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December 2014

 

Regrettably, the summer rains have still not fully materialised, but many alien invasive plants are nevertheless actively growing and need to be controlled before they set seed. Weed eradication is unfortunately an on-going operation and one has to be stubbornly persistent since there will always be re-infestation from neighbouring properties where the problem is not managed properly.

This month, we will look at two families of herbaceous (non-woody) weeds that originate from Central America and have become naturalised in our province. Since they have showy flowers, they were most likely introduced as ornamental plants.

They are:
Family Asteraceae (Daisy Family)
Tithonia diversifolia - Mexican Sunflower
Tithonia rotundifolia - Red Sunflower

Family Lamiaceae (Sage Family)
Salvia coccinea - Scarlet or Texas Sage
Salvia tilifolia - Lindenleaf Sage

Descriptions:

Mexican Sunflower

Description: A bushy annual or perennial, 1.5-3.5 m. High. Leaves: Dark green; hairy; pale velvety below; up to 150 mm long and 120 mm wide; largely egg-shaped and deeply 3-5 lobed; leaf stalks are winged. Flowerheads: Bright yellow; solitary on long stalks which are swollen and velvety below the heads; several together in branched heads; flowering April –June. Invades: Savannah, grassland, roadsides, riverbanks, mainly at lower altitudes (0-600 m.); common around Nelspruit. Origin: Central America, including Mexico.

Red Sunflower (Locals will recognise this as Jakob Regop)


Description: A bushy annual, 1.5-2.0 m. High. Leaves: Dark green; rough hairy; up to 150 mm long and 120 mm wide; triangular-egg-shaped, sometimes deeply three-lobed; leaf stalks winged. Flowerheads: Bright orange-red; large and showy; up to 90 mm across; solitary on long stalks which are swollen and velvety below the heads; occurring at terminals of the main and side branches; flowering February to July. Invades: Roadsides, wasteland, riverbanks, at moderate altitudes (600-1400 m.). Origin: Central America, including Mexico.

Scarlet or Texas Sage

Description: A many-branched herb, 300-600 mm high. Leaves: Pea green; hairy, in oppositely arranged pairs; scalloped margins; size variable (up to 75 mm long x 50mm wide). Flowers: Tubular; bright red; 30mm long. Invades: Being hardy and seeding prolifically and being tolerant of full sun to full shade, it can invade most areas. Origin: Mexico, but widespread in eastern USA, Central America, Northern South America and the Caribbean.

Lindenleaf Sage

Description: An erect, hairy herb, growing up to 1m. high. Leaves: Bright green, soft, hairy; oppositely arranged, with alternate pairs at right angles to the next pair. Flowers: Tiny (5-10 mm long); blue; arranged on spikes up to 250 mm long; flowering in late summer to autumn. Invades: Roadsides, rocky hillsides and often forms dense clumps under tree canopies. Origin: Mexico. Central America, and Northwestern South America.
Control of these plants is best achieved by hand pulling while they are still young and small. Dense infestations require foliar applications of herbicide (and a wetter to prevent run-off from hairy foliage), whilst below waist height.

Sources: Sapia Newsletters; Wikipedia; Alien Weeds and Invasive Plants (L. Henderson).

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