Report of Progress 961

Southwest Reserch Extension Center Report of Progress 961 Knss Stte University Agriculturl Experiment Sttion nd Coopertive Extension Service

K STATE Southwest Reserch-Extension Center efficcy of miticides Applied t Tssel Stge for control of spider mites in corn, 2005 by Lrry Buschmn, Holly Dvis, Rndll Currie, nd Phil Sloderbeck SUMMARY Spider mite popultions strted out low, but reched 785 mites per 2 plnts by 30 Aug. (46 dys post tretment). The popultions were mostly Bnks grss mites (BGM) in July, but by the end of the seson, nerly 90 percent of the popultion ws twospotted spider mites (TSM). The stndrd tretment, Comite, gve some erly control, but hd little impct on the lte-seson TSM popultions.. The Oberon, Onger, nd Zel tretments seemed to give erly-seson control of BGM, but hd limited impct on TSM popultions lte in the seson. The Agri-Mek tretment ws pplied lte, due to equipment problems, nd gve inconsistent control of the BGM popultions, but did seem to provide some control of TSM lter in the seson. Predtor numbers were very low for most of the seson, but predtor mite popultions incresed lte in the seson, when spider mite popultions were high. No differences in predtor mite popultions were observed mong tretments. Grin yields were highest in some of the Onger nd Oberon tretments, but they were not significntly different from the Check, probbly s result of soil vribility in the field. PROCEDURES Field corn, N73-F7 (GT/LL/YGCB) (112-dy mturity), ws plnted April 26 with John Deere MxEmerge 6 row plnter t rte of 35,000 seeds/cre in whet stubble under center-pivot irrigtion system (Field N34) t the Southwest Reserch- Extension Center, Finney County, Knss. A test with 10 tretments ws set up in rndomized complete-block design with four replictions. Plots were four rows (10 ft) wide nd 50 ft long, with 4-row (10 ft) border of untreted corn on ech side nd 10-ft lley t ech end. The field received 170 lb of N s nhydrous mmoni nd ws irrigted 16 times, receiving 14.5 inches of wter. The plots were mnully infested with Bnks grss mites (BGM) July 12 by tying on mite-infested leves collected from cornfield in Stevens County. We infested 6 plnts in ech plot, 3 for ech of the two center rows. Tretments (except #6) were pplied July 15, when the corn ws lte whorl stge to tssel stge (6 ft). The spryer broke down, so tretment #6 could not be pplied with the other tretments. Tretment #6 ws pplied August 1, when the corn ws in the soft dough stge, with other post-tssel tretments in the djcent plots (see compnion report). The tretments were pplied with high-clernce spryer using 10-ft boom with two nozzles directed t ech row (one on ech side of the row on n 18-inch drop hose). The nozzles were directed up into the plnt. The spryer ws clibrted to deliver 14 gl/cre t 2 mph nd 40 psi. Spider mites were smpled by collecting hlf the leves from 4 plnts (4 hlf plnts = 2 plnts) from the two center rows in ech plot. Erly in the seson, we smpled plnts next to the infested plnts. The plnt mteril from ech plot ws plced in seprte lrge pper bgs nd trnsported to the lbortory, where the plnt mterilws plced in seprte, lrge 76-liter Berlese funnels. A 100-wtt light bulb ws used to dry the vegettion nd drive rthropods down into collecting jr contining 70% methnol. The lcohol smples were filtered on ruled white filter pper, nd spider mites, predtor mites, nd thrips were counted under binoculr microscope. A subsmple of spider mites (bout 20) ws mounted on microscope slide. The slides were exmined to determine the proportion of BGM nd TSM in the popultions from ech plot. Pre-tretment spider mite smples were collected July 14, nd post-tretment smples were collected July 18, 22, 29, nd August 5, 12, nd 30. Spider mite counts were trnsformed with Tylor s power trnsformtion for sttisticl nlysis, nd were bck-trnsformed to mites per 4 hlf-plnts for presenttion. Grin yield ws collected by mchine hrvesting two rows from 70

