New pesticides for bugs in soybeans or Weighing up the buggy options

Transcription

1 New pesticides for bugs in soybeans or Weighing up the buggy options ABSTRACT: Hugh Brier, Kristen Knight and Joe Wessels, QDPI/FSI, Kingaroy Recent entomological events have major implications for soybean pest management in Australia. Restrictions on endosulfan use in soybeans (both voluntarily and by law) has increased the use of Decis (deltamethrin) for podsucking bug control in soybeans. While Decis gives effective control of podsucking bugs, it is detrimental to beneficial insects and greatly increases the risk of subsequent mite and heliothis outbreaks. The past season has also seen outbreaks of the soybean aphid, Aphis glycines Matsumura, in eastern Australia. This pest is readily controlled with dimethoate, but again, use of this product is likely to flare heliothis and mites. Repeats of major mite outbreaks in soybeans as experienced during the summer of 1999/2 would pose a major threat to the industry and require a major re-focus of IPM strategies and whole pest spectrum management. This paper discusses trial results from bug and mite pesticide trials in project DAQ481, where this research is headed, and strategies to minimise the likelihood of mite outbreaks in soybeans. INTRODUCTION: Recent entomological events have major implications for soybean pest management in Australia. Restrictions on endosulfan use in soybeans (both voluntarily and by law) has increased the use of Decis (deltamethrin) for podsucking bug control in soybeans. While Decis gives effective control of podsucking bugs, it is detrimental to beneficial insects and greatly increases the risk of subsequent mite and heliothis outbreaks. Several new generation pesticides have been trialed against mirids, podsucking bugs and beneficial insects in pulses and soybeans in GRDC funded project DAQ481 (Pulse IPM). The performances of new generation pesticides Confidor (imidacloprid), Regent (fipronil), and Steward (indoxocarb) against bugs (podsucking and mirids) are presented in this paper, as are the performances of alternative (to deltamethrin and endosulfan) currently-registered pesticides dimethoate and trichlorfon. Trichlorfon plus salt may have potential in Australian soybeans. In Australia, trichlorfon is registered in soybeans against green vegetable bug at 1.25 L/ha, but in Brazil is registered against podsucking bugs at.48l/ha plus salt (at 5g/L of tank mix water). Because project DAQ481 targets a range of pulse pests, not all results reported are for soybeans or for podsucking bugs. However, they are included in this paper to illustrate the performance of new and alternative products of relevance to, or with potential in, soybeans. The past season has also seen outbreaks of the exotic soybean aphid, Aphis glycines Matsumura, throughout eastern Qld and NSW. While this new pest is readily controlled with dimethoate, use of this product is likely to flare heliothis and mites. Major twospotted mite, Tetranychus urticae Koch, outbreaks in soybeans, as experienced during the

2 summer of 1999/2, pose a major threat to the industry. The mite threat necessitates a major re-focus of IPM strategies, action to secure the registration of an effective miticide in soybeans, and an alternative to dimethoate for soybean aphid control. This paper reports on efficacy trials evaluating five potential miticides in soybeans, and on the probability of achieving registration of these products. Results: (pertinent data from project DAQ 481) Figure 1: Efficacy of Decis, Dimethoate, Steward (indoxocarb code DPX) and Regent (fipronil) against podsucking bugs (PSB) (Nezara viridula and Piezodorus hybneri) in mungbeans at 5 days after treatment (5 DAT). Numbers following Steward and Regent treatments, eg DPX 3, are rates in g a.i./ha. % Control Decis REGENT 25 DPX 6 REGENT 12.5 DPX127.5 DPX 3 Dimethoate Figure 2: Efficacy of new-generation Bayer products, compared to Decis, against green vegetable bug, Nezara viridula (L.), in artificial infestation trial in soybeans. All Bayer products are at 5 g ai/ha. Decis at registered rate of 5 mls/ha. Products X and Y are developmental products.

