While at first glance this may look like your classic excessive moisture symptom, after looking a little closer it actually appears to be quite the opposite. Considering the chlorosis is mainly present on the inter-veinal parts of the foliage I ruled this out to be a nutrient imbalance instead. Most likely deficient in either iron or manganese since the chlorotic areas are between the veins, while the veins themselves remain green. It's also common for manganese deficiency to cause dead spots and patches. How could this happen? I have a few theories:1. Excessive rainfall could've washed away the nutrients from the soil.2. Period of drought; plants need water present in order for the roots to extract available nutrients in the soil as soluble salts.3. Nutrient cycle above ground could've broke. Right next to this small group of plants was a very large tree that was clearly deceased, with only some growth left at the top (probably 60 feet up). Since nutrients can come from dead leaves, wood, and animal droppings that break down in the soil- the presence of this matter being significantly decreased could've contributed to these symptoms.