Previous research has shown that PBA HurricaneXT has a high level of tolerance to both post-sowing pre-emergent (PSPE) and post-emergent (PE) applications of imazethapyr (Spinnaker®). This has resulted in a permit for use of this chemistry in ‘XT’ varieties. The ‘XT’ varieties have also shown improved tolerance to many other, but not all, Group B herbicides, including sulfonylureas (such as Ally®), triazolopyrimidines (such as Broadstrike®) and other imidazolinones (such as Raptor®) over intolerant varieties (such as PBA Flash).
With sulfonylureas being a common additive to many summer knock-down sprays, as well as being used regularly in preceding cereal crops, there has been intense interest in exploiting this improved tolerance to these chemistries in the form of soil residues. However, minimal work has been done in this area and, to date, variable responses have been generated. This trial was designed to simulate potential response to residual Group B herbicides in the new ‘XT’ lentil varieties.
The Southern Pulse Agronomy program, funded by GRDC, DEDVic, SARDI and NSWDPI, undertakes a range of agronomic trials to ensure that the benefits of new pulse varieties are maximised and delivered to growers.
TAKE HOME MESSAGES
- PBA HurricaneXT has improved tolerance to the sulfonylurea herbicides, indicating potential benefits where residues may be an issue in cropping systems.
- Where herbicide residues are not an issue and the use of imazethapyr is not required, varieties such as PBA Bolt, PBA Ace and PBA Jumbo2
AIM
To identify levels of tolerance to ‘residual’ Group B herbicides in lentil cultivars with improved tolerance to Group B herbicides
TRIAL DETAILS
Location: Curyo
Soil type: Sandy loam without sub-soil constraints
GSR (Apr-Oct): 135mm (approx.)
Crop type: Lentils – PBA HurricaneXT, CIPAL 1208 and PBA Flash
Sowing date: 19 May
Seeding equipment: Lucerne points, 4 rows, 36cm row spacing, sown inter-row into standing stubble
Target plant density: 120 plants/m²
Harvest date: 29 October
TRIAL INPUTS
Seed treatment: P-PickleT® and Gaucho®
Fertiliser: MAP + Zn (2.5%) @ 60kg/ha applied at sowing. Appropriate granular inoculant was applied to ensure optimal nodulation.
Herbicide:
Pre-sowing Trifluralin 480 @ 600ml/ha + simazine 900 @ 600g/ha + glyphosate 480 @ 2L/ha
In-crop Clethodim 240 @ 500ml/ha + haloxyfop 520 @ 30ml/ha (see Table 1)
Insecticide: Alpha-cypermethrin 100 @ 160ml/ha
METHOD
Twenty three herbicide treatments were applied (see Table 1) to three lentil varieties (PBA HurricaneXT, CIPAL 1208 and PBA Flash) in a replicated split-plot trial design. The herbicide treatments included two imidazolinones (imazathapyr and imazapyr), two sulfonylureas (chlorsulfuron and metsulfuronmethyl), one triazolopyrimidine (triasulfuron) and one Group I (clopyralid). All chemicals except the imidazolines were applied at varying rates to simulate potential residual concentrations. Visual herbicide damage, grain yield and grain weight were assessed.
The trial was also replicated at two other sites to ensure understanding of responses across soil types and rainfall zones.
RESULTS AND INTERPRETATION
CROP DAMAGE
Visual herbicide damage symptoms were severe where most treatments had been applied to the intolerant genotype PBA Flash, with many treatments resulting in complete death (Table 1). The lowest amount of crop damage occurred when the lower rates of clopyralid, triasulfuron and metsulfuron-methyl were applied.
CIPAL1208 showed a similar response to PBA Flash, except when imazethapyr, imazpic and triasulfuron were applied. In these instances, less damage was observed. The only treatment to show no significant damage was imazethapyr. PBA HurricaneXT showed no significant damage to all the Group B herbicides except when chlorsulfuron and triasulfuron were applied, PSPE at the full rate (R), and when imazapyr was applied at four times the rate (4R). The response to imazapyr is similar to that observed in previous trials.
Significant damage occurred at all rates of clopyralid.
GRAIN YIELD
For the intolerant genotype PBA Flash, all herbicide treatments except the lower rates of metsulfuron-methyl, triasulfuron and clopyralid caused significant or complete yield loss (Table 2). Within the tolerant lines, CIPAL1208 showed significant yield loss to most of the chlorsulfuron treatments and higher rates of other herbicides. Both imidazolinone treatments caused no significant yield loss. PBA HurricaneXT only suffered significant yield loss where imazapyr was applied or where high rates of chlorsulfuron (PSPE) and clopyralid were applied.
Responses were similar to those observed previously and reflect the difference in forms of Group B herbicide tolerance. CIPAL1208 only has tolerance to the imidazolinones and partly to the triazolopyrimidines, but no tolerance to the sulfonylureas. PBA HurricaneXT, has much broader tolerance. Previous research, which was replicated here, has shown it has excellent tolerance to all imidazolinone herbicides except imazapyr. The work here also demonstrates increased levels of tolerance to various sulfonylurea herbicides, particularly at residual levels expected after the previous season’s cereal crop.
COMMERCIAL PRACTICE
Herbicide tolerant lentils have the potential to deliver significant farming systems benefits through: improved weed control; increased control options in lentil crops and in the previous rotation phase; and decreased pressure on herbicides currently employed for broadleaf weed control in lentils. However, it is important to adhere to chemical product label rates, plant back periods and directions for use.
Growers are also reminded that PBA HurricaneXT is not the highest yielding lentil variety when herbicides residues are not an issue and the use of imazethapyr is not required. Varieties such as PBA Bolt, PBA Ace and PBA Jumbo2 all have long-term yields five to ten per cent greater than PBA HurricaneXT in the southern Mallee. In 2014, trials at the Curyo site indicated yields in these varieties 30-40% (0.3 to 0.4t/ha) greater than PBA HurricaneXT.
Continuous monitoring of weed resistance levels and discussion about methods to maximise the benefits of this herbicide tolerance technology for the whole farming system should continue. The benefit of PBA HurricaneXT has already been demonstrated, with it being the largest ever release for a lentil. It is expected to be the dominant variety within two to three years.
ACKNOWLEDGEMENTS
This research was funded by GRDC, DEDVic, SARDI and NSWDPI (DAV00113).
