- A spray tillage tool was constructed which incorporated the use of a commercially available row guidance system and differential global positioning system to provide precise placement of mechanical tillage devices and nozzles in a crop canopy and to tigger applications of chemical solutions. The tool was evaluated in a LEPA irrigated cotton production system where perennial weeds were the targeted pest. Results indicate that the variability of cotton lint yield within the test area was more highly correlated to crop water use factors than other factors including perennial weed infestation. The site-specific control of perennial weeds should have a long-term positive effect on weed control, but did not show an economic advantage over traditional cultural practices within the two years of the experiment. Precision cultivation for the control of dense populations of woollyleaf bursage in cotton was very positive.