En EspaŅol

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
rate this answer
Not Yet Rated

Friday - June 06, 2008

From: Austin, TX
Region: Southwest
Topic: Cacti and Succulents
Title: Leaves turning black on Agave americana
Answered by: Barbara Medford


Dear Mr. Smarty Plants- We have a ~5-year-old agave americana that began to have leaves turn yellow (to black in some areas) just this past spring (2008). A neighbor's tree had started to overhang the plot it was in, putting it in substantial shade, so I cut away several large branches from the tree, thinking that lack of sun could be part of the problem. Is there anything else I can do?


We really hate it when someone asks us about an obvious problem with a plant, and when we do research we are told this plant has "no serious pests and diseases," which is pretty much what we got on your Agave americana (American century plant) spots. One thing we did find out, from our own webpage (link above) is that the Agave can tolerate light shade, but really needs sun. But, we did find two websites that admitted there could be anthracnose, a fungal disease, in agaves that could cause those spots.

Michigan State University Extension Agave Disease Problems

Arizona Cooperative Extension Problems and Pests of Agave - This is a PDF document, and you will have to page down to Page 6, lower right hand column, for "Fungal Lesions." Anthracnose of agaves is discussed as a problem during moist conditions or occasionally when the garden is overhead irrigated, as in a sprinkler system or too much rain (hardly a problem right now in Austin). Unfortunately, a plant in too much shade will be more prone to fungal diseases because the sun would ordinarily retard the fungal production, drying out the moisture on the plant. The advice given for treatment is to remove the diseased leaves. And let us warn you, we have discovered that there can be severe and uncomfortable skin blistering from contact with the juices in the leaves when they are cut. Go prepared in long pants, long sleeves, heavy leather gloves, closed-toe shoes and maybe even protective goggles. Once a leaf has gone black, you can be pretty sure it is dead and needs to be removed and disposed in such a way as to prevent further spreading of the fungus to other succulents. This site did suggest one possible chemical treatment, but stated that its actual efficacy is not substantiated. We tried to find pictures of agaves with the anthracnose spots, so you could compare them to your plant, but were unsuccessful. In summary, more sun, less water, and cut out the affected leaves - VERY CAREFULLY!


More Cacti and Succulents Questions

Plants for pool area in Florida
May 09, 2008 - My husband and I have a pool with 4 planters and are looking for plants that we can put into our screened in pool area. We live in Central Florida and looking for ideas of plants that are slow growin...
view the full question and answer

Plants for hanging flower boxes from Austin
July 27, 2013 - I have two long flower boxes 17" x 15" x 25 feet long one on the north side of the apt and one on the south made of metal suspended about four feet from the ground. One will get the morning sun and ...
view the full question and answer

Hanging plants for Austin, TX
May 18, 2014 - I'm looking for a hanging potted flower suggestion for Austin. Most locations are shaded under a large tree, but some locations may have several hours of afternoon sun. I'd love to see some hummin...
view the full question and answer

Native plants of Taos and Los Alamos NM from Houston
April 07, 2012 - Hi, Mr. Smarty Plants, can you recommend a guidebook for the native plants of the Taos/Los Alamos region? (I'm most interested in forbs.) I'll be headed there in May--is there anything I should es...
view the full question and answer

Potted crown of thorns cactus cold tolerance in Marble Falls, TX
December 02, 2009 - I have a large potted crown-of-thorns cactus. Can it remain outside this winter in the Texas Hill Country?
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2015 Lady Bird Johnson Wildflower Center