Recovery from terminal and fruit damage by dry season cotton crops in tropical Australia.

We conducted a 2-yr field study on growth and yield compensation in cotton (Gossypium hirsutum L.) after artificial pest damage in Kununurra in NW Australia. The aim was to assess the responses of cotton grown in tropical Australia to simulated Helicoverpa damage early in the season (tip damage) and during fruiting (square removal). In this region, cotton is grown in an inverse temperature regimen to cotton grown in temperate regions, and it is possible that tropical cotton crops exhibit different responses to pest damage (Yeates 2001). To examine this, we imposed manual damage treatments by excising plant tips before squaring (flower bud production) and removing all large squares at 800 degree-days DD, (at base 12 degrees C; early square loss) or 1,200 DD (mid-square loss). We found high levels of tolerance in tropical cotton to simulated pest damage (particularly early square loss) equaling or possibly surpassing the compensatory response of cotton grown in temperate Australia. While yield did not differ between damage and control treatments, the trend suggests an increase in yield resulting from tip damage and early fruit loss. Compared with temperate crops, the delay in maturity caused by damage was minimal, owing to high rates of boll opening (up to 11% d(-1)). Early season tip damage resulted in a significant increase in lateral branch growth that later contributed to a higher fruiting potential. The altered canopy of tip-damaged plants also increased light interception, particularly in the upper canopy. Both of the above factors could confer a greater tolerance to subsequent fruit damage in tipped plants.