Dormant Oil Research Articles

Non-target effects of agrichemicals applied in the fall or during the dormant season on subsequent development of Exobasidium leaf and fruit spot of blueberry

The basidiomycete Exobasidium maculosum causes Exobasidium leaf and fruit spot, an early-season disease of blueberry in the southern United States. Previous research suggested that the pathogen oversummers and overwinters epiphytically on the surface of blueberry bark and buds, most likely in its yeast stage. This is supported by the finding that a single dormant application of lime sulfur provides substantial control of the disease the following spring. As a surface resident for much of the year, E. maculosum is thus exposed to various horticultural and pest management practices which may affect its epiphytic population dynamics and impact subsequent disease development. The magnitude and consistency of such non-target effects was evaluated in multi-year field trials on susceptible ‘Premier’ and ‘Tifblue’ rabbiteye blueberry in southern Georgia. One fall application of stylet oil (timed to mimic sprays for blueberry bud mite control) or two fall applications of captan (timed to coincide with the management window for fungal foliar diseases) did not suppress Exobasidium leaf and fruit spot the following spring, whereas two fall applications of lime sulfur reduced the disease significantly (by 74.3% on average), albeit not to the same level as the late dormant lime sulfur standard (close to 90% average reduction across leaf and fruit spot intensity). A single late dormant spray of the growth regulator hydrogen cyanamide (a caustic compound with antimicrobial activity) suppressed disease intensity in most trials, but disease reduction was only partial (averaging 56.2% for leaf lesion density and 39.3% for fruit spot incidence). In contrast, a late dormant application of dormant oil consistently increased both leaf lesion density (by 80.7% on average) and fruit disease incidence (by 78.6%). The pronounced non-target effects associated with these off-season applications could explain variations in Exobasidium leaf and fruit spot risk among blueberry sites and years.

The evaluation of winter kaolin clay and dormant oil applications on chill accumulation and yield in the California pistachio (Pistacia vera) cultivars ‘Kerman’ and ‘Peters’

The California pistachio cultivars 'Kerman' and 'Peters' have an estimated requirement of 58 and 60 chill portions, respectively. In California's Central San Joaquin Valley, the recent combination of warmer winter temperatures and sharply decreased fogs have resulted in a reduction of winter chill accumulation. In 2015 and 2016, kaolin clay was applied to dormant pistachio trees attempting to increase chill accumulation by reflecting radiant heat. Four treatments including kaolin clay, kaolin clay plus 470 dormant oil, 470 dormant oil, and an untreated control were made to nine year old pistachio trees. Kaolin clay applications (33 kg ha-1) were applied twice with the first application occurring after leaf drop in mid-December and the second occurring in early-January. A 6% 470 dormant oil solution was applied at 150 L ha-1 on February 6th, 2016. Treatments were approximately 1.9 ha in size and were replicated four times utilizing a randomized complete block design. Temperature sensors measuring external wood temperature on the north and south side were installed on a single tree in multiple blocks. Yield was determined for each plot and evaluated for size and quality. Local weather station measurements indicate that adequate chill was received in 2015-2016. Never-the-less, wood surface temperatures in kaolin treated trees were lower than the untreated control, producing an increase in chill portion accumulation by ~15%. Yield, however, was higher in the 470 dormant oil than in the kaolin clay or untreated control (3,330 kg ha-1 vs. 2,796 and 2,774 kg ha-1, respectively). Results suggest that kaolin clay may be useful in increasing chill portion accumulation, but only if applied early in the dormant period. Our results also confirmed earlier reports that dormant oil increases pistachio yield in marginal to adequate chill years. Both techniques should be utilized as tools to help mitigate variable climate within pistachio orchards.

