Answer: Unfortnately, based on your description I am not able to diagnose the problem for you. Geraniums are potentially subject to a wide range of disease problems that could cause both spotting and yellowing, and they are also sometimes subject to soil deficiencies that can cause discoloration. I would suggest you consult with your local county extension to obtain a more specific identification of the problem, and based on knowing that, decide what to do. If a chemical control is needed, they will have the most up to date information on what to use and how/when is best to apply it for maximum results.
In the meantime, remove the affected foliage and dispose of it in the trash to limit sources of reinfection in case it is a pest or disease problem. Avoid wetting the foliage when you water. You could also top dress with a good quality compost and try a foliar feed with a water soluble fertilizer such as 10-10-10 plus micronutrients to see if that helps at all. Read and follow the label directions for how much to use. Also, keep in mind that geraniums need lots of sun and good air circulation to do well.
Good luck with your geraniums, I'm sorr y I can't be more specific long distance.
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