Some fungal Diseases

Trouble shoot problems you are having with your cactus.
Post Reply
User avatar
hegar
Posts: 4596
Joined: Mon Jan 23, 2006 4:04 am
Location: El Paso, Texas

Some fungal Diseases

Post by hegar »

I have been trying to respond to numerous questions about cactus stem lesions and keep repeating myself. So I thought, it might be a good idea to give a few examples of fungal pathogens - some which do attack cacti and others that infect other plants - on this thread. I hope, that this will help the concerned forum user with figuring out, if a fungus is to blame for the condition of their plant. Keep in mind, that this is only a very limited presentation of fungal pathogens you might encounter.
The major classes of fungi you as a grower will experience are the ascomycetes,(which as immature fungi are split into hyphomycete and coelomycete fungi) and the basidiomycetes, of which the most important group is known as rust fungi. A true rust is a rather rare occurrence among fungi. I am only aware of one time, where a rust pathogen was found on the fruit of a Hylocereus plant. Rust colored lesions on cacti are thus not caused be a rust fungus. I am attaching two images of the appearance of rust pustules, but they were not found on cacti.

First, some of the symptoms/signs of Hyphomycete fungi. The images are labeled with the pathogen and its host plant.
Fusarium sp lesion on Fer_wisliz x7.5.jpg
Fusarium sp lesion on Fer_wisliz x7.5.jpg (70.51 KiB) Viewed 33144 times
Fusarium sp on Chamaedorea sp002.jpg
Fusarium sp on Chamaedorea sp002.jpg (71.61 KiB) Viewed 33144 times
Fusarium sp on F_wislizenii-.jpg
Fusarium sp on F_wislizenii-.jpg (79.92 KiB) Viewed 33144 times
Pseudocercospora sp on Choisya ternata (lower leaf surface)002.jpg
Pseudocercospora sp on Choisya ternata (lower leaf surface)002.jpg (87.59 KiB) Viewed 33144 times
One of the features of a hyphomycete is a fuzzy growth which consists of fungal mycelium from which arise structures called conidiophores, which bear spores that are not enclosed.

The next group is called "Coelomycetes". There the spores are enclosed in a structure made up of fungal cells. Depending on the appearance of these structures (cushion-like, with slit-like opening (acervulus), or spherical structures fully enclosing the spores and often with an ostiolar opening (pycnidium). To indicate the small size of these structures, there is either a ruler in mm or a bar visible on the images.
Pestalotiopsis sp on Opuntia sp stem001.jpg
Pestalotiopsis sp on Opuntia sp stem001.jpg (50.52 KiB) Viewed 33144 times
Stagonospora gigantea  on Agave sp001.jpg
Stagonospora gigantea on Agave sp001.jpg (52.44 KiB) Viewed 33144 times
Just to show you what a true rust may look like, I did photograph two kinds of plant leaves. As you can see, the color is not necessarily rusty brown, but can range from off-white to yellow, reddish brown, all the way to black. The rust found on the Hylocereus was identified as an Aecidium, which tells me, that the spores in the rust lesions were most likely yellow, similar to those shown for the pathogen of Fouquieria splendens (last image).
Malva sp with Puccinia heterospora rust.jpg
Malva sp with Puccinia heterospora rust.jpg (88.75 KiB) Viewed 33144 times
Puccinia vexans on Fouquieria sp. leaf2.jpg
Puccinia vexans on Fouquieria sp. leaf2.jpg (74.46 KiB) Viewed 33144 times

Harald
User avatar
TimN
Posts: 3443
Joined: Mon Aug 06, 2007 9:01 pm
Location: Phoenix, Arizona USA

Re: Some fungal Diseases

Post by TimN »

Dang, that stuff looks scary close-up! I have on occasion gotten rust-colored lesions on a few plants. It's hasn't spread to other plants and I've treated it successfully with commercial sulfur fungicide. The fungus dies, but the scars remain.

I'd always referred to it as rust, but from what you've written it's probably not "true" rust. If I ever have another event, I'll be sure to look much closer.

Good stuff!
Disclaimer: I'm in sunny Arizona, so any advice I give may not apply in your circumstances.

