Curtis Rainbolt Everglades REC University of Florida Evaluation of hexazinone and diuron combinations for preemergence weed control in Florida sugarcane Curtis Rainbolt Everglades REC University of Florida

Introduction Limited number of PRE herbicides registered for use in FL sugarcane Atrazine Ametryn Flumioxazin Metribuzin Diuron Pendimethalin Combination of hexazinone/diuron was recently labeled for FL sugarcane

PRE Challenges A majority of FL sugarcane is grown on muck soils Typically have 70-85% organic matter Requires high use rates and residual control is typically short Very high weed pressures Grower reluctance to make true PRE applications

Introduction Atrazine at 3-4 lb/A + ametryn at 0.25 -1 lb/A is the most common treatment Typically applied POST to cane and early POST to weeds Typically results in light to moderate phytotoxicity Higher rates of ametryn can be used when cane is growing slowly

DuPont™ K-4™ 60 WG product Commercial premix of 13.2 % hexazinone and 46.8 % diuron In plant and ratoon cane, can be applied PRE at 3.75 to 4 lbs/A Can be applied POST to ratoon cane less than 18 inches tall Post application when daily temperatures exceed 80 F may result in crop injury

Objectives Determine optimum rates and ratios of hexazinone + diuron for PRE control of significant weed species Evaluate the effect of rate on crop injury

Materials and Methods 4 trials were established in spring 2005 Plots were 4 rows by 50 ft long Sprayed with tractor sprayer at 20 GPA Weed control and crop injury evaluated visually

Herbicide treatments K4 at 4lb/A K4 at 6 lb/A K4 at 8 lb/A K4 at 4 lb/A + Sencor at 1 lb/A K4 at 6 lb/A + Prowl H2O at 3.5 qt/A K4 at 4lb/A + Direx at 2.5 lbs/A and K4 at 6 lb/A + Direx at 2.5 lbs/A Prowl H2O at 2.6 qt/A + Aatrex at 3 qt/A + Evik at 1 lb/A (Studies 1 and 2) Prowl H2O at 3.5 qt/A + Aatrex at 4 qt/A + Evik at 0.25 lb/A (Studies 3 and 4)

Site 1 Applied March 15, 2005; Cultivar: CP80-1743 2nd ratoon 10 DAT Crop injury was 5 to 6% with K4 at 10 lb/A, K4 at 4 lb/A + Direx, and K4 at 6 lb/A + Direx By 34 DAT, injury was no longer visible Control of alligatorweed was 18 to 48% 22 DAT and 15 to 33% 34 DAT with K4 treatments Common purslane was controlled 89 to 95% 50 DAT

Alligatorweed 22 DAT with 8 lb/A K4

Weed Control Control of fall panicum was 91 to 96% with all treatments 22 and 34 DAT

K4 at 4 lbs/A + Direx Untreated Control

Site 2 Applied March 21, 2005 Cultivar: CP89-2143 1st ratoon Control of Alexandergrass ranged from 94 to 99% 18 DAT All treatments controlled common lambsquarters 95 to 100% 18 and 32 DAT

Alexandergrass control at Site 2

untreated control 47 DAT K4 4lbs/A 47 DAT K4 10 lbs/A 47 DAT K4 6lbs + Prowl H2O 3.5 qt/A 47 DAT

Crop injury at Site 2

Stunting from K4 treatments

Sites 3 and 4 Both applied on April 11, 2005 Both CP80-1743 first ratoon Site 3 was cultivated and Site 4 was no till Crop injury was similar at both sites, ranging from 3 to 10% 14 DAT

Weed Control at Site 3 14 DAT fall panicum and alexandergrass control was 90 to 99% with all treatments Purple and yellow nutsedge were suppressed 23 to 30% 14 DAT

Weed Control at Site 3

Untreated control 39 DAT K4 at 10 lb/A 39 DAT

Weed Control Site 4 14 DAT fall panicum and giant bristlegrass were controlled 89 to 96% by all treatments Giant bristlegrass control was 93% or higher with all treatments 39 DAT

Conclusions Crop injury occurred at all sites, but was at acceptable levels in CP80-1743 Crop injury was excessive in CP89-2143 and tended to increase with higher rates and additional Direx Fall panicum and alexandergrass control initially was similar with all treatments, but higher rates typically had longer duration

Future Research Determine effect of growth stage and cultivar on phytotoxicity Develop use rates for sugarcane grown on sandy soils

Acknowledgements Thanks to DuPont for supporting these trials Thanks to Glades Sugar Farm for providing field sites

Any questions?