Externalities of pesticide application on apple in Kashmir valley

This study has investigated the pesticide-use practices in relationship with external costs on health/environmental hazards in apple-dominated areas of Kashmir valley. The study has revealed unscientific/indiscriminate application of pesticides on apple; on an average, the apple orchards are sprayed 9 times, though few farmers even go beyond 12 sprays. Pesticides which are more costly and not recommended for a particular stage of fruit development are also sprayed in the study area. It is surprising that only one farmer has sprayed summer oils on his apple orchard. The use of unidentified/unlabelled pesticides has been found prevalent in the study area. There are huge technological gaps in the use of pesticides; dormant oils, fungicides and insecticides/acaricides are used 61 per cent, 32 per cent and 36 per cent more than the recommendations, respectively. The gaps have been found wider at the farms of farmers who purchase pesticides on cash or credit from contractors-cum-traders who are known for their misguiding roles. The study has provided an account of various environmental externalities of pesticide-use and has estimated costs (damage cost and damage abatement cost) associated with them, employing actual expenditure at market price and contingent valuation procedures. Pesticide health risk models have been specified for quantifying the probability of falling sick of health disorders, viz. dermatological, gastro-intestinal, neurological, respiratory and ophthalmological. The logit regression estimates ascertained that the use of more toxic pesticides significantly increase the probability of falling sick. The study has put forth a few policy suggestions for encouraging scientific application of pesticides and reducing the negative externalities arising from pesticide-use.

Japanese Maple Scale Activity and Management in Field Nursery Production

Japanese maple scale, Lopholeucaspis japonica Cockerell (Hemiptera: Diaspididae), is an armored scale found on the bark of many woody nursery and landscape plants. Scale crawler and male flight activity was monitored in middle Tennessee in fields of cherry (Prunus serrulata Lindl. ‘Kwanzan’) for two seasons. Two generations of crawlers were observed, with a large peak of activity in late May and a second, less pronounced peak in August. Male flights occurred twice a year, in April and July. Spray and drench applications of insecticides were trialed in 2014 and 2015. Dormant oil applications reduced overwintering scale populations by 76%. Drench applications of imidacloprid in 2014 suppressed scale populations by 58% by four months following application and the following summer those same trees had no observable scale infestation. Summer trunk applications of pyriproxyfen were effective at managing scale crawlers while horticultural oil alone had no measurable effect. When scale populations were high at the outset of spring 2014, a dinotefuran drench application was ineffective after 90 days. Dinotefuran gave greater control in 2015 when scale populations were low prior to application. Based on these results, a multiple component program for field management of Japanese maple scale is recommended.

Technologies for noise monitoring of abnormal seismic processes

Robust noise technologies for analyzing a seismic acoustic signal that allow using its noise as a carrier of information at the beginning of abnormal seismic processes preceding an earthquake are proposed. A station which receives seismic acoustic signals from the deep strata of the earth with the help of 3–6 km-deep steel bores of dormant oil wells has been designed based on this technology. It monitors the beginning of the latent period of the earthquake development. The experiments carried out at these stations on Qum Island in the Caspian Sea since May 1, 2010 and in the town of Shirvan in the southern region of Azerbaijan since November 20, 2011 confirmed the reliability and validity of the monitoring results and identification of the earthquake in the radius of 300–500 km with a 10–15 h lead as compared to conventional seismic stations.

