Avoiding Stink Bug Damage and Flat Pod Syndrome in Soybean with a MGVI Cultivar and Planting Date Beaumont, TX 2005 Agronomic and Cultural Information Land Preparation: Disked test area (Morey silt loam) on Mar 17 and pulled beds on Mar 21 Cultivated beds prior to planting for all planting dates Planting Dates: Herbicide: Insecticide: Sampling: Harvest: RA 452 (MGIV) planted on Apr 7 (one planting date) NC ROY (MGVI) planted on Apr 27, May 13, Jun 8 and Jul 11 Both cultivars planted at a rate of 8 viable seed per foot of row Plot size = 8 rows, 30 in. row width, 47 ft long Experimental design: split plot with 4 replications each of treated (T) and untreated (U) plots Applied First Rate @ 0.75 oz/acre and Dual II Magnum @ 2.5 pt/acre (PRE)to all planting dates with a 2-nozzle hand-held spray boom (110-04 nozzles, 50 mesh screens, 25 gpa) Plots designated as ATreated@ were sprayed multiple times with Orthene 90S @ 1.0 lb (AI)/acre (Table 1) as stink bugs appeared in plots in an effort to achieve complete control of stink bugs and also lepidopterous larvae. Plots were sprayed with a 2-person hand-held boom [13- No. 2 cone nozzles, 50 mesh screens, 20 ft spray swath (8 rows), 21 gpa]. Insects were collected from each plot at approximately 2 wk intervals (Table 1) with a 15 in. muslin sweep net. Twenty sweeps were made down the length of a 47 ft row in each plot. The adjacent row was sampled on the next sweep date. Contents of the net were placed in a plastic bag, frozen in the lab, and insects later identified and counted as time permitted. Prior to analysis, insect data were transformed using square root (x + 0.5). Focus was on these species: Southern green stink bug ( SGSB) Red-banded stink bug, Piezodorus guildinii, (PG) Brown stink bugs, phytophagous species (BSB) Velvetbean caterpillar (VBC) Soybean looper (SL ) Green cloverworm (GCW) Threecornered alfalfa hopper (TCAH) The 4 middle rows (47 ft long) of each plot were harvested for yield and seed quality with an Almaco SPC20 plot combine. Yields were adjusted to 13% moisture and 60 lb/bu. 57
Table 1. Orthene 75S application dates and soybean growth stage at time of insect samplings across planting dates. Beaumont, TX. 2005 20 sweeps NC ROY sampling date RA 452 (Apr 7) (Apr 27) (May 13) (Jun 8) (Jul 11) Jun 9: Applied Orthene 75S @ 1.0 lb (AI)/acre to RA 452 and NC ROY (Apr 27) Jun 10 R2 R1 V5 na na Jun 28: Applied Orthene 75S @ 1.0 lb (AI)/acre to RA 452 and NC ROY (Apr 27 and May 13) Jun 30 R3/4 R2 V12 V4 na Jul 13 R4 R3 R1 V11 na Jul 27 R4/5 R4 R2/3 R2 V3 Aug 5: Applied Orthene 75S @ 1.0 lb (AI)/acre to RA 452 and NC ROY (Apr 27 and May 13) Aug 10 R5 R4/5 R4 R2 V7 Aug 22: Applied Orthene 75S @ 1.0 lb (AI)/acre to RA 452 and NC ROY (Apr 27, May 13, Jun 8) Aug 23 R5/6 R5 R4 R3/4 R2 Sep 2: Applied Orthene 75S @ 1.0 lb (AI)/acre to RA 452 and NC ROY (all planting dates) Sep 4 R6 R5/6 R5 R5 R4 Sep 14: Applied Orthene 75S @ 1.0 lb (AI)/acre to RA 452 and NC ROY (all planting dates) Sep 19 R7 R6 R5/6 R5/6 R5 Discussion The data for RA 452 planted in early April show that stink bugs, particularly Piezodorus guildinii (PG), were problematic, even in treated plots (Table 2). PG numbers began to increase after July 27 when soybeans were at R4/5, peaked during mid to late August at R5/6 and dramatically decreased in September at R7. Even in treated plots, we did not satisfactorily control PG which suggests this species is more difficult to control than other stink bug species. Also, our insecticide spray timings on Atreated@ plots may have been Aoff a little@. We sprayed on August 5 and 22 but we probably should have sprayed an additional time between these dates. However, the data for RA 452 confirm previous research results which show that in