ech plot. There ws considerble vrition in the plnt height nd grdient in the yield going down the field, so we clculted the field yield trend by clculting the verge yield cross 6 rows of plots going down the field. The position mens were smoothed by using rolling verges. Then this field yield trend ws used s the covrite in the ANOVA of grin yield. The F- vlue for the covrite ws 3.5717; tht for tretment ws 2.3672. RESULTS AND DISCUSSION Bnks grss mite nd TSM popultions verged 12 mites per 2 plnts on July 14. The Bnks grss mite popultions in the untreted control incresed to 126 mites per 2 plnts by August 5, nd then declined to 38 mites per 2 plnts by August 12 (Tble 1). The TSM popultions in the untreted control were present t very low numbers during July, but they incresed rpidly in August, from 6% on August 5 to 89% on August 30. By this time, the TSM popultion verged 694 mites per 2 plnts in the untreted plots (Tbles 3 nd 4). There ws period of wet wether in erly August tht seemed to be ssocited with the collpse of the BGM popultions ws followed by incresing TSM popultions. This confirms previous observtions in this region tht the species composition often shifts from mostly BGM erly in the seson to TSM lter in the seson. The stndrd erly-seson miticide, Comite, gve good erly control (up to 100%) of BGM (Tble 2), but it did not seem to ffect the lte-seson popultions of ttsm (Tble 3 nd 4). The seson-totl control of both spider mites ws only 20% (Tble 5). The percentge of TSM in the popultion did not differ meningfully between the Comite tretment nd the control (Tble 4). The three rtes of Onger gve excellent BGM control, 72 to 98% from 7 to 21 dys fter tretment (DAT) (Tble 2). The seson-totl BGM control ws 41 to 78% (Tble 2). These tretments seemed to hve little impct on the lte-seson TSM, seson-totl control of TSM ws 1 to 28% (Tble 4). The sesontotl control for both spider mites ws only 32 to 57% (Tble 5). There seemed to be significnt increse in the percentge of TSM in the Onger plots 21 DAT (Tble 4), probbly s result of the significnt impct of these tretments on the BGM during this period. There ws no cler indiction of rte response mong the three rtes of Onger tested, nd the highest rte ws the tretment tht seemed to brek down first. The two formultions of Oberon lso gve excellent BGM control, 50 to 97% out to 21 DAT (Tble 2). The seson-totl BGM control ws 61 to 64% (Tble 2). The impct of these tretments on the Tble 1. Bnks grss mites per 4 hlf plnts (=2 plnts) in plots treted with miticides*. Southwest Reserch -Extension Center, Grden City, Knss, 2005. BGM/4 hlf-plnts July 14 July 18 July 22 July 29 Aug. 5 Aug. 12 Aug. 30 No.Tretment Rte Pre-tret. 3 dys 7 dys 14 dys 21 dys 28 dys 46 dys 1 Check 19 29 79 14 b 126 38 81 2 Comite II 6EC 2.25 pt 8 11 0 d 8 bc 41 b 20 141 3 Onger 1E 6 oz 9 16 8 bc 2 c 4 c 30 11 4 Onger 1E 8 oz ``7 18 8 bc 1 c 2 d 4 7 5 Onger 1E 12 oz 3 11 15 bc 1 c 5 cd 9 84 6 b AgriMek 0.15 EC 8 oz 3 12 19 b 47 43 b 38 5 7 Oberon 240EC 8.5 oz 9 5 3 bcd 2 c 3 cd 37 21 8 Oberon 480EC 4.25 oz 9 12 2 cd 3 bc 15 bcd 20 60 9 Zel 0.66 oz 14 11 9 bc 3 bc 22 bcd 25 65 10 Zel.0 oz 2 27 9 bc 6 bc 23 bcd 10 24 F-test P vlue 0.7394 0.3248 0.0023 0.0016 0.0024 0.3382 0.2496 Mens followed by the sme letter re not significntly different (P < 0.05, LSD) b Tretment 6 ws not pplied until August 1, so it ws Check until the August 5 smple. 71

