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

 
Daniel Friedman, San Miguel de Allende, Guanajuato, Mexico, 2012

  • CACTUS MOLD Article Sumary & Abstract - 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?
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Abstract: This article describes mold growth on pricklypear or Mexican Nopal cactus plants in the wild and on cactus kept as houseplants. We investigate the cause, cures, & prevention of mold infection of Mexican Pricklypear cactus plants, the effects of mold growth on cactus plants, and the identification of mold genera/species commonly found growing on cactus.

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Cactus Mold

Mexican Nopal pricklypear cactus Tuna fruits (C) D FriedmanDaniel Friedman, San Miguel De Allende, Guanajuato, Mexico

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. An online provides live links to references and to larger images of the photographs herein. See http://inspectapedia.com/Cactus_Mold_PAAA_2012.php

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

Black & Other Dark Colored Molds on Cactus Plants - seeking identification details

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 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.

List of fungi associated with cactus plants

Mold colony on cactus (C) D Friedman

At above left our photo shows a typical colony formation on the surface of a Nopal 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:

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 of a leaf, not cactus) 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:

Other Pricklypear Cactus Nopal or Tuna Photographs

Nopal cactus pads being de-spined and sold in the main market, San Miguel de Allende, 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.


Nopal cactus pads prepared for sale (C) Daniel Friedman Steve Goldstein Nopal pricklypear cactus fruit, squashed to show its rich red interior fruit (C) Daniel Friedman

References:

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