Forbes, A. R.

MacCarthy, H. R.

English

Journal of the Entomological Society of British Columbia

~'''TOMOr.U''l< ·.\L SOCIETY <)1-' I:lBITI"1I CO Ll '!\lIlU. Pi" .... (l~S~) I. VOl .. 56. Nm'. 4.1~15~1 CONTROL OF APHIDS AND CATERPILLARS ON BRUSSELS SPROUTS IN BRITISH COLUMBIA A. R. FORBES AND R. R . MACCARTHY Research Station Canada Agriculture, cl o The University of British Columbia , ' Vancouver , British Columbia'. The cabbage aphid, Brevicoryne brassicae (L.), is a serious pest of brassica crops in British Columbia . The recommended control measures with malathion and TEPP have not always been satisfactory, especially on Brussels sprouts, broccoli, and cauliflower. With new and potential-ly useful systemic and contact insec-ticides available or about to become available it was necessary to work out new recommendations. This paper re-ports the results of exploratory field tests conducted at Vancouver in 1958. Brassica crops are also attacked each season by other pests, which were considered when evaluating the insecticides against cabbage aphid; these were: imported cabbageworm, Pieris rapae (L.), diamond-back moth, Plutella maculipennis (Curt.), cab-bage looper, Trichoplusia ni (Rb.) , and green peach aphid, Myzus persi-cae (Sulz.). Methods and Materials Brussels sprouts was used as the test crop since it presented the most difficult problem in control under B.C. conditions. The aphids get into the sprouts where they are shielded from sprays and dusts. It lends itself well to continuing appraisal of leaves and of the harvested product. This crop also has a long growing period and must be protected until harvest is complete, which may be in November or even later. Cultural procedures followed those of commercial growers as closely as possible . The variety of Brussels sprouts used was Long Island Improv-ed, the one most commonly grown in the area. Plants were started in the seedbed May 8 and transplanted to the field June 12. The seedbed and the plants at transplanting were ,Contribution No. 12. treated with heptachlor dust to con-trol root maggots. Eight treatments and the check were replicated 4 times in randomized blocks. Each plot consisted of two rows of 10 plants each. Table I shows the insecticides, formulations, rates per acre per application, and dates of application. Di-syston granules were applied to the soil around the base of the plants, but the other insecticides were applied as sprays at the field scale rate of 100 gallons per acre with a compressed air sprayer. The method of spraying gave results similar to those that would have been obtained in field applications : the spray nozzle was directed above and beside the plants but the rate did not permit in-dividual spraying of each plant or thorough coverage of the lower leaves, especially the undersides. The sur-factant Triton B 1956 (Rohm & Raas Co., Philadelphia 5, Pa.) was added to each spray at the rate of 4 ounces per 100 gallons. Portable barriers (figures 1 and 2) were placed around the plots during spraying. These were made of 1 x 4 inch cedar with corner braces, and covered with sign cotton cloth as used for advertising. Di-syston was first applied when the aphids appeared in the field . The first application of all other materials was on July 30, when there were 194 colonies of B. brassicae on 60 leaves, i.e. when the infestation was well established. Counts were made 14 times at weekly intervals from August 8 to November 14 from an upper, a middle, and a lower leaf from each of 5 plants at random per plot. Data recorded were: numbers of colonies of cabbage aphids, numbers of adult green peach aphids, numbers of each of the 3 spe-cies of caterpillars, and estimates of the percentage of leaf surface dam-:14 ~; ~ T" .\I"I.""I! · .\1. S", ·n :TY ')I" 13HITI"'1 C OIX .\II:J .\. PH'W . (l~i)!.I). V"I.. ;;6. No\'. 4. ]!:t5 ~ TABLE 1.