Mediterranean fruit fly (Dipt., Tephritidae) suppression in persimmon through bait sprays in adjacent coffee plantings*

Abstract: Oriental persimmon, Diospyros kaki L., in Upper Kula on the island of Maui (Hawaii) is attacked by the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Recent suppression trials using mass trapping with a synthetic food‐based bait, initiated in alternate host crops before the start of persimmon season, had shown promise as a means of reducing C. capitata population levels. However, this did not adequately suppress C. capitata population where there were adjacent plantings of coffee, Coffea arabica L., a favoured alternate host, which bears fruits before and during the persimmon season. To improve C. capitata population suppression, we applied a spinosad‐based bait spray to coffee plants, starting before persimmon fruits became susceptible to oviposition by the Mediterranean fruit fly. The bait spray suppressed the C. capitata population and led to reduced infestation of both coffee cherries and persimmon fruits. Percentage parasitization of C. capitata in coffee cherries by established biological control agents, primarily Fopius arisanus (Sonan), was not significantly different in unsprayed vs. sprayed plots even after 11 weekly sprays. These results suggest that mass trapping, combined with spinosad‐based bait sprays, are control components that are compatible with biological control and can be combined in an integrated pest management system for C. capitata.     

Management of Alternaria blight of radish seed crop (Raphanus sativus L.)

Radish (Raphanus sativus L. var. Tasaki Mula) was used in this investigation. On foliar spray, among the three fungicides (Iprodione, Mancozeb and Carbendazim), Iprodione (0.25%) followed by Mancozeb (0.3%) provided the maximum control of Alternaria blight and increased seed yield during the first cropping season (2004–2005). The results in second cropping season (2005–2006), 10 December (early) transplanting with three sprays of Iprodione resulted lowest leaf area diseased, whereas plants in 25 December (normal) transplanting had the lower pod area diseased. In third cropping season (2006–2007), 25 October transplantation with BAU-Biofungicide (2.0%) and Iprodione (0.25%) foliar application showed significant effect in reducing Alternaria blight and increased seed yield by 120.45% and 97.73%, respectively over non-sprayed control. Bio-Biofungicide ranked second in reducing the disease, but ranked first in increasing seed yield. The cost benefit analysis of management practices for radish seed crop during 2005–2006 revealed that stickling transplanting in 25 December (normal) with two sprays of Iprodione (0.25%) yielded the highest return (BCR 3.27), whereas negative result (BCR ? 0.89) has been estimated in case of non-sprayed control plots in late transplanting (10 January). However, cost benefit analysis of cropping season 2006–2007 revealed that BAU-Biofungicide (2.0%) six sprays yielded the highest return (BCR 4.41) followed by six sprays of Iprodione (BCR 3.90). Finally, it may be concluded that Integration of early transplanting (25 October) with foliar sprays ofBAU-Biofungicide (2.0%) was found best for eco-friendly management of Alternaria blight of radish seed crop with significantly higher seed yield.     

A comparison of fungicides for the control of raspberry spur blight

Effective control of raspberry spur blight (Didymella applanata) and increased crop yields in the following season were obtained in a plantation of cv. Mailing Jewel with a programme of four or five sprays commencing when the new canes first appeared. Treatments were applied at 14-day intervals and continued until c. 2 wk before harvest. Thiram (0.16% a.i), benomyl (0.025% a.i.), dichlofluanid (0.10% a.i.) and captan (0.10% a.i.) gave good control of the disease but as benomyl and dichlofluanid were also effective in controlling powdery mildew (Sphaero-theca macularis) and Botrytis cinerea on the berries these fungicides appear to be the most suitable.     

