First, you rip or cut the landscape fabric away (and strongly suggest you plan to remove ALL of it once the azalea has been addressed). The chlorosis is due to lack of iron, so treat with an iron chelate. Directions should be on the label. Finally, it is the soil pH that is creating the iron issue so you will need to lower pH. Sulfur is the recommended product. It takes time for the chemical reaction that lowers pH to happen and it is not a permanent fix. Soils tend to return to their original pH with time, so this is something that will need to be repeated periodically.

You can also fertilize after the bloom cycle with cottonseed meal - a fairly mild organic product that is also an acidifier.

Likely there is enough iron in the soil already, so I would advise against adding more without getting your soil tested first. The alkaline soil makes it biologically unavailable for the plant. Adding sulpher will temporarily change the pH of the soil, allowing the plant to access the iron it needs. I like to throw a handful or two around the base of the plant every 4 weeks or so throughout the growing season.

Since it takes anywhere from 3-12 months for sulfur to lower soil pH (depending on soil type) to not use an iron chelate is just postponing returning the azalea to good health!! If you follow the product directions, you will not create an iron imbalance in the soil as chelated iron is fully soluble and any that is not taken up by the plants will simply dissipate throughout the soil profile.

Using cheated iron to treat a chlorosis issue due to a skewed pH is a well-recommended treatment.

btw, most fertilizers intended for low pH or acid loving plants include iron chelate as an ingredient.

the plants are very shallow rooted.. and ripping out the fabric may seriously affect them ... so be prepared for that ...

if this really is a significant local issue.. yo might want to discuss with your COUNT"Y AG or extension office ... they might have more precise suggestions for your area ..

ken

Agree with Ken...call your local extension service. My training tells me no matter how much iron chelate you out down, the azalea cannot access it due to the current soil pH. I live in Illinois, where we have very alkaline soil. I use the method I described above successfully for years. You cannot change the pH of your soil permanently, but the Sulphur provides a short term solution. Here is an article from my local nursery. Buy, truly, a call to your local extension service will give you the best advice specific to your location.

Sulfur is not a fast short term solution. As mentioned, it takes time for the chemical reaction that results in the change in pH to occur. Precisely how long depends of soil type and the degree of alkalinity but it is not an immediate process by any means. Months at any rate. And in the meantime, the azalea is suffering.

And if you bother to research how chelated iron works, because it is fully soluble and therefore immediately available to uptake by plant roots, it doesn't matter what the current soil pH level is. That is why it is the recommended treatment for chlorosis with ANY soils that are not sufficiently acidic to free up available iron ions.