Carolina redroot (Lachnanthes caroliniana) vegetative growth and rhizome production as affected by environmental factors and planting depth

Carolina redroot [Lachnanthes caroliniana (Lam.) Dandy] is a frequent weed of New Jersey cranberry (Vaccinium macrocarpon Aiton) bogs that competes with the crop for nutritional resources. Studies were conducted in 2018 to determine the effects of planting depth, soil moisture, lighting conditions, rhizome water content, and duration of rhizome submersion under water on L. caroliniana shoot emergence, vegetative growth, and rhizome development. Only planting depth greater than 12 cm significantly reduced shoot emergence (54%), biomass shoot and root production (27% and 65%, respectively), and rhizome formation (65%) compared with a 2-cm depth. Complete inhibition of new rhizome production was observed when the rhizome water content dropped to 30%. Soil moisture <= 30% decreased shoot biomass by >= 53% compared to 60% soil moisture, but marginally affected root biomass and had no impact on rhizome formation. Rhizome submersion for at least 120 d had minor effect on shoot emergence but reduced plant biomass by >= 28% and completely inhibited the formation of rhizomes. Finally, shading did not influence emergence but had a more dramatic effect on root and shoot biomass, which were reduced by 53% and 75%, respectively, and prevented the development of new rhizomes. This study demonstrates the plasticity of L. caroliniana to drought stress or long-lasting flooding conditions, therefore preventing consideration of cranberry bed temporary flooding or limitation of irrigation volume and frequency as viable management options. Sanding would not provide a layer of material sufficiently thick for reducing L. caroliniana shoot emergence. Reducing the quantity of light reaching the soil with black tarps or promoting rapid crop canopy closure are options that can complement the use of mesotrione for controlling L. caroliniana. Future research should address the practicality of these options, especially in bogs with low L. caroliniana pressure when early-summer weed regrowth occurs following dissipation of PRE herbicide activity.