosa das plantas foi medida por meio de um medidor portátil analisador de gases por infravermelho. A fluorescência da clorofila a foi avaliada por meio de um fluorômetro portátil de luz modulada. A aplicação de ambos os herbicidas causou diminuição no processo de assimilação de CO2 pelas plantas, o que reduziu a fotossíntese líquida e a condutância estomática. O herbicida 2,4 D causou os efeitos mais severos nas variáveis relacionadas à fluorescência da clorofila a. Baixos valores de rendimento quântico máximo foram observados após a aplicação dos herbicidas, dos quais o dicamba foi o mais prejudicial. Ambos os herbicidas danificam o aparelho fotossintético das mudas de oliveira. 2,4D 24D 2 4 Olea europaea. europaea . europaea) 670 (67 ae a.e ha1 ha 1 720 (72 aplicadas 0 156 56 1,56 313 3 13 3,13 625 6 25 6,25 12 5 100 dessecação 8 CO 15 ha- calda infravermelho modulada estomática 24 2, prejudicial 4D 67 (6 72 (7 1,5 31 3,1 62 6,2 10 ( 7 1, 3, 6,

ABSTRACT The use of auxin mimics herbicides in agriculture is widespread in a great diversity of crops. The indiscriminate use of herbicides can cause adverse effects in the plants. Among the plant species that stand out for being highly competitive and resistant to biotic and abiotic stresses, it is the brazilian peppertree (Schinus terebinthifolius Raddi.). The objective of this work was to evaluate the phytotoxic and photosynthetic alteration effects of different rates simulating the drift of the herbicides 2,4-D and Dicamba in brazilian peppertree seedlings. The experiment was carried out in a completely randomized design with four replications. The treatments were arranged in 2 x 8 factorial design (herbicide x doses). The factor herbicide consisted the herbicides 2,4-D and Dicamba, and, the factor doses eight percentages of the herbicide applied. Phytotoxicity and alteration of photosynthetic and fluorescence of chlorophyll a parameters were evaluated. Increased rate of the 2,4-D and Dicamba cause phytotoxicity to the plants, whose Dicamba promotes greater injuries. Dicamba was the herbicide that caused the greatest damage to the photosynthetic apparatus on brazilian peppertree plants, while for 2,4-D the plants showed higher recovery potential after herbicidal exposure.