Update:
Foliar Insect Abundance
2015 Full Season Soybean: Because the overall number of arthropods was very low, insects were combined into plant feeders and beneficials for analysis. Plant feeding insects included flea beetles, leafhoppers, plant-feeding thrips, caterpillars, weevils and aphids, and had significantly lower abundance in the plots treated with Cruiser as compared to the control and fungicide treatments; plots treated Gaucho had significantly lower insects than fungicide, but not control plots (Treatment F3,15.89=9.9742, P=0.0034). Beneficial insects included minute pirate, predatory, and lacewings, and Cruiser plots had significantly lower numbers of beneficial insects compared to fungicide treated or control plots (Treatment F3,18.66=3.8676, P=0.0261).
2015-2016 Winter Wheat: Insect abundance was measured through visual inspection twice in the winter and three times in the spring. The two winter dates were combined for analysis, and the three spring dates were combined for analysis separately. In the winter, only aphids were present; in the spring, aphids and cereal leaf beetle were both observed, and their numbers were combined for analysis. The only beneficials that were present were parasitized aphid mummies; however, their numbers were too low for analysis. In the winter, the number of aphids was higher on the second sampling date (Date F1,43=4.6846, P=0.0360). Aphid abundance was significantly lower in the Cruiser and Gaucho treatments as compared to the control and fungicide treatments (Treatment F3,43=12.3011, P<0.0001).
In the spring, the number of plant-feeding insects (aphids and cereal leaf beetle) was significantly lower on the third sampling date compared to the first and second (Date F2,71=47.7823, P<0.0001). There was no significant difference between the control, Cruiser and Gaucho treatments, although the fungicide only treatment had a significantly higher number of aphids than the Cruiser treatment (Treatment F3,71=2.9207, P=0.0399).
2016 Double Cropped Soybean: Foliar insects were visually assessed twice, at the V2 and R1 stages, by evaluating the mean number of insects per 10 trifoliates. The most prevalent plant feeding insects were leafhoppers, plant-feeding thrips and caterpillars, and a smaller number of weevils, aphids and spotted cucumber beetles. While there was a significantly higher number of plant feeding insects present on the second date, (Date F1,43=37.9665, P<0.0001), plant feeding insects did not differ significantly between treatments (Treatment F3,43=2.4211, P=0.0790). Beneficial insects included minute pirate bugs, predatory thrips, and lady beetles, which were present in higher numbers on the second sampling date than the first (Date F1,43=19.4815, P<0.0001). However, beneficial insects did not differ significantly between treatments (Treatment F3,43=2.3794, P=0.0829).
2017 Corn: At the V4 stage, we counted the number of plants showing signs of root damage, which did not differ significantly between treatments (Treatment F3,15=1.0504, P=0.3992). Visual counts for insects were conducted three times. Because the sampling method was different each time, data from the three dates were analyzed separately. The first set of samples were taken at the V7 stage. The most abundant plant feeding insects were plant thrips, followed by leafhoppers, aphids and flea beetles. Plant feeding insects were not significantly impacted by treatment (Treatment F3,15=0.2970, P=0.8270). The only beneficial arthropods observed were lady beetles and spiders. Beneficial arthropods also did not differ significantly between treatments (Treatment F3,15=0.3360, P=0.7796). At the R1 stage, we counted the number of arthropods per 10 plants through destructive sampling. Primary pests observed were plant hopper and plant bugs, which did not differ significantly between treatments (Treatment F3,15=0.2972, P=0.8268). Predators observed at R1 stage included minute pirate bugs, spiders, lacewing eggs and lady beetles. Predators were not significantly different between treatments (Treatment F3,15=2.7294, P=0.0807). At the R3-R4 stage, pests and predators were scouted visually for one ear each from ten plants per plot. The pests observed were plant thrips, sap beetles, dirt-colored seed bugs and corn earworm. The number of pests was significantly higher in the Cruiser treatment than the fungicide treatment but did not differ significantly between the other treatments (Treatment F3,15=3.3996, P=0.0455). The predatory arthropods observed at the R3-R4 stage were minute pirate bugs, lacewing eggs, lady beetles and spiders. Predators were not significantly different between treatments (Treatment F3,15=0.3295, P=0.8041).
Plant Stand and Yield
2015 Full Season Soybean: Initial soybean stand counts showed that plots with the Gaucho treatment had a significantly higher stand count compared to Cruiser, fungicide and control plots (Treatment F3,15=15.1055, P<0.0001). Plant height measurements revealed no significant difference between seed treatments (Treatment F3,15=0.7884, P=0.5190). Overall yield, corrected to 13% moisture, also failed to demonstrate a significant treatment effect (Treatment F3,15=0.6266, P=0.6089).