DORMANT APPLICATIONS OF A SOYBEAN OIL ADJUVANT PLUS ETHEPHON REDUCE PEACH FLOWER BUD SURVIVAL

Early removal of flower buds, flowers or small fruitlets increases peach fruit size and commercial value. Due to the lack of labeled or consistent thinning chemicals, peach growers usually wait approximately 30 days after bloom before hand-thinning fruit, which decreases fruit growth potential. Experiments were conducted near Seneca, South Carolina to determine the efficacy of combining Vegetoil (VO), an emulsified soybean oil adjuvant (93% soybean oil), with Ethrel (E) (a.i. 21.7% Ethephon) for pre-bloom killing of peach flower buds. ‘Contender’, ‘Cresthaven’ and ‘Rubyprince’ peach trees were sprayed once in January 2008 with 10% VO containing Ethephon concentrations of 25 (only ‘Rubyprince’), 50 or 75 ppm. Dormant oil (DO) at 3% and VO at 10% were the control treatments. In 2009, 10% VO with 75 ppm Ethephon was sprayed on ‘Cresthaven’ and ‘Rubyprince’ trees on either 1 of 5 different dates ranging from 12 January to 16 February. In 2008, Vegetoil reduced ‘Contender’, ‘Cresthaven’ and ‘Rubyprince’ flower bud survival by 10, 20 and 30%, respectively compared to the DO control and by 20-25, 50-60, and 45-55%, respectively when VO was combined with different Ethephon concentrations. The VO plus E treatments reduced fruit yield by 25-35% in ‘Cresthaven’ and 45-60% in ‘Rubyprince’ compared to the DO control. ‘Rubyprince’ yield was also significantly affected (i.e., reduced) because of a late spring freeze. ‘Contender’ fruit yield was only slightly reduced by the Vegetoil plus Ethephon treatments. Mean fruit size increased 10-15% with the VO and E treatments. The 2009 flower bud survival, fruit set and yield were significantly reduced by the VO plus E treatments for all application times. The earliest application date was the most effective in thinning flower buds for both cultivars.

Spring Cold Injury to Winegrapes and Protection Strategies and Methods

Active frost protection methods may be expensive, but a correctly selected and operated system can provide more consistent crops and improved cash flow in years of potentially damaging cold events at postbudbreak stages of grape development. The selection of an active frost protection system depends on a number of factors, including the prevailing climatic conditions that occur during the spring season at the vineyard location, the costs associated with different frost control systems as well as considerations related to the reliability and relative simplicity of operating the equipment associated with each method. In winegrape production areas in North Carolina, hoar (white) frosts are the predominant cold threat in the postbudbreak period. A wind machine can be a very cost-effective investment on sites that are prone to a damaging frost event in 1 of 5 years or with a higher frequency of occurrence. However, wind machines have less overall usefulness in growing areas where there is also potential for black frosts (a more damaging radiational event than a hoar frost) and frosts/freezes (events with subfreezing temperatures and winds in the range of 2.2 to 4.5 m·s−1). For black frost events, a well-designed overvine sprinkling system can provide nearly 6 °C protection; sprinkling is also an appropriate management option for frost/freeze events. Windborne freezes are far less common at the postbudbreak stages but represent the most damaging type of cold event that can occur in eastern and midwestern winegrape regions in the United States. Methods that reliably delay budbreak (e.g., dormant oils, evaporative cooling with targeted sprinklers) may represent the best near-term opportunity for growers to decrease or avoid vine injury from freeze events such as the early April Easter freeze of 2007 that devastated grape vineyards through much of the midwest and southeastern United States.

Oil emulsions enhance transcuticular movement of captan in apple leaves

The purpose of this study was to determine whether oil emulsions enhanced penetration of captan, a chloroalkyl thio heterocyclic non-systemic fungicide through apple leaf cuticles. Cuticles from apple leaves were isolated with enzymes and treated with 1% soybean oil emulsified with Latron B-1956 ® and K1, and two commercial soybean oil emulsions, dormant oil and SunSpray on the outer morphological surface. Where captan and oil were applied together, the percentage of captan that penetrated the cuticle never exceeded 3.5% even under a worst-case scenario but this could be sufficient to cause phytotoxicity. When applied on the outer morphological surface of the cuticle, all oil formulations increased captan penetration by more than 50% over the amount penetrated through control cuticles. The greatest penetration of captan was through cuticles treated with dormant oil. A significant amount of captan (51% over the control amount) penetrated through the inner morphological surface of the cuticle. Captan penetration was more than 40% greater through the abaxial than through the adaxial cuticles. Increasing captan concentration increased captan penetration and a linear relationship existed between captan concentration and captan penetration through the cuticle. The study clearly showed that oil emulsions facilitated penetration of significant amount of captan through the cuticle, which may have serious implications for phytotoxicity of leaves.

