Summer is upon us and in its wake follows an abundance of invasive alien weeds. The following four category one weeds in our area should be at the top of your hit list: They are bugweed, lantana, pompom and queen of the night.

Bugweed / Luisboom

Bugweed, Solanum mauritianum, is an alien invader that originated in South America and forms part of the potato family (Solanaceae).

It is a thornless branched shrub or small tree, two to ten metres high. All parts of the plant are hairy except older stems. The oval-shaped leaves, which emit a strong smell when bruised, have a dull green and velvety appearance above, while the undersurfaces are white.

Purple flowers are produced in compact terminal clusters throughout the year. The berries, also in compact terminal clusters, are poisonous when they’re still green. They turn yellow as they ripen.

Bugweed invades forest margins, plantations, wooded kloofs, roadsides, wasteland, watercourses and open spaces. It is the principal weed of South Africa’s timber forests. 

Recommended herbicide: Foliar spray
Confront @ 0.60% = 90 ml/15 ℓ or 6 ml/ℓ or Plenum @ 0.25% = 37.5 ml/15 ℓ or 6 ml/ℓ.

Proposed control method: Stump treatment
Cut stumps while plants are actively growing. Apply Timbrel @ 3% = 450 ml/15 ℓ or 30 ml/ℓ or Access @ 1% = 150 ml/15 ℓ or 10 ml/ℓ or Plenum @ 1 % = 150 ml/15 ℓ or 10 ml/ℓ.
Apply to freshly cut stumps, especially the cambium.

Lantana

The colourful lantana shrub, lantana camara, was imported from the Americas as an ornamental garden shrub that grows 0.5–2 m high. Lantana’s flower clusters are a mix of yellow, blue, orange or red and white florets. They typically change color as they mature, resulting in inflorescences that are two- or three-colored.

The plant has invaded agricultural land because the berries from garden plants are eaten by birds and distributed far afield. Lantana is responsible for a high percentage of national stock deaths in South Africa because it contains pentacyclic triterpenoids that cause hepatotoxicity and photosensitivity when ingested by grazing animals such as horses, cattle, goats and sheep.

Recommended herbicide: Foliar spray
Access @ 0.75% = 112.5 ml/15 ℓ or 7.5 ml/ℓ or Plenum @ 1.5% = 225 ml/15 ℓ or 15 ml/ℓ.

Proposed control method: Stump treatment
Access @ 1% = 150 ml/15 ℓ or 15 ml/ℓ or Plenum @ 1.5% = 225 ml/15 ℓ or 15 ml/ℓ.
Apply on freshly cut surfaces.

Seedlings and coppice (0,5-1 m): Apply as full cover spray to foliage.

Pompom

Pompom, Campuloclinium macrocephalum, is native to Argentina, Brazil, Central America and Mexico. This weed was introduced in South Africa as an ornamental plant and the earliest record in the Pretoria National Herbarium is of a specimen collected in 1962. The earliest record of its spread to the wild is from Fountains Valley in the early 1960s.

Today it has taken over a large proportion of our country’s grasslands. It threatens the survival of grasslands and wetlands throughout South Africa as it can tolerate a wide range of habitats.

This 1.3 m high plant is an erect, perennial herb that carries fluffy pink to light purple flowerheads from December to March. The stems are green to purplish, and annually die back to a root crown. The leaves, which have serrated margins, are scattered along the length of the stem, but clustered at the base to form a rosette, up to 80 mm long and 20 mm wide.

The pompom has fluffy seeds that are dispersed in the wind. It can also regenerate from underground rhizomes.

Recommended herbicide: Foliar spray.
Brush-Off @ 25 g/100 ℓ = 3 .75 g/15 ℓ or Climax @ 35 g/100 ℓ or 5.25 g/15 ℓ or Access @ 0.35% = 52.5 ml/15 ℓ or 3.5 ml/ℓ or Plenum @ 0.375% = 56.25 ml/15 ℓ or 3.75 ml/ℓ.

Proposed control method
Cut off the flowers and place in a plastic bag immediately to be burnt once dry. Use a single application (full-cover spray) on actively growing plants and once in the late summer before the onset of winter. Spot-spray re-growth if necessary.

Queen of the night / Nagblom

Queen of the Night cactus, cereus jamacaru, was imported from South America as an ornamental garden plant with attractive white flowers. This large, upright-growing, cylindrical cactus species has green or blue-green, ribbed lateral branches, which grow in segments.

This cactus spread from gardens into the surrounding veld where it outcompetes indigenous vegetation and invades pastures. It has mainly been spread by birds and mammals which feed on the fruit, but can also propagate vegetatively - stems that touch the soil will root.

Birds deposit the cactus seeds at their roosts, which causes cactus thickets to develop under trees. These thickets prevent stock and game from finding shade, which causes loss of condition, especially in hot areas.

Biological control is available, and can be arranged. The mealybug, Hypogeococcus pungens, kills cactus seedlings before they are even noticed by the landowner.

Recommended herbicide: Foliar spray
Confront @ 1% = 150 ml/15 ℓ or 10 ml/ℓ or Garlon @ 1% = 150 ml/15 ℓ or 10 ml/ℓ or MSMA @ 5% = 750 ml/15 ℓ or 50 ml/ℓ.

Proposed control method: Plant treatment
MSMA use 1ℓ / 2 ℓ water
Large plants: Injection treatment in October. With a sharp instrument make one hole into the soft tissue of each stem shorter than 2,5 m and two holes in each stem taller than 2,5 m. Inject 2 ml of the mixture into each of the holes.

Inoculate in spring or summer.
Add Actripon @ 0.5% to herbicides where indicated. Add Ecoblue dye 1 ml/ℓ to herbicides if required.

For more information, contact the Agricultural Research Council at 012-427-9700 begin_of_the_skype_highlighting.