Ask Mr. Smarty Plants

There are over 200 species of Agave that range throughout the desert southwest and into Mexico, and they are adapted for arid environments. They grow in sandy desert soil without rainfall for months at a time. Too much water is probably more deleterious than too little water because the water fills up the air spaces in the soil and the roots can't breathe.

You have been successfully growing the plant for seven years so lets look for things that might have changed this spring; does it still have well drained soil? has the watering changed? is the sun exposure different? What about the lemon tree? Does watering it provide any water for the Agave? Are you using overhead watering (sprinklers)? 

The removal of the leaves earlier may have provided an avenue for infection from insect pests or fungal dsease. This publication of the Arizona Cooperative Extension, Problems and Pests of Agave, provides information about both insects and fungi that can infect Agaves. A shorter description can be found in Agave Disease Problems from Michigan State University Extension.

If your Agave isn't receiving extra water fron the lemon tree, and you find no evidence of insect or fungal damage, you may decide that the plant is stressed due to lack of water (you've only had 3.97 " of rainfall this year). To alleviate these stress symptoms, let a water hose run very slowly at the base of the plant for one morning (2 -3 hours), and then repeat the process two weeks later. If things improve, reduce the watering to once a month. When the night time temperature gets below 61° F, discontinue watering.

It is always good to get advice from someone who can look at the plant, so  I would also suggest that you contact the folks at the Maricopa County Office of University of Arizona Cooperative Extension for some help closer to home.