Bentley, Walter J.

Day, Kevin

Martin, Lee

Ribeiro, Brian

Rice, Dick

Undetermined

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Section 4. Chemical control/new productsFURTHER INVESTIGATIONS IN THE MANAGEMENT OF SAN JOSE SCALEWITH NARROW RANGE HORTICULTURAL OILWalt Bentley, Lee Martin, Dick Rice, Brian Ribeiro, and Kevin DayUniversity ofCalifornia Kearney Agricultural Center and Tulare County Cooperative Extension9240 S. Riverbend Ave., Parlier, CA 93648This study was initiated in 1999 to evaluate the efficacy ofnarrow range horticultural oilsapplied during the delayed dormant period to plums for control of San Jose scale (SJS)(Quadraspidiotusperniciosus). In 1999, either Volck Supreme or Orchex 692 oil applied at thegreen tip stage of growth (8 gallons of oil in 400 gallons ofwater per acre) gave significantlybetter (P<0.05, Fisher's Protected LSD) control of SJS than no treatment (Bentley et al, 1999).Infestation ofBlack Amber cultivar did not exceed 1.50% with either oil (untreated check10.75%). Infestation of the Queen Rosa cultivar was less than 5% (untreated check 14%).Additionally, in August harvested Royal Diamond and Rosemary cultivars, there was asignificant (P<0.05, Fisher's Protected LSD) interaction between the efficacy of oil spray, asmeasured by harvest infestation, and the abundance of SJS measured by the previous yearsinfestation.In 2000 we further studied the efficacy of a delayed dormant oil application (8 gallons ofExxon100Dormant Spray Oil) on SJS fruit infestation of these same cultivars, as influenced by thevolume ofwater/oil mixture applied.Methods and MaterialsThe 2000 study was done in a 3.5-acre block ofmid-June-harvestedplums (Black Amber andQueen Rosa cultivars) and late-July harvested plums (Royal Diamond and Rosemary cultivars).On February 11, individual plots of trees were sprayedwith 8 gallons ofExxon 100DormantSpray Oil in either 100 gallons or 400 gallons of spraymixture or left untreated. Treatmentswere made with an FMC air carrier sprayer driven at 2 mph. The desired volume per acre wasachieved by changing nozzle size. The individual plots of the mixed Black Amber and QueenRosa plums consisted of 64 trees and treatments were replicated four times in a randomizedcomplete block design. Harvest (200 fruit from central trees from each plot) occurred on6/16/2000 (Black Amber) and 6/21/2000 (Queen Rosa). An analysis of variance was performedon the number of SJS infested fruit.Two experiments were performed in the late July harvested plums. Individual plots were smallerthan that used in the earlier harvested fruit and consisted of 30 trees. Using four replicates, onetrial was designed to compare the 100-gallonper acre rate, the 400-gallon per acre rate, and anuntreated check. A randomized complete block design was used. A paired experimental designwas also evaluated where 10 replicated treatments were used to compare the efficacy of 100 and400 GPA in reducing SJS infestation. The additional replicates allowed for a more powerful testof the efficacy of the two treatments. The late harvested plums were Royal Diamond (harvested7/26) and Rosemary (harvested 7/28) cultivars. The determination of infestation for each variety89was made by sampling 200 fruit from the central two rows of trees in each plot. An analysis ofvariance measuring the number of scale infested fruit was performed in both experiments. In allevaluations a single scale on a fruit would classify it as being infested.ResultsBoth the 100 GPA and 400 GPA treatments gave significantly (P<0.05, Fisher's Protected LSD)better control SJS than the untreated check. There was no difference between the 100 and 400GPA treatments. Infestation in the Black Amber cultivar was 0.88, 1.38, and 14.38% for the 400GPA treatment, the 100 GPA treatment and the untreated check respectively. Infestation in theQueen Rosa cultivar was 1.50,2.50, and 15.13% for the 400 GPA, 100 GPA, and untreatedcheck respectively. The Royal Diamond harvest infestation was 5.5,13.63, and 19.88% for the400 GPA, 100 GPA, and the untreated check respectively. The 400 GPA treatment resulted insignificantly (P<0.05) fewer scale infested fruit man the untreated check. The 100 GPAtreatment was not significantly different (P<0.05) from the 400 GPA treatment or the untreatedcheck. Infestation on Rosemary at harvest was 5.00, 7.75, and 18.75% for the 400 GPA, 100GPA, and untreated check treatments respectively. Both the 400 GPA and 100 GPA treatmentsresulted in significantly (PO.05) fewer infested fruit than the untreated check. There was nodifference between 400 GPA and 100 GPA treatments.The 10 replicate paired comparison between the 400 GPA and 100 GPA treatments resulted in ahighly significant (P<0.01) difference in scale infested fruit for both the Royal Diamond andRosemary cultivars. For Rosemary plums, the 400 GPA treatment resulted in 4.55% infestedfruit and the 100 GPA treatment resulted 11.2% infested fruit. The Royal Diamond plums had8.85 and 13.4% infested fruit in the 400 and 100 GPA treatments respectively.DiscussionThe 2000 study established the benefits of a narrow range superior horticultural mineral oil(Exxon 100 Horticultural Spray Oil) in reducing San Jose scale infestation in four cultivars ofplum. This confirmed work done in 1999 showing similar efficacy. There was no cleardifference in infestation based on the volume of spray mixture applied to plums when fourreplicates were used to evaluate treatment effects.Where additional replicates were evaluated, in a paired comparison, in each of two late Julyharvested cultivars, clear differences were seen between 100 and 400 GPA in reducing SJSinfestation. Ten replications result in a more sensitive statistical test. Because ofnon-uniforminfestation by SJS throughout the test orchard, additional replications are needed to establishsignificant differences.Horticultural mineral oils can be used to manage SJS in plums with acceptable efficacy againstSJS. There are a number ofbenefits to using such a program. First, the use ofoil alone reducesthe cost of the pesticide to the grower. Unless SJS populationsare extreme, an 8-gallonrate ofoil can be applied with minimal infestation at harvest, eliminating the need for anorganophosphate or insect growthregulator. Secondly,horticultural mineral oils can be used tocombat insecticide resistance. Oils physically smother the insect; efficacy is not dependent upon90the detoxification ability of the target pest. Thirdly, oils can be used safely with minimal hazardto those applying the spray. Also, horticulturalmineral oils are allowable for organic farmers.Based on the results obtained with paired comparison of 100 & 400 GPA, using 10 replications,fruit harvested after the end ofJune should be sprayed with the higher volume of spray mixture.Thismaynot be neededfor fruit harvested in June. Laterharvested fruit is exposed to at leastone andpossibly two additional generations of SJS. The greater volume of spraymixtureappears to givebetter coverage of wintering scale, in the parameters of this study. The greatertime needed to apply a 400 GPAmixture is a disadvantage. If a farmer contractswith a privateapplicator the additional application time will cost more.91

Further investigations in the management of San Jose scale with narrow range horticultural oil

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Further investigations in the management of San Jose scale with narrow range horticultural oil

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