(103) Effects of Dormant Application Timing in `Bartlett' Pear

Pear growers in California's Sacramento River Delta and, to some extent, other pear-growing areas in California, use dormant oils for pest control and dormant bud growth stimulation. It is generally believed that well-timed applications can advance flowering, improve uniformity of flowering and fruit ripening, and improve vegetative budbreak. Traditionally, dormant oils have been applied in late December to mid-January, based on experience and calendar date. However, bud development and full bloom dates may differ from year to year, with variable weather cycles and chill accumulation experienced by the plant. In the 2004–05 dormant season, some dormant oil applications timed at intervals calculated by chill portions (defined by the Dynamic Model) advanced and compressed the bloom period. Fruit size (diameter and weight) and total estimated yield were improved by dormant oil treatments applied within a certain range of chill portion accumulation without reduction in total number of fruit per tree, while the percentage of undersized fruit was decreased by 65% to 83% when compared to the untreated control. The use of chill portions and the Dynamic Model to time applications of dormant oil appears to benefit fruit quality. Although chill was not limiting in the trial dormant season, there may be benefit even in years when chill accumulation is adequate.

(102) The Dynamic Model and Rest-breaking Agents in California `French' Prune Production

Use of rest-breaking chemicals may partially substitute for chill requirement in “French' prune. Many California prune growers use oil in the dormant season to tighten and advance bloom, with application timing judged by experience and calendar date. Other rest-breaking agents have become commonly used in California cherry production and their application is generally timed by chill portion accumulation, calculated by the Dynamic Model. We evaluated the effects of treatments of dormant oil or CAN17 (calcium ammonium nitrate) + Entry on budbreak and bloom progression in `French' prune with applications timed at regular intervals. While most treatments improved fruit set and reduced reproductive bud death, an optimum range for both types of rest-breaking treatments was found for advancement and compression of bloom. All rest-breaking treatments advanced fruit maturity equally, compared to the untreated control, as measured by fruit firmness. Although chill hour (hours ≤7°C) calculations might also be used for timing these treatments, when chill portion and chill hour accumulations are compared for the 2004–05 dormant season at several different sites, differences from site-to-site are small for chill portions, and much greater for chill hours. This fact supports experimental evidence from numerous California trials in sweet cherry in which rest-breaking treatment timings based on the Dynamic Model tend to be more consistent than the timings based on the “chill hour” model.

Managing Calico Scale (Hemiptera: Coccidae) Infestations on Landscape Trees

Calico scale, Eulecanium cerasorum (Cockerell), an invasive pest of shade trees, has reached outbreak levels in landscapes and on horse farms in Kentucky, U.S. We evaluated efficacy and timing of conventional and reduced-risk foliar insecticides as well as trunk-injected or soil-applied systemics for managing E. cerasorum. Acephate, bifenthrin, carbaryl, cyfluthrin, and pyriproxyfen killed young settled crawlers on individually sprayed shoots. Whole-canopy pyrethroid sprays, however, gave <66% control, underscoring the difficulty of reaching settled crawlers within large shade trees. Horticultural oil and insecticidal soap were relatively ineffective even with full spray coverage. Preventive sprays with bifenthrin or pyriproxyfen in mid-May, at first egg hatch, intercepted crawlers before they settled on leaves. Dormant oil failed to control overwintered nymphs or reduce subsequent numbers of adults or crawlers. A plant antitranspirant applied in late March provided 33% suppression. Trunk-injected imidacloprid was ineffective, whereas dicrotophos (bidrin) gave at best <50% control. Soil injection with imidacloprid in November, December, or March failed to reduce subsequent densities of adults on branches or crawlers on leaves. Reasons why it is difficult to eliminate calico scale in mature landscape trees are discussed in the context of the pest’s feeding sites and behavior.

