Dear Cecilia Lutz

a candidate for some environmental stress rather than a pathological or disease related issue. The affected areas on the leaves may be related to a nutritional imbalance (phosphorus deficiency, yellow due to nutrient deficiencies, Several Deficiency Symptoms Iron, Manganese and Zinc together) or a root malfunction in the plant or even a contact type injury from something applied/sprayed to the soil or directly to the leaves.  You may consider having the soil tested for nutrient availability and reviewing any chemicals applied to the foliage (such insecticides against whitefly, picture show traces).  Watch the new leaves as they form for the same symptoms.  If they look OK, then this fading and curling may be temporary.  Also check closely on both sides of the leaves for any insects.  You may also snip off a few affected leaves and show them to your local plant nursery or garden center for their comments since these folks may have seen these symptoms before. Also freezing weather , possibly caused by poor drainage, overwatering. For  all disease Symptoms http://www.bioversityinternational.org/uploads/tx_news/FAO_lBPGR_technical_guidelines_for_the_safe_movement_of_citrus_germplasm_501.pdf

http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1492.pdf

Hoping this will be helpful            

Regards

Prof. Houda Kawas

Dear Cecilia Lutz

a candidate for some environmental stress rather than a pathological or disease related issue. The affected areas on the leaves may be related to a nutritional imbalance (phosphorus deficiency, yellow due to nutrient deficiencies, Several Deficiency Symptoms Iron, Manganese and Zinc together) or a root malfunction in the plant or even a contact type injury from something applied/sprayed to the soil or directly to the leaves.  You may consider having the soil tested for nutrient availability and reviewing any chemicals applied to the foliage (such insecticides against whitefly, picture show traces).  Watch the new leaves as they form for the same symptoms.  If they look OK, then this fading and curling may be temporary.  Also check closely on both sides of the leaves for any insects.  You may also snip off a few affected leaves and show them to your local plant nursery or garden center for their comments since these folks may have seen these symptoms before. Also freezing weather , possibly caused by poor drainage, overwatering. For  all disease Symptoms http://www.bioversityinternational.org/uploads/tx_news/FAO_lBPGR_technical_guidelines_for_the_safe_movement_of_citrus_germplasm_501.pdf

http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1492.pdf

Hoping this will be helpful            

Regards

Prof. Houda Kawas

Dear Cecilia,

I agree with prof. Kawas and suppose it is a physiological disorder.

REgards, Franci

Hi Cecilia : if you had treated the plant with any chemicals of fertilizer it will give same symptom as toxicity. I don't think is a pathogen symptom

Hi Dr.Cecilia,

This may happen due to lack some nutritional, or the evaporation very higher that imbalance

Thanks for all the answers!!! They were very helpful!

... I found similarities with some problems with boron (toxicity).

Regards!!

You most welcome

Houda

Hi Dr.Cecilia,

You are welcome

Sincerely

 Dr. Cecilia,

   Very good after noon, this symptom showed iron deficiency Boz  vein clearing also appear on leaves. Control-solution of ferrous sulfate @ 0.5% spray

Dear Cecilia I agree with the nutritional disorder hypothesis proposed by Dr. Kawas. You can make a foliar test for to compare the nutritional content in leaves and all plat. Also check the presence of some pathological symptom. Please see: 

http://ipm.ucanr.edu/PMG/C107/m107bpleaftwigdis.html

http://www.dpi.nsw.gov.au/content/agriculture/horticulture/citrus/management/nutrition/quick-reference-guide

http://www.haifa-group.com/files/Guides/Citrus.pdf

Dear Cecilia, The Apical symptoms with interveinal chlorosis is somewhat typical for iron chlorosis. Take a reading of the soil pH and if it alkaline your are probably dealing with iron chlorosis. As addition confirmations take a ten leaf sample from the apex region and due the atomic spectral analysis to see defiencies and excesses. If it is indeed a iron deficiency I would use sequestrene iron chelate according to instructions and you may want to change the pH of propagating medium to avoid the problem in future testing. Iron deficiencies are common at over 7.3 pH and not using an issue if the medium is 5.7 to 6.7 pH. Hope his is helpful. PRH

Dear Cecilia Lutz,

The optimum pH range for Citrus is 5.5-6.8. At this pH range the iron is ready evailable for plants. Do chek the nutritive elements in soil first..What is about bottom leaves? Do they senesce? Place few leaves into humid chamber (plastic sack) to look for fungal infection. If case of fungal growth, you should carry out mycroscopy to identify the fungus and its sensitivity to fungicides.

Its may be blight disease. SO you have to go for isolation techniques.

Dear Cecilia, it looks more like a manganese deficiency displaying a typical spider network of green veins in comparatively yellowish background. Another problem with such leaves displaying such symptoms , if you analyse them  through leaf analysis chemically , it will show deficiency of more than one nutrients ..