Tble 2. Percentge of control of Bnks grss mites in plots treted with miticides*, Southwest Reserch -Extension Center, Grden City, Knss, 2005. percentge control for BGM R rte July 18 July 22 July 29 Aug. 5 Aug. 12 Aug. 30 Seson No. Tretment 3 dys 7 dys 14 dys 21 dys 28 dys 46 dys Totl 1 Check 2 Comite II 6EC 2.25 pt 56 100 33 60 35 0 16 3 Onger 1E 6 oz 34 88 86 96 6 84 68 4 Onger 1E 8 oz 21 88 88 98 86 90 78 5 Onger 1E 12 oz 43 72 90 94 63 0 41 6 AgriMek 0.15 EC 8 oz 49 0 91 21 7 Oberon 240EC 8.5 oz 81 96 84 97 0 69 64 8 Oberon 480EC 4.25 oz 50 98 78 86 37 13 61 9 Zel 0.66 oz 60 88 81 81 30 14 51 10 Zel.0 oz 0 80 28 70 55 52 46 Tretment 6 ws not pplied until August 1, so it ws Check until the August 5 smple. Tble 3. Twospotted spider mites per 4 hlf plnts (=2 plnts) in plots treted with miticides*, Southwest Reserch-Extension Center, Grden City, Knss, 2005. tsm/4 hlf-plnts July 14 July 18 July 22 July 29 Aug. 5 Aug. 12 Aug. 30 No.Tretment Rte Pre-tret. 3 dys 7 dys 14 dys 21 dys 28 dys 46 dys 1 Check 0.0 0.0 0.0 4 4 34 694 2 Comite II 6EC 2.25 pt 0.0 0.0 0.0 1 7 11 673 3 Onger 1E 6 oz 0.0 0.0 0.0 0 1 25 696 4 Onger 1E 8 oz 0.0 0.0 0.0 1 3 9 511 5 Onger 1E 12 oz 0.0 0.0 0.0 0 5 15 587 6 b AgriMek 0.15 EC 8 oz 0.0 0.0 0.0 7 2 15 403 7 Oberon 240EC 8.5 oz 0.0 0.0 0.0 0 2 16 726 8 Oberon 480EC 4.25 oz 0.0 0.0 0.0 2 4 15 424 9 Zel 0.66 oz 0.0 0.0 0.0 1 4 19 613 10 Zel.0 oz 0.0 0.0 0.0 2 5 11 496 F-test P vlue 0.1729 0.8792 0.9452 0.8824 Mens followed by the sme letter re not significntly different (P < 0.05, LSD) b Tretment 6 ws not pplied until August 1, so it ws Check until the August 5 smple. lte-seson TSM vried from 0 to 59% on the smples 21 to 46 DAT (Tble 4). The seson-totl control for both spider mites ws only 31 to 60% (Tble 5). There ws no cler indiction of difference in performnce of the two Oberon formultions. The BGM popultions in the Agri-Mek tretment were similr to the untreted check until August 5, 4 dys fter the tretment. The Agri-Mek tretment gve inconsistent control of BGM popultions (49 nd 91% control on August 5 nd 30, respectively, but control ws 0% on August 12 (Tble 2)). The 72 seson-totl BGM control ws only 21% (Tble 2), but this tretment seemed to impct the lte-seson TSM popultions (42 to 55% control 21 to 46 dys fter tretment (Tble 4)). The seson-totl control for both spider mites ws 52% (Tble 5). The 8-oz rte of Agri-Mek used here did not work s well s the 16-oz rte used in 2003, but the 16-oz rte is estimted to cost $64 n cre. The two rtes of Zel gve fir to excellent BGM control, 28 to 88% 7 to 21 DAT (Tble 2). The seson totl BGM control ws 46 to 51% (Tble 2),

