Thiamethoxam Seed Treatments Have No Impact on Pest Numbers Or Yield in Cultivated Sunflowers
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FIELD AND FORAGE CROPS Thiamethoxam Seed Treatments Have No Impact on Pest Numbers or Yield in Cultivated Sunflowers 1 2,3 MICHAEL M. BREDESON AND JONATHAN G. LUNDGREN J. Econ. Entomol. 108(6): 2665–2671 (2015); DOI: 10.1093/jee/tov249 ABSTRACT The use of neonicotinoid seed treatments is a nearly ubiquitous practice in sunflower (Helianthus annuus) pest management. Sunflowers have a speciose pest complex, but also harbor a di- verse and abundant community of beneficial, nontarget organisms which may be negatively affected by pest management practices. Here, we investigate how the foliar and subterranean arthropod pest com- munities in sunflower fields were affected by a thiamethoxam seed treatment over three site years (two years on one farm, and another year at an additional field in the second year). Thiamethoxam and its me- tabolite clothianidin in leaf tissue were quantified throughout the growing season, and yield differences between treatments were measured. Across site years, foliar herbivores and key pests of sunflowers were Downloaded from unaffected by the seed treatment. Likewise, subterranean herbivores were unaffected. Thiamethoxam was measurable in leaf tissue through the R1 plant stage, while its metabolite clothianidin was detected throughout flowering (R6). No difference in sunflower yield was observed between treatments across site years. This research suggests that neonicotinoid seed treatments in sunflowers do not always provide economic benefits to farmers in the form of pest reductions or yield improvements. Future research should focus on sunflower integrated pest management strategies that limit nontarget effects of http://jee.oxfordjournals.org/ agrochemicals, while providing greater economic returns to farmers. KEY WORDS Helianthus annuus, herbivore, neonicotinoid, metabolite, clothianidin Producers commonly use neonicotinoid seed dressings causing unregulated nerve excitation (Matsuda et al. to control early-season herbivory on a wide variety of 2001, Meijer et al. 2014). This overstimulation of a tar- crops (Elbert et al. 2008). Neonicotinoids are a class of get cell can cause paralysis and eventually lead to the water-soluble insecticides which, when applied as a death of the insect (Goulson 2013). by guest on July 26, 2016 seed treatment, are present systemically through the Pests of sunflowers (Helianthus annuus; Asterales: plant’s roots (Van Rozen and Ester 2010), green tissue Asteraceae) are challenging to manage in North Amer- (Sur and Stork 2003), nectar (Schmuck et al. 2001), ica for several reasons. First, many wild varieties of and pollen (Laurent and Rathahao 2003). The insecti- sunflower are native to this region, and so have cide gradually becomes less concentrated as the plant coevolved with a diverse suite of indigenous pests grows and as the insecticide is metabolized (Naultetal. (Charlet et al. 1992, Rogers 1992). For example, there 2004, Moser and Obrycki 2009). Metabolites of neoni- are 20 insects of concern recognized in the northern cotinoids applied as seed treatments can be found at Great Plains (Knodel et al. 2010). Many of these pests measurable levels within treated plant tissue (Nauen feed inside the sunflower’s large head and stem which et al. 2003). These chemicals often display insecticidal provides physical refuge for an insect, making the tim- qualities similar to the active ingredient used to treat ing and placement of insecticide a challenge (Knodel the plant (Benzidane et al. 2010), but are often over- et al. 2010). Managing these head-feeding pests is fur- looked in risk-assessment studies focused on the envi- ther complicated because many varieties of sunflowers, ronmental fate of the active ingredient. Upon although self-compatible, still experience a yield benefit consumption of treated plant-tissue by an insect, neoni- from insect pollination (Jyoti and Brewer 1999), and so cotinoid toxins compete with naturally occurring neuro- insecticide application needs to be balanced against transmitters for the same binding sites on a target cell, pollination services (Rogers 1992). Finally, there is very low tolerance for seed-damaging pests in sunflowers destined for certain markets (e.g., the confection mar- ket; Brewer and Schmidt 1995). In general, insecticides Mention of trade names or commercial products in this publication are the primary tool that farmers use to manage pests is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department in their sunflower fields (Rogers 1992 , Prasifka and of Agriculture. Hulke 2012). It is not uncommon for producers to use 1 Department of Biology and Microbiology, South Dakota State multiple applications of broad-spectrum insecticides University, Brookings, SD 57007. during a single growing season. In addition to insecti- 2 USDA-ARS, North Central Agricultural Research Laboratory, Brookings, SD 57006. cidal sprays, conventional producers very frequently 3 Corresponding