WALNUT SCALE - DEVELOPMENT OF AN EFFECTIVE MONITORING METHOD AND PHENOLOGY MODEL Richard L. Coviello, Mark Freeman, Richard E. rice, William H. Krueger, Phil Phillips ABSTRACT Results from sampling in Fresno Coutny during 1983 indicated a developmental threshold of 50 F. with an upper limit of approximately 90 F. 1984 data from Fresno County and Glenn County show that 48 F. fits the data better, with an upper limit between 80 and 84 F. The lowered upper limit may be the result of the much warmer weather this year in which the deleterious effects of heat on insect growth would be expressed more clearly. Samples of a timing trial applied in 1983 show that the treatment applied at first generation crawler emergence reduced the population of scale through two seasons, while the dormant and delayed dormant treatments were the same as the untreated check by the end of 1984. A screening trial was applied at the delayed dormant and crawler emergence periods in 1984. Supracide@ and Lorsban@ applied at crawler emergence showed somewhat better performance through the season than Supracide at delayed dormancy. Zolone@, when applied at either crawler emergence or at codling moth timing, had no effect on scale. However, Zolone and Supracide at crawler emergence significantly reduced predator mites while Lorsban did not. OBJECTIVES Resul ts from last year I s research on walnut scale indicated that both adult scale and the immature crawler stages could be readily trapped on double-sided cellophane tape. These trap counts could then be used to ascertain when adults and crawlers were active and vulnerable to insecticides. Temperatures were also observed near the sampling site and these along with the trap data were used to construct a preliminary day-degree model of the scale phenology. An insecticide timing trial was during the scale life cycle, a Treatment at crawler emergence Our objectives this year were as also conducted to determine when, treatment would be most effective. reduced the population the most. follows: 1. To validate the preliminary phenology model that was developed last year by continued sampling in Fresno County and by sampling in Glenn County and Ventura County to give a broad temperature range for the scale activity. 2. To continue to sample the timing trial to see how long the treatments remain effective. 3. To evaluate selected insecticides for control at delayed dormant or crawler emergence. -67-
PROCEDURE Trapping was done as described in the Walnut Research Reports, 1983, p. 56. The phenology sampling, timing trial and the screening trial were all sampled in a similar manner. The timing trial is described in the Walnut Research Reports, 1983, p. 56. The screening trial included Supracide@ 2E at two rates plus one, including oil at the delayed dormant and crawler emergence, Lorsban@ 50W at crawler emergence and Zolone @ 3E at crawler emergence and at the codling moth treatment timing. See Table 3 for treatment dates and rates. Treatments were applied vlith a handgun sprayer at 400 gallons per acre. There were untreated trees between each of five single tree replications. RESULTS Data for the phenology model are still being analyzed; however, preliminary analysis indicates that the lower threshold is about 48 degrees F. while the upper threshold is between 80 and 85 degrees F. An accumulation of between 2000 and 2200 day-degrees appears to be required per generation. Last year's data showed a higher upper threshold of 90 degrees F.; however, temperatures were much warmer this year and the deleterious effects of the heat may have shown up more clearly. Data from Ven'tura Co. show a much lower population than in Fresno or Glenn Counties (Table 1). The pattern of emergence for the first generation was similar, but the scale numbers were apparently too low for the second generation to show up on the tapes. Scale counts at the end of last season's sampling in the timing trial indicated that the crawler treatment was still holding, while the dormant and delayed dormant 'treatmentswere losing effectiveness. 