Many dragon fruit cacti have spots on their stems and these spots may be sign of an infection. However, other non-infections injuries such as a scaring from physical trauma or sunburn may result in a similar appearance. This article will outline the key characteristics of the most common Dragon Fruit diseases.
Most importantly, having this knowledge will help you to avoid buying infected plants. In addition, many of these same pitaya problems listed here can also infect other plants in addition to cacti. Therefore, the information provided below may be transferable to your other garden loved-ones. The best option is prevention which includes keeping your Dragon Fruit cacti healthy and using sterile pruning techniques. For a complete guide to growing healthy Dragon Fruit, check out my article on How To Get Your Dragon Fruit Cactus To Fruit.
The fungal infection known by the scientific name Botryosphaeria dothidea causes blotchy red/brown spots on the stems of Dragon Fruit cacti. These spots are typically flat but slightly raised compared to adjacent normal areas. Sometimes these spots have an appearance of a bulls eye (see first picture below). Other times, this infection can result in multiple irregular spots that may coalesce together (see second picture below). This disease may first present as yellow areas on a branch that then develop the darker spots mentioned above. This disease does not seem to be deadly but has been reported to decrease plant vigor and fruit production by up to 44%. Because of unsterile pruning practices, this disease has become rather common in many parts of the world.
Other plants with this Botryosphaeria dothidea infection:
Apparently, this infection can impact a lot of other plants too. For example, the first article to describe this disease in Dragon Fruit also states that, “This same fungus has been previously reported to cause panicle and shoot blight and canker diseases of pistachio, peach, apple, forest trees, chaparral bushes, and many other plant species.” In rhododendron plants, heat stress and drought will increase the severity of the disease. Since we don’t have a lot of data for dragon fruit, we could look to how this fungal infection is treated in other plants for insight.
Other plant treatments for Botryosphaeria dothidea:
For walnuts, the UC California Agricultural Research Center, says that for Botryosphaeria dothidea infected walnut trees, you should prune dead branches or blighted shoots and avoid sprinkler irrigation that wets the canopy. That same walnut reference document lists the fungicides registered for treating Botryosphaeria blight in pistachio trees. Some of the more effective chemical treatments for pistachio trees listed are the antifungals pyraclostrobin and trifloxystrobin. As reference, the product Armada 50 WDG Fungicide contains trifloxystrobin and Bonide Chemical Fruit Tree and Plant Guard contains pyraclostrobin.
In addition, according to the USDA Agricultural Research Center, for apples and pears, copper fungicides have proved effective for Botryosphaeria dothidea in Japan. I am somewhat skeptical that a topical spray could cure this infection. However, a topical spray is rather appealing and this would be my personal first attempt at treatment. As another potential option, a systemic antifungal such as thiophanate-methyl might also work. The problem with systemics is that they will kill a lot of other good fungi in the soil. Overall, studies are still underway for Dragon Fruit and (to my knowledge) there is nothing definite for them yet.
Botryosphaeria dothidea spread:
This fungi, (and other plant infections) can be spread by trimming/pruning tools that have not been sterilized between plants. Direct contact between plants can also be a way to spread disease.
There are also sap sucking bugs can also spread disease. Specifically, bugs in the Leptoglossus genus (aka leaffooted bugs) have been known to be a vector that can spread the Botryosphaeria dothidea fungus to other plants. I caught a pic of a Leptoglossus sucking on a flower-bud of one of my Cereus Cacti. The one in the pic below looks a lot like Leptoglossus occidentalis. However, That particular one is said to feed on pine, so it must be some other close relative. Regardless, this genus is a bunch of destructive sapsuckers that can spread disease and are not welcomed. The University of California has a nice short article about what to do about the leaffooted bugs (if you are a pistachio farmer)… but same ideas apply.
For additional reading:
For additional reading on this topic, I have listed some scientific journal references on this Botryosphaeria dothidea fungal infection.
- One of the pictures below is from the article with the rather long-winded title; “Conidial germination of Botryosphaeria dothidea and histological alterations on stems of pitahaya”
- In addition, here is a link to a research paper on the topic of treating Botryosphaeria dothidea.
- This next 2003 paper states they were the first to describe this infection it in dragon fruit, Botryosphaeria dothidea causing stem spots on Hylocereus undatus in Mexico
Colletotrichum gloesporiodes (aka Anthracnose) is the name of another fungi that can infect dragon fruit cacti. The lesions from this fungal infection look like concentric haloes on stems and fruit (see picture below).
- The journal article, A brief overview on pitahaya (Hylocereus spp.) diseases discusses this disease briefly.
Yet another fungal pathogen has the scientific name Bipolaris cactivora. This disease can cause black-brown spots on dragon fruit flowers and fruit. This infection can also cause branch/stem rot.
- For more info, here is journal article on the subject titled, First report of Bipolaris cactivora causing fruit blotch and stem rot of dragon fruit (pitaya) in Israel.
