What Are Biocontrol Agents, and Why Is It So Important to Control Feral Cacti on My Dragon Fruit Farm?

One of the things that attract people to farming dragon fruit is that they are a relatively low-input crop. Being cacti, they need less water than traditional fruit crops, and since they do not have close relatives native to the African continent, they generally have far fewer pests than many better-known orchard subjects.

However, while the Department of Agriculture is very careful to monitor, control, and prevent the importation of crop pests and diseases from overseas, there is one class of specialized pests that have been actively imported and released for the control of invasive feral cactus species. These pests can directly affect your dragon fruit crop. They are known as biocontrol agents and require a two-step method of integrated control: both direct (on your plants) and pathogen reservoir destruction (removal of feral cacti from your farm).

The Three Most Potentially Damaging Biocontrol Agents

1. Alcidion cereicola

Alcidion cereicola is a beetle species that tunnels into cladodes. Both adults and larvae feed on cactus, causing the collapse of cactus material and subsequent rot. Treatment involves:

• Pruning off and burning infected material
• Using systemic insecticides in cases of severe infestations

The feral cacti species targeted by this pest are Cereus species (apple cactus) and Harrisia species (Queen of the Night).

2. Hypogeococcus pungens

Hypogeococcus pungens is a mealybug species that causes “witches’ broom” type growth on growing points, progressively killing the plant. Control measures include:

• Cutting off the affected growths
• Treating the plant with a contact insecticide

The feral cacti species targeted by this pest are also Cereus species and Harrisia species.

3. Cactoblastis cactorum

Cactoblastis cactorum is a biocontrol agent specifically released for prickly pear cactus (Opuntia species). This moth species lays eggs that develop into cactus-eating caterpillars. Control involves:

• Cutting off infected material
• Applying contact or systemic insecticides in cases of severe infestations

Learn more about Cactoblastis cactorum

Best Practices for Managing Biocontrol Agents

While systemic insecticides can theoretically be used for long-term control of all three pests, treatment protocols have not been established for safe fruit production in dragon fruit. They should only be used as a last resort.

By far, the easiest and most cost-effective way to prevent constant re-infection of your crop is to remove all feral cacti from your farm as part of your integrated pest management plan. These cactus pests are highly host-specific, and without a breeding reservoir, they will become locally extinct and cease to be a problem in your orchards.

Important Note

Feral cacti often co-occur with indigenous Euphorbia species (like “Naboom”), which do not host cactus pests at all and should not be removed. You can easily differentiate them by lightly scratching the skin—Euphorbia will leak a white latex that looks like milk.

Host Species of These Pests

1. Cereus Species

This cactus is very common across South Africa. It is column-forming and variable in appearance, with spines that can be long or even absent. Monstrose forms can also be found, but all types produce large, white nocturnal flowers and red or pink-skinned, white-fleshed edible fruit.

2. Harrisia Species

More common in bushveld regions, Harrisia is a close relative of dragon fruit. It bears white-fleshed pink fruit with fins, has large white nocturnal flowers, and can even climb trees. Two species are recorded in South Africa, both similar in appearance.

Opuntia Species

There are several Opuntia species (prickly pear) problematic in South Africa. They vary in size but all should be controlled unless you are actively farming them.

4. Hylocereus undatus

The feral white-fleshed dragon fruit is a listed invasive species in South Africa, which is why you need permits for some of your varieties. If present on your farm, you’ll find it climbing trees and flowering and fruiting in the canopy. These wild plants can harbor various pests that will jump directly to your orchard plants, making their removal a priority.

Need Assistance?

As a member of the Amorentia Marketing Company and grower of the Amorentia Sweet Dragon Fruit cultivars, you have access to scientific support through the ASDF Technical WhatsApp group and the services of our scientific consultant, Jason Sampson. Contact our offices to find out more.