Background and aim
Post-emergent weed control continues to be an issue; particularly the lack of herbicides to effectively control wild radish (Raphanis Raphanistrum). Previous work indicates that chickpeas crop-topped at the right time to control weed seed set yield 80% or less of unsprayed controls. In 2016, chickpea lines from the national breeding program were screened at Geraldton to identified early maturing material. A promising early flowering line was tested against some of the commercially available cultivars. The aim was to determine if very early maturing chickpea lines can be crop-topped at suitable time to reduce weed seed production without large yield losses.
Chickpea, cultivars Neelam, PBA Striker, Genesis 836 and a breeding line CICA1541 were sown 10km east of Mingenew on 26 May using a plot cone seeder. Plots were 20 metres long by 1.54 metres wide. Plots were blocked for desiccation treatment to enable herbicide application with a 10 metre wide ute mounted boom. Measurements included plant density, hand harvest for biomass at maturity, and yield components; pods per plant, seed per plant and aborted/undeveloped seed per plant and machine harvested yield.
Treatments included the four varieties/lines by three crop desiccation times. Plots were desiccated using gramoxone on either 2 October (mid-podding) or 16 October (late podding). A third unsprayed control treatment was included in which plants were left to mature without chemical being applied. These plants were mature and ready for harvest on 30 October.
Rainfall at the site was 293mm for the year and 172mm from sowing to maturity.
Plant density was measured on 29 June. As expected there was no effect of the crop-topping treatments, as they had not yet been applied, this indicates even establishment over the site.
Plant development was delayed due to the late emergence with the first few plants in the plots flowering around mid-August. By early September all varieties were at full flower and within a short period of approximately two weeks flowering had almost finished and pod set initiated (Table 3). With the narrow flowering window there was little difference in phenology between varieties, in fact, CICA1541 was slightly behind the others in contrast to our earlier experiences in 2016 where CICA1541 flowered and matured earlier than most other lines when sown on 6 May at Woorree. On 2 October, the first time of crop-topping, flowering had finished and plants were at mid pod-fill (Figure 1).
|Variety||10 Aug 2017||7 Sep 2017||18 Sep 2017||2 Oct 2017 (first crop-top timing)||16 Oct2017 (second crop-top timing)||25 Oct 2017|
|Genesis 836||First flowers||100% flowers, first pods formed||5% flowers, podding||0% flower, podding||40% senescence||100% senescence|
|Neelam||First flowers||100% flower, first pods starting to form||5% flowers, podding||0% flower, podding||40% senescence||100% senescence|
|CICA1541||0% flower||100% flower, no pods||20% flowers, podding||0% flower, podding||20% senescence||100% senescence|
|PBA Striker||5% flower||100% flower, first pods formed||5% flowers, podding||0% flower, podding||60% senescence||100% senescence|
Total dry matter was low, averaging 274g/m2. Varieties differed in dry matter production (P <0.001), CICA1541 with more biomass than the other varieties. Dry matter was reduced by crop-topping on 2 October (P <0.001).
Average site yield was 1.1t/ha. There was no significant difference between yields of the varieties when averaged across times of crop-topping. Crop-topping reduced yield (P <0.001); the 2 October treatment by 41% compared to the unsprayed control and the 16 October treatment by 10% (Figure 2).
Plants of each variety had a similar number of seeds. Crop-topping on 2 October reduced seed number per plant to approximately 75% of the 16 October and the unsprayed control treatments (P <0.001) (Table 5). There was a large range in the number of undeveloped seeds per plant between the varieties, CICA1541 having the most (Table 5). Crop-topping on 2 October resulted in more than twice as many undeveloped seeds as the 16 October and the unsprayed control treatments. The number of empty pods per plant also differed between varieties (P <0.001), CICA1541 and Genesis836 with more empty pods than the other two varieties. This larger number of undeveloped seeds and pods with no seeds from CICA1541 indicates that this line has a higher yield potential than the named varieties in the trial. Crop-topping early on 2 October resulted in approximately twice as many empty pods as the 16 October and the unsprayed control treatments (Table 5).
|Seeds/plant||Undeveloped seeds/plant||Empty pods/plants|
|Variety||Crop- topping 2 Oct||Crop- topping 16 Oct||Nil crop- topping||Average||Crop- topping 2 Oct||Crop- topping 16 Oct||Nil crop- topping||Average||Crop- topping 2 Oct||Crop- topping 16 Oct||Nil crop- topping||Average|
|P value variety||NS||<0.001||<0.001|
|P value crop-top||<0.05||<0.001||<0.001|
|P value interaction||NS||NS||<0.05|
Crop-topping at the right time to control weed seeds resulted in a 41% reduction in yield and reduced seed quality. This may have been exacerbated by seasonal conditions with the very late emergence of the crop restricting the length of growing season. However, the timing of weed seed set and chickpea maturity are likely to respond in a similar way to seasonal conditions and even the earliest maturing lines mature after weed seeds are viable.
Thanks to DPIRD’s Geraldton Research Support team and Stephanie Boyce for managing the trial (17GE03) (GRDC project number: DAW00227). The Mingenew Irwin Group and Darrin Lee for site management. Kristy Hobson for supplying CICA1541 seed, Coorow Seeds for supplying Genesis 836 seed and Alosca Technologies for supplying inoculant.
PBA Striker is protected under the Plant Breeders Rights Act 1994.