NC State Floriculture

 

Low Substrate Iron Corrective Procedures

Brian E. Whipker, James L. Gibson, Paul V. Nelson, Todd J. Cavins, and John M. Dole

Disclaimer: Growers should read and follow all label directions. Test the corrective procedure on a small number of plants prior to applying it to the entire crop.

Possible Causes
Corrective Procedures
Not using a fertilizer containing Fe (eg. calcium nitrate + potassium nitrate).

1. Use a fertilizer that contains Fe.
2. Dissolve 1 to 2.5 pounds of iron sulfate [FeSO4.7H2O] in 100 gallons of water. Apply to the root substrate and rinse the foliage after application. Iron sulfate will increase the root substrate EC level and may release toxic levels of minor elements from the root substrate exchange sites. Test on a few plants first. Do not over apply.

Foliar sprays have a greater risk of plant injury. Avoid applications during the midday heat. Plant uptake is enhanced by prolonged drying time, which occurs during humid conditions, especially in the morning. Nutrient uptake through the leaves is also greater in the day than at night, making morning applications more desirable than evening sprays.

Substrate pH is too high, inducing iron deficiency. 1. Test the substrate pH to determine if it is too high (> pH 6.5).
2. Neutralize the alkalinity of the irrigation water with acid injection.
3. Switch from a basic fertilizer to an acidic fertilizer.
4. Apply iron sulfate (FeSO4.7H2O) as a substrate drench. Use 1 to 3 pounds per 100 gallons of water. Wash off the foliage after application.
5. Recheck the pH values to make sure they are within the acceptable range.

Little or no Fe provided through the irrigation water. 1. Use a fertilizer that contains Fe.
Don't forget to check out the Plant Root Zone Management (PRZM) Manual for more information! Want to know more? Click here!

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