This is classic nutrient deficiency, probably caused by insufficient available iron in the soil. This is usually much more of a problem with certain plants grown in unamended desert soils in desert landscapes. It will be even more marked if the soils are kept continuously wet and located in a southern- or west-facing exposure. Plants like Indian hawthorn grow best in relatively rich soils with plenty of organic matter. They don’t do well in desert soils without organic matter. You can try using fertilizer sprays of iron to see if you make it green again. Soil-applied iron fertilizers will not perform well this time of year. It’s best to use soil-applied iron fertilizers in late winter or early spring when the plant is first starting to grow. Iron doesn’t move well once inside the plant. Indian hawthorn is notorious for not responding well to iron sprays because of the leaf surface. For this reason I would also purchase a spray additive, called an adjuvant or spreader, to mix with the i