Zone Managment In Center Pivot Irrigated Fields – Improving Efficiency In Insect Control Termination Using Cotman In Spatially Variable Cotton Fields

Progressive growers in Arkansas incorporate site-specific zone management practices in center pivot sprinkler irrigated fields, reducing both seeding and fertilizer rates in the lower yielding non-irrigated portions of the field relative to irrigated crop areas. We wanted to find out if this zone approach was practical for use in an insect pest management program.  Are differences in plant growth and pest risk among irrigation zones sufficient to be worthy of extra time and effort required for increased sampling time by scouts? During the 2011-2012 growing seasons, we monitored large commercial fields to compare crop growth and tarnished plant bug infestations across irrigated and rainfed management zones -- irrigated “circles” and rainfed “corners”.  Crop monitoring using COTMAN and sampling for tarnished plant bug were made season long in three sites per field for each management zone.  COTMAN crop growth curves showed significant spatial and temporal differences in crop maturity. Days to cutout differed from 1 to 3 weeks between zones. Such maturity differences are sufficiently large to warrant differential crop protection practices in late season if infestation levels exceed action thresholds. In 2012, plant bug numbers increased above recommended action levels in late season, and we installed an embedded, replicated strip trial in one field to evaluate insect control termination in a conventional blanket spray compared to management zone approach. Plants in the rainfed zone were well past the “safe” stage while those in the irrigated zone were still in the susceptible stage for tarnished plant bug. Results from the control termination trial support the use of zone management in timing insect control termination. Rainfed cotton produced lower lint yields than irrigated cotton. There was no yield penalty associated with eliminating the final insecticide application. Insecticide costs were reduced 14% with the zone approach compared to a broadcast application.