Collapsing building © Daniel FriedmanFungal / Mold Growth on Prickly Pear Cactus
Opuntia Mill.

  • CACTUS, NOPAL PRICKLY PEAR MOLD - CONTENTS: what genera/species of mold commonly grow on or injure cactus plants (family Cactaceae) such as the Mexican Nopal or prickly pear cactus (photo at left, - Opuntia Mill. ) and Saguaro in the wild as well as cacti in landscaping, gardens & kept as houseplants ?Photographs of mold growth on the Nopal cactus, Opuntia Mill.What are the causes, cures, & preventive methods for cactus mold?
  • POST a QUESTION or READ FAQs about problems with mold growth on cactus plants: cactus mold identification, cactus mold causes, & cactus mold remedies
  • REFERENCES
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Investigation of mold growth on the Nopal cactus and treatments for cactus mold contamination or growth:

The Mexican Nopal, or in English "prickly pear cactus" or "Barbary Fig cactus" is a member of the group Opuntia Spp. within the Cactaceae family. Mold growth appears to be more common on cactii such as the Nopal when growing in higher and less arid regions such as the village of la Yerbabuena, near the foot of the volcano above Colima, Mexico.

This article describes mold growth on the Mexican Nopal cactus plants in the wild and on those grown as a food crop. With a fungal growth sample collected from Nopal growing in Yerbabuena, Colima Mexico. in 2011 we began seeking an accurate identification of the fungus, and an exploration of its properties both on the plant and as a possible seasonal contributor to the aerobiological milieu.

Our project will also investigate and document the causes and effects of mold infection of Mexican pricklypear cactus plants, and the identification of other mold genera/species commonly found growing on and affecting those important plants.

Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.

Mold Growth on Cactus: genera/species of mold that infect cactus plants

Mexican Nopal pricklypear cactus Tuna fruits (C) D FriedmanDaniel Friedman

The Mexican Nopal, or in English "prickly pear cactus" or "Barbary Fig cactus" is a species or group of species of Opuntia Spp. within the Cactaceae family. While some sources [22] claim over 200 species in that group, the USDA lists 59 species and 75 accepted taxa within the Genus Opuntia Mill.[20]

I am particularly interested in fungi found on species of Nopal found at altitude in more wet or humid highlands of Mexico.

These include fruit-bearing pricklypear species (Opuntia ficus indica) that are widely used as a food (both the cactus fruit or Tuna and the younger cactus pads or nopalito) and drink product (an intense purple juice in water) in Mexico as well as an export product in the form of Nopal fruits, Nopal juice, and in power and cosmetic forms. [22]

Some might think that because cactus plants generally grow in dry locations that they never suffer from fungal attack, but that's certainly not the case.

The page top photograph of a mold-infected Nopal (pricklypear) cactus plant was taken in Yerbabuena, Colima Mexico. Yerbabuena is a tiny village located at a comparatively high altitude and close enough to Mexico's Pacific coast to receive more rainfall than some other areas of the country.

I have observed both superficial fungal growth on the intact skin of cactus plants and plants injured or destroyed by fungal attack. Experts report fungal invasion of cactus plants by other vectors such as through wounds, cuts, and direct penetration of the cactus.

Black mold on a Nopal cactus in Yerba Buena, near Colima, Mexico (C) Daniel Friedman

Above: small round black fungal colonies on a Nopal in Yerba Buena in Colima, Mexico.

Also see MOLD GROWTH on SURFACES, PHOTOS - What Does Mold Look Like on Various Materials & Surfaces? An extensive photographic guide to mold as it is found growing on various building materials & surfaces.

Appearance of Mold on Cactus: on the plant & under the microscope

Black & Other Dark Colored Molds on Cactus Plants

Cactus mold growth at 1200x (C) D Friedman

Mold growth on cactus is more common in areas where cacti such as the Mexican Nopal (below left) grows in higher and less arid regions such as la Yerbabuena, near the foot of the volcano above Colima, Mexico. (Photographs by DF, la Yerbabuena, Colima, Mexico, November 2011) Pricklypear cactus (Opuntia Mill. are also found in the U.S. in Florida and Hawaii as Opuntia cochenillifera.