author, e-mail: [email protected]. use neonicotinoid seed treatments to control early Published by Oxford University Press on behalf of Entomological Society of America 2015. This work is written by US Government employees and is in the public domain in the US. 2666 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 108, no. 6 season sunflower pests. The extensive adoption of was reduced to 1.61 liter/ha. Fields at Dakota Lakes neonicotinoid seed treatments use has created a situa- were sprayed with sulfentrazone (0.29 liter/ha) the fall tion where interested producers have difficulty finding before planting occurred, and in the spring shortly after sunflower seeds that have not been treated (European planting the fields were sprayed with a mixture of Academies Scientific Advisory Council [EASAC] 2015). glyphosate (rate: 1.17 liter/ha) and pendimethalin There are no peer-reviewed studies as of yet that (Prowl H2O; 2.92 liter/ha). No fertilizer was applied at evaluate the need for, or effects of, neonicotinoid seed the Brookings location in either 2013 or 2014. At treatments in sunflowers. The persistence of neonicoti- Dakota Lakes, nitrogen was broadcasted at a rate of noids and toxic metabolites within a variety of treated 84.06 Kg/ha on June 1, 2014. crops also has not been formally substantiated and re- Insect Collections. Foliar Herbivores. In 2013, quires further investigation (Bonmatin et al. 2015). The the foliar arthropod communities within sunflower present study tested the null hypotheses that thiame- fields were assessed eight times between the V-6 and thoxam, a commonly used neonicotinoid seed treat- R-7 sunflower stages (Schneiter et al. 2003)atthe ment, does not affect yields, crop profitability, or pest Brookings location. In 2014, foliar insect communities populations in oilseed sunflower production systems in were assessed 10 times at Brookings and six times at central and eastern South Dakota. To further character- Dakota Lakes between V-2 and R-6 sunflower stages. ize the sunflower agroecosystem, thiamethoxam and its The herbivorous arthropod communities on entire toxic metabolite clothianidin were measured within leaf plants were visually assessed. On each of the sampling tissue throughout the growing season across three site dates, randomly selected sunflower plants from each Downloaded from years. field were examined, and all herbivorous arthropods found on the foliage, stems, and flowers were placed in 70% ethanol to be later curated and identified. At the Materials and Methods Brookings location in 2013, 10 plants from each field Sunflower Production and Experimental on each date were examined. In 2014 at the Brookings Design. The experiment was replicated at one location location 20 plants per field were examined on the first http://jee.oxfordjournals.org/ (Brookings) in two successive growing seasons, and at two dates, 15 plants on the second and third dates, and an additional location (Dakota Lakes) in the second 10 plants per field on all of the remaining dates. In growing season. On June 14, 2013, at the eastern South 2014 at the Dakota Lakes location 15 plants per field Dakota Soil and Water Research Farm (USDA-ARS) were examined on the first date and 10 plants were near Brookings, SD (44.3064 N, 96.7881 W), sun- examined per field on all of the remaining dates. flowers (Helianthus annuus, Pioneer, Variety: 63M80- Soil Arthropod Community. In 2013, soil herbivore N422) were planted in six, 30.5- by 30.5-m fields. communities at the Brookings location were assessed Borders (12 m wide) of untreated Sorghum Sudan (Sor- on six occasions between planting and the R-6 plant ghum X drummondii, Millborn Seeds Inc., Variety: stage. In 2014, soil herbivores were assessed eight MS9000) grass were planted around and in between times at Brookings and six times at Dakota Lakes by guest on July 26, 2016 the fields to separate them. Three of the fields were between the V-2 and R-6 stages. planted with untreated seeds while the remaining three In 2013, four soil cores from each field (10 cm diam- were planted with seeds that had been treated with eter, 10 cm deep) were collected using a golf-hole cup thiamethoxam (Cruiser, Syngenta, Greensborough, cutter from randomly selected locations within sun- NC) at a rate of 0.25 mg a.i./seed. Fields were planted flower rows. In 2014, three soil cores were taken in in a randomized block design with a seeding rate of each field on every sampling date. On each collection 76,601 seeds/ha. date cores taken within individual fields were pooled On May 23, 2014, at the Brookings, SD site there and extracted from the soil over 7 d using a Berlese were eight, 24.5- by 36.5-m fields planted to sunflowers funnel. The arthropods collected in this manner were (Helianthus annuus, Mycogen, var 8H288CLDM) at a stored in 70% ethanol, for later curation and rate of 76,601 seeds/ha. Half of the fields were treated identification. with a thiamethoxam seed dressing prior to planting at Insecticide in Plant Tissue. Leaf Tissue Collec- a rate of 0.25 mg a.i./seed and half of the fields were tion.