Critical period of weed interference in pineapple crop in Reunion Island

As the first fruit produced, the 'Queen Victoria' pineapple (Ananas comosus [L.] Merr.) holds an important role in the economy of Reunion Island. Pineapple cropping systems rely heavily on synthetic inputs, such as herbicides or plastic mulch to suppress weeds that are one of the most significant biotic constraints for pineapple producers. Sustainable alternative solutions are needed, but studies on weed control in these cropping systems are limited. The objectives of this study were to assess i) the critical period of weed interference, i.e. the period that can reduce the crop production, ii) how weeds affected pineapples, and iii) which weed species are mainly present. We conducted a field experiment in Reunion Island in 2022. The 3-replication design included 2 factors: weed-pineapple coexistence duration (8 levels: 0, 2, 4, 6, 8, 10, 12 and 14 months) and weeding period (2 levels: weeds are controlled before or after weed- pineapple coexistence). The results showed that the longer weeds grow in the field, the higher the yield loss: weed-free plot yields reached 33.9±5.9 t.ha-1, compared with 0.14±0.13 t.ha-1 for the plots with the most weeds. The critical periods of weed interference were from 91 to 341 and 104 to 259 days after planting corresponding to 5% and 10% yield losses, respectively. At flower induction, pineapples in weed-free plots had almost three times of leaves as in weedy plots, and D-leaf, the diagnosis leaf used as an indicator of crop growth, was 1.3 times longer and 3.4 times heavier. The pineapple quality at harvest was also affected by weeds, but with highly variable results. Finally, we observed forty-one species, but only five were highly frequent and abundant, including two Poaceae considered as particularly noxious, Panicum maximum and Urochloa distachya. These results suggest that reducing pineapple yield losses requires an appropriate weed management especially at the beginning of the crop cycle. Knowing the critical period of weed interference and the effect of crop/weed competition on pineapple production and quality will contribute to develop appropriate weed management practices and more sustainable cropping systems.