Donald R. Cook, Eugene “Gene” Burris, B. Roger Leonard and Jerry B. Graves
Thrips are early season insect pests of cotton in Louisiana. Injury to cotton seedlings resulting from thrips’ feeding can delay crop maturity and reduce yields. Delayed crop maturity can further expose the crop to damaging infestations of lateseason insects and adverse environmental conditions that hinder defoliation and harvest. These environmental conditions can reduce lint quality and yield. Timely application of fall agronomic practices necessary to the following year’s crop also may be delayed. Evaluating treatments
Stoneville 474 cotton seed was planted at both locations of the Northeast Research Station in early May in both 1996 and 1997. These trials were planted on a Commerce silt loam and Sharkey clay soils at the St. Joseph location and on a Gigger silt loam soil at the Winnsboro location.
The insecticides in these trials included Orthene 80S (6.4 ounces of active ingredient per hundredweight seed) and Gaucho 3.84S (4.0 ounces of active ingredient per hundredweight seed) applied as seed protectants, Orthene 90S (0.9 pound of active ingredient per acre) and Admire 2F (0.2 pound of active ingredient per acre) sprayed in the seed furrow, Temik 15G (0.5 pound of active ingredient per acre) as a granule in the seed furrow and an untreated control.
Control of thrips was measured by randomly selecting five plants per plot at 7, 11, 15, 19, 23 and 27 days after emergence in 1996 and at 7, 11, 16, 19, 23, 27, 31 and 35 days after emergence in 1997. Plant samples were processed using whole plant washing procedures to remove insects. These data for individual sample dates were pooled to determine treatment effects across the entire sampling period. All treatments provided control
At the Sharkey clay site, plots treated with Orthene 80S, Orthene 90S, Admire or Temik had significantly fewer total thrips (adult plus immature insects) compared to plots treated with Gaucho or the untreated plots in 1996 (Figure 1). In 1997, plots treated with Orthene 80S, Gaucho or Temik had significantly lower numbers of thrips compared to plots treated with Admire or the untreated plots.
At the Gigger silt loam site, all insecticide treatments significantly reduced thrips numbers compared to those in the untreated plots in 1996 (Figure 2). In 1997, plots treated with Temik had significantly lower numbers of thrips compared to plots treated with Orthene 90S, Orthene 80S, Gaucho or the untreated plots.
At the Commerce silt loam site, all insecticide treatments significantly reduced the numbers of total thrips compared to the untreated control in 1996 and 1997 (Figure 3).
In 1996, all insecticide treatments significantly reduced days to defoliation and harvest and increased the percentage of first harvest compared to the untreated control across soil environments. In 1997, all insecticide treatments significantly improved crop maturity compared to the untreated control. At first harvest, all insecticide treatments resulted in significantly more lint yield compared to the untreated plots in both 1996 and 1997. There were no significant differences among treatments for final lint yield in 1996 or 1997 (Table 1). Although there were no significant differences observed for final yield, crop maturity was delayed in the un-treated plots.
All insecticide treatments provided satisfactory control of thrips in all three soil environments, with few exceptions. Also, these insecticide treatments resulted in an earlier maturing crop and higher yields at first harvest. These benefits would allow producers to harvest earlier and avoid inclement fall weather and late-season insect infestations. Acknowledgments
The authors wish to thank the summer field personnel at both locations of the Northeast Research Station, as well as Karen Williams and Ralph Sheppard for their assistance in data collection, plot maintenance and pesticide application. Also, the authors wish to thank Cotton Incorporated and Louisiana cotton producers for their financial support of this project.
Donald R. Cook, Research Associate, Department of Entomology, LSU Agricultural Center, Baton Rouge, La.; Eugene “Gene” Burris, Associate Professor, and B. Roger Leonard, Associate Professor, Northeast Research Station, St. Joseph, La.; and Jerry B. Graves, Professor Emeritus, Department of Entomology, LSU Agricultural Center, Baton Rouge, La.
(This article was published in the winter 1999 issue of Louisiana Agriculture.)