October 2008. A member from Florida, USA, asked how to control Crotalaria spectabilis (Showy Crotalaria) which is toxic to horses and cattle. The problem concerns a 10-acre field that horses cannot be put on due to this poisonous weed. Pulling out has been tried, but the field is so densely covered that it would take a lifetime. Mowing does not help, in fact it makes matters worse if seed pods are present, even before drying into the “rattlebeans”. The herbicide 2-4-D has been tried in a test area, but the spray seemed to bead up on the leaves and did little damage to the plants. Burning the field might be an option.
Based on experience with C juncea which is grown as a green manure crop the following management practices were suggested:.
1. Immediately after the harvest of the main crop, allow one irrigation. This will prompt all Crotalaria seeds to germinate. In about 25 to 30 days, when the plants have reached nearly 2 feet (and more importantly, prior to flowering), plough them into the soil. Then repeat with a lighter irrigation and a shallow turning of soil at the next flush.
2. 2,4-D would be ideal if you can use adjuvants.
3. If you are not already using CDA controlled droplet application – sprayers (air assisted) – these could add to the efficiency of spread of the herbicide.
Another member wondered if glyphosate would also be effective.