Attract and kill for codling moth Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae) control in Syria

The possibility of controlling the codling moth Cydia pomonella (Linnaeus) using an attract and kill approach as an alternative to chemical sprays with contact insecticides was investigated in widely separated orchards. The results of a 4‐year study have shown that, using an attract and kill approach, three applications/season kept infestation rates in treated orchards below the economic injury level except in one with a too high codling moth population density. The mean number of male codling moths/trap/week in attract and kill‐treated orchards was much lower in comparison with control orchards which were treated with the usual cover sprays of insecticides. The results also showed that the efficacy of attract and kill under orchard conditions decreased with time and the relationship between time effect and codling moth death rate was very strong. These data indicate that the attract and kill technique applied at a rate of three application per season resulted in good control of codling moth in well managed orchards in Syria.     

Sugar feeding by coccinellids under field conditions: the effects of sugar sprays in soybean

Sucrose was applied weekly throughout the growing season at three US locations (South Dakota [SD], Maryland [MD], and Kentucky [KY]), and coccinellids and aphids (Aphis glycines Matsumura [Hemiptera: Aphididae]) were sampled 24 h later. Total coccinellid densities were 50–77% greater in sugar-sprayed soybean than in untreated plots. Coccinella septempuncata L., Hippodamia convergens Guérin-Méneville, and Harmonia axyridis Pallas were more abundant where sugar was applied. Coleomegilla maculata (DeGeer) was found in equally low numbers in all treatments. Aphid densities were similar in both treatments, and only reached economically threatening levels in SD. Coccinellids digested sugar meals within 1 h of consumption (measured using the cold anthrone test). Despite this narrow window of detection, field-collected coccinellids frequently tested positive for fructose. Under natural conditions, sugar is commonly ingested by coccinellids and sugar sprays increase coccinellid densities and their consumption of sugar. Sugar sprays did not enhance biological control of aphids in this experiment.     

Biological control by Clonostachys rosea as a key component in the integrated management of strawberry gray mold

Gray mold, caused by Botrytis cinerea, is an important strawberry disease. As gray mold control is difficult, there is a need to evaluate integrated methods to successfully manage the disease. The efficiency of integrating Clonostachys rosea sprays, fungicide sprays, and crop debris removal to manage gray mold was evaluated in field experiments conducted in 2006 and 2007. Leaf colonization by C. rosea (LAC), average number of B. cinerea conidiophores (ANC), gray mold incidence in both flowers (Iflower) and fruits (Ifruit), and yield were evaluated weekly. In both years, LAC was higher in the treatments with no fungicide. When compared to the check, ANC, Iflower and Ifruit were most reduced in treatments that included C. rosea sprays. Maximal reductions were achieved with the combination of C. rosea sprays, fungicide sprays and debris removal (96.62%, 86.54% and 65.33% reductions of ANC, Iflower and Ifruit, respectively). Otherwise, maximal yield (103.14% increase as compared to the check) was achieved with the combination of the three treatments. With just C. rosea sprays, ANC, Iflower and Ifruit were reduced by 92.01%, 68.48% and 65.33%, respectively, whereas yield was increased by 75.15%. Considering the individual effects, application of C. rosea was the most efficient treatment. Chemical control was effective only in plots without debris removal. Elimination of crop debris was the least effective method in reducing gray mold incidence in both flowers and fruits. The integrated control approach enhanced the efficacy of the individual methods of gray mold control and provided high strawberry yield. An important component of this integrated approach it the biological control with C. rosea.     

Threshold‐based spraying decision programmes for the red spider mite Tetranychus marianae on eggplant

