Boxer Gold® safety in oats

Take home messages

• Boxer Gold^® was found to have no yield penalty on Mitika and Wintaroo oats in 2016 (GSR 371mm), contrasting the 9.7 per cent yield penalty in 2015 (GSR 141mm).
• Although yield was not affected, biomass was reduced when Boxer Gold was applied in-crop.
• Safety of Boxer Gold use in oats is highly reliant on seasonal conditions and should be undertaken with caution.

Background

The production of oats for hay, grain and as a grazing crop has increased significantly in recent years. There is increasing demand for good quality oaten hay for export and for grain as a source of raw or processed feed for livestock which attracts a premium over other hay and grain alternatives.

Oats are a competitive crop capable of producing more tillers than other cereal crops. However, the herbicide options to control ryegrass in oats are limited which means that oats must be grown in ‘clean’ paddocks or cut for hay to prevent seed set. While this is a sound integrated weed management (IWM) strategy, the presence of ryegrass impurities in hay downgrades its quality and, consequently, potential returns.

There are three main herbicide options available for the control of ryegrass in oats:

• Diuron^® (Diuron) – registered for the suppression of annual ryegrass, barley grass and silver grass in WA
• Dual Gold^® (S – metalachlor) – registered for the suppression of annual ryegrass
• Glean^® (chlorosulfuron) – was registered for annual ryegrass control, but this registration
  ceased on 30 June 2015.

Diuron^® and Dual Gold^® are effective only for suppression of ryegrass and are reliant on rainfall after application to work effectively. Glean has a long re-cropping interval (>9 months) for barley and legume crops, and many ryegrass populations are now resistant.

Boxer Gold^® has been used to control annual ryegrass in wheat and barley for over 10 years. It is used either IBS, as a split application (IBS and PSPE) or post emergent (one to three leaf ). Boxer Gold^® is not registered for use in oats. Its positional selectivity relies on the difference between the depth of wheat and barley roots in the soil compared to grass weeds and placement of the herbicide treated soil. Rainfall helps move herbicide into the seed zone where the roots and emerging shoots of grass weeds generally lie and are susceptible. Cereal roots emerge below this band of herbicide activity and so are not affected by it.

Boxer Gold^® has been shown to have limited efficacy on wild oats so given the close familial
relationship between wild oats and oats the potential exists for Boxer Gold^® to be used in oats for the control of annual ryegrass.

BCG carried out a trial investigating Boxer Gold^® safety in oats in 2015 at Berriwillock where it was shown to produce a 9.7 per cent yield penalty when applied to oats (McClelland 2015). This was in a season with poor spring rainfall which may have exacerbated the effects.

This trial was repeated in 2016 to explore the crop safety of Boxer Gold^® in oats under very different seasonal conditions. In-crop applications were used to fully examine crop tolerance.

Note: Some of the herbicides used in this trial are not registered for use in certain crops, and were tested for experimental purposes only. Always read the label and adhere to directions when using herbicides.

Aim

To investigate the tolerance of oats to Boxer Gold^®.

Paddock details

Trial details

Trial inputs

Pests and disease were managed according to best management practice.

Method

A replicated field trial was sown using a complete randomised block trial design. All plots received consistent agronomic management with the exception of the in-crop treatment applications where Boxer Gold^® was applied at two separate timings (Table 1). Assessments included establishment counts, NDVI, biomass, grain yield and grain quality.

Table 1. In-crop herbicide treatment applications, dates and rates.

Results and interpretation

There was found to be no measurable grain yield penalty from using Boxer Gold^® in Mitika and Wintaroo in 2016 despite differences in biomass during the season (Table 2).

This is a contrast to the 2015 trial results which found close to 10 per cent yield penalty when Boxer Gold^® was applied. This was likely due to the favourable seasonal conditions this year eliminating moisture as a limiting factor. Growing season rainfall in 2015 was 141mm compared with 371mm in 2016, so the poor season and dry spring in 2015 likely exacerbated the negative effect of the Boxer Gold^® application.

This year, there were effects of herbicide damage present in both varieties of oats up to GS70 shown in both biomass and NDVI data. The later timing application (GS21-22) appeared to have a greater effect than the earlier application (GS13) which was indistinguishable from the control by GS70. However, this may have just been a consequence of the earlier treated plots having more time to recover as there was no yield penalty at either timing.

Variety did not influence response to Boxer Gold^® in this trial with Mitika and Winteroo both affected similarly. There was also no effect on grain quality from Boxer Gold^® application. Mitika had a mean protein of 13.3 per cent, test weight was 50.45kg/hL and screenings were 2.95 per cent. Wintaroo had a mean protein of 13 per cent, test weight was 51.2kg/hL and screenings were 4.66 per cent.

Table 2. Treatment mean NDVI, biomass and yield.

Commercial practice

Boxer Gold^® use in oats may be viable, giving growers greater flexibility in paddock selection for oat crops. This may allow other factors to be considered (eg. potential production) rather than considering only the ryegrass burden in the paddock.

From research over two years it is apparent that the seasonal conditions can have a significant impact on the effect of Boxer Gold^® on oat yield and it is best applied in a year with higher rainfall – although this is near impossible to predict at the time of application. Crop safety of Boxer Gold^® relies on both physiological and positional selectivity. Timing, amount of rainfall and soil type will also influence efficacy and crop safety of Boxer Gold^®. Due to the importance of positional selectivity for crop safety, it would be expected that if used in oats, crop safety would be greatest when applied pre-emergent IBS rather than in-crop early post emergent. A later application may mean a better idea of the seasonal forecast but also means reduced ryegrass control if ryegrass is past the one-leaf stage. Sowing later could be a good management strategy as it would delay emergence and allow for an early hit on young ryegrass.

A grower may be prepared to accept a potential loss of 10 per cent in a dry year if ryegrass control is improved and there is the possibility that in good seasonal conditions there may be no penalty. Any short-term loss may well be compensated by the long-term benefits of reduced seed set; although this may only be viable in paddocks destined for grain as almost a tonne per hectare of biomass loss in hay could significantly reduce production.

It must be remembered that these results are examining the tolerance of Boxer Gold^® use in-crop up to GS22 and Boxer Gold (not registered in oats) is generally applied IBS, PSPE or up to GS11-13. These results are only from two years of research and so should be viewed with caution and examined under a range of seasonal conditions.

On-farm profitability

The results of the previous two years of trials has promising potential for the use of Boxer Gold^® for ryegrass control in oats. However, this practice needs to be carefully considered depending on of the intended end-use of the oat crop.

In a hay crop a trade-off would need to be made between hay yield and quality, particularly if producing export quality hay. If producing milling oats the cost of a Boxer Gold^® application ($39/ha) and any potential yield penalty would need to be weighed against the cost of cleaning seed ($15-30/t depending on level of ryegrass removal).

In oats sown for seed it may be more viable to spray a section of the paddock and cut the rest for hay, prior to ryegrass seed set. The benefit of controlling weeds and avoiding a weed blow-out will improve future production and should not be ignored. However, at $39/ha ($15.7/L) it is an expensive herbicide option and the spray cost and potential yield penalty need to be balanced with the benefit of weed control and potential returns.

Growers also need to consider the limitations of herbicides like Boxer Gold^® that require moisture to be active which means that at the optimal stage for ryegrass control, conditions may not be conductive to herbicide application.

References

McClelland T., 2015, 2015 BCG Season Research Results, ‘Boxer Gold^® safety in oats’ pp. 128-131.

Acknowledgements

This trial was funded by BCG members through their membership.