Discolored leaf contour


My Pyracantha shows a diffused discolored contour of its leaves. Some have also dark dots on the discolouration area. The center remains green.

Fertilisation is done correctly with a combination of Biogold monthly and, Humic acids + Aminoacids + Kelp every other week. Soil is Akadamaa and pumice. Light is abundant as they are kept in plain sun on the terrace. Does anyone know what it could be?

Wow… that is a lot of fertilizer! I have attached a link to leaf scorching.
Dealing With Leaf Scorching and Tip Burn (thespruce.com)
One of the causes is salt burn from excessive fertilizer. Alkaline water, excess sun, and overspray of lawn or garden chemicals are all possible causes as well. If you only water when the soil is getting dry, and protect from intense sun, then a chemical cause is the main suspect. Do you use the fertilizer to gain rapid growth? It may be beneficial to review the Fertilizer 101 live stream. Fertilizer 101 | Bonsai Mirai Live

Learn lots, share with others, steal ideas from the best!

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Thanks Bob, the link offers a very interesting summary.

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I only use organic fertilisers, so the risk of creating excessive salt should be limited. It is not a period of the year with too strong sun… excessive light/heat should not be the case even if it is in full sun. I suspect it could be the recent application of Ridomil Gold (metalaxil-m fungicide) even if I have used it already in the past at the same dilution… so I am doubtful.

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