Abstract

Plant chlorosis is a condition recognized in plants by the paleness and yellowing of foliage and stems. It is caused by the reduced levels of chlorophyll normally present in these parts. Disease, poor growing conditions or deficiency of iron, manganese or zinc have all been associated with this condition. Any interference with the uptake of minerals needed for the formation of chlorophyll or the absence of any of these essential minerals in a rapidly growing plant will result in chlorosis. Iron is the mineral most often lacking or having reduced availability.

During development of a phytoremedial device for koi ponds, the condition was recognized in two test systems. It was subsequently recognized in two private koi ponds. The plant species affected were the terrestrial plant impatiens, Impatiens sp. and coleus, Coleus blumei growing hydroponically and the aquatic plants water hyacinth, Eichhornia crassiaes and parrot's feather, Myriophyllum aquaticum. Water analysis for iron content on the 4 systems was done and the source water for the systems was tested for comparison. Additionally, 3 other koi ponds were analyzed to survey average iron levels in pondwater in the region (see Chart). The iron level in pondwater can be affected by input from water changes and food and uptake by plants and algae. Based on trial and error, it would appear that minimal amounts of iron (0.01-0.02 mg/l) were adequate to prevent the condition but that maintaining a stable level of iron in pondwater was difficult. This was due to very rapid plant growth under favorable conditions of high nitrates and phosphates found in koi ponds and water changes inadequate to supply ample replacement iron. Input of iron from food was not analyzed but was assumed to be relatively stable. The addition of a powdered chelated iron product (Sprint 330) was tried and proved successful in correcting the condition. This is added to the water at the rate of ½ tsp. per 1000 gals. After 24 hrs of circulation, iron levels tested at about 0.12 mg./l. and gradually dropped. It was found that addition of the product at this rate every 14 days maintained healthy plant growth. This protocol has been continuous for 2 years in 2 indoor systems and in seasonal usage in 1 outdoor system. No adverse affects have been noted in the koi. Spawning and growth rates of fry in the indoor systems were within normal limits.

References

1.  Smith MD. The Ortho Problem Solver, 4th edition. Ortho Books, Box 5006, San Ramon, CA 94583-0906. pgs. 24, 720.