Beaumont MGIV soybeans planted in April can be attacked by high populations of stink bugs during pod formation and pod fill. The period of vulnerability lasts about 3 wks depending on environmental parameters and soybean response to these variable conditions. Lepidoptera were not a problem which also confirms previous research. Yields in both treated and untreated plots of RA 452 were extremely low due to stink bug damage. Delayed maturity was observed in both treated and untreated plots which is a response to stink bug damage and possibly drought conditions during most of the summer. The drought also may have affected yields. For NC ROY planted April 27, stink bugs were not as abundant as they were on RA 452 planted in early April, but they did appear during R5 (Table 3). We did not obtain good control of stink bugs and only partial control of Lepidoptera. Yields were higher for NC ROY planted April 27 compared to RA 452 planted April 7. We think the higher yields are primarily due to less stink bug pressure. 58
Discussion (continued) For NC ROY planted May 13, June 8 and July 11, stink bug pressure was minimal and yields in the treated plots ranged from 24 to 31 bu/acre (Tables 4, 5 and 6). Best yields were produced by the June 8 planting date treated with Orthene 90S. Untreated plots in these three planting dates suffered considerable defoliation damage by Lepidoptera, predominantly velvetbean caterpillar (VBC). We believe significant yield losses in the untreated plots of the May 13 and June 8 planting dates were due to Lepidoptera and not stink bugs (Table 7). In conclusion, results show that stink bug populations were highest and were very damaging on RA 452 planted the first week of April (Table 8). Stink bugs (mainly PG) were present in lower numbers on NC ROY planted April 27, but damage was still significant. In both cases, stink bugs (predominantly PG) attacked during pod fill (R5/6). We believe the later planting dates of NC ROY avoided the stink bug pressure, but were exposed to higher Lepidoptera (predominantly VBC) populations. However, Lepidoptera are generally easier to control than stink bugs, particularly PG. We did not observe a Aherding effect@ of stink bugs from earlier to later planted soybeans. Data suggest that in Beaumont stink bug populations peak during pod fill of MGIV soybeans planted in April. Thus, planting a later MG cultivar in May or June, such as a MGVI with good yield potential, can avoid excessive stink bug pressure (as opposed to a MGIV cultivar) and be harvested early to avoid inclement weather (as opposed to a later maturing MGVII or VIII soybean). We believe each soybean growing area on the Texas Upper Gulf Coast (e.g. Wharton, Victoria, Calhoun, Fort Bend, Matagorda and Jackson Counties) has a unique climatic and environmental profile which influences stink bug populations and soybean development. We also believe stink bug population dynamics may be somewhat stable across years in each soybean growing area. Consequently, determining stink bug population dynamics for each area and selecting cultivars and planting dates to avoid damaging populations when soybeans enter critical pod fill are important research needs for the immediate future. Hurricane Rita made landfall in Southeast Texas on Sep 23. Although lodging across rows was minimal the entire plot area was nearly prostrate. Foliage was stripped and partial pod loss occurred. Soybeans generally matured abnormally after the hurricane resulting in yield loss and seed quality reduction throughout the test. See Tables 2-8 below. 59