Tim
User avatar
hegar
Posts: 4596
Joined: Mon Jan 23, 2006 4:04 am
Location: El Paso, Texas

Re: Some fungal Diseases

Post by hegar »

I do have another lesion with an identified fungal pathogen. This time the small "pimples" visible especially on the right piece of a prickly pear pad yielded the fungus Neofusicoccum sp. However, the specialist verifying the diagnosis determined, that I was dealing with a saprobe, i.e. a secondary fungus, which may be mildly pathogenic, but infects only dead or dying plant tissue. So the main reason for the lesions could be due to some other agent, not necessarily a fungus.

Harald
Neofusicoccum sp. on Opuntia sp. Cladode2.jpg
Neofusicoccum sp. on Opuntia sp. Cladode2.jpg (72.98 KiB) Viewed 31225 times
User avatar
DesertSun
Posts: 322
Joined: Sun Feb 11, 2018 5:33 pm
Location: Zone 9b

Re: Some fungal Diseases

Post by DesertSun »

Thank you so much hegar! Very helpful!
"The best fertilizer is the gardener's own shadow"
Chinese proverb
User avatar
hegar
Posts: 4596
Joined: Mon Jan 23, 2006 4:04 am
Location: El Paso, Texas

Re: Some fungal Diseases

Post by hegar »

Hello Cactus Friends,

finally, because a member of the Dallas, Texas Cactus Club asked me to help with the diagnosis of a cactus problem, I am now able to add another fungal pathogen to the cactus pest list. This pathogen does form large, almost black looking sunken lesions. The one photographed on a pad of Opuntia basilaris measured 6 cm in diameter and was almost perfectly circular.
The pathogen does have the common name Prickly Pear Leaf Spot and its scientific name is Phyllosticta concava. The lesion does have a characteristic wide light-colored corky margin. When I pushed slightly against the lesion, the whole disk cleanly fell out!
This fungus infects mostly members of the Opuntia genus. It is mentioned among other sources in the Arizona Cooperative Extension Service AZ 1399 with the title: "Problems and Pests of Agave, Aloe, Cactus and Yucca" on page 5.
The first image shows the cactus pad with its distinctive lesion, while the second one depicts some of the blackish fungal fruit bodies (pycnidia), which do produce the spores of the fungus. That image is magnified 60x.

Harald
O_basilaris with Phyllosticta concava lesion1.jpg
O_basilaris with Phyllosticta concava lesion1.jpg (87.38 KiB) Viewed 22825 times
Opuntia-Lesion-x60.jpg
Opuntia-Lesion-x60.jpg (131.73 KiB) Viewed 22825 times
User avatar
hegar
Posts: 4596
Joined: Mon Jan 23, 2006 4:04 am
Location: El Paso, Texas

Re: Some fungal Diseases

Post by hegar »

Today a question was asked by a blog member from Spain about some odd-looking root system on his Echinopsis sp. plants.
To me the images immediately suggested the presence and damage manifestation of root know nematodes (Meloidogyne sp.).
Although nematodes are - at least to me - microscopic eelworms, they are generally listed under the headline of "Diseases" in books and other references. I did not include them in my post about fungal pathogen of cacti, because to me they are neither fungal nor are they pathogens.
However, some of them are known to be vectors of plant diseases and their feeding does open avenues of entry into a host plant, including those microorganisms that can lead to the dreaded cactus root rot.
I am attaching some old digital images I took of a Corphantha sp. in my front yard, whose root system showed the tell-tale swelling of some root areas. That is the location in which the female Root Knot Nematode had made its home, which it never leaves until its death. Only the "butt part" is near the root surface, so the eggs - which are produced in sticky masses - can be expelled into the soil near the plant. The juveniles that hatch then do look for plants nearby, moving along in tiny water channels between soil particles. The females embed themselves in the root and inject a chemical, which causes the plant to form "giant cells". These cells provide the female nematode with sustenance and because of their cancer-like growth they do cause the swelling. Because that abnormal growth interferes with the movement of water and nutrients, the plant will become stunted and look wilted.