- Additional info can also be found on the article titled, A brief overview on pitahaya (Hylocereus spp.) diseases.
Cactus virus X:
‘Cactus Virus X’ causes blotchy chlorotic spots, mottling, necrosis and yellowing on dragon fruit cactus stems (see picture below). The pattern of of light and dark green areas on a branch is sometimes referred to as a mosaic pattern. As far as I know, there is not much you can currently do for a viral infection such as this.
- The image below is from the ppt titled Viruses and Viral Diseases of Cacti and Succulents, authored by Deborah Mathews, Ph.D at UC Riverside.
- For some rather technical research writing on the subject, check out the journal article titled Detection and incidence of Cactus virus X in pitaya in Taiwan
- More info available from the journal article titled Cactus mild mottle virus is a new cactus-infecting tobamovirus.
Stem soft rot caused by Enterobacteria:
This wet rotting disease typically infects the ends of dragon fruit branches. This infection is caused by the gram negative bacteria called Enterobacteria. I have seen this type of thing burn itself out and I have also seen it take over a plant. To be safe, I would cut off the diseased branch(es) at a point where there was no visible sign of disease. Then carefully dispose of the sick branch and sterilize your cutting tools when done. Studies have shown that the rotting appears 15 days after inoculation with the bacteria. Apparently, plants deficient in calcium and nitrogen may develop more severe symptoms. On that note, keeping your Dragon Fruit cacti healthy may help you to avoid this disease.
- Additional info about this rotting infection can also be found on the article titled, A brief overview on pitahaya (Hylocereus spp.) diseases.
All infectious diseases can-and-will be transmitted from plant to plant by pruning/trimming tools. There is also a strong possibility that these diseases can also be spread by direct contact of roots and stems that touch each other. Some insects (such as Leptoglossus sp mentioned above), can also spread infectious disease from plant to plant.
For some difficult diseases, many have advocated destroying infected plants and starting over in a different location. Your best bet is prevention; inspect plants before you buy and keep your tools clean. On that note….
Sterilize your pruners!
- It is really important to sterilize your trimmers/pruners between plants. There are many infectious plant diseases that are unknowingly spread from plant to plant by cutting/trimming instruments. This is true for any plant, but particularly so for Dragon Fruit cacti… many of which have been infected with systemic diseases because of sub-optimal sanitizing techniques.
- There are a many sanitizing options including household cleaning solutions, alcohol, and hydrogen peroxide. These chemicals only need to be applied to the cutting blade. Many of these liquids require some application time before they are adequately sterilized.
- Another faster option is heat sterilization of your cutting blade with something such as a small hand held torch. The torch technique, is convenient and fast, but obviously results in the tips of your trimmers being hot… Which are then a potential burn hazard to you and to your plants… as well as being a general fire hazard. Definitely don’t try burning things in your garden/yard if you are in a fire danger area (which is most of California). And my favorite disclaimer of all, “don’t try this at home.”
- Interestingly, I just found this other tool that actually spritzes your hand pruners with sterilizing fluid with each cut. I have no idea how well this product works, but it is an interesting take on addressing the problem. For reference, here is a link to that product Hand Pruners with Spray Applicator.
- While I was getting my hair cut today another thought came to mind. I wonder if that Barbicide chemical they put hair cutting scissors in would also kill unwanted plant microbes. Seems like it should do the job, and apparently it is fully biodegradable. All of that said, I have never heard of anyone else using a barbers/hair salon disinfectant such as Barbicide for this purpose.
Sunburn can have an appearance similar to some of the other diseases listed below. Sunburn can be a problem when a plant is moved quickly from a shady area to a full sun location. Growing in areas of more intense sunlight such as the desert can also lead to sunburn injury.
This injury may present as areas of yellowing, corking, scabbing and pealing. You can expect this injury to be seen on the most sun exposed sides of the plant (South/top of the plant). On that note, sunburn can also sometimes look very similar to Botryospaheria dothidea infection. However, the distribution of the stem lesions should be different. Specifically, if something looks questionable but is on the under-surface of a plant, then it is not sunburn. In this situation, you should consider one of the infectious diseases listed above as the cause.
Sunburn problems similar to the above can also be the result of increased sensitivity to sunlight from topical chemicals. This phototoxixcity is classically the result of spray chemicals such as horticulture oils, fungicides, insecticides, etc which can increase sensitivity to the sun. By example, this type of increased sensitivity to the sun can also happen to us people as a result of topical exposure to oils and juice from citrus (esp limes).
This topical cactus injury results in a scar on a branch from a short term chemical exposure + sun. Once the offending agent is removed, the problem should not spread. This lack of spreading after removing the chemicals is another way to help differentiate between sun injury and infection.
Corking is a normal part of cacti aging. In this process, lower parts of the plant often mature-change to a hard, dry, grey bark-like appearance. This should first occur from the bottom of a plant and slowly work its way up from there. If a process does not follow this slow ‘bottom-up’ progression, then it is probably not corking.