Project Title: Developing Stink Bug Thresholds for Late Maturity Group Soybeans on the Upper Gulf Coast. Beaumont, TX

Transcription

1 Project Title: Developing Stink Bug Thresholds for Late Maturity Group Soybeans on the Upper Gulf Coast. Beaumont, TX Principal Investigator: M.O. Way Associate Professor, Entomology Texas Agricultural Research & Extension Center 1509 Aggie Drive Beaumont, TX (409) (phone) (409) (fax) ( ) Introduction Stink bugs can be serious problems (usually late in the season) on late maturity group (MG) soybeans on the Upper Gulf Coast of Texas. Little data have been collected on the effects of stink bug damage to late MG soybeans grown in Texas. Questions needed to be answered are: 1) When do stink bugs typically attack late MG soybeans? (What soybean stage of development coincides with damaging levels of stink bugs?) and 2) What population densities of stink bugs cause economic damage? Both these questions are linked and so are the answers. Thus, the objectives of this experiment were to monitor stink bug populations on MGVII soybeans relative to soybean stage of growth and determine the relationship between soybean stage of growth and stink bug damage. Materials and Methods The experiment was conducted in 2001 at the TAMU Agricultural Research and Extension Center at Beaumont. The experiment was originally designed as a randomized complete block with four treatments and four replications. Treatments were: 1) untreated, 2) control stink bugs from R3 ÿ maturity, 3) control stink bugs from R5 ÿ maturity, and 4) control stink bugs from R7 ÿ maturity. Plot size was 8 rows (30 inches between rows) x 90 ft. On 18 May, plots were planted with Hartz 7550 RR soybeans and sprayed by a tractor-rig with Squadron at 3 pt/acre. On 24 May, soybeans in all plots emerged through Levac soil to produce a good stand. Weeds were controlled throughout the experiment with timely cultivations. On 7 Jul, soybeans were just beginning to bloom (R1, V9). Very few insects were observed in plots at this time. On 26 Jul, very few insects were observed in plots. On 30 Jul when soybeans were R2/3, very little insect activity was observed in the experiment. Insects were sampled in all plots on the following dates: 14 Aug, 6 Sep, 13 Sep, 20 Sep, 27 Sep, 5 Oct, 15 Oct, 23 Oct, 9 Nov and 20 Nov. Samples consisted of 20 sweeps in each plot using a 15 inch diam sweep net. Contents of the net were placed in plastic bags which were frozen. At a later date, bags were thawed and arthropods identified and counted. On 15 Aug and 2 Oct, all plots were sprayed with Dimilin 2L at 4 oz/acre to control Lepidoptera defoliators (with no effect on stink bugs). Dimilin 2L was applied to minimize Lepidoptera damage in order to detect treatment differences due to stink bug damage. Dimilin 2L was applied using a two-person spray rig (13 nozzles, tip size, 50 mesh screens, 21.7 spray swath, final spray volume 12.3 gpa) pressurized with CO 2 (20-30 psi). Orthene 90S at 1.0 lb (AI)/acre was applied to control stink bugs in the following treatments at the following times and soybean growth stages: 96

2 Treatment (Stink bugs controlled from:) Date / stage of soybean growth R5 ÿ maturity Sep 7/R5 R5 ÿ maturity Sep 20/R5 R5 ÿ maturity R7 ÿ maturity Oct 18/R7 Untreated - Orthene 90S applications were made with the same spray rig and procedures used for Dimilin 2L applications. On Oct 22, plots were rated for defoliation by randomly removing 15 leaflets (five from the top, middle and bottom of the canopy) from each plot. Leaflets were taken to the lab and % defoliation estimated using a template for comparison. On 26 Nov, the middle two rows of each plot were harvested with a combine. Yields were adjusted to 13% moisture. Seed from plots was rated for quality. Insect count data were transformed using x and all data analyzed by ANOVA and DMRT. Results The Dimilin 2L applications controlled Lepidoptera except for an outbreak of fall armyworm on 5 Oct (Tables 1-4 and 18). The outbreak was concentrated on the west side of the experimental field where three of four R7 ÿ maturity plots were randomly assigned. Thus, fall armyworm populations were significantly higher in R7 ÿ maturity plots on 5 Oct (Table 18). Although Lepidoptera densities were relatively low in all treatments during the experiment, defoliation was significantly less in the R5 ÿ maturity treatment compared to the untreated (Table 19). This difference may have masked, somewhat, treatment effects due to stink bugs. Stink bug populations were relatively low throughout the experiment on all sample dates (Tables 5-9). Because stink bug populations did not begin increasing in plots until R5, R3 ÿ maturity and R5 ÿ maturity treatments were combined to give eight replications of R5 ÿ maturity treatment. Phytophagous stink bugs consisted of two species - southern green stink bug (SGSB), Nezara viridula, and brown stink bug (BSB), Euschistus servus - with BSB making up about 75% of the adults in the untreated. Stink bug populations in the untreated increased during pod fill and decreased thereafter (Table 9). Application of Orthene 90S to the R7 ÿ maturity plots on 18 Oct did not effectively control stink bugs (Table 9). Threecornered alfalfa hopper (TCAH) populations were high in untreated and R7 ÿ maturity plots during pod fill (Tables 10-12). Thus, damage from this insect may have masked stink bug treatment effects. Yield was not significantly different among treatments, probably due to relatively low populations of stink bugs in the experiment (Table 19). However, R5 ÿ maturity plots outyielded the untreated 4.1 bu/acre. Seed quality was significantly better in R5 ÿ maturity treatment compared to the untreated which suggests that relatively low densities of stink bugs during R5-6 can reduce seed quality. (On 20 Nov, very few insects were collected, so data from this date are not reported.) 97

