Impacts of seed grading and tool sequence on tolerance to mechanical cultivation in carrots ( Daucus carota )

Carrots are challenging to produce due to slow emergence and early growth which limits their tolerance to biotic and abiotic stresses, including those imposed by mechanical cultivation. In field studies conducted in Holt, MI in 2021 and 2022, we evaluated the effects of carrot seed grading and in-row mechanical cultivation tool sequence on carrot survival, weed mortality and yield. We tested two key hypotheses: 1) carrots grown from large seed size fractions (LS carrots) would have greater root anchorage force and height than those grown from small seed size fractions (SS carrots) and hence greater tolerance to uprooting and burial imposed by finger weeders (FW) and hilling disks (HD); and 2) alternating in-row cultivation tools with different mechanisms of action (HD-FW) would reduce carrot mortality and improve weed management efficacy relative to continued application of a single tool (FW-FW). At the time of the first cultivation event, LS carrots had greater anchorage force and height than SS carrots in both years, and greater tolerance to cultivation (lower mortality) in 1 of 2 years. The HD-FW sequence provided improved weed control efficacy and carrot yield compared to the FW-FW sequence in 1 of 2 years. However, at early cultivation events, the selectivity of both tools was low regardless of seed size category, and all treatments required supplemental hand weeding. At later cultivation events, no differences in carrot mortality based on seed size were detected. LS carrots resulted in 17-23% increase in yield compared to SS carrots, regardless of cultivation tools used. These results suggest that more intensive seed grading coupled with cultivation tools and settings targeting weed burial can enhance profitability of carrot production.