Our Mexican Nopal cactus mold photo (at left, 1200x) seeks expert help with confirming its identity, and is discussed below.

Below (right) and tentatively identified as a Lasiodiplodia theobromae -like fungus are microscopic images (approximately 600x) of the mold we found growing on the Mexican Nopal cactus.

The conidia (spores) are obovate to pyriform, with a thick cell wall, dark brown, smooth, with a single transverse septum near the base. They appear to grow in opposed pairs on either side of the hypha. The upper larger segment of the spore is generally darker than its base.

We also found, no surprise, species of Cladosporium sp. on this cactus surface. Some experts report that superficial molds such as powdery mildew may appear on some cactus houseplants. Mildew on cactus will appear white or gray-white and is principally a cosmetic issue. [1]


Photo of mold on Nopal cactus, la Yerbabuena, Colima, Mexico  (C) Daniel Friedman Photo of mold on Nopal cactus, microscopic image ca 600x (C) Daniel Friedman

Lab microphotographs and work to identify the black cactus mold shown above are in process - Ed.

Photo of mold on Nopal cactus, microscopic image ca 600x (C) Daniel Friedman

Question: cause & treatment for black mold on cactus

(Feb 5, 2015) Darlene said:
I have a Suharo that looks healthy but it has several hard black circles close to the bottom of the cactus. Is the mold? and what should I do to stop it?
Thanks

Reply:

Darlene

Over-watering or too much shade are factors that can increase the risk of mold growth on a cactus but of course by e-text I can't see what's going on with your plant.

If you like use the email found at our CONTACTS link (page bottom) to send me some photos of your Saguaro (Carnegiea gigantea) cactus common in the Sonoran desert and in the Organ Pipe Cactus National Monument in the U.S. A 5-armed sajuaro is likely to be as much as 200 years old.

Below is a photograph of round black fungal attack on a different cactus, the species discussed on this page, the Nopal.

Round black "circles" or fungal attack on a Nopal cactus (C) Daniel Friedman

List of fungi associated with cactus plants

Mold colony on cactus (C) D FriedmanAt left our photo shows a typical colony formation on the surface of a cactus plant, viewed by stereo microscope. Here are some of the many fungal species associated with cactus plants and/or the soils around them.[16] Keep in mind that many fungi may be helpful to certain cactus species both in soils and at cactus roots and at other plant locations or in controlling cactus pests[13][19].

But some fungal genera/species are indeed reported to invade or attack and damage or even kill cactus plants including:

Comment: Apressoria or hyphopodia on cactus

(Sept 8, 2015) Ludovic said:
The mold you show here is none of the one suggested. The peg-like projection from the darkly colored hyphae are called 'appressoria' or 'hyphopodia', used to anchor on their substrate and also suck up nutrient from it. The ones you show are characteristics of epiphyllous fungi in the Orders Meliolales (or black mildew) or Asterinales, depending the ascoma (=fruiting body, spore containing structure) associated with them. Did you find big spore with 3 to 5 cells (Meliolales) or small spore with only 2 cells (Asterinales)?

I love fungi but I have no idea how to treat plant that carry them. It seems to me that these fungi proliferate in particularly wet places (tropical?). I saw many of them on almost all sorts of plants in some very wet part of Costa Rica. I dont know if that will help.

Reply:

Thank you Ludovic, I've continued to collect fungal growth from succulents, particular cactus plants in central Mexico. From the in-situ look these do not seem to be a mildew - the surface is very scaly and hard. When I'm back I'll take a look through the microscope to see what spores we can isolate - if any. Possibly during wet weather they'll make a cameo appearance. But generally these are appearing at various altitudes up to 7000 ft but in a usually-dry climate.

