Black Blisters / Pustules / Scabs on Trichocereus cacti and the causes

Hi Guys ๐Ÿ™‚

In this Blog I will be talking about the black spots / blisters / scabs commonly seen on some types of Cereus cactus plants most commonly seen on Trichocereus and Pilosocereus cacti as in photos of my cacti below ๐Ÿ™‚

black spots on cacti, black spots on trichocereus, black spots on san pedro,

Black spots /blisters oozing out a sticky dark almost black resin on my Trichocereus ย scopulicola cactus plant

Black spots /pustles on my Pilosocereus azureas cactus plant

These black blisters /pustules /marks /spots/ blotches ( excuse the million different descriptions haha ) are common and although unsightly to see and can often cause alarm for the grower they are more than often harmless and only an aesthetic problem ๐Ÿ™‚

The black marks /blisters /pustules /spots /blotches often appear dry as flat or raised bumps on the skin of the cactus and will then often blister and will ooze out a dark almost black coloured sticky resin.

Black spots /pustles on my Trichocereus cacti appearing as raised black bumps that start to go white ย and then sometimes tan coloured over the coming weeks as seen in this photo here.

ย So why does it happen ?

Trichocereus and Pilosocereus cacti contain many chemicals just under their skin, the common Pilosocereus cactus has a very beautiful blue appearance due to the many natural chemical composition in their cells in the skin of the cactus and just underneath the skin, and Trichocereus cacti contain alkaloids in their cells just under the skin and a simple knock to the plant or changes in temperature or humidity very suddenly can often cause these blisters to appear ๐Ÿ™‚

Sometimes a cactus can also develop these black marks /blisters if they take in too much water too fast especially in the early Spring after their long Winter resting period and over fertilising can also cause this, and many plant insect bug sprays used to treat pests on plants will often cause the skin of these cacti to blister and turn black and scabby.

Stress can also cause these Cacti to blister ( yes plants suffer from stress just like humans do haha ) and the simple act of moving a plant from one position to another may encourage these ‘stress’ blisters or spots to form ๐Ÿ™‚

What can be done ?

The best way of prevention is to be extra careful to avoid big drops in temperature suddenly and also to avoid spraying with insect pest sprays if possible as the chemicals in these insect pest sprays often interfere which the alkaloids present in these cacti’s skin. Watering too much too fast straight after the resting period can also cause these black blisters too appear, this is due to the plant taking in water into their cells too fast which I believe is one of the biggest causes of black blisters on these cacti.

I often notice these black blisters form on my Trichocereus cacti when I move them in from the house to the greenhouse for the Spring and Summer months probably due to a number of reasons: 1, stress from the cactus being moved. 2, a change in temperature and environment. 3, watering gets increased. 4, fertilising gets increased 5, insect pest sprays due to a recent outbreak of Spider mite in our greenhouse ( even though we try to avoid using pest sprays as much as poss )

The good news is these black marks /spots /blisters will eventually fade to form a white crusty scab and the plant will carry on growing as normal with no harm to the cactus other than aesthetics, and just like us all we all carry our scars and little war wounds haha ๐Ÿ™‚

Black spots /blisters on my Trichocereus cacti are not the most attractive haha but thankfully ย not life threatening and these black marks will fade to silvery grey over the coming weeks ๐Ÿ™‚

Natural corking on Cacti as they age is perfectly normal and only a cause for concern if the plant appears soft or mushy at the base of the cactus, or if the cactus shows signs of black or brown soft rot, then in this case emergency surgery is needed to remove the rot before it spreads up the whole of the cactus, but rot looks completely different to natural corking, and at the bottom of this Blog I have posted up two videos that I have made for my You Tube channel Desert Plants of Avalon on ‘How to save a Cactus from Rot’ and also a video talking about Natural Corking on Cactus plants ๐Ÿ™‚

Here is a video I have made for my You Tube channel Desert Plants of Avalon on these black spots / marks and blisters and I share with you the ones we have on our Trichocereus and Pilosocereus cacti ๐Ÿ™‚

Here is a video I have made for my You Tube channel Desert Plants of Avalon on Natural corking on cactus plants and what it looks like ๐Ÿ™‚

Here is a video I have made for my You Tube channel Desert Plants of Avalon on How to save a Cactus from Rot :

I hope that you have found this info interesting and knowledgeable should you encounter this on your Cereus cacti ๐Ÿ™‚


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