Effect of Fallow Period Weed Control on Wireworm Populations in Sugarcane

1. Effect of Fallow Period Weed Control on Wireworm Populations in Sugarcane C. Rainbolt and R. Cherry Everglades REC University of Florida/IFAS

2. Introduction • Wireworms, the larval state of the click beetle, are a pest of many crops in FL • Melanotus communis, ‘corn wireworm’ is the most significant in sugarcane

3. Wireworm Damage • Typically only a pest in plant crop • Feed on buds and root primordia during germination and after the crop emerges

4. Impact on Crop • Reduces overall shoot population • Feeding holes can serve as an entrance point for red rot • Leads to non-uniform patchy stands • Reduces yields in plant and subsequent ratoon crops

5. Fallow Period Weed Control • Following harvest the sugarcane stubble is destroyed • Some growers utilize the fallow period to address weed problems • Fallow period weed control is often a combination of mechanical and chemical • Others allow weeds to grow uncontrolled

6. Insect-Weed Relationships • The impact of weed control practices on insect populations if rarely considered • Weeds often serve as alternate hosts for insect pests

7. Related Research • Research in Sweetpotato has shown less wireworms in weed free compared to weedy fields (Seal et al. 1992) • Speculated the reduction in wireworms from mechanical fallow was a result of plowing exposing pupal wireworms to heat, low moisture, and other stresses • Cuthbert et al. 1959 suggested that reduced populations are due to adults avoiding fields in which there is insufficient cover

8. Our Objective To evaluate the effect of chemical and mechanical weed management practices on wireworm populations in fallow fields in Florida

9. Experiment Establishment • The experiment was established in April 2006 at the Everglades Research and Education, Belle Glade, FL following harvest of a second ratoon sugarcane crop • The field was disked 3 times to minimize the remaining sugarcane stubble • Experimental design was a randomized complete block with 5 replications and plots were 12 m wide by 30.5 m long

10. Treatments • Fallow treatments were disking, herbicide application, and a non-treated control • Disking was achieved with a single pass of a 3.05 m disk harrow • Herbicide application was glyphosate at 0.89 kg per ha + 2,4-D at 0.21 kg per ha • Weed control operations were conducted June 7, July 18, and August 29, 2006

11. Data Collected • Pre-treatment samples for weeds and wireworms were taken in all plots during April 2006. • Plots were again sampled for weeds and wireworms in July and October 2006 • The July and October sampling dates coincide with maximum flight activity and oviposition of different wireworm species

12. Wireworm Sampling • Wireworm populations were sampled by collecting four randomly located 50 x 50 x 30 cm soil samples within each plot • After digging, each soil sample was visually examined for wireworms in the field by one person for 20 minutes • Wireworms were stored in alcohol and taken to a laboratory for identification using a microscope

13. Wireworm Sampling

14. Weed Sampling • Weed populations were sampled within five randomly located 0.4-m2 subplots in each plot • Weeds were counted and recorded by genus and species • Mean differences in wireworm and weed populations were determined using a Least Significant Difference (LSD) test

15. A A Weeds per meter2 B B B B

16. Fallow Treatments Untreated Control Herbicide Disking

17. A wireworms per sample A B B B B

18. Wireworms by species

19. Results • Wireworm counts were less in weed free plots • Weed control method, herbicidal or mechanical (disking), did not have an impact • Exact reasons for reduced wireworm populations is unknown

20. Related Research • Impact of weed species on wireworm adult oviposition