I'd be grateful for any citations / references you can add for cactus-infecting cacti.

White & Light Colored Mildew & Other Molds on Cactus Plants

Mildew on a Jasmine plant, closeup (C) Daniel Friedman

White stuff found on both indoor and outdoor plants (photo at left) including cactus plants may be mildew,

If the cactus is being kept in a too-wet or too-humid environment. Mildew infection of a cactus is more likely for plants grown out of their native (dry) environment, and when the cacti are kept close to other mildew-infected plants.

Because the skin on most succulents is so thick, mildew may do less damage to a cactus than to other plants.

However other white and light colored molds found in buildings and on some plants can be harmful to people and animals as well, such as some species of Aspergillus sp. and Penicillium sp. See WHITE MOLD PHOTOS for photographs of white mold growth in buildings.

Other "white stuff" we see on cactus plants may be a left-over deposit from having sprayed or washed the cactus plant with vinegar or other solutions.


Mildew spores (C) Daniel Friedman

Watch out: some "white stuff" on cacti and certainly on other plants may be mealybugs not a fungal infection, but deserving action.

Our photo (above left) shows what mildew spores look like under the microscope.

Photographs of mildew on plants are at MILDEW in buildings ? and advice on curing & preventing mildew on plants is at MILDEW REMOVAL & PREVENTION


Treatments for Cactus Mold Growth

Some, perhaps most molds molds observed on cactus plants may not actually harm the plants but may remain a cosmetic issue for hobbyists. Popular cactus mold cures include:

Question: treatments for white fungus on cactus

(May 20, 2014) mark said:
White mold or fungus treatment on Nepal cactus

(Oct 11, 2015) steven said:
have a 12 foot cactus and i see white mold on it. How do I save it or is it doomed?

Reply:

Mark, I guess you meant to type Nopal. Indeed there can be more than one genera/species of fungi on a plant, or the same fungus may appear differently at different growth stages.

I'm doubtful that a spray fungicide is the best approach for the plant - at least not before diagnosing the cause of the fungus growth. For example an over-wet plant may continue to have trouble.

Australia's Garden Web (www.au.gardenweb.com) has listed these fungicides used successfully on cactus plants

Benlate
Fongarid
Hortico Rose dust fungicide and insecticide
Sulphur powder
Yates Garden Spray insecticide fungicide

Depending on where you live, different products may be available.

Watch out: if you are harvesting nopal for food use be sure to read the MSDS and toxicity data for the fungicide that you are considering.

White "Mold" on Cactus that is Cochineal, Not Mold

Cochinilla en Nopal, Artes de Mexico, El Nopoal, No. 59 at InspectApedia.comReader Question: tons of white mold on cactus trees

2016/08/22 Jane C. Ti said:

Dear Cactus Specialist, Our Cactus trees which are about more than 12 ft. tall, & they did have pink fruits, guess = Prickly Pears; are all sick with tons of white mold, please see the attached picture. Would you please advise me, regarding: how to rescue these poor sick ones. Thanks in advance! Sincerely looking forward to hearing from you at your convenience! Desperately, Jane

Reply:

[Click to enlarge any image] Shown here, la Cochinilla (Cochineal) on a Nopal cactus, illustrated in "el Nopal", Artes de Mexico, No. 59.

Jane:

With regret, I'm a cactus-interested investigator but not a cactus expert by any means.

Your description sounds like one of the species of Nopal or prickly-pear cactus (Opuntia is the "prickly pear cactus" genus in the cactus family, Cactaceae). There are about 90 species of Opuntia.

You can use our page bottom CONTACT link to send us photos for posting or comment.

From what I've read as an amateur, fungal diseases on cactus plants are difficult to treat, in my opinion largely because the fungus is environmentally caused - all molds are everywhere all the time: it's the local condtions that make a mold flourish and become a problem.

