Rent Shop Volunteer Join

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?

Share

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

Thursday - April 05, 2012

From: Fort Worth, TX
Region: Southwest
Topic: Pests, Cacti and Succulents
Title: Insects on yucca from Ft. Worth TX
Answered by: Barbara Medford

QUESTION:

I have a plant labeled Yucca Soft Leaf recurvifolia that I planted about 5 years ago,& was beautiful until last summer when it became infested with thousands of fast, tiny, dark insects. I sprayed with Whitney Farms Outdoor Insect Killer (pyrethins, mostly) and that seemed to kill most, but the plant is reinfested, and the leaves are either dead or pale, light green, & spotty. Can it be saved?

ANSWER:

Yucca recurvifolia does not appear in our Native Plant Database, but this article on the plant from the Master Gardeners of the University of Arizona Pima County Cooperative Extension can give you some information on it. It appears that the reason Yucca recurvifolia does not appear in our database is because it is a synonym for Yucca gloriosa (Moundlily yucca), according to the USDA Plant Profile. Both are native to North America and the southeastern states. Of course, Fort Worth is hardly in a southeastern state, but we can probably address your question by searching on pests and diseases of yuccas.

We should first mention that we are neither plant pathologists nor entomologists. Without that kind of training and without being able to see the plant, about all we can do is give you some references with pictures to help you. We also want to mention that most insects and diseases do not strike healthy plants, but plants that are weakened by improper care, watering or fertilizing.

The Horticultular Site Diseases of Sansevieria and Yuccas:

Arizona Cooperative Extension Problems and Pests of Agave, Aloe, Cactus and Yuccas

The more we read about the problems you are having with your plant, the more we are convinced that the little black bugs are not causing the problem, but that the problems with the yucca are attracting the bugs; that is to say, fungus gnats. Yuccas are desert plants, they need to be planted in a well draining soil, perhaps half of it  made up of decomposed granite. From the article from the Arizona Cooperative Extension Program, scroll down to Page 4 and read the articles under "Poorly-drained soils" and "Irrigation." At the bottom of the same page, read "Fungal diseases." On Page 5, you will find pictures of fungal lesions.

Your final question involved asking if your plant could be saved. Frankly, this is a decision only you can make. It sounds like you need to begin at Square One preparing a planting hole in full sun, amending your (probably) clay soil with a well draining cactus soil and decomposed granite, NOT sand. The gnats are not going to leave until the diseased material is gone, so removing the plant and disposing of it should discourage the gnats. Yuccas are survivors, and it could be that in your excavations, you will find some healthy root to plant a new yucca. From GardenGuides.com, here are instructions on How to Plant a Yucca Root. Just remember, good drainage, plenty of sun, no overhead watering (like a sprinkler system), no fertilizer, and minimal watering.

Pictures of Yucca recurvifolia

 

More Cacti and Succulents Questions

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

Branches of yucca being blown down in Torrance CA
August 19, 2010 - I have a Yucca tree about 30 ft tall. Lately when the wind picks up in Torrance we have had about 3 branches fall out of the tree. Can you help me with this. I don't want to cut all of the branches...
view the full question and answer

Propagation of Agave americana by seed
July 11, 2007 - Dear Mr Smarty Pants, My Century Plant is fulfilling its one wish and blooming flowers from its massive stalk. Although I am very sad to see it go, it is certainly a sight to behold. This plant, ...
view the full question and answer

Removing faded flowers from plants in Georgetown, DE
July 28, 2012 - I bought a chamase rose quartz that was in bloom. now the buds are dead, should i remove them or just leave them on the plant. they wont just fall off. and the tips of the plant has new growth.
view the full question and answer

Mystery cactus in Williamson County, Texas
May 27, 2008 - We have a cactus plant on our place that I have not seen anywhere else in central Texas. The flowers are bright yellow with wine-red centers, but very sparse--only one flower blooms at a time. The p...
view the full question and answer

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