The influence of elevated levels of micronutrients on the growth and f
lowering of French marigold (Tagetes patula L.) was investigated. Plan
ts were grown with nutrient solution containing 0.25, 0.5, 1, 2, 3, 4,
5, or 6 mM boron (B), copper (Cu), iron (Fe), manganese (Mn), molybde
num (Mo), or zinc (Zn) and toxicity development was monitored. The thr
eshold micronutrient concentrations that induced visible foliar toxici
tysymptoms were 0.5 mM B, 4 mM Cu, 4 mM Fe, 2 mM Mn, 1 mM Mo, and 5 mM
Zn. The dry matter yields during the 5 week experimental period were
reduced when micronutrient concentrations exceeded 0.5 mM B, 3 mM Cu,
3 mM Fe, 6 mM Mn, 0.5 mM Mo, and 5 mM Zn in the fertilizer solution. L
eaf chlorophyll contents decreased when the nutrient solution concentr
ations of Cu, Fe, and Mn were greater than 0.5 mM, 3 mM, and 2 mM, res
pectively. Visual toxicity symptoms of the six micronutrients were cha
racterized.