-Treaments against cabbage aphid on Brussels sprouts at Vancouver, B.C., 1958. Insecticidr None - check TEPP' 20% emulsion malathionz 57 % emulsion Thimetz 47.5% emulsion N.A. Cyanamid 12,880 2 46% soluble cone. (Dime tho ate) N.A. Cyanamid 18,706 2 25% soluble cone. Di·syston3 5% granules Systox3 Phosdrin 4 soln. Toxicant per acre, per application I h. 0.25 1.25 1.00 1.00 1.00 1.00 0.50 0.45 ,Later Chemical Co., Vancou ve r 14, B.C. 2 Cyanamid of Canada Ltd. , Toronto 5, On t. 3 Chemagro Corp. , New York 16, N.Y. Treated July 30, Aug. 12, 25, Sept. 5, 15, 22 July 30, Aug. 12, 25, Sept. 5, 22 July 30, Aug. 18, Sept. 15 July 30, Aug. 25 July 30, Aug. 18, Sept. 15 July 7, 30, Sept. 2 July 30, Aug. 25 July 30, Aug. 12, 25, Sept. 8, 22 4 Shell Oil Company of Canada , Toronto I , Ont. ; 12.3 Ibs. of toxicant per ga ll on. Fig. I.-Portable barriers around plot during spraying. Fig. 2.-Portable barriers being assembled around plot. 1 ' ::<Tn~f'"f)(; " .11 . S()('n~TY nF HRITI S II ('nl .I · "RI.\. PH"' . '1 ~~!11. \ ·n l .. fi6. 1\", .. 4. H15~ o o Fig. 3.-Diagram of mature leaf of Brut·sels sprouts with typical mid-season population of cabbage aphid s. This leaf has 13 colonies. aged by caterpillars. Where cabbage aphids covered large areas of the leaves, as in the checks, a circular area of covered leaf one half inch across, as estimated by inspection, was counted as one colony. A cabbage aphid in isolation, apterous or alate , settled On the leaf was also counted as one colony (figure 3) . At harvest 10 mature sprouts were taken, one from each of 10 plants per plot, every week for 7 weeks. These were weighed, inspected for caterpil-lar damage and examined by dissec-tion for the presence of aphids. Ac-cording to the absence or location of aphids they were categorized as clean , commercially acceptable , or rejected . ~6 ~>\Tn .\fnr.II( ;l<" . \L SO" ] ETY OF BHfT f S TT (:Ol.f · ~fflf " . PHIH' . (1.9fllll. VOl .. ~6 . Nn\'. 4. 1!Hi9 DISYSTON 18706 100 100 12880 THIMET 100 100 SYSTOX CHECK 100 1000 V) w 900 > < w PHOSDRIN ....J 0 ..., 100 800 z 0 V) 700 w z MALATHION 0 ....J 200 600 0 u u. 0 100 500 a:: w CD ::e ::J 400 Z 300 300 200 200 100 100 OCT. NOV. Fig. 4.-Populations of cabbage aphids on leaves of Brussels sprouts in all treatments ;Jt Vancouver, B.C., 1958. Clean sprouts had no aphids in or on them; commercially a c c e pta b I e sprouts had one or two aphids where th ey were easily washed off; rej ected sprouts had aphids within the leaves wh ere ordinary washing would not dislodge them. Differences between the treatments were assessed by anal -ysis of variance . Sprouts treated with Thimet, 12,880, 18,706, Di-syston, Systox, and Phos-drin were analyzed for residue by chemists of the British Columbia Re-search Council. Samples were taken from the field and immediately frozen on October 10 and 24. They were anal-yzed in February, 1959. Results and Discussion Aphids were first noted on the plan ts on July 7; by July 29 there were high populations of both cab-bage and green peach aphids. The population of cabbage aphids in the check plots built up steadily until September 5 after which it declined (figure 4) . A fungus infection, brac-onid parasites, syrphid larvae, chryso-F:l'"Tfnlo r,O(;((,AJ. S O('!F,TY OF HIl ITT i' H ~OLFM RIA . PIlO(' . (HI5!) 1. VOr.. fi 6 . N ov. 4. 1959 :17 TABLE II-Aphid population totals from 14 weekly leaf counts', August 8 • November 14, 1958, on Brussels sprouts at Vancouver, B.C. Brevicoryne Myzus Percentage Treatment brassicae Percentage persicae control colonies control adults Di-syston 215 96 497 11 Systox 358 93 304 46 12,880 352 93 182 67 Thimet 538 89 283 49 Phosdrin 563 89 357 36 18,706 531 89 165 70 Malathion 1074 78 810 0 TEPP 1722 65 763 0 Check 4958 558 , Each weekly count f r om an uppe r , a mid dle, a nd a lower leaf from each of 5 plants p e r plot , 20 plants per t r eatment. pid larvae, and cool damp weather contributed to the decline. The popu-lation of green peach aphids rose un-til August 15 but fell rapidly ther e -after. Populations of cabbage aphids in all treatments during the season are shown graphically in fi gure 4. Data on the effectiveness of the treatments a ga inst aphids are summarized in Tables II and III. The systemics gave markedly better control than mala-thion or TEPP. Di-syston was the out-standing material a gainst cabbage aphids but had little effect on green peach a phids, probably because the latter were confined to the old leaves. Systox and 12,880 were promising against cabbage aphids. Phosdrin re-duced the population of cabbage aphids each time it was applied but it required 5 applica tions. 