Interveinal chlorosis of the new leaves usually means iron problems. A few scattered rosemary plants had symptoms and they had one thing in common. They were under a dripping irrigation nozzle that kept the substrate overly saturated and may have limited the plant from obtaining iron. In addition, lime had been added to the top of the pot and the dripping water helped make it more available to increase the substrate pH.
On a recent extension trip, we were able to scout an impressive crop of rosemary plants being grown in the shape of Christmas trees. Three plants out of 20,000 isn't much. Those 3 plants all had interveinal chlorosis of the new leaves.
These are typical iron (Fe) deficiency symptoms. All three plants also had in common that they were the only ones exhibiting symptoms and they were being grown under a dripping irrigation nozzle. All of the surrounding plants were normal green. This was a case of excessive moisture limiting Fe uptake by the plant. In addition, a dose of limestone had been added to the top of the pot.
It appears the extra moisture helped make more of the limestone available to modify the substrate pH. A pourthru test found the pH to be elevated at 6.6. Similar symptoms can also develop in the case of another physiological disorder caused by cold growing conditions, abiotic factors such as root rot, and the less common Fe deficiency due to inadequate levels being provided.
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