Host an Event Volunteer Join Tickets

Support the plant database you love!

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

Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

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

QUESTION:

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?

ANSWER:

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

Sap from agave causing reactions from Edgewater FL
April 06, 2012 - Not only was I stuck with the century plant thorns and needle like ends when I was digging up its pups, but I also broke the carrot-like root of a few when I was transplanting and got the white sap on...
view the full question and answer

Century plant dying after bloom
April 06, 2006 - Help!! I want to save my Century Plant from dying. I have already lost one and I don't want to lose this one. Can cutting the stalk before it gets too big save this beautiful plant? Please, pleas...
view the full question and answer

Runaway Agave Americana from Pacific Palisades CA
April 29, 2013 - We live near open space on Santa Monica Mountain State Park. Our Association planted non-native, invasive Agave Americanas all over the adjacent slopes, and we are trying to get the exploding pups and...
view the full question and answer

Controlling Cochineal Insects on Cholla Cactus
July 07, 2011 - We have cochineal insects on a cholla cactus. Will they kill the plant? What should we do to get rid of them if water spraying them won't work?
view the full question and answer

Problems with Strawberry Hedgehog cactus from Temple TX
June 03, 2012 - I had purchased a Strawberry hedgehog Cactus (echinocereus stramineus) a few years ago from the Wildflower Center's annual plant sale and planted it then. It has now started to brown from bottom to t...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.