Harald

P.S.: The Root Knot Nematode is by far not the only one, which does damage to plant roots, including cacti. There are many other plant-parasitic nematodes present. Most of them are found in or near the root.

M. incognita on cactus1.jpg
M. incognita on cactus1.jpg (73.42 KiB) Viewed 22677 times
M. incognita in cactus root.jpg
M. incognita in cactus root.jpg (66.2 KiB) Viewed 22677 times
M.incognita females in cactus root tissue1.jpg
M.incognita females in cactus root tissue1.jpg (28.21 KiB) Viewed 22677 times
Cactus Root rot caused by M.incognita.jpg
Cactus Root rot caused by M.incognita.jpg (28.94 KiB) Viewed 22677 times
User avatar
7george
Posts: 2628
Joined: Tue Dec 30, 2014 7:49 pm
Location: Calgary, Canada
Contact:

Re: Some fungal Diseases

Post by 7george »

I have dealt for many years with root nematodes and know that nothing but cutting off all affected roots and rooting the plant again fixes the situation with affected plants. Most times one has to go up to the base of the stem high and sometimes fungi already have penetrated deep enough to make the situation terminal... So when you deal with plants growing outdoors in the ground the means of avoiding this infestation are quite limited. For soil mixes for potted plants better try not to use any component dug from outside like soil, dirt but just commercial mineral ones. Or sterilize that leaf mould or other thing coming from the nature.

Also I know that some granulated chemical products can kill that pest but used just outdoors.
TERBUFOS/Counter 15G soil insecticide-nematicide
https://en.wikipedia.org/wiki/Terbufos
Last edited by 7george on Tue Jul 20, 2021 5:05 pm, edited 1 time in total.
If your cacti mess in your job just forget about the job.
°C = (°F - 32)/1.8
User avatar
greenknight
Posts: 4813
Joined: Tue Apr 30, 2013 4:18 am
Location: SW Washington State zone 8b

Re: Some fungal Diseases

Post by greenknight »

Predatory nematodes can control pest nematodes - unfortunately, the don't persist when the soil dries out, so not much use for cactus pests. They work great in the vegetable garden.
Spence :mrgreen:
User avatar
hegar
Posts: 4596
Joined: Mon Jan 23, 2006 4:04 am
Location: El Paso, Texas

Re: Some fungal Diseases

Post by hegar »

Hello 7george and greenknight,
controlling nematodes is not an easy thing indeed. While these small worms do look very fragile - and in a way they are - they do seem to be rather successful to remain in the soil, because their eggs, cysts or defense mechanisms will allow them to survive.
In addition to predatory nematodes, there are other biological agents, which will decimate nematodes. One of them would be a bacterium named Pasteuria. This organism does form endospores, which can be found on the integument (cuticle or skin) of infected nematodes. I am attaching two images I took, showing these endospores, which resemble antipersonnel mines. The ones attached to the Meloidogyne sp. juvenile is host specific. It is Pasteuria penetrans.
Another nematode nemesis is found in the world of fungi. I found a nematode trapped by the hyphal thread of such a fungus. It does form loops, and when a nematode wiggles through one of thes loops it tightens around the nematode, which is then digested by the fungus.
Of course, there are also biological substances that can be used to reduce the plant-parasitic nematode population. Supposedly, the roots of Marigold plants will be effective, as will be a product made of crab or shrimp shells named Chitosan. There are quite a number of other substances, including the most effective one the chemical fumigant.
Another thing is to use solarizathion of the soil, which can kill the majority of pest nematodes within the top foot layer of the soil.
Growing cacti in the ground does not allow the use of some of these substances or methods. I have used Vydate in the past, but this chemical is not avaiable to the general public (restricte use pesticide).

Harald
Helicotylenchus with Pasteuria sp4.jpg
Helicotylenchus with Pasteuria sp4.jpg (87.23 KiB) Viewed 13063 times
Meloidogyne sp. with Pasteuria infection1.jpg
Meloidogyne sp. with Pasteuria infection1.jpg (26.98 KiB) Viewed 13063 times
nematode trapping fungus.jpg
nematode trapping fungus.jpg (26.52 KiB) Viewed 13063 times
Post Reply