The red spider mite, Tetranychus marianae McGregor (Acari: Tetranychidae), has been an important pest of eggplant Solanum melongena L. (Solanaceae) and other vegetables in the Mariana Islands. The damage due to T. marianae has been severe and caused huge economic losses. Because no threshold levels are available for T. marianae, many growers are applying up to 12 chemical applications per eggplant cropping period. This is not only expensive, but also results in lower yields because of extensive foliar damage and development of resistance in mites to chemicals. To diminish the calendar‐based chemical applications and to preclude damage to foliage and fruit quality, this study was undertaken for the development of a threshold level for optimum timing of chemical applications for T. marianae. In the direction of this aim, an attempt was made to generate different threshold levels by applying chemical spray (Sun‐spray 6E, 5 ml/l) within 12 h after reaching the threshold levels at 2, 4, 6, 8 and 10 mites/leaf, as well as current recommended calendar‐based sprays and non‐sprayed control in a replicated block design for the dry and wet seasons of 2010 at two locations (Yigo and Inaranjan) in Guam (USA). Based on T. marianae‐infested leaves, incidence of T. marianae and yield levels, the plots sprayed at 2 or 4 mites/leaf in the dry season and 2–8 mites/leaf during the wet season had significantly lower leaf damage and incidence of T. marianae compared with a greater number of mites/leaf in calendar‐based sprays and control plots. At the greater threshold levels, the mean yield was significantly reduced in comparison with the mean yield obtained when plots were sprayed at a threshold of 2–8 mites/leaf. Therefore, it is concluded that the optimum threshold chemical spray for T. marianae on eggplant is 4 mites/leaf during the dry season and 8 mites/leaf in the wet season.     

The effect of border sprays and between‐row soil tillage on Drosophila suzukii in organic blackberry production

Drosophila suzukii (Matsumura) is a major pest of soft‐skinned fruit. Females have an enlarged serrated ovipositor that is used to cut into ripening fruit and lay their eggs. Larvae develop inside infested fruit, rendering fruit unmarketable. Previous research has indicated that D. suzukii can move from adjacent woodlands into cultivated fields. Furthermore, multiple generations can occur in a single season as a result of fallen, infested fruit in the fields. Our hypothesis was that border sprays and soil tillage of field aisles can reduce D. suzukii presence in commercial blackberry fields (Rubus spp.). To test our hypothesis, we conducted split‐plot field trials in organic blackberry fields for 3 and 4 weeks in 2014 and 2015, respectively. Treatments were border sprays (whole plot, pyrethrins + azadirachtin) and tillage (subplot, ~15 cm). We evaluated adult D. suzukii in both years and berry infestation and natural enemies in 2015 only. We found that plots with border treatments had fewer D. suzukii (larvae and adults) than plots without border sprays. Tilling the soil between rows of blackberry bushes did not have a significant effect on adult captures or larval infestation of fruit. Natural enemies were unaffected by the border spray and tillage treatments. Our results confirmed our hypothesis that border sprays can be utilized to reduce populations of D. suzukii in organic blackberry fields, while maintaining populations of natural enemies. However, the effect of soil tillage is unclear and requires further investigation. Additional research should investigate the timing of border sprays and their effect on high infestations of D. suzukii as well as quantify fruit fall and depth of burial to reduce D. suzukii emergence using soil tillage.     

The stimulating effect of some fungicides on Glomerella cingulata in relation to the control of coffee berry disease

The non-parasitic strain of Colletotrichum coffeanum Noack which colonizes the maturing wood of Coffea arabica produces its perfect stage (Glomerella cingulata) on the branches. Assessments of the relative abundance of this in relation to preceding rainfall have shown that for unsprayed branches, but rarely for sprayed ones, the correlation is negative and highly significant. Various fungicides stimulate G. cingulata greatly, and this stimulation persists for many months. One other saprophytic component of the micro–flora is similarly stimulated, but with two others all the fungicides used depress sporulation. It is suggested that when the main source of infection of coffee berries is the pathogenic conidia from the wood, the mechanism of long–term control by early–season sprays may lie partly in this stimulation of some fungal competitors of the pathogen.     

