25 IREC Farmers' Newsletter No. 199 — Autumn 2018 Green mirids were introduced to cages installed in the cotton crop at the IREC Field Station to impose high pest pressure in the contained crop to understand the pest’s effect on final fruit retention and yield. PHOTO: Kieran O’Keeffe issues such as the use of animal manures, the impact of mirids and silverleaf whitefly, options for herbicide resistance management and the potential of growth regulants. Investigating benefits of animal manure Deakin University researcher, Dr Wendy Quayle, reported on the CRDC- funded Optimising the management of manures in southern NSW cotton production project, which is investigating the benefits of using animal manure in cotton production systems. Poultry manure (chicken litter) at different rates and in combination with basal nitrogen fertiliser (anhydrous ammonia or granular urea) is being compared to a non-manure fertiliser programme. The trial also has control treatments of no added nitrogen, to enable calculation of nitrogen supplied to plants by mineralisation of organic matter. Results showed that lint yield, growth parameters, nitrogen use efficiency, and macro and micro nutrient uptake were maximised when the total amount of nitrogen applied was 240 kg N/ha, which was based on 4.0 t/ha of chicken manure in combination with nitrogen fertiliser, applied within one month of pre-planting. Manure had a moderating effect on soil pH decline and increased soil nitrate, phosphorous (Colwell-P) and microbial activity, according to application rate. Dispersion, water retention and potential nitrogen mineralisation were unaffected. It appears that including manure at 4.0 t/ha in combination with relatively low nitrogen fertiliser rates is providing in-season nutrient supply with fertiliser nutrient efficiency benefits and at Whitton, a fairly compacted site, the combination tending to optimise yields, compared with ‘fertiliser only’ programmes. Furthermore, the organic material applications are increasing longer-term, background levels of soil nutrients and increasing soil biological function. The manure trial has also supported research into spectral indices, obtained by drone-mounted sensors, for tracking spatial and temporal variability of plant nitrogen status, as well as predicting lint yield. Yield predictions for the 2017–18 season in the trial can be viewed on Twitter (CeRRF_Griffith) and these will be compared to yield achieved at commercial harvest. Understanding the impact of mirids As part of a larger CottonInfo project, Kieran O’Keeffe, CottonInfo Regional Extension Officer, undertook a mirid trial. The aim of the trial was to find out whether high pressure of green mirids in cotton during early squaring in November and December really makes a difference to final fruit retention and yield. The use of cages and introduction of additional green mirids proved to be an easy and effective way to impose high pest pressure in cotton. When the crop reached early squaring (around five squares per plant) cages were installed and mirids introduced into the crop for a two-week period. Once the cages were removed, fruit count (squares, flowers, bolls) of the area under the cage was done. As the season progresses and the crop reaches 30–40% open, weekly maturity assessments will be made. Open bolls will be picked, counted and stored. This will be repeated fortnightly until all bolls are opened. A yield assessment will then be completed and compared to the non- caged cotton. Combatting whitefly in cotton Emma Ayliffe, consultant with SummitAg, is investigating ‘soft’ spray management options for the control of silverleaf whitefly in cotton. The trial comprises four treatments and a control, with the treatments being: l  Biopest oil l  horticultural soap l detergent l  straight water. The aim of the trial is to try and disrupt the whitefly population and keep the insects under thresholds required for conventional spray treatment. The first spray application of treatments was made in late January, with a second application two weeks later. Throughout the season, whitefly population will be monitored and recorded to gauge the impacts of these treatments and assess the long-term impact on population. While the Whitton site is the only location where this specific work is being conducted, the Australian Cotton Research Institute (ACRI) at Narrabri is researching chemical insecticide options for whitefly. The data collected from the IREC Field Station trial will be fed into the larger ACRI project. Emma is also trialling the use of wasps as a bio control of whitefly. Parasitic wasps have been released with leaf samples collected from the release area ten days after release, to see if parasitism has occurred. If results are favourable with visible signs of parasitism then a second release will be made late February. Managing herbicide resistance Herbicide resistance in Australia is a huge issue, and the southern irrigation areas are no exception. Eric Koetz, Research Agronomist at NSW DPI, used the IREC Field Station to demonstrate herbicide resistance management options. One of the most concerning issues is the development of glyphosate resistance. Eric advised that managing glyphosate resistance requires a multi-pronged attack on weeds. The industry Herbicide Resistance Management Strategy sets out the importance of rotating away from glyphosate as the main tactic for weed control, i.e. using rotations of products with varying modes of herbicide action. Eric’s demonstration consisted of two replications of three treatments for the control of barnyard grass. The treatments were: l  Control — glyphosate only l  Terbyne® — applied at 1 kg/ha, active ingredient terbuthylazine l  Stomp® — applied at 3 L/ha, active ingredient pendimethalin.