Herbicide Matrix

Take home messages

• Herbicide matrix designs can enable researchers, growers and advisers to screen a large number of herbicide products to identify the most effective brew on a range of weed species.
• The lack of rainfall at the site and heat stress meant conditions and weed sizes were not ideal for some herbicides.
• The most effective products across the range of crop and weed species were Velocity^®, Paradigm Arylex^®, Intervix^® and Ally^® plus Agtryne^®.

Background

The concept of a herbicide matrix is not new. In fact, it was one of the very first trials conducted by BCG. Typically, these trials are demonstration only (no replication) and used to highlight the negative effects of using particular herbicides on certain crops. As a result, the findings and observations are not always published. Nevertheless, they can be handy to gauge what activity certain mixes give in different seasons, particularly in the presence of an unusual and varied mixture of weeds.

The Mallee’s constantly evolving farming systems and management practices have seen changes in both the type of crops grown as well as in the weed spectrum. Under stubble retained systems, controlling volunteers can be problematic, especially since the increase in the area sown to pulses has led to them becoming a weed in cereals and oilseeds. The need to kill volunteer pulses without the use of residual herbicides such as Lontrel^® is becoming increasingly challenging.

Note: Some of the herbicides tested in this demonstration were not registered for use on the pulse crops to which they were applied, and were used only for research purposes. Any off-label use of herbicides is the user’s responsibility, including residue control, environmental safeguards, occupational health and safety and animal welfare.

Aim

To demonstrate a range of new and current herbicides for controlling certain weeds and volunteer crops.

Trial details

Location:                             Quambatook

Soil type:                             Sandy clay loam

Annual rainfall:                    225mm

GSR (Apr-Oct):                    165mm

Crop types:                          Lentils, chickpeas, lupins, faba beans, vetch, field peas

Sowing date:                        22 June

Seeding equipment:            Knife points, press wheels, 30cm row spacing

Spray application date:       17 September

Weather details:                   Temperature 18.4°C, humidity 47%, wind 10km/hr, overcast

Water rate:                            100L/ha

Nozzle type:                         AIXR110-015

Trial inputs

Fertiliser:                              Granulock Supreme Z @ 55kg/ha at sowing

Herbicides:                           refer to table No. 1

Insecticides:                         Fastac @ 200ml/ha was applied to the entire trial for aphids.

Method

This demonstration was sown into a field peas stubble at the BCG research site at Quambatook. The various pulse crops were sown to ensure an even distribution in each treatment. The reason for including these crops was to determine products that have activity for their control (as volunteers), not for the purpose of determining crop safety and the use of the product or mixture in those crops.

The site was particularly unusual in that it contained populations of challenging broadleaf weeds such as fumitory, thistles, turnips, mustards and poppies. A knockdown was applied before the trial was sown. The trial was sown late (June 22) and rainfall was below average for the season. Plants were considered stressed when the trial was sprayed with the herbicide treatments (Table 1).

Visual rating of efficacy was conducted by five independent assessors with each treatment rated on a 1 (no effect) to 5 (dead) scale. The values presented are the average scores of the five assessors. The trial was terminated on the day of the final assessment to prevent seed set.

Table 1. List of the treatments used in the demonstration and their mode of actions. 

Results and interpretation

The trial was established late within the sowing window, which meant that the timing of the herbicide applications was later in the season than it would be commercially and plant growth was slow. Subsequently, many of the weeds were relatively stressed and of moderate to large size (Table 2) when the treatments were applied. This would see products such as diflufenican (Brodal) struggle, as they work best when weeds are small and actively growing.

Table 2. Growth stages of the different weeds at the time of spraying.

Figure 1 shows the rainfall recorded from the time the treatments were applied until the assessments were made. Following the application, the site did not receive rainfall for another 23 days. This would have affected the uptake of some herbicides, such as metribuzin (Lexone^®) and simazine because these products work best when applied just before a rainfall. The assessment was taken only 10 days after the 12mm of rain, which may not have been sufficient time for some herbicides to completely kill the weeds. Unfortunately, to prevent weed seed set, the trial had to be terminated at that time.

Figure 1. Daily rainfall in September and October, treatments applied and assessment dates.

The most effective products across the range of crop and weed species were Velocity, Paradigm Arylex, Intervix and Ally plus Agtryne (Table 3). Flight, Sharpen and Spinnaker also provided a good to moderate level of control across the crop types but less efficacy on the weeds. As expected, the Imi-tolerant lentil was less affected by group B herbicides than the conventional type.

Broadstrike, Tigrex and Brodal mixes failed to have much activity on the pulse crops and little effect on the weed species. This is what would be expected, given the size of the weeds, insufficient rainfall after application and the plants not actively growing. It is important to note that the rate of Tigrex used was below commercial rates. At those rates, comparisons can be made between the other diflufenican (Brodal) mixes. Igran, Agtryne and Affinity are known to have good activity on white iron weed but in this trial the size of the plants may have meant those products struggled to successfully control the weed.

The group G products (Valor, Sharpen and Affinity) were very effective at controlling the pulses. Ecopar was the least effective on the pulses with the exception of vetch and faba beans. Ecopar is likely to get registration in faba beans, so this result does possibly reflect timing; crop stress may have contributed as well. All of these products, however, failed to have any effect any on the other weed species apart from the poppies. It is plausible that the addition of a higher rate of MCPA amine or the use of 2,4-D amine would have improved control, particularly in some of the weed species. The addition of the oil in the Valor treatment significantly improved efficacy, having a much greater effect on the crop species but little on the weeds. Increasing the rate of Ecopar only improved control slightly, but it should be noted that there was no oil used.

Table 3. Efficacy ratings (ave. of five assessors) between the different treatments. 1 (no effect) and 5 (dead).

Commercial practice

It is important for growers to ensure they grasp a basic understanding of how herbicides work and how dry seasons may limit the efficacy of some commonly used products. Learning about the various options and discussing them with your agronomist, or visiting demonstrations similar to this one, will be the best way to improve your knowledge.

This trial should not be seen as justification for the use of any of these herbicides in the various crop species unless they are registered. Subtle effects that may have affected yield could not be determined, nor were the crops examined managed as a commercial crop would have been. The demonstration was simply designed to compare products for controlling volunteer pulses and certain weed species.

Acknowledgements

The trial was funded by Farm360 with in-kind support from BCG staff members.