Summer Weed Control

With thunderstorms predicted to bring rain in many areas this week, summer weeds already germinated will freshen up with the added moisture and a second germination of some weeds is highly likely. 

This also brings an opportunity for suitable spraying weather, so we have a chance to take control and combat these weeds.

Key Points to consider when planning to spray summer weeds

Now is a perfect time to review your summer weed control options and sure up herbicide supply. Here is a quick and handy reminder of what to consider when planning your summer weed control: 

• Identify the weed species. GRDC have a fantastic guide available on their website. 

• Analyse the risks to control or not control.

• Know the right control options post emergent & residual.

• Carefully plan application timings - consider weather conditions, plant stress, weed growth stages etc

• Read product labels and observe conditions.

• Address herbicide resistance issues.

• Alternative IWM (integrated weed management) options strategic cultivation & grazing.

Early Action

Controlling summer weeds early will conserve valuable soil nitrogen and moisture for use by the crop during the following season. Early weed control is also important as it achieves several benefits within your overall paddock management strategies including: 

• Utilises weed growth for feed by spray grazing if livestock are present.

• Controls volunteer cereals to prevent disease carryover.

• Minimises nutrient loss from the soil.

• Prevents vine build-up, mini sand dunes and residue management problems at seeding.

• Conserves moisture, particularly closer to sowing

• Control options are cheaper when weeds are small.

Controlling a 'Green Bridge'

Controlling Summer weeds prevents a 'green bridge' plant material, crop volunteers and weeds, growing out of season that can act as hosts to pests and diseases, allowing them to move from one season's crop to the next. A green bridge can allow cross over of:

• Diseases: cereal rust, root lesion nematodes, crown rot and viruses

• Pests: aphids, slugs, mites, web worms, cut worms, Lucerne fleas, beetle larvae

Spray Tips for Summer Application (Particularly when using 2,4D)

Conditions during summer (hot, dry or humid) are not generally considered good conditions for applying herbicides. So it is often early in the morning or at night when the majority of spraying is done. Other critical considerations include: 

• Use equivalent nozzles that produce very coarse (VC) droplets.  Using larger nozzles behind the wheels of the sprayer will help the droplets penetrate the dust stirred up by the wheels. Drift guard or low drift nozzles are great for 24D or glyphosate in summer.

• Coverage can be quite poor in stubbles- use appropriate water rates with larger droplets to penetrate canopy.

• Use higher water rates per hectare, to give better efficacy (80-100L)

• Use slower application speeds (below 20km/hr); and set boom height to 50cm

• Sulphate of ammonia 1% granules or 2% liquid will greatly improve efficacy in warm conditions, although this is only to a certain degree, spraying early morning or late afternoon or ideally after rain will improve efficacy.

• Add 1-2% oil or 0.5% LI700 in warm or windy conditions.

• Always keep a ratio of 2 parts Glyphosate to 1 part Ester when controlling summer grass weeds- this includes volunteer cereals.

• Monitor Delta T to minimise droplet loss in warm / dry conditions- avoid high temperature and low humidity conditions.

• Ensure correct identification of weed species as this can cause costly failure.

Plantback Restrictions

Finally, be aware of plantback restrictions in front of legumes and canola when adding spikes, especially group B's such as Ally or Glean. Atrazine and Dicamba can be reliable substitutes.

If in doubt, contact us for further advice on choosing mixtures; other spikes may be preferable for different rates.

Helen Lethlean, FarmCo lead agronomist - 0488010195; helen@thefarmco.com.au