This 4 year project spanned a critical juncture as the CQ industry transitioned from Bollgard II® to Bollgard® 3 enabling more flexible growing arrangements. The local industry had been presented with the results of a 4 year study on the interaction between the local climate and cotton production with a key finding being that late-winter sowing may mitigate yield variability and stagnation. With a choice of planting very early or late this project benchmarked commercially-grown crops during the adoption period. An analysis of the growth of crops sown at different times would better inform decision making during a period of considerable change. Anticipating that pest management issues may again re-emerge in CQ with the increased 5 month sowing window, strategic sampling was also undertaken to re-assess Helicoverpa recruitment within the CQ farming system and compare it with a similar study conducted 20 years prior. The project also delivered national biosecurity leadership for the cotton industry within the CottonInfo program.
The project outcomes were
• Crop benchmarking confirmed that late-winter sowing best matched flowering and boll development with the summer solstice and a lower incidence of cloud or heat stress. An earlier harvest also reduced the risk of pre-harvest weathering, collectively enabling over 40% higher yields than traditional spring sowing without additional crop inputs. Traditional spring and later sowings coincided unfavourable climate with the more susceptible growth phases of late boll filling or early flowering respectively. Declining solar radiation and temperatures prevented yield recovery for the latest summer-sown crops.
• Growing crops on (second cycle flowering) is an effective tactic for overcoming pre-harvest weathering damage with the additional lint produced recovering lost yield whilst also diluting the contribution of damaged fibre and thus improving lint quality. Yield produced during the second cycle of flowering is akin to late December-sown crops (5-7 bales/ha). The combination of two boll cycles can enable very high final yield although crop periods well exceed 200 days.
• Double picked cotton produced very high yields (18-19 bales/ha). Sown in early August, the first crop is picked late January (11-12 bales/ha) and then ratooned and double picked in May (7 bales/ha) with base grade lint produced by both picks. Crop period exceeded 250 days.
• Helicoverpa recruitment in the farming system has changed markedly. Recruitment in chickpeas is a fraction of what it was (0-4900/ha) compared to 20 years ago (50,000-100,000/ha) with higher commodity price and new generation insecticides enabling judicious control. Bollgard cotton acts as a population sink with no meaningful recruitment. Pigeon pea refuges hosted the highest densities of pupae/m2 suggesting that these areas make a significant contribution from a RMP perspective. However, within the broader farming system the collective acreage is miniscule. The contribution of non-Bt exposed Helicoverpa from other crops (natural refugia) is much lower than historical studies would suggest.
• The awareness of farm biosecurity practices has risen amongst growers and industry through the delivery of biosecurity extension products and simultaneously the spread of endemic pests and diseases such as black root rot, Verticillium wilt and mealybug. The adoption of farm biosecurity practices has risen, with 44% of growers completing a farm biosecurity plan (identifying hazards and action plan). Going forward, it will be important to have external motivational drivers (e.g. rewards or incentives) to further increase the adoption of farm biosecurity plans by other growers in the Australian cotton industry.