Tble 4. Percentge of control of twospotted spider mites in plots treted with miticides*, Southwest Reserch-Extension Center, Grden City, Knss, 2005. percentge popultion TSM Percentge control for TSM A ug. 5 Aug. 12 Aug. 30 Aug. 5 Aug. 12 Aug. 30 Seson No. Tretment Rte 21 dys 28 dys 46 dys 21 dys 28 dys 46 dys totl 1 Check 6 b 48 89 2 Comite II 6EC 2.25 pt 18 b 37 79 0 69 3 8 3 Onger 1E 6 oz 43 46 97 68 27 0 1 4 Onger 1E 8 oz 48 64 95 30 72 26 28 5 Onger 1E 12 oz 45 57 87 0 56 15 19 6 AgriMek 0.15 EC 8 oz 6 b 32 88 53 55 42 41 7 Oberon 240EC 8.5 oz 31 b 35 93 59 52 0 1 8 Oberon 480EC 4.25 oz 23 b 32 85 7 56 39 40 9 Zel 0.66 oz 21 b 42 90 10 44 12 12 10 Zel.0 oz 23 b 52 89 0 68 29 31 F-test P vlue 0.0832 0.5697 0.4082 Mens followed by the sme letter re not significntly different (P < 0.05, LSD) but these tretments seemed to hve less impct on the lte-seson TSM, with seson-totl control of 12 to 31% (Tble 4). The seson-totl control for both spider mites ws only 33 to 53% (Tble 5). There ws no cler indiction of rte response mong the two rtes of Zel tested. During the erly prt of the seson, July 14 nd August 5, predtor mite popultions were low, 0.35 to 0.9 per 2 plnts, becuse spider mite popultions were lso low, <50 mites per plnt (Tbles 1 nd 3). In lte August, however, when the mite popultions incresed from <50 to >1190 mites per 2 plnts, the predtor mite popultions incresed from 0.9 to 116.3 mites per 2 plnts. (Tble 5). This ws the only predtor popultion tht seemed to increse s spider mite popultions incresed. The lte-seson predtor mite numbers were not significntly different cross the miticide tretments (Tble 5). Thrips popultions, Frnkliniell spp., decresed from 3.0 to 0.9 per 2 plnts during the smpling period. They were smpled during the post-tssel period, when thrips numbers re usully smller thn they re during the erly to mid-whorl stges. In the pst, these thrips seemed to be importnt erly-seson fculttive predtors of spider mites. The spider mite popultions generlly increse rpidly during the corn reproductive stge, when the thrips popultions re low. Sixspotted thrips, Scolothrip spp., were present, but popultions were low during the smpling period, 0.06 to 0.25 thrips per 2 plnts. These thrips re reported to be importnt predtors of the spider mites, but we hve recorded them only infrequently. Predtor popultions were too low erly in the seson, when tretments were pplied, to determine if there were differences in their responses to the miticide tretments. Although there were some significnt differences in yields mong tretments, nd the coefficient of vrition (CV) ws only 7.9%, interprettion is difficult. The highest yields were in the Oberon 480EC nd 8 oz. Onger 1E tretments, which hd the highest seson-totl percentge of control, but they were not significntly different from the untreted check. The tretments were good enough to protect enough yield to be clerly identified in this tril. 73

Tble 5. Numbers of predtor mites, seson-totl numbers of spider mites, nd grin yield for plots treted with miticides*, Southwest Reserch-Extension Center, Grden City, Knss, 2005. P predtor mites/4 hlf-plnts Spider mites /4 hlf-plnts Grin A ug. 5 Aug. 12 Aug. 30 Seson totls yield No. Tretment Rte 21 dys 28 dys 46 dys BGM TSM Sum % Control bu/cre 1 Check 1.5 9.8 109 434 756 1190 62.2 b 2 Comite II 6EC 2.25 pt 2.0 9.3 152 295 b 699 994 20 166.2 b 3 Onger 1E 6 oz 0.5 20.5 158 118 cd 749 867 32 155.8 b 4 Onger 1E 8 oz 1.5 2.3 159 77 d 542 619 57 174.6 5 Onger 1E 12 oz 0.8 13.0 119 172 bcd 615 787 41 169.8 b 6 b AgriMek 0.15 EC 8 oz 0.3 6.3 67 232 bc 444 674 52 154.5 b 7 Oberon 240EC 8.5 oz 0.0 18.3 119 130 cd 749 880 31 164.8 b 8 Oberon 480EC 4.25 oz 1.5 2.8 107 146 bcd 452 597 60 178.6 9 Zel 0.66 oz 0.5 4.8 75 199 bc 663 862 33 175.2 10 Zel.0 oz 0.5 6.0 100 142 bcd 519 661 53 155.6 b F-test P vlue 0.0787 0.1102 0.6397 0.0139 0.8682 0.0430 Mens followed by the sme letter re not significntly different (P < 0.05, LSD) b Tretment 6 ws not pplied until August 1, so it ws Check until the August 5 smple. BGM femle. BGM mle. 74

Knss Stte University Agriculturl Experiment Sttion nd Coopertive Extension Service, Mnhttn 66506 SRP 961 August 2006 K-Stte Reserch nd Extension is n equl opportunity provider nd employer. 300