Older Agave Yellowing and Not Looking Healthy

Q. My agave is 10 years old and just isn’t looking healthy. I’m afraid of losing it and the surrounding plants. Can’t figure out if it’s too much or too little water. Your expertise would be appreciated.

Not a whole lot of information but I am guessing it's a watering issue. Agaves are usually from the desert Southwest. But it could be agave weevil that damaged the plant earlier in the year.

A. Most problems with agaves are from boring into the trunk and roots by the agave weevil and less to do with water. Eventually the immature forms of this insect tunnel into the base and trunk of susceptible plants. Look for them.

Agave weevils give birth through their eggs to destructive smaller grubs about 3/8 inch long. They infest the trunk and roots of agave and a few yucca. Look for their damage on older plants later in the year.

This is one of the many types of American agaves showing collapse of the leaves due to probably agave weevil.

All agaves should have a systemic insecticide applied by spray or soil drench in the spring, no later than March or early April. With spray insecticides it’s important to spray the lower leaves and the surrounding soil at this time. With soil drench insecticides it’s important to apply it to the soil immediately around the plant at the appropriate time. American agave, in particular, is very susceptible to this pest. Be sure the appropriate insecticide is used by reading the label.

Example of a liquid garden systemic insecticide that gives at least a couple of months control of insects (picture taken from Amazon)

            The agave weevil lays its eggs in susceptible agaves and some yucca when temperatures begin warming in the spring. These eggs are laid by the agave weevil inside the lower leaves, close to the trunk, around that time. A single application of a systemic insecticide is needed around that time. I don’t know of any proven organic methods that control this insect.

            If you are still concerned about watering and drainage, make sure that these plants are not watered daily. All perennial plants need the soil to drain away from their roots. Some plants like agave and cacti should never be planted at the bottom of a ridge. Tops are usually okay but not bottoms. Too much water accumulates in those low spots for agave. Other plants may need a continuous moist soils not most agaves and other plants that originate from the desert Southwest.