Wet finish provides opportunity and risk
Author: Andrew McFadyen | Date: 24 Nov 2015
By GRDC northern panelist Andrew McFadyen
A wet finish to this season’s harvest across parts of the northern cropping zone has handed a double edged sword to many growers.
The overwhelmingly positive news is that it’s deposited valuable millimetres in the soil moisture bank in readiness for the next crop but at the same time, it has kick started weed germination.
This will move post-harvest weed control to front-of-mind for growers, who will be eager to maximise the effectiveness of control measures, preserve precious stored soil moisture and protect the yield potential of next season’s crops.
Sometimes significant damage is done to the prospects of growing a profitable crop in the next sequence of a rotation if growers park headers in the shed, head to the beach for a holiday and forget to spray out those summer weeds.
Research supported by the Grains Research and Development Corporation (GRDC) has shown that growers can significantly increase stored plant available water and the availability of nutrients, particularly nitrogen, by controlling weeds early. Of course this also paves the way for increases in crop yield and grain quality.
By having spray equipment at the ready, using robust rates and adhering to best management spray application recommendations on water rate, environmental conditions, droplet size and boom height, growers can prevent potential crop damage and give the next rotation a real boost.
Effective control can be achieved by spraying while weeds are small; leaving them too long can be a costly failure requiring additional control measures and risking the development of herbicide resistance on farm.
It’s important to remember that any weeds which have already set seed should be sampled and sent away for herbicide resistance testing. This particularly applies to problem weeds such as annual ryegrass and wild oats (black oats).
With the escalation of herbicide resistance issues in the north, growers are increasingly looking to incorporate non-chemical control tactics which can be an effective control measure and help preserve the life of existing chemistries.
In mixed farming systems, this may include grazing harvested crops to reduce the weed presence. However to be integrated successfully, this strategy requires consideration of the implications for stubble coverage and future soil moisture capture/storage.
As most growers would be aware, when it comes to herbicide application there are some key factors that impact on efficacy including adjuvant selection which is critical to the performance of most active ingredients.
Adjuvants improve herbicide efficacy by reducing evaporation and drift, increasing droplet survival on leaf surfaces and increasing penetration of herbicide active ingredients into the plant.
Of course efficacy is also significantly impacted by temperature and humidity, travel and wind speed, droplet size and viscosity of spraying liquid so it’s really important from a cost/benefit and sustainability perspective to adhere to best management recommendations on spray equipment and conditions.
Growers looking to take advantage of moisture for a summer plant could consider applying a pre-emergent herbicide initially to control weeds in the germination stage.
The first flush of weeds is usually the worst and applying a pre-emergent herbicide can be an effective early knock. This can be later followed up with a knockdown herbicide application if necessary.
A range of helpful resources relating to weed control, herbicide resistance and weed seed testing is available via the IWM Hub in the resources section of the GRDC website.
- Andrew McFadyen is an agronomist and manager with Paspaley Pastoral Company near Coolah NSW with more than 15 years’ agronomy and practical farm management experience. He is an active member of the grains industry with former roles on the Central East RAC, NSW Farmers Coolah branch and planning committees for GRDC Updates. He is also a board member and the current chair of Grain Orana Alliance.
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