Ecology and management of Ericaphis fimbriata (Hemiptera: Aphididae) in relation to the potential for spread of Blueberry scorch virus

AbstractAphids were sampled in commercial blueberry, Vaccinium corymbosum L. (Ericaceae), fields in southwestern British Columbia, Canada, from 2001 through 2003. Ericaphis fimbriata (Richards), the dominant aphid, overwintered as eggs on blueberry and emerged in late February and March during bud break. Apterous adult fundatrices were found during April. The fundatrices produced both alate and apterous virginoparae. There was a positive curvilinear relationship between production of alatae and aphid density on flower clusters, but not on leaf terminals. Peak densities in late June or early July varied from 300 to 9000 aphids per plant in different fields, suggesting that there may be considerable variation in Blueberry scorch virus transmission rates among fields infected with the virus. Production of alate virginoparae (percentage of all fourth-instar aphids with wing pads) declined from May through August. Sexual morphs were produced in late September and October. The efficacy of postbloom insecticide applications in June, by growers, was variable. Experimental trials showed that dormant oil is not effective in preventing aphid emergence. Aphids on blueberry should be controlled before bloom, before alatae are produced and large populations occur, but the efficacy of this approach in reducing virus transmission needs to be tested.

Assessing dormant season organophosphate use in California almonds

Organophosphate (OP) pesticides were recommended during the dormant season to control overwintering insects such as peach twig borer, San Jose scale, European red mite, and brown mite in California almond and stone fruit orchards. However, since 1990, dormant OP use had fallen under increased scrutiny due to surface water contamination concerns. Studies have shown positive correlation between OP use and residue load in surface water. The purpose of this study is to assess the trends and regional patterns of OP use in almond orchards, and to identify factors that may have influenced those trends, including weather, pest pressure, and use of alternatives to OP such as pyrethroid, dormant oils, and Bacillus thuringiensis (Bt) for the assessment of the impacts to surface water quality. Pesticide use data from the California Department of Pesticide Regulation were analyzed. Regression analyses were used to assess trends from 1992 to 2000, and a geographic information system (GIS) was used to visualize the spatial variation in pesticide use. Results from this study indicated that, statewide, dormant OP use decreased while the use of some alternatives, such as dormant pyrethroid, no dormant insecticides, and in-season pyrethroid, oil alone, and Bt, increased in the last 9 years. The significant decreasing trend of OP use was observed for the measures of kilogram per hectare crop planted, percentage of total planted hectare treated, and numbers of growers who applied dormant OP. The reduction of dormant OP use appeared in all major almond-growing counties. Correlation analyses revealed that more rain was associated with less dormant OP use. A higher percent of almond damage, or rejects, was related to higher OP use in the following dormant season and in-season periods. However, the effects of weather and percent of nut rejects can only explain small portion of the variations in dormant OP use. Therefore, in addition to weather and pest pressures, economic pressures and various outreach and extension programs may also have played a role in encouraging farmers to reduce their use of dormant OP.

Response of Grapevines to Soybean Oil Application

Chancellor, Chambourcin, and Chardonel grapevines were treated with soybean oil-based adjuvants and then compared to untreated (control) vines for phytotoxicity, date of budbreak, yield components, and fruit composition. The purpose of dormant oil application was to delay budbreak without affecting date of fruit ripening, yield, or fruit composition. In the first year, Prime Oil and Amigo were applied at a 10% concentration (v/v) to runoff with a backpack sprayer on three different dates during the dormant season. Prime Oil but not Amigo was phytotoxic to dormant buds in all three cultivars. Both oil treatments led to a significant budbreak delay in all cultivars ranging from 1 to 20 days as compared to control vines. A reduced carbon dioxide exchange from oil-treated buds was associated with a delay in bud development. At harvest, cultivars that sustained bud injury from Prime Oil treatment had reduced yields and delayed fruit maturity; conversely, Amigo did not affect yield components or fruit composition. In the second year, six rates (0%, 2%, 4%, 6%, 8%, and 10%) of Amigo oil were applied to Chambourcin and Chardonel grapevines and none was phytotoxic to either cultivar. Rates of 8% and 10% (v/v) delayed budbreak in Chardonel, but not in Chambourcin. None of the rates resulted in any deleterious effects on fruit set, yield components, or fruit composition in either cultivar. Grapegrowers may consider soybean oil application as an efficient and affordable practice that may protect early cultivars against spring frost injury by delaying the date of budbreak.

