2,4-D and early weed ID the focus of summer weed workshops

Growers shown how coarser spray quality can improve summer weed control

Latest News
Andrew Storrie, AGRONOMO, comparing high-pressure air induction nozzles to produce VC to XC spray quality required for using 2,4-D at the Merredin Summer Weed Workshop. PHOTO Glen Reithmuller

Andrew Storrie, AGRONOMO, comparing high-pressure air induction nozzles to produce VC to XC spray quality required for using 2,4-D at the Merredin Summer Weed Workshop. PHOTO Glen Reithmuller

Aa

Early weed identification and spraying in tough conditions the focus of WA summer weed management workshops.

Aa

Key points

  • New regulations on 2,4-D mean that growers will have to use high-pressure air induction nozzles with a minimum operating pressure of 3 to 4 bar
  • Coarser spray droplets are not affected by higher Delta T values
  • Look more closely at weed seedlings before spraying to ensure correct identification and herbicide selection
  • Ensure meteorological conditions are measured at the spray site

Improved early identification and the new 2,4-D use regulations emerged as the uppermost issues for growers and agronomists attending advanced weed management workshops across Western Australia in February.

Sixty-three growers and consultants attended the five half-day summer weed management workshops at Mingenew, Merredin, Esperance, Corrigin and Kendenup. The main topics covered were improved early identification of summer weeds, updates on the new 2,4-D use regulations and how coarser spray quality can improve summer weed control.

Using spray qualities of VC or coarser means droplets are less affected by evaporation so spraying at higher Delta T's may still be an option for efficacious weed control, provided weeds are free of stress.

Growers and agronomists were keen to understand how the new regulations for the use of 2,4-D would affect their spraying operations and were pleased that using coarser spray qualities could improve spray coverage and weed control in summer. Trial work by the Toowoomba-based Northern Grower Alliance has shown that when using well-translocated herbicides, such as 2,4-D on larger sowthistle and fleabane, there was no difference in control between TTi and AIXR nozzles producing ultra coarse (UC) and coarse (C) spray qualities respectively.

Attendees were also keen to discuss how to improve spraying under difficult summer conditions with extensive discussions on meteorology, making the best use of Delta T, behaviour of different summer growing weed species under adverse conditions, the behaviour of tank mixes and adjuvants.

Agronomists Giles McMeikan and Shon Cruttenden competing to identify summer weed seedlings at the GRDC Summer weed workshops in February, 2019. PHOTO AGRONOMO

Agronomists Giles McMeikan and Shon Cruttenden competing to identify summer weed seedlings at the GRDC Summer weed workshops in February, 2019. PHOTO AGRONOMO

Using spray qualities of VC or coarser means droplets are less affected by evaporation so spraying at higher Delta T's may still be an option for efficacious weed control, provided weeds are free of stress.

Measuring Delta T at weed level with a handheld weather meter can detect moisture stress - though most summer grasses use the C4 photosynthetic pathway can comfortably tolerate temperatures up to 35°C when there is sufficient soil moisture available.

A weed-level Delta T value lower than the measure at 1.5 metres is a good indication the weeds are not stressed. Plants should not be wilted or bluish in colour.

The absence of stress allows growers to extend the available spray hours per day.

Research to investigate the impact of spraying under higher Delta T scenarios will occur over the coming summer season.

Spray quality

The effect of wetters and oils on spray quality. The 'fining' of the spray by using a non-ionic wetter provided a clear visual contrast to the effect of oil, which significantly reduced the percentage of fine droplets

Early ID

Another important part of the workshop was training in early identification of weeds. Correct early identification is extremely important to ensure the correct herbicides and rates are used.

After an introduction to the basics of weed seedling identification, workshop participants were split into teams to complete a quiz to match the descriptions of 12 seedlings to potted seedlings. Ten-times power hand lenses and the new GRDC Identifying Western Australian summer weeds manual were used to identify the seedlings. Many growers were surprised by the differences, between otherwise similar-looking species when compared under magnification.

The major summer fallow weeds, as highlighted by participants, were fleabane, mintweed, prickly lettuce, caltrop, melons, button grass, couch, common heliotrope, matricaria, roly-poly, Afghan (thorny solanum) thistle, small-flowered mallow, pigweed, Asphodelus and wild radish. Blackberry nightshade was only an issue near Albany.

It is amazing to see the detail of different weeds when you look at them through a 10-times hand lens. What initially appear to be the same weeds are actually very different. - Andrew Storrie, AGRONOMO

Some weeds tend to be more regional, with fleabane being more important in southern areas but widespread. Button grass and couch were more common in the northern wheatbelt, along with the invasion of native woody species such as flannel bush. Matricaria was limited to around the Merredin area while Afghan thistle was a problem around Corrigin. Stemless thistle and Asphodelus were considered problems only at Esperance.

Andrew Storrie from AGRONOMO facilitated and presented at all five workshops and was supported by either Dr Catherine Borger or Ms Alexandra Douglas from the WA Department of Primary Industries and Regional Development.

Another five summer weed management workshops will be held at Dalwallinu, Moora, Wickepin, Kojonup and Ravensthorpe in spring 2019.

More information: Andrew Storrie, andrew@agronomo.com.au

GRDC Research Code ARN1811-001WSX

GRDC Western Identifying Western Australian Weeds Manual

Spray Application Manual - Module 2: Product requirements

Maintaining efficacy with larger droplets - New 2,4-D application requirements

GRDC Nozzle Selection Guide

Pulse width modulation - nozzle selection guide

Aa