Updated November 6, 2019:
Two predatory mite species were identified from soybean fields: Proprioseopsis mexicanus and Neoseiulus fallacis (Acari: Phytoseiidae). Not much is known about P. mexicanus in the scientific literature, although it is widespread throughout North America. Neoseilus fallacis can be an important predator in orchards. Predator populations were extremely low.
Two of the surveyed fields in Sussex County were treated for two spotted spider mites along with other pests. Treatment timing corresponded with an early reproductive stage fungicide application. Spider mite populations peaked at the end of June due to hot dry weather, and crashed at the beginning of August. Kent County mites peaked in mid-July and crashed afterwards, likely due to rain events. Very few mites were intercepted in New Castle County.
Thrips populations were greatest in New Castle County. Direct thrips feeding injury is not normally considered to negatively impact soybean unless beneficial insects are not present, populations are greater than 12 per leaflet, and soybean fields are under severe drought stress. Thrips can vector a virus, soybean vein necrosis virus, but the virus impact on yield and the economic return of insecticide applications is uncertain. At this time, insecticide applications are not recommended.
The 3 most significant defoliators in 2018 were bean leaf beetles, green cloverworm, and soybean looper. Green cloverworm and soybean looper populations peaked in early September. It is extremely important to correctly identify these two species; cloverworms are easily controlled with pyrethroids while loopers are not. Soybean looper populations were greatest approximately 1 week after corn earworm populations peaked. Most fields treated for earworms were treated with a pyrethroid, which soybean loopers are not susceptible to. August pyrethroid applications can disrupt natural enemies that would feed on soybean looper eggs and early instars. If a field is treated with a pyrethroid this late in the season, follow up scouting is necessary to ensure soybean loopers do not establish. Green cloverworm populations were higher than usual in late July and August, but crashed by the beginning of September due to fungal pathogens favored by wet September weather. Several fields were visited in September in Sussex and Kent counties in which corn earworm, yellow striped armyworm, green cloverworm, and soybean looper had succumbed to pathogens in their 4th and 5th instars. Bean leaf beetle populations were greatest in Kent County, concentrated in two of the survey fields. Early season populations did not appear to influence stand establishment, mid-season populations are minor defoliators. Bean leaf beetle and Japanese beetle feeding is highly visible, concentrated on the uppermost leaves. However, when scouting for defoliation, the entire plant canopy needs to be assessed, and in visited fields, the overall canopy was very robust despite highly visual top canopy feeding. Late season bean leaf beetle populations can window-pane pods and affect quality in addition to feeding on foliage. Japanese beetle populations were low, peaking during the last half of July. None of the surveyed fields sustained significant defoliation during peak beetle activity period.
Kudzu bug was only found in a kudzu patch in late August near Laurel, DE. No kudzu bugs were observed in soybean fields.
One of the surveyed fields in the SW quadrant of Sussex County was treated for corn earworm. Corn earworm populations required treatment in numerous fields near Laurel and Seaford. Earworm populations in Kent and New Castle were low and peaked two weeks later than in Sussex. Populations quickly declined in September due to the aforementioned fungal pathogen outbreak in the worm populations.
In general, stink bug populations were low and did not reach economic thresholds in any surveyed fields. Populations peaked at a greater level in Kent County, well below threshold levels. Brown marmorated stink bug populations were very low in soybean, comprising 1.2% of the population. Field edges may be infested while the rest of the field is relatively free of stink bugs. In such cases, edges should be sampled more intensively and an effective treatment can focus on edges, sparing the field interior.
Dectes populations were greatest in Kent County, and were active for an 8 week period. New Castle Dectes populations were slightly lower and were active for 5 weeks; Sussex Dectes populations were lower and were active for 7 weeks. Stem samples were collected from 7 surveyed fields; infestation levels ranged from 4 – 56%. The most heavily infested field (56% infested stems) had 19 cumulative Dectes adults over a 4 week period, representing 400 sweeps. However, the percentage of infested stems in another surveyed field that had 14 adults over a 3 week period was nearly half (26%) that of the field with 19 Dectes in it. A third field had 15 adults over a 4 week period, but stem infestation was even lower at 16%. Sunflowers were sampled in 4 locations in Sussex County. Sunflower stem infestation ranged from 0 and 36% while adjacent soybean stem infestation was between 0 and 7%. Cocklebur was also sampled from one site with 28% stems infested whereas the adjacent soybean field had extremely low Dectes stem infestation. Exploring the interaction between Dectes, soybean, and other hosts could lead to additional management tactics.
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The 3 most significant defoliators in 2018 were bean leaf beetles, green cloverworm, and soybean looper. Green cloverworm and soybean looper populations peaked in early September. Soybean looper populations were greatest approximately 1 week after corn earworm populations peaked. Most fields treated for earworms were treated with a pyrethroid, which soybean loopers are not susceptible to. August pyrethroid applications can disrupt natural enemies that would feed on soybean looper eggs and early instars. If a field is treated with a pyrethroid this late in the season, follow up scouting is necessary to ensure soybean loopers do not establish. Green cloverworm populations were higher than usual in late July and August, but crashed by the beginning of September due to fungal pathogens favored by wet September weather. Corn earworm populations required treatment in numerous fields SW Sussex County. Earworm populations in Kent and New Castle were low and peaked two weeks later than in Sussex.
Two predatory mite species were identified from soybean fields. Predator populations were extremely low. Two of the surveyed fields in Sussex County were treated for two spotted spider mites along with other pests. Treatment timing corresponded with an early reproductive stage fungicide application. Spider mite populations peaked at the end of June due to hot dry weather, and crashed at the beginning of August. Kent County mites peaked in mid-July and crashed afterwards, likely due to rain events. Very few mites were intercepted in New Castle County.
Thrips populations were greatest in New Castle County. Direct thrips feeding injury is not normally considered to negatively impact soybean unless beneficial insects are not present, populations are greater than 12 per leaflet, and soybean fields are under severe drought stress. Thrips can vector a virus, soybean vein necrosis virus, but the virus impact on yield and the economic return of insecticide applications is uncertain. At this time, insecticide applications are not recommended.
Bean leaf beetle populations were greatest in Kent County, concentrated in two of the survey fields. Early season populations did not appear to influence stand establishment, mid-season populations are minor defoliators. Bean leaf beetle and Japanese beetle feeding is highly visible, concentrated on the uppermost leaves. However, when scouting for defoliation, the entire plant canopy needs to be assessed. Japanese beetle populations were low, peaking during the last half of July. None of the surveyed fields sustained significant defoliation during peak beetle activity period.
In general, stink bug populations were low and did not reach economic thresholds in any surveyed fields. No kudzu bugs were observed in soybean fields. Dectes populations were greatest in Kent County, and were active for an 8 week period. New Castle Dectes populations were slightly lower and were active for 5 weeks; Sussex Dectes populations were lower and were active for 7 weeks.
Percent crop yield losses to insect pests was 2.78% in 2018, and total costs in terms of pest treatments and lost yield exceeded $3 million in 2018.