The range of broad-leaved weeds found in crops is generally larger than in grasses, however a few such as capeweed, doublegee and wild radish are widespread. Others, such as soursob, sorrel, dock, fumitory, self sown legumes and wire weed are of significant local importance.
- Capeweed - the most common broad-leaved weed given its widespread occurrence in pastures. Cost effectively controlled by a wide range of products.
- Doublegee - infestation is generally on a lesser scale but dormancy and staggered germination pose problems with regard to optimum timing of herbicides. Seed production can begin at relatively early growth stages (four leaves) especially on stressed or later emerging plants and that if the aim of control is to reduce seed production, delays in application to ensure adequate emergence may be counter productive.
- Wild radish - some of the most widespread weeds of cereal crops. Staggered germination and dormancy make their control difficult.
Annual ryegrass and wild oats are two of the most competitive weeds of cereal crops. The conditions of cereal cropping favour their germination and vigorous growth, which when combined with their high seed populations from preceding crops or pasture, can often lead to very large reductions in potential yield. Both species exhibit staggered germination which often leads to poor control.
Where these weeds emerge after seeding and before crop emergence, a knock-down treatment can be used to burn off the small grass seedlings, but it is important to ensure that no crop emergence has occurred. Do not use glyphosate based knock-downs in this way. These grasses are often a problem in emerging crops after early seeding. Control options include:
- delayed seeding
- shallow cultivation-tickle.
Annual ryegrass toxicity (ARGT)
ARGT is a disease of grazing livestock that results fro the ingestion of annual ryegrass seed heads that have been infected by the toxin forming bacteria Rathayibacter toxicus. The bacteria adhere to seed-gall nematodes (Anguina funesta) in the soil and enter the plants, with the nematodes, as they attempt to complete their life cycle. Bacteria colonise the galls, displacing the nematodes and toxicity develops as the plants hay off.
There isa zero tolerance to ARGT in export hay. In Western Australia te considered safe level of ARGT in feed is 200-300 galls per kilogram of grain and hay. The requirement for export hay is less than one gall per kilogram.
Conditions which favour the development of ARGT are:
- paddocks with moderate to high frequency of cropping
- high density of ryegrass
- short growing seasons
- spread of contaminated materials from ARGT areas
- late hay cutting.
Export hay is often grown to aid in ryegrass control, but all export hay is tested for ARGT prior to processing. To ensure the continued acceptance of WA hay into export markets it is critical that supplies remain ARGT free. Deformed heads, bacterial galls, and sometimes slime can be detected in the field but lab tests are recommended to determine the levels present.
A number of biological controls offer potential, including Safeguard and twist fungus.