Table 2. Insect data for RA 452 (MGIV) planted on Apr 7. Beaumont, TX. 2005 Treatment a @ R2 @ R3/4 @ R4 @ R4/5 @ R5 @ R5/6 @ R6 @ R7 Jun 10 Jun 30 Jul 13 Jul 27 Aug 10 Aug 23 Sep 4 Sep 19 T 0 0 0 0 1 2 0 0 U 0 0 0 1 3 3 1 1 T 0 0 1 0 0 0 0 0 U 0 0 0 1 7 16 0 0 T 3 1 2 4 1 12 0 0 U 3 1 1 1 28 24 0 0 T 0 0 0 0 0 0 0 0 U 0 0 0 0 1 1 0 0 T 3 1 3 4 1 12 0 0 U 3 1 1 2 36 41 0 0 T 0 0 1 2 1 1 0 0 U 1 0 0 0 0 3 1 0 Table 3. Insect data for NC ROY (MGVI) planted on Apr 27. Beaumont, TX. 2005 Treatment a Jun 10 Jun 30 Jul 13 Jul 27 Aug 10 Aug 23 @ R1 @ R2 @ R3 @ R4 @ R4/5 @ R5 Sep 4 @ R5/6 T 0 0 0 1 3 9 1 0 U 0 0 0 1 4 13 1 1 T 0 0 0 0 0 6 1 1 U 0 0 0 0 0 4 2 0 T 1 0 0 0 1 5 1 0 U 2 0 0 0 1 7 0 1 T 0 0 0 0 0 1 1 1 U 0 0 0 0 0 3 1 1 T 1 0 0 0 1 12 3 2 U 2 0 0 0 1 14 3 2 T 0 0 0 0 1 1 0 1 U 1 0 0 0 0 3 1 0 Sep 19 @ R6 60
Table 4. Insect data for NC ROY (MGVI) planted on May 13. Beaumont, TX. 2005 Treatment a @ V12 @ R1 @ R2/3 @ R4 @ R4 @ R5 @ R5/6 Jun 30 Jul 13 Jul 27 Aug 10 Aug 23 Sep 4 Sep 19 T 0 0 0 2 5 1 0 U 0 0 0 3 20 6 4 T 0 0 0 0 1 0 0 U 0 0 0 0 1 2 1 T 0 0 0 0 1 0 0 U 1 0 1 0 2 0 3 T 0 0 0 0 0 0 1 U 0 0 0 0 1 1 1 T 0 0 0 0 2 0 1 U 1 0 1 0 4 3 5 T 0 0 0 0 1 1 1 U 1 0 0 0 2 0 0 Table 5. Insect data for NC ROY (MGVI) planted on Jun 8. Beaumont, TX. 2005 Treatment a @ R2 @ R3/4 @ R5 @ R5/6 Aug 10 Aug 23 Sep 4 Sep 19 T 1 8 3 0 U 2 28 9 6 T 0 0 0 0 U 0 0 1 2 T 0 0 0 2 U 0 0 1 4 T 0 0 0 0 U 0 0 2 1 T 0 0 0 2 U 0 0 4 7 T 0 1 0 0 U 1 2 0 0 61
Table 6. Insect data for NC ROY (MGVI) planted on Jul 11. Beaumont, TX. 2005 Treatment a @ R2 @ R4 @ R5 Aug 23 Sep 4 Sep 19 T 3 1 0 U 23 11 4 T 0 0 0 U 0 0 2 T 0 0 0 U 0 0 0 T 0 0 1 U 0 1 1 T 0 0 1 U 0 1 3 T 0 1 0 U 1 0 1 See Tables 7-8 below. 62
Table 7. Yield and seed quality of the five planting dates. Beaumont, TX. 2005 Cultivar (planting date) Treatment a Yield (bu/acre) Seed quality (1-5) b RA 452 (Apr 7) T 4.0 5.0 U 3.3 5.0 NC ROY (Apr 27) T 18.3 3.5 U 13.8 3.5 NC ROY (May 13) T 25.4 3.5 U 11.4 4.0 NC ROY (Jun 8) T 30.9 3.0 U 18.8 3.5 NC ROY (Jul 11) T 23.8 3.0 U 20.4 3.0 Statistical analysis (split plot) of yield and seed quality for the five planting dates: Main plot: Cultivar (planting date) Yield (bu/acre) Seed quality (1-5) RA 452 (Apr 7) 3.7 c 5.0 a NC ROY (Apr 27) 16.0 b 3.5 b NC ROY (May 13) 18.4 b 3.8 b NC ROY (Jun 8) 24.8 a 3.3 b NC ROY (Jul 11) 22.1 a 3.0 c Sub plot: Treatment (Treated or untreated for soybean insect pests) Treated 20.5 a 3.6 a Untreated 13.5 b 3.8 b Interactions: Main plot x sub plot Cultivar (planting date) x treatment SIG NS a Treatment: treated (T) or untreated (U) for soybean insect pests b Seed quality: visual estimate (1 = excellent, 5 = very poor) Means in a column followed by the same letter are not significantly different (NS) at the 5% level (ANOVA, LSD). 63
Table 8. Statistical comparison (split plot) of stink bug populations in the five planting dates. Beaumont, TX. 2005 Sampling date Cultivar (planting date) 0 no. stink bugs a Growth stage Jun 10 RA 452 (Apr 7) 3.0 a R2 NC ROY (Apr 27) 1.5 b R1 Jun 30 RA 452 (Apr 7) 1.0 a R3/4 NC ROY (Apr 27) 0.0 b R2 NC ROY (May 13) 0.5 ab V12 Jul 13 RA 452 (Apr 7) 2.0 a R4 NC ROY (Apr 27) 0.0 b R3 NC ROY (May 13) 0.0 b R1 Jul 27 RA 452 (Apr 7) 3.0 a R4/5 NC ROY (Apr 27) 0.0 b R4 NC ROY (May 13) 0.5 b R2/3 Aug 10 RA 452 (Apr 7) 18.5 a R5 NC ROY (Apr 27) 1.0 b R4/5 NC ROY (May 13) 0.0 b R4 NC ROY (Jun 8) 0.0 b R2 Aug 23 RA 452 (Apr 7) 26.5 a R5/6 NC ROY (Apr 27) 13.0 b R5 NC ROY (May 13) 3.0 c R4 NC ROY (Jun 8) 0.0 c R3/4 NC ROY (Jul 11) 0.0 c R2 Sep 4 RA 452 (Apr 7) 0.0 c R6 NC ROY (Apr 27) 3.0 a R5/6 NC ROY (May 13) 1.5 a R5 NC ROY (Jun 8) 2.0 ab R5 NC ROY (Jul 11) 0.5 bc R4 Sep 19 RA 452 (Apr 7) 0.0 c R7 NC ROY (Apr 27) 2.0 bc R6 NC ROY (May 13) 2.0 bc R5/6 NC ROY (Jun 8) 4.5 a R5/6 NC ROY (Jul 11) 2.0 bc R5 a Sum of SGSB, PG and BSB (nymphs + adults) Means in a column followed by the same letter are not significantly different at the 5% level. 64