Description:
Columbus grass (Sorghum almum)
A more robust species than S. halepense (q.v.), sometimes reaching 4.5 m in height. It is a short- term perennial. The most satisfactory method of distinguishing between the two is by the articulation of the pedicelled spikelet. In S. almum the spikelet breaks off with the uppermost portion of the pedicel at maturity; in S. halepense there is a clean abscission at the base of the spikelet. S. almum usually produces short rhizomes, more or less pointing upwards, which are not as extensive or aggressive as those of S. halepense, but reach a depth of 50 cm.
Distribution:
It originated in Argentina as a probable hybrid between Sorghum halepense and a member of the series Arundinacea. It has now been introduced into several tropical countries.
Season of growth:
Spring to autumn.
Tolerance to herbicides:
If Columbus grass does become a weed it can be eradicated by ploughing in most cases. If this is ineffective or not possible, control can be effected by post-emergence sprays as explained for Johnson grass (Sorghum halepense).
Distribution Map:
Columbus grass (Sorghum almum) Distribution in North America shown in green.
Grazing management:
S. almum should be grazed heavily once the crop is 50 cm high to prevent it from growing too coarse and from growing away from the grazing animals. Precautions must be taken to avoid prussic acid poisoning. It is advisable with any young Sorghum spp. crop to use a tester animal to graze the crop first for 20 minutes; if no toxicity is evident
Close up of the Columbus grass (Sorghum almum) Weed.
then the whole herd can be put on to the crop. It is best to give the herd only half an hour’s grazing the first day, an hour the second, and then two to three hours the third, with a full day’s grazing from then on. A rain-grown crop should provide two to three grazings per season. For maximum regrowth, stubble is left at 15 cm to renew growth.
Toxicity:
In common with other Sorghum species, Columbus grass contains dhurrin, a cyanogenetic glucoside which can be toxic. The Queensland Department of Primary Industries recorded HCN equivalents of 0.06 and 0.081 percent in the plants. Danger is greatest in plants carrying young shoots, either from the base or from old stems. Hungry animals turned on to wet pasture are most susceptible. Affected animals breathe heavily, they stagger about and display muscle tremor, become anchored and lie down. They die if not treated. Their mucous membranes remain red and do not become blue (Knott, personal communication).
Three treatments are effective for animals showing early signs of HCN poisoning:
1.Inject a mixture of sodium nitrate and sodium thiosulphate (photographic hypo) in water into a vein or under the skin. Recommended dose rates vary, but are approximately 3 g sodium nitrite and 15 g sodium thiosulphate in 20 ml water for cattle; l g sodium nitrite and 2 g sodium thiosulphate in 15 ml water for sheep. Excessive doses can cause nitrite poisoning.
2. Inject sulphuric ether under the skin; 10 ml for cattle, 5 ml for sheep.
3. Drench with sodium thiosulphate (photographic hypo) in water, 55 g in 550 ml for cattle; 10 g in 100 ml for sheep. This is the usual farm treatment.
Potentially toxic amounts of nitrite have been noted in some S. almum plants but no cases of nitrite poisoning have been reported.
Sourced From: www.fao.org/ag/AGP/AGPC/doc/Gbase/data/pf000318.htm