12,880 and 18,706 were the best m a t erials against green pea ch aphids. TABLE III-Control of cabbage aphids and yield at harvest on Brussels sprouts dt Vancouver, B.C., 1958. Clean Sprouts Marketable Sprouts Yield2 Treatment Number ' Percentage Number ' Percentage gm. Di-syston 59.0 84 68.0 97 1256 Systox 49.2 70 63.5 91 1236 12,880 48.7 70 61.5 88 1213 Thimet 45.2 65 60.5 86 1173 Phosdrin 43.7 62 58.5 84 1212 18,706 36.2 52 58.2 83 1146 Malathion 28.0 40 52.5 75 1233 TEPP 27.7 40 49.2 70 1121 Check 20.7 30 51.2 73 882 L.S.D. at 5% level 7.9 6.8 138 1 % level 10.8 9.2 188 1 Maxim um of 70. 2 Aver age weig h t of 70 sp r out,. TABLE IV-Percentage control of caterpillars on Brussels sprouts al' V.,ncouver, B.C., 1958. Percentage control based on : Treatment Damaged Total Leaves with more Undamaged sprouts' caterpillars2 than 5% damage 2 leaves 2 Phosdrin Malathion Thimet 12,880 TEPP 18,706 Systox Di-syston 76 64 34 21 21 6 3 0 87 81 61 56 31 12 36 4 44 24 27 16 22 6 25 11 31 13 0 0 0 0 0 0 ,Sample of 280 sprouts: 40 taken e a c h week from Odober 2-No ve mbe r 14. 2 Sample of 840 leaves: 60 take n each wee k from Au g u st 8-Novembe r 14. All treatments greatly increased the yield of sprouts and there were no sig-nificant differences between treat-ments in this respect. The increases in weight ranged from 27 per cent for TEPP to 42 per cent for Di-syston. Thus controlling cabbage aphids in-creased both the yield and marketa-bility of sprouts. Against caterpillars, Phosdrin and malathion were the best materials (Table IV). Di-syston, 18,706, and Systox gave virtually no control. TEPP and malathion were applied 6 and 5 times respectively, or every 7 to 13 days during the season, but nev-er reduced the populations to accept-ably low levels (figure 4). Other in-secticides were reapplied each time the weekly counts of cabbage aphid colonies showed more than 50 per 60 leaves. Thus Phosdrin required 5 ap-plications, Thimet, Di-syston, and 18,706 required 3, and 12,880 and Sys-tox required only 2, to maintain the population levels shown (figure 4) . Green peach aphids occurred al-most exclusively on the old, lower leaves. Over the 14 weeks, 0.5 per cent occurred on upper leaves, 3 per cent on middle leaves and 96 per cent on lower leaves. This and the fact sys-temics may not be effectively trans-located to leaves that are not grow-ing rapidly may account for their relatively poor performance. TEPP and malathion gave no control of green peach aphids because the meth-od of spraying and rate of application did not permit coverage of the lower leaves. The cabbage aphid occurred at all levels on the plant as follows : 19 per cent occurred on upper leaves, 37 per cent on middle leaves, and 44 per cent on lower leaves. The method of counting aphids gave valid data on their relative numbers and their location . Results were con-sistent among different counters. For cabbage aphids, colonies were count-ed , since this is a gregarious species and the colonies provided discrete units that were counted easily and rapidly. For green peach aphids adults were counted, since this is a solitary species and the aphids are found dispersed over the leaf. For-tunately green peach aphid popula-tions remained low so that counting the adults was not unduly time con-suming. The portable barriers used during spraying worked well in practice, so that buffer rows were not needed . They eliminated spray drift and per-mitted spraying even on windy days. The ba rriers were light and easily moved into position (figure 2) . E S T O ,I IIJi .