Crop maturity can be manipulated by choice of cultivar, insect management, nutrition or water. Early crop maturity may allow growers to pick the crop in a timely manner to avoid quality down grades and perhaps save on water or late season insect protection. However, this needs to be balanced against the fact that in the Australian environment earliness may cost between 0.6 and 1.0 bales/ha per week in lost yield. In this paper we will bring together some pieces of ongoing research which are dealing with understanding and quantifying the mechanisms and management techniques that affect the timing of crop maturity in the Australian cotton industry.

To examine the reasons for genetic differences in crop maturity we have explored in a series of field experiments the difference between late and early cultivars in their ability to supply resources to the fruit. In terms of capturing light and converting it into growth we found that there was a small amount of variation. The cultivars had a similar capacity to intercept light per unit of leaf area. They also had a similar capacity to convert the light they intercepted into photosynthate and hence dry matter. The characteristic that varied most between the cultivars was the way that the fruit load developed. Earlier fruit load development led to an earlier crop cut out and hence earlier maturity. We aim to better understand how this principle can be utilised in crop management.

The timing of crop maturity can also be manipulated by a range of management factors. Insect control retention, and hence fruit retention, is a key driver. Variety, nitrogen, water and growth regulants such as mepiquat chloride are four other factors. In another set of field experiments it was shown that it was far easier to generate differences in maturity by modifying fruit retention rates early in the season. Higher fruit retention through the use of Ingard transgenic varieties and the use of lower action thresholds for pest management were able to induce a variation in crop maturity that was three to four times greater than that caused by manipulating nitrogen, water and mepiquat chloride.

Cultivar choice that varies the rate of fruit production, and pest control (fruit retention) appear to be key components of managing crop maturity in the Australian environment. Research into earliness and the mechanisms that drive the timing of crop maturity is continuing. This includes research at the farming systems scale, crop agronomy and physiology. The capacity of the crop to compensate for insect damage and the concept of crop determinacy are two components also being examined, as the desire for early fruit retention needs to be optimised for integrated pest management.