2015-2016 Winter Wheat: Stand density was measured at emergence and one-week post emergence at both field locations. While stand count was significantly higher on the second sampling date (Date F1,43.85=45.8290, P<0.0001), it was not significantly impacted by treatment (Treatment F3,43.85=1.2540, P=0.3018). Plant height, measured six weeks post planting, was not impacted by treatments (Treatment F3,18.79=1.0949, P=0.3757). Yield, corrected to 14% moisture, was not significantly different between treatments (Treatment F3,15=2.6362, P=0.0877).
2016 Double cropped soybean: Stand density was measured at emergence and one-week post emergence as the number of plants per two row meters. Stand density was not significantly impacted by date (Date F1,43.99=3.3860, P=0.0725) or treatment (Treatment F3,43.99=1.4873, P=0.2311). Plant height was measured at the R1 growth stage. There was no significant difference in height between treatments (Treatment F3,15=1.2284, P=0.3340). Yield, corrected to 13% moisture, did not differ significantly between treatments (Treatment F3,15=0.3051, P=0.8213).
2017 Corn: Stand density was measured as the number of plants per 2 row meters shortly after emergence. Gaucho and Cruiser treatments had significantly higher stand density than the control, but not the fungicide treatment (Treatment F3,15=5.9607 P=0.0070). Yield, corrected to 15.5% moisture, did not differ significantly between treatments (Treatment F3,15=0.5558 P=0.6522).
Winter Annual Flowers
2016: Neonicotinoid residues were not found in any of the samples from 2016.
2017: No neonicotinoid residues were found in the chickweed samples from Queenstown or the henbit samples from Beltsville. Trace amounts (unquantifiably low amounts reported as “trace” by the testing lab) of imidacloprid were found in four of the chickweed samples from Beltsville. Given that the chemical was present in plots of all four treatments in very low concentrations, its presence does not appear to be correlated to the experiment.
Arthropod Community Composition
Insect collected through pitfall traps, litter extraction, sticky cards and sweep netting are being identified and analysed.
Soil Quality and Microbial Analyses
Soil respiration as measured by the Solvita test kit did not differ significantly between treatments in full season soybean (Treatment F(3,99)=1.5054, P=0.2179), winter wheat (Treatment F(3,71)=0.5662, P=0.6391), double cropped soybean (Treatment F(3,71)=0.4396, P=0.7254) or corn (Treatment F(3,97.9)=0.9328, P=0.4279). Samples collected after corn harvest were sent to the Cornell Nutrient Analysis Lab for measurement of soil quality parameters (pH, wet aggregate stability etc.). DNA is being extracted from soil samples that were stored for microbial analysis. After DNA extraction is completed, the abundance and community composition of soil microbes will be evaluated using quantitative PCR and Illumina sequencing.
Conclusions
Visual insect sampling and yield – The use of NSTs reduced early season pest abundance in full season soybean and wheat, but not in double cropped soybean or corn. NSTs also reduced beneficial insects in full season soybean. Stand count and plant height measurements indicate that the use of NSTs did not improve plant growth through pest protection or direct stimulation in most cases. Pest abundance was low throughout the study; in the absence of pest pressure, the neonicotinoid seed treatments did not improve yield in any of the crops.
Winter annual flowers – In this case, neonicotinoid residues from NSTs were not taken up by winter annual flowers and did not pose a threat to pollinators. However, persistence of neonicotinoids in soil and uptake by flowering plants could vary based on factors such as temperature, soil type and flowering plant species.
Soil Quality and Microbial Analyses - Previous studies on the impact on neonicotinoids on soil microbes have found that neonicotinoids have a greater impact on community composition than on overall microbial abundance or richness. Thus, even though the Solvita results did not show a treatment difference, there could be differences in the composition of the soil microbial community. This could impact soil health if the nitrogen fixing portion of the community is impacted. Therefore, we are evaluating community composition through Illumina sequencing. Additionally, the Solvita test measures overall soil respiration, which encompasses various types of organisms. By conducting qPCR of the 16S rRNA gene, we will quantify differences in prokaryotic abundance, which may be different than the overall CO2 measured by the Solvita test.
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In terms of yield and pest suppression, the study "Impact of Repeated Use of Neonicotinoid Treated Seed in Grain Crop Rotations on Non-target Invertebrates & Soil Microbes" suggests that there is no economic benefit associated with using neonicotinoid treated seeds (NST) when pest pressure is low. The use of NSTs reduced early season pest abundance in full season soybean and wheat, but not in double cropped soybean or corn. NSTs also reduced beneficial insects in full season soybean. Stand count and plant height measurements indicate that the use of NSTs did not improve plant growth through pest protection or direct stimulation in most cases. Neonicotinoid residues from NSTs were not taken up by winter annual flowers and did not pose a threat to pollinators. However, persistence of neonicotinoids in soil and uptake by flowering plants could vary based on factors such as temperature, soil type and flowering plant species.