The critical period for weed competition in parsley (Petroselinum crispum (Mill.) Nyman ex A.W. Hill) in Mediterranean areas

Weeds are one of the major limiting factors for economically viable parsley production. Field experiments were carried out in central Greece, in 2010 and 2011 to determine the effect of competition from a natural weed flora on growth, photosynthesis and yield of parsley (Petroselinum crispum (Mill.) Nyman ex A.W. Hill). Two treatments were applied; weeds were either allowed to infest the crop or plots were kept weed free for an increasing duration of time (0, 10, 20, 30, 40, 50 days after crop emergence). Total dry biomass of weeds increased as the duration of weed infestation increased. Amaranthus retroflexus L., Datura stramonium L. and Solanum nigrum L. contributed most of the total weed dry weight because of their large size and density. Total weed biomass in both growing seasons decreased with increasing duration of the weed-free period and there were no significant differences between years. Moreover, weed competition reduced parsley dry weight by 93% and 95% in 2010 and 2011, respectively. Late weed competition did not affect parsley dry weight as that at early competition. Dry weight of parsley was reduced by 87–91% when plots kept weed-infested for the first 40 days after crop emergence, while plots kept weed-free for similar period provided 8–10 times higher dry weight. There was significant negative correlation between the dry weight of parsley and weed dry weight. Parsley dry weight was dramatically decreased with weed competition duration longer than 20 days after crop emergence. Results indicated that early weed removal is necessary to prevent yield loss.

► Parsley has a slow growth rate which results in strong weed competition.
► Data on parsley biomass from increasing weed-free or weed interference adequately fit the Gompertz and logistic models.
► The parley should be kept weed free between 8–12 and 39–40 days after crop emergence to avoid yield losses in excess of 10%.
► After the 40 DAE the competition of weeds will not significantly impact on parsley growth.