3 9 8 7 % mortality Control Prod X Prod Y Confidor Decis Figure 3: Efficacy of Trichlorfon (Trich), Confidor (imidacloprid), Decis (deltamethrin), and Dimethoate against green and brown mirids (Creontiades spp.) in navybeans, 3 days after treatment (3DAT). Plus (+) salt treatments have salt added at rate of 5g per L of water. Green & brown mirids/m Soft Bug Options 3DAT JBPRS May Control Trich.48 Confidor 25 Regent 12.5+SALT DPX 3 + Salt Trich.48 + Salt Trich 1.25 Confidor 25+ Salt Decis Rogor

4 Figure 4: Performance of new generation pesticides Steward (indoxocarb or DPX) and Regent (fipronil), and old generation products Dimethoate and Decis, against damsel bug, Nabis kingbergii Reuter, an important heliothis predator in soybeans. % Nabis relative to control Dimethoate DPX127.5 DPX 6 DPX 3 REGENT 12.5 REGENT 25 Decis Figure 5: Performance of new-generation pesticides Regent (fipronil), Steward (indoxocarb or DPX), Confidor (imidacloprid) and secret product X, and oldgeneration products Dimethoate (Rogor), Decis, and Trichlorfon, against brown smudge bug, Deraeocoris signatus (Distant), and spiders, important heliothis and green vegetable bug predators respectively.

5 Beneficials per metre Control Decis REGENT 12.5+SALT TRI.48 TRI 1.25 TRI.48 + SALT ROGOR DPX 3 + SALT CONFIDOR 25 CONFIDOR 25+ SALT BSB SPIDERS X Figure 6: Effect of potential new generation bug pesticide indoxocarb (DPX) against heliothis Helicoverpa armigera (Hübner) in soybeans, compared to existing registered product Decis (deltamethrin) and new-generation heliothis pesticide Tracer (spinosad, code DPX3). 2.5 Heliothis per metre of row DAT 4 DAT 7 DAT. Control Decis Tracer DPX3 Figure 7: Effect of dimethoate on subsequent caterpillar activity (grub days) in mungbeans. W1-W3 denote single applications during a 3-week period. ALL denotes weekly applications over a 3-week period. Dimethoate applied at 8 mls/ha. Heliothis

6 = Helicoverpa armigera (Hübner) Looper = soybean looper, Thysanoplusia orichalcea (Fabricus). 14 Cumulative grub days/m Control W1 W2 W3 ALL heliothis loopers Figure 8: Performance of 5 potential miticides against two-spotted mite, Tetranychus utricae Koch, in soybeans. Trial conducted by Linda Heuke (NSW Agr., Narrabri, with assistance from Lewis Wilson, Cotton CRC Narrabri). 14, Mites per 2 leaflets 12, 1, 8, 6, 4, 2, 28-Mar- 31-Mar- 4-Apr- 11-Apr- Date (sprayed 28/3/) Control Talstar Agrimec Pegasus Comite Intrepid