1984 data show that the crawler treatment is still significantly better 'than the others throughout the year, (Table 2). Results of the screening trial are shown in Table 3. All treatments of Supracide appear to give statistically equivalent control at the end of the year, but nwnerically the delayed dormant treatment is considerably higher than the crawler treatment. Lorsban is as effective as Supracide. Both Zolone treatments statistically had higher crawler counts than the untreated check; however, this should not be taken to suggest that Zolone actually stimulates scale production. Scale parasites stuck to the tapes were counted throughout the season to determine 'treatment effects on them ('I'able4). There were no differences in cumulative numbers at the time the first treatment went on. At the end of the season, however, differences were apparent with the crawler treatment being significantly lower than the check and somewhat lower than the delayed dormant treatment. It is difficult to determine whether the effects are directly on the parasites or if their lower numbers resulted from the reduction in the scale population. Predator 4 ). The mi tes were mi tes had also monitored in the screening trial, (Table two definite peaks in population during the -68-
season, one occuring on September 13, at an average of 3.7 per tape. Mite counts fell to zero on July 19. Data analysis of the cumulative predators in each population peak showed a definite impact of the delayed dormant treatment in the first peak, which was reversed by the second peak. The crawler treatment had significantly lower numbers of predators in the latter half of the season. The Zolone treatments had very few predators, even when applied at the codling moth timing. The results of the timing trial and screening trial suggest a reasonable approach to scale control may be to treat alternate rows every other year after the beginning of spring crawler emergence. The crmvler treatment appears to last at least two years and by leaving alternate untreated rows, the population of scale and aphid parasites would be maintained within the orchard. -69- ---
Table 1 Walnut Scale Phenology Preliminary Results -Location Thresholds Lower: Upper Day-Degrees Population Peak~1 1st Generation 2nd Generation Males Crawlers Males Crawlers Fresno Co. 48:84 2234 36.6 243.0 5.40 139.5 Glenn Co. 48:80 2018 5.78 393.25.20 53.93 - Jj Jj Ventura Co. 0.17 3.98 Number of scale per tape per day. Insufficient data for calculating. Table 2 Walnut Scale Tinling Trial Cumulative Number of Scale for Each Generation 1st Generation 2nd Generation Treatment and Date Males Crawlers Males Crawlers Dormant 505.0ab 7973.4 b l28.0ab 4628.8 b 2//83 Male Flight 233.0a 3956.2ab 154.0 b 4677.6 b 3/23/83 Crawler Emergence l08.0a 107.8a.8a 327.0a 6/1/83 Control 760.6 b 8422.0 b 199.8 b 4060.4 b Means followed by the same letter(s) are not significantly different (DMRT=0.05). -70- -- - - --- - -
Walnut Scale Screening Trial Table 3 Cumulative Scale in Each Generation 1st Generation 2nd Gener.ation Treatment. Males Crawlers Males Crawlers " 1..1!i../ Supracide 2E 295.6a 576.6a 38.8a 688.0a 2 lbs a.i./a 1/ Supracide 2E 324.6a 985.6ab 33.8a 1322.4ab 1 lb a.i./a 1..1 Supracide 2E + oil 239.8a l573.6ab 40.2a 946.2a 1 lb a.i. + l%/a 2/ Supracide2E 746.6 b 3925.4ab l6.6a 296.0a 2 lbs a.i./a Supracide 2E 640.8 b 2791.8ab 35.6a 390.0a 1 lb a.i./a Supracide 2E + oil 817.4 b 3668.8ab 27.4a l40.2a 1 lb a.i. + l%/a Zolone 3E 735.6 b 14301.2 c 310.6 c 6358.8 c 2 lbs a.i./a Lorsban 50W 664.6 b 2583.8ab l5.8a 104.8a 1 lb a. i. /A?) Zolone 3E 736.6 b 13340.0 c 189.6 b 4902.4 c 2 lbs a. i. /A Control 582.8 b 6292.6 b 100.Oab 3060.2 b 1/ -Treatments applied 3/8/84 during delayed dormant period. 2/ -Treatments applied 5/22/84 during crawler emergence. 3/ -Treatment applied 5/4/84 at codling moth timing. 4/ -Numbers followed by the same letter(s) are not significantly different (DMRT=0.05). -71- --~.:.....
Table 4. Walnut Scale Screening Trial Parasite and Predator Counts.I.I Parasites Predators Treatment Pretreat End of Season 1st Half 2nd Half -- ---.------ 1.1!il Supracide 2E 0.9 21.7ab 4.2 cd 37.0a 2 1bs a. LI A 1.1 Supracide 2E 1.1 15.1abc 3.2 d 17.7 bcd 1 1b a.i./a Supracide 2E + 1.1 oil 0.9 12.9 bc 1.6 d 7.6 cd 1 1b a.l + l%ia 21 Supracide 2E 1.8 7.4 c 19.5 b 3.5 d 2 1bs a.l/a ]j Supracide 2E 1.2 6.7 c 14.6 b 4.2 d 1 1b a.l/a Supracide 2E + oil 1.4 10.5 c 16.2 b 3.6 d 1 1b a.l + l%ia Zolone 3E 1.1 10.5 c 12.5 bc 3.4 d 2 1bs a.l/a Lorsban 50W 1.7 608 c 18.8 b 29.7ab 1 lb a. LI A Zolone 3E 1.6 15.5abc 15.1 b 3.7 d 2 1bs a. i.1a Control 2.5 24.4a 28.3a 19.3 bc -Treatments applied 3/8/84 during delayed dormant period. 21 -Treatments applied 5/22/84 during crawler emergence. 31. -Treatment applied 5/4184 at codling moth timing.!il Numbers followed by the same letter(s) are not significantly different (DMRT=0.05). ~I Cumulative number per tape. -72-.,