<><l Il ', II , S , W II ':T Y IJ I.' I l l n T I ~ 1 1 ('O l.t ' III:I.\ . P ,«)!'. ( UlG9 J . V O L . 56, Nol'. 4, 195U 39 No residue was detected in an y of th e sprouts except in those treated with Phosdrin and h arvested on Oc-tober 10 . In these the inhibition of cholinesterase was 8.3 per cen t gr eat-er than in the untreated ch eck. The PAINTED LADY, Vanessa cardui, on Vancouver Island This cosmopolitan butterfly was common in Saanich , during 1958. Not since 1952 h ave I seen it in such num-bers. As a matter of fact only a single specimen, in 1957, came to my notice between these dates. In 1958 I first noted it on May 18, a nd the last da te recorded was October 1. Soon after a rriving in th e district, from where I do not know, egg laying sta rted on the two species of thistles abundant in the area, n amely Ca nada thistle, Cirsium canadensis, and bull thistle , C. l anceolat a . It seemed to prefer the latter. On June 18 I ob-served a female hovering a bout the head of a bull thistle where it was ovipositing so intently tha t it con-tinued to lay even when I pulled the stem towards me for a closer look. In a ll , though not n ecessarily laid by this individual, 12 eggs were found , either on the involucre of the t er -minal flower h ead , or on the upper -most leaves just beneath the inflor-escence. I snipped off th e top of the plant conta ining the eggs and placed it under a muslin screen . The result-ing caterpilla rs were reared to ma -t urity. Adults emerged on July 17, one month a fter the eggs were la id . During the course of the summer la rvae in a ll stages of development were in evidence, varying from ligh t yellowish green to a lmost completely black . Clumps of thistles soon assum-ed a bedraggled appearance, th e bare leaf stalks festooned with the rem-nants of th e silken cubicles in which the la rvae lived or h ad lived . Pupae were ra rely seen , however , as the caterpillars leave th e food plant for intervals in days, between last treat-ment and the October 10 harvest were : Thimet , 25 ; 12,880, 46; 18,706, 25 ; Di-syston , 38 ; Systox, 46 ; Phos-d rin , 18. less exposed quarters. Once in a while a chrysalis was found hanging within a very open-meshed tent along the leaf sta lks of the host plant. Fresh specimens of adults were common by July 18 and continued to be so well in September. There is considerable overlapping of broods but with an average of one month for a complete life cycle and a consta n t succession of ova there could be two or more generations in on e season, especially in a long, mild autumn as in 1958. From an economic point of view this is a useful insect, considering the ravages it commits a mong the thistles. Wha t becomes of the hosts of in-dividuals seen up to October I? They must do one of three things : Hiber-na te; but I h ave never come across them h ereabouts, even early in the spring as in the case of the Mourning cloak a nd Angle Wing, both of which a re known to hibernate. Emigrate; if so it is not noticeable. Or die before winter ; here again I h ave no evidence in support of such a h appening. Most likely they a re h ere in the fi rst place as an overflow from Mexico or some other wa rm climate. They succeed well enough during the summer in their n ew h aunt, but are una ble to withstand the ensuing winter. R. South in "The Butterflies of the Bri t ish Isles" 1947 sta tes that North Africa is thought to be the centre for this s p e c i e s, which periodically spreads a ll over the t emperate world, wh ere it thrives for a time but even-tually disappears, until a nother wave of migrants from the original source re-popula tes its fa r flun g range. G . A. HARDY Provincia l Museum, Victor ia , B.C. 

Control of aphids and caterpillars on Brussels sprouts in British Columbia

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Control of aphids and caterpillars on Brussels sprouts in British Columbia

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Journal of the Entomological Society of British Columbia