Spineless prickly pear (Opuntia spp.) is quickly making a name for itself as a sustainable and cost-effective source of livestock fodder, especially in drier regions where traditional grazing is under pressure.

In addition to its nutritional value and moisture retention capacity, the plant also offers economic opportunities for farmers looking to diversify their production systems. However, successful prickly pear farming requires a thorough understanding of pests and diseases that threaten the plant, as well as proper management practices such as weed control and pruning. In this third instalment of our series, we look at key practices to enhance plant health and yield potential.

Pest and disease control

Prickly pear moth (Cactoblastis cactorum)

This moth primarily appears in two seasons: from September to October, and again from February to March. After emerging, the moths mate within two days, and females begin laying sticks of eggs on the plant’s thorn tips the following day. The eggs hatch within hours, and the young larvae penetrate the cladodes, developing over a period of three to four months into fully grown, bright orange larvae with black stripes.

Control strategies include the timely removal of infected egg sticks and cladodes. This material must be immediately removed from the orchard and destroyed to prevent further spread of the pest.

Cochineal (Dactylopius spp.)

Cochineal insects typically form colonies on the leaves. The females cover themselves with a waxy layer that protects them from the environment, making them difficult to spot. Each female can lay up to 1 000 eggs, with the nymphs hatching quickly and spreading easily — especially on hot days when their tiny hairs allow them to be carried by the
wind to other plants. These insects feed on the plant’s sap and secrete a toxic substance that eventually kills the cladodes.

Specific insecticides can be effective, provided the wax layer is first broken, as it otherwise acts as a protective barrier. The use of knapsack sprayers is not effective and therefore not recommended. In severe infestations, systemic agents such as Kohinor or Bandit can be used. However, note that these products are not registered specifically for prickly pear and are used at the farmer’s own risk.

Black rot and soft brown rot

Watch for black or dark brown spots on the edges or surface of the cladodes — clear signs of black rot or soft brown rot. As soon as such symptoms are observed, the affected leaves should be cut off immediately. Ensure that pruning tools are thoroughly disinfected after each plant. The removed cladodes can be used as livestock feed, but must be fed away from the orchard to prevent re-infection.

Weed control

Prickly pear has an extremely shallow root system — up to 80% of the roots lie less than 10 cm below the surface. This means weeds directly compete for available moisture, which can negatively affect growth potential. Weed control must therefore be applied with care. Mechanical methods such as hoeing or using tine implements are not
recommended as they can damage the root system. In areas where grasses become problematic, a grass herbicide like Agil can be used. As with pest control products, farmers should note that it is not specifically registered for prickly pear and is used at their own risk.

Irrigation

Although mature prickly pears can survive with as little as 200 mm of water per year, the optimal rainfall for fruit production is between 400 to 600 mm/year depending on soil type. Reasonable fruit yields can be achieved under dryland conditions in summer rainfall areas, but where rainfall during the fruit development period (September to February) is less than 300 mm, supplementary irrigation should be applied.

Drip irrigation on heavier soils and micro-sprinklers on sandy soils are ideal where water is scarce. Approximately 20 to 25 mm of water/ha per irrigation is sufficient. Farmers should monitor the dissolved salt content of irrigation water, as prickly pears are sensitive to high salt levels.

Pruning

In orchards where sufficient water and nutrients are available, prickly pears grow vigorously. Annual pruning is therefore important — not only to control shape and size, but also to aid in pest control, particularly against cochineal, which prefers to hide in dense, overgrown areas.

Pruning guidelines include:

• Retain only two daughter cladodes per mother cladode.
• Plants should not grow taller than 2 metres.
• Branches should not touch the ground.
• Avoid overlapping or contact between leaves — this creates shelter for pests and limits spraying effectiveness.
• Remove and destroy all cladodes that show signs of disease or pest damage.
• All pruned material and plant debris under the trees must be removed from the orchard immediately.

By applying these practices, farmers can maintain healthy prickly pear plantations and unlock their maximum value as an alternative livestock feed. In part 4, we shall look at fodder production.

For any further enquiries, visit Witkraal Boerdery’s website at www.witkraal.co.za