Why measure weed densities?
An accurate assessment of the weed population will help to indicate:
- type, size and number of weeds
- the type and rate of herbicides to apply
- how successful a spraying operation may have been
- the potential yield loss posed by weeds
- the need to retreat an area as a result of poor control
- an indication of possible herbicide resistant weeds.
Counting weed seedlings
- Using a quadrant, place it at random along the monitoring path
- Identify and count the number of each weed
- Total the number for each weed type measured at the ten sites to give the number of each weed type per square metre.
This information in turn will allow you to develop appropriate weed control strategies for future crops/pastures. There are tools available (Table 1) to help focus this information to make an informed decision and identify the probable cause of poor weed control.
| Consider | Why | Where to go |
|---|---|---|
| Modes of action | Its important to use a diversified approach to weed management to prevent resistance | WeedSmart app |
| Managing your seed bank | It is important to know what you are dealing with underground | Weed Seed Wizard |
| Identification of | Critical to correctly identify weeds | GRDC Weed ID app |
Why control weeds?
It is important to take into consideration the consequences of weed survival on the following crops in the rotation. Aspects to consider includes;
- the risk of disease carry over
- the need to sow the next crop later than the optimal time after controlling emerging weeds
- the ability (or inability) to be able to selectively control weeds in the following crop
- rapid development of resistant weeds due to controlling high numbers of weeds with herbicides
- the possibility of harvest contamination.
Rule of thumb: Adopt a zero tolerance to weeds.