575 Effect Of AVG and Dormant Oils on Bloom Delay In `Redhaven' Peach

Peach production is significantly reduced and severely limited by frost injury in regions frequently exposed to late spring freeze conditions. Peach flower buds become increasingly susceptible to low-temperature damage from the period of completion of rest through fruit set. Delaying dehardening and/or flower bud development is an effective way to avoid frost damage. Bio-regulator applications, affecting dormancy or bud development, can delay flowering and dehardening of the buds and can help in avoiding spring freeze injury. Spring applications of AVG and dormant oils on 8-year-old `Redhaven' peach trees were evaluated. AVG applications effectively delayed bloom by 2 to 5 days. The most effective treatment was two applications of 2000 ppm AVG, which delayed bloom by almost 5 days. Repeat applications of AVG were more effective than the single dosage treatments. The 1000 ppm, repeat application delayed bloom by 4 days. A single application of 5000 ppm AVG resulted in severe phytotoxicity. The wetting agent levels were also varied and AVG applications were most effective in combination with 0.2% `Sylgard'. AVG, apparently, delayed bloom by delaying bud development following the completion of rest. The dormant oil sprays were ineffective in achieving bloom delay. The specific leaf weight characteristics of the treated trees were not affected except for the 5000-ppm AVG application, which reduced SLW. Fruit characteristics such as maturity, weight, and soluble sugar concentration were not affected by any of the spring applications (except for the 5000-ppm AVG application, which was phytotoxic). Our studies indicate that AVG is effective in delaying bloom in peaches by up to 5 days. This has the potential to substantially increase peach yields in years with a late spring freeze.

Site Redevelopment Strategies for Dormant Oil and Gas Facilities

Site Redevelopment Strategies for Dormant Oil and Gas Facilities

252 Oil Emulsions Enhance Transcuticular Movement of Captan into Apple Leaves

Oil sprays increase the phytotoxicity of captan to apple foliage. The purpose of this study was to determine if oils increase the penetration of captan through leaf cuticles. Enzymatically isolated apple leaf cuticles were used as a model system to study captan penetration. A bioassay was developed using the inhibition of growth of Penicillium cyclopium on potato-dextrose agar as a measure of captan penetration through the cuticle. Captan penetrated through both surfaces, but significantly more penetrated through the abaxial cuticles than the adaxial cuticles. Increasing the captan concentration increased the captan penetration through the abaxial cuticle in a linear relationship. Captan penetration through the cuticle was increased by 63% when cuticles were treated with captan plus 1% emulsified soybean oil. Abaxial cuticles treated with captan plus emulsified soybean oil or with captan plus SunSpray Ultra-Fine oil had >125% greater captan penetration than cuticles treated with only captan. Cuticles treated with captan plus dormant oil (petroleum oil) had 220% more captan penetration than the captan only treatment.