3 Table 1. Soybean looper densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. soybean looper/20 sweeps Untreated b 0 R5-maturity c 1.0 R7-maturity a 0 NS NS NS NS NS NS NS NS Table 2. Green cloverworm densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. green cloverworm/20 sweeps Untreated R5-maturity R7-maturity NS NS NS NS NS NS NS NS NS 98

4 Table 3. Velvetbean caterpillar densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. velvetbean caterpillar/20 sweeps Untreated a 0 R5-maturity b 0 R7-maturity b 0 NS NS NS NS NS NS NS NS Table 4. Lepidopteran larvae densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. lepidopteran larvae/20 sweeps Untreated 6.5 a a 0 R5-maturity 2.8 b b 1.0 R7-maturity 2.0 b a 0 NS NS NS NS NS NS NS 99

5 Table 5. Phytophagous stink bug nymph densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. phytophagous stink bug nymphs/20 sweeps Untreated a 1.0 a 2.5 b a 1.3 R5-maturity b 0.1 b 0.3 c b 1.4 R7-maturity b 1.0 a 6.8 a a 0 NS NS NS NS NS a Means in a column followed by the same or no letter are not significantly different at the 5% level (ANOVA and DMRT). Table 6. Southern green stink bug adult densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. southern green stink bug adults/20 sweeps Untreated R5-maturity R7-maturity NS NS NS NS NS NS NS NS NS 100

6 Table 7. Brown stink bug adult densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. brown stink bug adults/20 sweeps Untreated a a R5-maturity b b R7-maturity a a NS NS NS NS NS NS NS 101 Table 8. Phytophagous stink bug adult densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. phytophagous stink bug adults/20 sweeps Untreated a 1.8 ab a R5-maturity b 0.6 b b R7-maturity a 2.5 a a NS NS NS NS NS NS

7 Table 9. Phytophagous stink bug nymph + adult densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. phytophagous stink bug nymphs + adults/20 sweeps Untreated a 2.8 a 4.3 b 8.0 ab a 2.0 R5-maturity c 0.8 b 0.9 c 2.3 b b 2.0 R7-maturity b 3.5 a 8.0 a 10.0 a a 0.5 NS NS NS NS 102 Table 10. Threecornered alfalfa hopper nymph densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. threecornered alfalfa hopper nymphs/20 sweeps Untreated a R5-maturity b R7-maturity ab NS NS NS NS NS NS NS NS

8 Table 11. Threecornered alfalfa hopper adult densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. threecornered alfalfa hopper adults/20 sweeps Untreated a 42.0 a 24.0 a 19.3 a a 0 R5-maturity b 7.0 b 10.4 b 2.9 b b 0.1 R7-maturity a 44.5 a 17.8 a 31.0 a a 0 NS NS NS NS Table 12. Threecornered alfalfa hopper nymph + adult densities relative to MGVII soybean stage of development, Bmt., TX, 2001 Mean a no. threecornered alfalfa hopper nymphs + adults/20 sweeps Untreated a 44.8 a 24.0 a 20.0 a a 0 R5-maturity b 7.3 b 10.4 b 3.1 b b 0.1 R7-maturity a 46.0 a 18.3 a 31.5 a a 0 NS NS NS NS 103

9 Table 13. Orthopteran nymph and adult densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. orthopteran nymphs + adults/20 sweeps Untreated b a 0.3 R5-maturity c b 0.3 R7-maturity a a 0 NS NS NS NS NS NS NS 104 Table 14. Banded cucumber beetle densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. banded cucumber beetle/20 sweeps Untreated R5-maturity R7-maturity NS NS NS NS NS NS NS NS NS

10 Table 15. Leafhopper nymph and adult densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. leafhopper nymphs + adults/20 sweeps Untreated R5-maturity R7-maturity NS NS NS NS NS NS NS NS NS 105 Table 16. Ambush bug densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. ambush bugs/20 sweeps Untreated a b R5-maturity b b R7-maturity ab a NS NS NS NS NS NS NS

11 Table 17. Spider densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. spiders/20 sweeps Untreated R5-maturity R7-maturity NS NS NS NS NS NS NS NS NS 106 Table 18. Fall armyworm densities relative to MGVII soybean stage of development, Beaumont, TX, 2001 Mean a no. fall armyworm/20 sweeps Untreated b R5-maturity b R7-maturity a NS NS NS NS NS NS NS NS

12 Table 19. Yield, seed quality and defoliation on MGVII soybean, Beaumont, TX, 2001 a Stink bugs Yield b Seed quality c Defoliation d controlled from: bu/a (1-5) (%) Untreated a 22.1 a R5-maturity b 11.7 b R7-maturity ab 16.9 ab NS a Means with the same or no letter are not significantly different at the 5% level (ANOVA and DMRT). b Yield adjusted to 13% moisture and 60 lb/bu c Seed quality: 1 = excellent, 5 = very poor d Defoliation based on 15 leaflets/plot sampled 22 Oct 107