Tel:082 923 4087 | Mail: jningram@iafrica.com



Aprl 2014

 

This month, we look at a well-known weed of the high rainfall eastern areas of South Africa, namely Bugweed (Luis boom) Solanum mauritianum. This highly invasive perennial weed has caused serious problems in Mpumalanga, KZN and parts of the southern and eastern Cape.


It was originally thought to be native to tropical Asia but has since been discovered to be native to South America. It has become an invasive weed on many islands in the Pacific, Atlantic and Indian Oceans.  It is also invasive in India, Australia, New Zealand and many Southern African countries.


Description: A shrub or small tree up to 4m. high (but can reach to 10m.), covered with whitish-felty hairs. It has no thorns, unlike the similar indigenous Solanum giganteum (Healing-leaf Tree), which is armed with curved spines and has glossy red ripe berries.


Leaves: Dull green, velvety above and white-felty beneath, they emit a strong smell when bruised.


Flowers: Purple, in compact, terminal clusters on densely felty stalks up to 100 mm, long, all year round.


Fruit: Spherical berries which start off green and turn yellow, in compact terminal clusters.


General: Grows vigorously in riparian areas, forest clearings and in timber plantations. Hairy leaves and stems are a respiratory tract and skin irritant. Unripe fruits are poisonous. The fruits also host the fruit fly. The fruits are attractive to frugivorous birds such as the Rameron or Olive Pigeon which facilitate dispersal of the extremely high seed density in the fruit. Seed is reputed to remain viable for many years.


Control: As with most weeds, an integrated control system is required. Mechanical clearing in conjunction with the use of herbicides have been the most effective control methods. Plants up to waist height can be foliar sprayed with “Starane”, an extremely effective product. The mix rate is very low: 20 ml. herbicide per 16 L. knapsack sprayer of water together with a wetter/sticker agent at 80 ml. per knapsack to prevent run-off of the mixture. Bigger plants require cutting back and a cut stump application of either “Hatchet”or“Chopper”. A 3% application rate (500 ml. per 16l. sprayer) in water is recommended.


Biological control agents have, in the past, proved to be difficult to develop due to the fact that Bugweed belongs to a an important food plant family including the Potato and Tomato and for this reason care needed to be taken to not endanger these important crops. However, a small black snout beetle or weevil, Anthonomussenta cruzis, proving to be a promising agent that prevents fruit set and reduces seed dispersal. Female weevils chew into buds and lay their eggs in small cavities in the buds. Once the small larvae emerge, they eventually consume entire flower buds, thus inhibiting opening of the buds and fruit development. Adult weevils will, in the absence of flowers, feed on apical leaflets and shoots, causing considerable damage.

Sources:

  • Sapia News and Aric website.
  • Alien Weeds & Invasive Plants (L Henderson)
  • Problem Plants of SA (C Bromilow).

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February 2014

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March 2014

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