Chlorosis is a symptom of failing plant health. It could be serious or minor, depending on the cause. It is a loss of chlorophyll in the leaf, causing a yellow appearance throughout the entire leaf. Interveinal chlorosis is a yellowing of the leaf, but with a distinct difference from simple chlorosis; the veins of the leaf remain green.
If left untreated, interveinal chlorosis can be detrimental to the plant. If it is a crop where leaves are important, such as spinach, the entire crop could be lost. If it is an ornamental or commercial crop, there is very little sales appeal to a plant with interveinal chlorosis. Even if it is just a houseplant, interveinal chlorosis can affect proper functioning of the plant leading to early decline, poor blooming and even poor yields.
Symptoms - As mentioned above, interveinal chlorosis is a yellowing of the leaves that only occurs on leaves where the veins still have chlorophyll. Chlorosis of the whole leaf is a nitrogen deficiency and is easily treated.
Causes - The potential causes of interveinal chlorosis are numerous; some chemical, some physical. Any of the following can potentially cause interveinal chlorosis: iron, manganese or zinc deficiencies, pH above 7.0, too much organic matter, too high of an EC, toxic levels of certain nutrients including phosphorus, copper, zinc or manganese, poorly drained or compacted soil, contact with herbicides, girdled roots, and competition from other plants. The surest method to determine the cause if it is not evident, is to perform a soil analysis, or an analysis of the nutrient solution if growing hydroponically.
Remedies - The corrective measure(s) will depend on the cause(s). In some instances, just adding appropriate amounts of the deficient nutrient will resolve the issue. If the issue is too high of a pH, adding sulfur will lower the pH and make iron more available. If EC or specific nutrient levels are too high, leach the soil with distilled water to try and flush out some of the excess salts. If the issue is herbicide contact, girdling roots or too much competition from other plants, the best course of action may be to remove the plant and start over elsewhere.
Why Location Matters
Where the interveinal chlorosis is occurring on the plant is a key to identifying the cause. If symptoms start at the top of the plant or in the new growth, it is very likely to be an iron deficiency. This could mean that there truly is a lack of iron or that your pH needs to be adjusted so that the plant can use the iron that is there. Chelated iron can be added to the soil or nutrient solution if testing indicates that the pH is where it should be, otherwise the first corrective measure should be a pH adjustment.
If the bottom leaves are showing signs of interveinal chlorosis, but not the top leaves, the cause is likely to be a magnesium deficiency. The plant is pulling all available magnesium to aid in development of new growth. A foliar application of magnesium- sulfate should help to clear that up or a dose of a calcium- magnesium fertilizer in the soil or water reservoir will help as well. If a dose of magnesium doesn’t solve the issue, and your plants are in a flowering or fruiting stage, the issue may actually be too much potassium. For hydroponic growers, flushing out the water and adding a fresh, balanced nutrient solution should do the trick. For soil growers, the area around the roots should be flushed with distilled or deionized water to try and leach out some of the potassium if possible. At the very least, cease any application of potassium-containing amendments for the time being.
Nitrogen deficiency may also appear as magnesium deficiency with interveinal chlorosis occurring at the bottom and middle of the plant, but while this is not unknown, it is rare. A shot of any water soluble nitrogen should show if that is the problem. If the yellowing does not reverse, then the problem is not likely to be a lack of nitrogen. Also, nitrogen deficiency is more commonly presented as simple chlorosis versus interveinal chlorosis.