Lentil tolerance to Brodal Options

Take home messages

• PBA Jumbo2 showed the greatest visual damage from Brodal Options^® application.
• In this season, and under good spray conditions Brodal Options^® did not affect yield.

Background

Brodal Options^® (diflufenican) is an important herbicide for the in-crop manangement of broadleaf weeds (controls wild radish, hedge mustard, turnip, deadnettle, prickly lettuce and gives suppression of capeweed, marshmallow, skeleton weed and amsinckia) in lentils.

It is known that Brodal can cause crop discolouration (chlorosis) and potential height reduction in lentil crops, however this is generally not associated with grain yield loss. Anecdotally, growers in the Wimmera and Mallee have observed greater visual damage in some varieties (eg. PBA Jumbo2) compared with others (eg. PBA Bolt). It is unknown if this observation is directly related to the variety or application timing, and if the greater visual damage relates to grain yield responses.

Generally, Brodal is applied early post-emergence after the third node stage and before the start of flowering at a recommended rate of 100 to 200mL/ha. Seasonal influences such as rainfall and temperatures around time of application may also play a part in the level of damage which may or may not be seen. Damage seen may include crop discolouration, appearing as white banding on leaves and stems, and crop height reduction. Soil type also plays a role in how Brodal affects crop health, it is important to note on lighter soils, lower rates of Brodal may be required to minimise crop damage.

Aim

To determine the effect of Brodal damage on grain yield of three lentil varieties (PBA Jumbo2, PBA Hurricane XT and PBA Bolt) sprayed at different growth stages.

Paddock details

Trial details

Trial inputs

Method

A replicated field trial was sown at Narraport using a complete randomised block design with three varieties and three Brodal application timings – 5th node (later than the intended 3rd node due to weather conditions), 7th node and 9th node compared with an untreated control. Brodal was applied at 150mL/ha at all timings.

Weather conditions were recorded at each application timing and no rain or frost events were recorded in the days prior to or directly after application.

Assessments included visual herbicide damage scores (0 – no damage; 9 – crop death), two to three weeks after Brodal applications, normalised difference vegetation index (NDVI) with a drone and grain yield.

Results and interpretation

The trial was sown into a fallow so subsoil moisture was good and the crop established well (although not a common lentil rotation). However it was a well below average rainfall year resulting in some variation being observed in the trial growth and development later in the season. This was likely driven by soil type (exacerbated in a dry year) and limited soil moisture late in the season or underlying subsoil constraints.

Herbicide damage scores

PBA Jumbo2 had greater visual herbicide damage than PBA Bolt or PBA Hurricane XT for each Brodal application timing (Table 1). Generally, the level of damage was low with slight discolouration on the leaves and stems. For all application timings and varieties, the crop recovered and new growth soon made it difficult to see which leaves had been affected by Brodal application. It is likely damage observed remained low as a result of favourable weather conditions at the time of all applications with no frost, rain or extreme weather events surrounding these times.

The soil type was heavy and therefore less susceptible to the level of crop damage that occurs on lighter soils. Recovery from Brodal was noted through damage scores later in the season and it was found that even up to 10 weeks post application it was easier to find the damaged leaves in PBA Jumbo2 compared to the other varieties. The damage from Brodal remains on the plant but is often difficult to observe when the plant has new growth that covers the affected foliage. Still seeing the effects 10 weeks after the 5th node application in PBA Jumbo2 is likely a result of this variety displaying the greatest symptoms from the application. It could also be said that the other varieties (PBA Bolt and PBA Hurricane XT) recovered faster and put on new growth quicker to overcome the damage from the Brodal application.

Table 1. Mean herbicide damage score 2-3 weeks after each Brodal Options^® application timing for all varieties (0 – no damage, 9 – crop death).

NDVI

Early in the season NDVI assessments showed significantly higher results in PBA Bolt than the other varieties, PBA Jumbo2 and PBA Hurricane XT. Later in the season NDVI assessments revealed lower NDVI results in PBA Bolt, which supports PBA Bolts growth habits as an earlier maturing variety. There was no main effect of Brodal use or interaction between NDVI and Brodal use, suggesting that the effect of Brodal was not substantial enough to detect using NDVI, and that there were no substantive differences between variety response to Brodal application.

Yield

Despite observing some herbicide damage on plots following Brodal applications, there was no impact on yield or interaction between variety and Brodal use. It should be taken into account that this trial was carried out on a fallow paddock. Usual farming practices would see lentils in the rotation following a cereal. Whereas this paddock had minimal stubble following a fallow, summer cultivation and a pre-sowing prickle chain. The crop was also not under stress from pre-emergent herbicide, disease or any insect damage and received no significant weather events around the time of sprays. This resulted in ideal conditions. The only effect noted was a variety response with PBA Bolt yielding 0.13t/ha more than PBA Jumbo2 and PBA Hurricane XT (Table 2). The higher yield is likely a result of PBA Bolt maturing earlier than the others in a dry season that lacked rainfall later in the year. Receiving no yield penalty despite the herbicide damage observed shows that it is important not to jump to conclusions and assume a reduced yield will follow when observing only slight damage to the plants.

Table 2. Grain yield of lentil varieties.

Commercial practice

The use of Brodal to control broadleaf weeds in lentil crops is essential to maximise yield and reduce weed seed banks. However it can be difficult to ensure crop safety is not compromised with so many factors influencing how a herbicide such as Brodal will perform. The expanding nature of farms and spraying programs means some crops in a program may be sprayed at less than ideal times, increasing the risk of damage to the crop from Brodal. Results of this trial suggest growers need not panic when observing only slight herbicide damage in lentil plants however an understanding of the conditions that predispose a crop to more significant damage are important. Applying Brodal to healthy crops provides a safe management option and always follow the label recommendations prior to application.

The difference in variety tolerance, although not specific varieties, is outlined on the label. If growers know which varieties are more likely to be affected, and at what growth stage, minimise these effects by choosing appropriate spray timings or weather conditions.

Further investigation is required to determine what level, if any, of visual damage from Brodal impacts on grain yield. A different result may be observed in a different season with an average or above average rainfall season, different soil type and spraying conditions.

Acknowledgements

This trial was funded by BCG members through their membership.