7 Discussion: Potential new bug pesticides (Figs. 1 and 2): Of the new-generation pesticides trialed, Confidor and Regent gave the best control of podsucking bugs. Regent was less effective at 12.5 g ai/ha than at 25 g ai/ha (= 62.5 and 125 mls/ha respectively). However, previous data (Brier 1998) suggests the 12.5 g ai/ha rate with the addition of salt is nearly as effective as the 25 g ai/ha rate (without salt), but is slower to achieve maximum mortality. Product Y also displayed potential but, since testing, has been declared as no longer commercially viable. This illustrates the commercial uncertainties facing many potential new products. Indoxocarb displayed considerably lower efficacy against podsucking bugs, particularly at the lower 3 g ai/ha rate (= 2 mls/ha). Dimethoate at 8.mls/ha gave unacceptable control of podsucking bugs (Fig. 1). Salt enhancement (Fig. 3): The addition of salt improved the performance of Trichlorfon and Confidor. Both products gave significant control of green and brown mirids (Creontiades spp.) in mungbeans, with the addition of salt, but failed to give significant control at the same rates without salt. Dimethoate (without salt) gave the best mirid control (zero mirids at 3 DAT), but differences between it and all other pesticides were not significant except for Trichlorfon and Confidor without salt at.48 L/ha and.25 g ai/ha (= 62.5 mls/ha) respectively. Impact on beneficials: Dimethoate was suprisingly soft (did not cause marked mortality for) on the damsel bug Nabis kingbergii in mungbeans (Fig. 4). However, Regent (at both rates) and Decis were hard on damsel bugs (ie, caused significant mortality). Indoxocarb was intermediate (between dimethoate and Decis) in softness (selectivity), albeit with a nonsensical rate response (most likely an artefact of variability in damsel bug numbers in the trial area). In contrast in a trial in navybeans, Regent and Decis had no significant impact on brown smudge bug (BSB), Deraeocoris signatus (Distant) (Fig. 5). BSB is a predatory mirid that was extremely abundant last season in pulses and soybeans. Trichlorfon, dimethoate (Rogor) and indoxocarb had only a slight to moderate effect on BSB mortality, albeit with non significant to just significant mortality. Confidor and product X gave the greatest (and significant) BSB mortality. The addition of salt had no effect on the performance of Trichlorfon or Confidor against BSB. With the exception of Decis, none of the above pesticides had a significant (adverse) effect on spider numbers (Fig. 5). Impact of Decis (deltamethrin) and dimethoate on caterpillars: Deltamethrin and dimethoate both significantly increased post-spray caterpillar populations (Helicoverpa armigera and Thysanplusia orichalcea) (Figs. 6 & 7). In the trial with dimethoate (Fig. 7), the greater the number of dimethoate applications, the higher the subsequent heliothis population.

8 Potential miticides (Fig. 8): With the exception of Talstar, all miticides tested (Agrimec, Comite, Intrepid, and Pegasus) gave satisfactory control of mites in a trial conducted (with the assistance of DAQ481 funding) by Linda Heuke at Narrabri. At 14 DAT (last sampling time), there was evidence of a mite resurgence for Talstar. CONCLUSIONS: The data indicates there are new generation products with potential for podsucking bug control in soybeans (eg Confidor and Regent), but that they may not be as selective against beneficial insects as initially hoped. However, the performance of these products will be further evaluated (at low rates plus salt) against podsucking bugs and beneficials. The search for an effective product with dual caterpillar/bug activity continues. Indoxocarb will be further evaluated with the addition of salt, to see if this approach improves its effectiveness against podsucking bugs, as well as its IPM potential at lower rates. Trichlorfon plus salt will also be evaluated to determine if the low rates used in Brazil in soybeans (.48L/ha + salt) are viable against podsucking bugs. The poor performance of dimethoate at the 8 g ai/ha rate suggests the registration in soybeans of this product, at the much lower rate of 34 ml/ha, should be reviewed. As well, the flaring of heliothis (Fig. 7) suggests this product should be used judiciously so as not to flare heliothis (or mites). The lack of salt effect against beneficial insects as reported here is encouraging but will need to be verified against a range of beneficial species. The beneficial data indicates beneficials cannot be treated as a homogenous group when evaluating the selectivity of new products. Because the relative (positive) impact of different beneficial insects has not been quantified in soybeans, the best (ultimate) way to test the IPM potential of new and old products may be to evaluate subsequent heliothis (and mite) activity in response to pesticide applications (as reported in Figs. 7 and 8). The miticide results (Fig. 8) bode well for the registration of an effective miticide in soybeans. While it is hoped to secure a Minor Use Permit for Pegasus in the coming season, commercial considerations (largely beyond the soybean industry s control) suggest that, at this stage, another product (Biomectin) is a more likely candidate for eventual registration. Biomectin has the same active ingredient as Agrimec, ie abamectin. ACKNOWLEDGMENTS Kristen Knight, Joe Wessels, Tracy Coughlin and Robert Alexander for technical assistance and data collation with trials reported in this paper.

9 Linda Heuke for conducting and Lewis Wilson for providing technical advice for mite trials at Narrabri last season. GRDC for funding project DAQ 481. Aventis, Bayer Australia and DuPont for funding pesticide trials reported here.