Summer weed management and stored moisture - Elders Rural Services

Summer weed management and stored moisture

Editorial written by Adam Pearce, Agronomist, Elders Forbes for the Summer 2020/2021 Seasons Magazine.


Eliminating weeds from a paddock while they are small makes a big difference to moisture conservation, not to mention the valuable nutrients weeds can rob from the soil.

We sometimes underestimate the impact big-name weeds like fleabane, heliotrope, sow thistle, melons and other summer weeds can have on final production. But it’s impossible to ignore in a paddock where the summer spray had a miss or that second spray wasn’t done.

Hit weeds while they are small, don’t wait for the next rain! The forecast rain event may fizzle and those weeds might suddenly be too stressed to take up the product effectively.

On the flip side, you might be left waiting for soils to dry out to become trafficable and then be faced with large, robust and expensive infestations. Apply herbicide as soon as the majority of weeds have germinated and will take a spray. This can be as early as 7 to 14 days after a rain event – every day delayed is dollars lost!

A few things to consider when organising a spray plan: how much area do I have to cover? Which paddocks are priorities, or have the most advanced weeds? What is the forecast weather in the next seven days and how many hours of spraying can I fit into optimal conditions? Consider the Delta T in hot weather, no wind or too much wind, inversion risks and refill times.

Nozzle selection
Use a minimum of Very Coarse (VC) Spray quality to reduce the percentage of “driftable fines”. It is now mandatory to use at least a VC spray quality when using ANY product containing 2-4,D but advisable to use eXtremely Coarse (XC) or Ultra Coarse (UC), as they further reduce driftable fines and are especially good in sub-optimal conditions. Driftable fines are a particular problem when inversions are present and can carry the product for a considerable distance. They are not limited to 2-4,D and can pose a big problem with any herbicide.

Larger nozzle sizes usually mean higher bar pressures and water rates of around 80 litres a hectare. This is higher than the traditional 50-70L/ha rates but compliance helps avoid losing these valuable products.

Get creative with water sources, access points, mobile nurse tanks and batching tanks to speed up the process.Importantly, some adjuvants can affect the amount of driftable fines produced from a nozzle, but this does not change the final spray quality classification, so choose adjuvants wisely and seek advice from your agronomist.

Very few nozzles deliver these larger droplet sizes, so speak to your reseller and agronomist about the best nozzles for your situation – the aim is to have two main nozzles that do both summer and winter spraying. Finally, ask an agronomist to test your water regularly, especially when using water other than rain water, as this can have a big impact on the final result.