Fungal and parasitic attack on Nopla and Organos cactus, Pozos, Guanajuato, Mexico (C) Daniel FriedmanIn the left of this photo you see a light gray-white fungus on the nopal and a common parasite climbing on the organos cactus in the right of the same image. These cacti were photographed in Pozos, in Guanajuato, Mexico.

At least one cactus "expert" (cactiguide.com) gives the depressing advice that you give up, take a clean healthy cutting and start a new plant. In my view that's not gong to cut it if problem source in the local environment - too much water, shade, or something else isn't also found and corrected. I'm doubtful that a fungicidal spray will be effective for dark scaly mold damage: the cacti I've examined with such black or dark molds were almost impossible to clean of mold growth.

But here's the good news. Often a white "mold" or "fungus" people think they see on cactus is not a fungal disease but rather an insect. In fact often a white fuzzy "deposit" seen on Opuntia is cochineal (Dactylopius coccus) a scale insect in the suborder Sternorrhyncha, from which the natural dye carmine is derived. Cochineal produces an intense red dye whose cultivation in pre-hispanic Mexico and whose later production was kept secret by the Spanish in Mexico.

Without over-pricking yourself, scrape off a bit of the white stuff and rub it between thumb and forefinger. If your fingers become stained with an intense red dye, that's Dactylopius coccus (some texts refer to it as a "mealybug" ).

If that's what's on your cactus you might be able to clean it off with a soft long-bristle brush and dish soap or an insecticidal soap. I'd avoid very strong power washing as it's likely to damage the cactus itself. Locally here in San Miguel de Allende our jardinero expert uses neem oil on several plant species to resist insect attack.

Other Pricklypear Cactus Nopal or Tuna Photographs

Photo of mold on Nopal cactus, la Yerbabuena, Colima, Mexico  (C) Daniel Friedman

Nopalitos are sold in local markets as well as larger supermarkets and are exported as well. The young nopalito pads are harvested and cleaned of thorns for sale. (Left and below left).

Nopal is sliced into strips or diced, then cooked alone (boiled or grilled) or with a mixture of onions and other herbs, and consumed as a vegetable.

The Nopal fruit or Tunas (see photo near page top and below right) are harvested using a long pole on the end of which may be a forked nail-pair used to hook the fruits. Tunas may be peeled and eaten as a fruit but quite often are immersed in water, on occasion with added sugar, to make a fruit beverage.


Photo of mold on Nopal cactus, la Yerbabuena, Colima, Mexico  (C) Daniel Friedman Photo of mold on Nopal cactus, microscopic image ca 600x (C) Daniel Friedman

Directories of 6 atlases or indices of building mold

...


Continue reading at CACTUS MOLD Article Sumary & Abstract of the article above published by PAAA, or select a topic from the More Reading links or topic ARTICLE INDEX shown below.

Or see MOLD CONTAMINATION IN BUILDINGS

Or see PAPAYA WHITE GROWTH

Or see San Miguel de Allende - 88 Great Photographs

Suggested citation for this web page

CACTUS, NOPAL PRICKLY PEAR MOLD at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

More Reading

Green link shows where you are in this article series.

INDEX to RELATED ARTICLES: ARTICLE INDEX to MOLD CONTAMINATION & REMEDIATION

OR use the Search Box found below at Ask a Question or Search InspectApedia

...

Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Questions & answers or comments about problems with mold growth on cactus plants: cactus mold identification, cactus mold causes, & cactus mold remedies.

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Publisher's Google+ Page by Daniel Friedman

Click to Show or Hide Citations & References

Support InspectApedia.com & See Fewer Advertisements

From Google's Contributor website: Contribute a few dollars each month. See fewer ads. The money you contribute helps fund the sites you visit.

Google-Contributor supports websites while reducing advertisements. You can support InspectApedia with a contribution of any amount you wish. Or you can contribute nothing and we'll still keep our website free to all readers - supported by advertising. Either approach is OK.