Physical Control

Manual removal of whole plants.

• Manual removal can be a very effective way of controlling Watsonia when it occurs in isolated patches in good bushland.

• The timing of hand removal work is particularly important in wetland situations as the soil needs to be wet enough to allow easy removal of the large clumps of corms but not so wet that trampling and soil compaction are a problem.

• Observation of Watsonia growing on sandier soils (for example Shenton Bushland ) indicate that the corms lie deeper and hand removal can more difficult than on the heavier soils.

Consider the consequences of disturbing the soil and possible erosion problems beforeyou start removing by hand. On steep slopes and heavy soils you can cause serious erosion problems and result in little regeneration of the native plant communities.

Removal of Seed Heads as a method of controlling reproduction and spread of Watsonia

• The removal of flowering stems from all plants in a given population prevents bulbil and seed production and therefore recruitment of new Watsonia plants into a given area (see Peter Day's notes on this site).
• Wait until flowering is finished as otherwise the plant may simply produce new stems and the effort is wasted.
• Using this method (in combination with chemical control) Peter and others have been very successful in controlling Watsonia in the Darlington area.

Chemical control

• The herbicide generally recommended for the control of Watsonia is glyphosate. Glyphosate is a non-selective herbicide (ie will kill native vegetation not just the target weed) and therefore needs to used with great care in bushland.
• When the Watsonia occurs in dense clumps with little native vegetation present then glyphoste may be applied by spraying (dilution 1:100).
• If there is a danger that native vegetation will be hit with spray then herbicide may be wiped onto individual plants via a small hand sprayer with a sponge over the nozzle, (1:10 dilution).
• The time generally recommended for spraying/wiping is September/October when the flower spikes are elongated. This however will depend on site conditions and seasonal factors and may take place any time from August through to the end of November.
• With correct use of herbicides at the right time of the year a 90% success rate can be expected.

Clearly then the correct control techniques for Watsonia, in Western Australia at least, are well understood. From the work done to date it seems that with a combination of controlling seed output and correct herbicide treatment Watsonia can eventually be eradicated from a site. However careful thought needs to be given to the best method to adopt given the location of the site in the landscape and to what will replace the Watsonia once it is removed. Soil type, slope and condition of the native plant community the Watsonia is invading all need to be taken into consideration.