Strawberry, black medic (Medicago lupulina), and Carolina geranium (Geranium carolinianum) growth under light-limiting conditions

Broadleaf infestations interfere with Florida strawberry production. Broadleaf POST herbicide options applied atop the crop are limited to synthetic auxins and not suitable for conventional multi-cropping and organic systems. Reducing light access and interception during weed emergence may reduce interference. Light-limited growth of two problematic broadleaves, black medic and Carolina geranium, and the most commonly grown strawberry cultivar (‘Florida Radiance’), were examined in the greenhouse. The experimental design was completely randomized, and the trial was repeated. Black medic was susceptible to reductions in incoming solar radiation, wherein reducing the daily maximum available light from 331 to 94 µmol m-2 s-1 reduced leaf number and area by 93% and 89%, respectively. Carolina geranium growth was less susceptible to reduced-light treatments, with leaf area and number each reduced by 66% when light was reduced from 331 to 94 µmol m-2 s-1. Belowground, Carolina geranium biomass was similarly reduced between the 331 and 94 µmol m-2 s-1 treatments. Strawberry was relatively tolerant to shading at 155 µmol m-2 s-1, but further reductions did increase mortality. Shade-induced weed suppression is a promising alternative strategy for conventional and organic Florida strawberry production. Targeted application during periods of weed emergence may play a role within integrated pest management strategies. This approach is most feasible for black medic management but may be useful for Carolina geranium in concert with other strategies.Nomenclature: Carolina geranium, Geranium carolinianum L. GERCA; black medic, Medicago lupulina L. MEDLU; strawberry, Fragaria × ananassa (Weston) Duchesne ex Rozier (pro sp.) [chiloensis × virginiana]