Hello everyone, I need a little help from the pro's!

My Meyer Lemon seems to be showing signs of a nutritional deficiency. It looks to me to be either Magnesium or Manganese but would like your opinions. Pretty much every leaf on the plant looks like the ones in the photo. All other citrus look ok.

Fertilizer seems to have the minors needed:
(Vigoro WSP 24-8-16) includes:
Boron – 0.02%
Copper – 0.07%
Iron – 015% (chelated)
Manganese – 0.05% (chelated)
Molybdenum – 0.0005%
Zinc – 0.06

Fertilizer program:
Growing months 1tbs per gal once a month
Winter – ½ tbs per gal every two months

Meyers leaves



OTHER CITRUS




Thanks for any help you can provide!

It is not magnesium deficiency. Is the nitrogen in your fertilizer derived from Urea? - Millet

I think Millet's on it -- biuret toxicity from inadequately purified urea in the fertilizer.
Malcolm

I strongly suspect that the seasonal temperature regime has a lot to do with those kinds of symptoms rather than the Bieuret in urea. I get those on my inground Meyer lemons, other types of lemons, Calamondins and kumquats every year, every winter,and yet I don't apply any urea fertilizer. Believe me, I know how to read fertilizer labels, more than the average graduate student.

These symptoms disappears as the season warms up and the juices on the trees flowing faster. In my case, this is something that naturally happens every year, and if you're not comfortable with this phenomenon, you can always remedy via foliar application.

Of course, if you still get these and your temperature range is 55 deg F min to 85 deg maximum in a greenhouse or solar room, then that is the only time to think about bieuret toxicity. With winter season still in full swing when you posted this problem, think about that such slow root activity and metabolism, and the diurnal fluctuation can cause imbalance in supply and demand such that plants cannot cope up.

If you citrus gurus notice, this is seldom observed withe oranges, mandarins and clementines, but common with lemon types and cold hardy citruses such as Yuzu, Fortunellas, Trifoliate... Why? Think about ecological adaptation...

I'm not sure but I think the yellowing caused by biuret toxicity ever goes away. I have a tree that the leaf tips turned yellow from biuret, and stayed yellow. - Millet

Joe, looking up Biuret Toxicity in the Compendium, it does state that leaf yellowing caused by biuret toxicity is permanent. The leaves will never regreen.- Millet

Fully agree with you there Millet! I was only referring to the original problem that if it disappears as the environment warms up, then it probably isn't biuret toxicity. If the symptoms are permanent, then it most probably is biuret toxicity. I'm just leaving some miniscule chance for the possible effects of other immobile micronutrients which can also have permanent symptoms.

A guess concerning the yellowing symptoms that you are seeing, that go away when the temperatures warms, is probably a nitrogen deficiency, that is commonly caused by cold weather. Nitrogen up take is slow during the winter, but increases as the weather warms. - Millet

Millet, the label states:
Total Nitrogen 24%
3.1% Ammoniacal
1.2% Nitrate
16.1% Urea
0.9% Other WS Nitrogen
2.7% Water insoluble Nitrogen

I have the plants on my screened-in porch, one wall is screened to the outside, the other three walls are part of the house. I have 1 mil plastic covering the screen during the winter months. The temps range anywhere from 32-33 at night (when temps outside get into the teens) to 80 in the daytime. There is an overhead fan and water fountain to help with humidity.

I did do a foliar feeding last week, should I maybe do this more often in the winter?

Thanks for your help,
John

As suspected, the fertilizer is high in Urea. Urea is the problem. Citrus is much more susceptible to biuret than other fruit trees. - Millet

Interestingly, if you don't mind the symptoms, the tree likely will grow just as fast and bear just as much fruit as if it didn't have those symptoms. But if you want nice green leaves, just switch to a zero-urea fertilizer, or a different brand that has more highly purified urea -- pure urea does not cause the problem; just the biuret which is a contaminant from the manufacturing process, which has not been adequately removed.

Thanks everyone, I knew the solution would be found here!

I will be going back to my old fert, I had just switched over to this stuff last summer.

Should I flush the pot a few times to remove salt and other unwanted buildup in the soil?

John

"Water Soluble Organic Nitrogen" virtually always means "urea." And there's nothing wrong with urea per se, IF it is very low in biuret. They may or may not tell you that on the label. So it's easiest to avoid urea altogether, for containerized citrus.