Effects of Light Quality on the Life Cycles of Crabgrass and Barnyardgrass

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Abstract
Large Crabgrass (Digitaria sanguinalis (L.) Scop.) and barnyardgrass (Echinochloa crusgalli (L.) Beauv.) plants were grown from seedlings to maturity under five light qualities of equal energy levels. For crabgrass, both fresh and dry weight yields of plant tops grown under red light and under cool white light were significantly greater than those under green, yellow, or blue light. Length of stem followed this same order. Effects of light quality on reproduction were not as consistent; green and blue light caused the largest numbers of seed heads to form, while yellow light delayed flowering and resulted in the least number and weight of seed heads. Somewhat similar responses to light were found with barnyardgrass plants, except that yields under yellow light were close to those under red light for this species. Blue light caused smallest plants in both kinds of weeds.