467 Overcoming Dormancy, Advancing Budbreak, and Advancing Fruit Maturity in `Bing' Sweet Cherry (Prunus avium L.): Surfactants/ Dormant Oils + Calcium Ammonium Nitrate or Hydrogen Cyanamide

In continuing trials (1995-current), we have used a variety of treatments to overcome inadequate chilling, coordinate bloom, improve leaf out and cropping, and advance/coordinate maturity in sweet cherry, cv. Bing. Treatments have included hydrogen cyanamide (HCN, Dormex) and various surfactants or dormant oils combined with calcium ammonium nitrate (CAN17). Chill hour accumulation, (required chilling for `Bing' = 850 to 880 chill hours) has varied greatly in each dormant season from 392 (Hollister, 1995-1996) to adequate, depending both on the season and location (central valley vs. coastal valley). In 1998, 4% HCN advanced budbreak significantly compared to any other treatment, although other chemical treatments also were more advanced than the untreated control. Dormex advanced completion of bloom 11% to 40% more than other treatments, although other dormancy-replacing chemicals were at least 16% more advanced in petal fall than the untreated control. Dormex contributed to slightly elevated truss bud death, as did 2% Armobreak + 25% CAN17. In 1998, fruit set was improved by 2% Armobreak + 25% CAN17 (79%) compared to the untreated control (50%); all other treatments statistically equaled the control. Fruit set was not improved by Dormex, although bloom was advanced by a few days in this treatment. As fruit set was increased by treatments, rowsize decreased (as did fruit weight), as expected, but no treatment resulted in unacceptable size. In 1997, fruit set was also improved by 2% Armobreak + 25% CAN17; however, fruit set was so low overall in that year that no real impact was found. In 1997 and 1998, 4% HCN advanced fruit maturity compared to other treatments, with darker, softer, larger fruit at commercial harvest. These and additional results will be presented.

Soybean Oil as a Prebloom Flower Bud Thinner for Peaches

Survival of peach flowers during spring or winter freezes and large fruit size at harvest are critical for profitable peach production in the Southeast. Delaying both bud swell in late winter and flower phenology in spring reduces the risk of flower bud death from cold temperatures. Preliminary research in Tennessee using soybean oil (SO) as a dormant oil spray in place of Superior oil showed SO delayed peach bloom, thinned flower buds, and increased fruit size. In 1997, a `Harvester' peach orchard in Monetta, S.C., and a `Redhaven' orchard near Clemson, S.C., were sprayed in early February with 0%, 6%, 8%, 10%, and 12% SO mixed with 1% (by volume) Latron B-1956. Number of dead flower buds and the flower bud stages for each SO treatment were recorded during the first pink to full bloom flowering period. Excess fruit were hand-thinned in late April. Fruit set, maturity date, weight, and yield/tree were taken. Bud death increased from 14% (control) to 17% to 20% at the 8%, 10%, and 12% SO rates for `Redhaven' and from 13% (control) to 21% at the 10% and 12% rates for `Harvester'. Phenology was delayed 3-4 days for `Redhaven' at 8%, 10%, and 12% SO, but no differences were noted in the `Harvester' trees. No differences in fruit maturity occurred. Fruit weight and yield/tree was higher for all `Harvester' SO treatments and the `Redhaven' 10% and 12% SO treatments. No shoot phytotoxicity was observed.

Effect of Strawberry Plant Physiological Status on the Translaminar Activity of Avermectin B1 and Its Efficacy Against the Twospotted Spider Mite (Acari: Tetranychidae)

Plant physiological status determines translaminar movement of avermectin B 1 in strawberry leaves, and the resulting noncontact residual kill of twospotted spider mite, Tetranychus urticae Koch. Significant T urticae mortality was obtained upon contact with avermectin B 1 with and without the addition of dormant oil, and with propargite. Noncontact residual kill of T. urticae by avermectin B 1 was greater on fruiting summer-type plants than on plants in winter semidormancy. When avermectin B 1 was applied only to the top surface of leaves, addition of dormant oil enhanced T urticae mortality on lower leaf surfaces of plants in winter semidormancy. T. urticae mortality was not affected by the addition of oil when plants were in either a spring-type vegetative growth state or a summer-type sexual state. The results of this study suggest an explanation for inconsistencies observed in field applications of avermectin B 1 for control of T. urticae.