Control of tomato grey mould on unheated crops using non- systemic fungicide sprays

High volume sprays of dichlofluanid (0.1 % a.i.) reduced total fruit numbers but gave better control of Botrytis cinerea infections of tomato stems, leaves and fruit than sprays at 0.05 or 0.025% a.i. Surface residues from the sprays at 0–1, 0.05 or 0.025% a.i. were respectively 5.4, 1.6, 0.7 μg/g fresh weight of ripe fruit at harvest. Tank-mixed zineb (0.12% a.i.) and captan (0.2% a.i.) were less effective and increasing the spray intervals from 1 wk to 2 and 3 wk reduced the fungitoxicity of captan and zineb more than that of dichlofluanid. Harvest residues on ripe fruit were 7.1, 2.8 or 2.4 μg/g when dichlofluanid (0.1 % a.i.) sprays were applied at 1, 2 and 3 wk intervals respectively. Good control of B. cinerea was achieved if the whole plant was sprayed initially with dichlofluanid as soon as the second truss was flowering and subsequent sprays were restricted to the upper section of stem including the four or five youngest trusses of buds, flowers and fruit. When used as a post-infection spray there was a period of c. 8 wk before dichlofluanid markedly reduced the incidence of grey mould. Tank-mixed zineb (0.12% a.i.) controlled Botrytis fruit spotting but not leaf and stem infections. Botrytis stem lesions extended more rapidly on zineb-sprayed plants than on unsprayed plants or on plants treated with captan or dichlofluanid.     

Control of Botrytis cinerea and Botrytis squamosa in overwintered salad onions by fungicide sprays

In 1974/75, 13 sprays of 0·2% a.i. thiram applied at 14 day intervals to overwintered salad onions reduced the incidence of Botrytis cinerea and significantly increased onion yields. In 1977/78 both B. cinerea and B. squamosa occurred, and 12 iprodione sprays at 0·1% a.i. applied at 14-day intervals or 6 sprays at 0·2% a.i. applied at 28-day intervals gave good control of B. cinerea and B. squamosa and significantly increased onion yields. Benomyl (0·1% a.i. at 14-day intervals, or 0·2% a.i. at 28-day intervals) failed to control either pathogen because of the development of carbendazim-insensitive strains of the fungi. Effective control of both pathogens and increased yields were obtained with an application of 0·4% a.i. thiram in October and November followed by an application of 0·2% a.i. iprodione in December and January.     

Impact of crimson clover dying mulch on two eggplant insect herbivores

Eggplant Solanum melongena L., is often colonized by two early season insect defoliators. The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), and flea beetles Epitrix spp., emerge from their overwintering sites in early spring and seek out emerging host plants such as eggplant. During the 2009 and 2010 growing season, field studies were conducted to investigate the impact of inter‐planting eggplant into a crimson clover (CC), Trifolium incarnatum L., winter cover crop on populations of flea beetles, CPB and their associated arthropod predators. The experiment consisted also of two levels of insecticide usage such as an application of azadirachtins plus pyrethrins followed by several applications of spinosad or no insecticide sprays as subplot treatments. During both study years, significantly fewer (adults, larvae and egg masses) were found on eggplant inter‐planted into CC than in bare‐ground (BG) eggplant plots. Although flea beetle abundance was greater in BG eggplant during 2010, they appeared to be less influenced by the presence of CC than were CPB. Additionally, there was no apparent impact of insecticide treatment on CPB populations on eggplant inter‐planted into CC. However, there was a decline in CPB following treatments with insecticides in BG eggplant plots. This suggests that a winter cover crop such as CC can be used to help manage CPB in eggplant, however, using this tactic in tandem with insecticide sprays may not result in greater CPB management.     

Control of aphid-vectored and thrips-borne virus spread in lily, tulip, iris and dahlia by sprays of mineral oil, polydimethylsiloxane and pyrethroid insecticide in the field

In this study control of spread by insect vectors of non‐persistent Lily symptomless virus and Lily mottle virus in lily, Tulip breaking virus in tulip, Iris mild mosaic virus, Narcissus latent virus and Iris severe mosaic virus in bulbous iris, and semi‐persistent Dahlia mosaic virus and persistent Tomato spotted wilt virus in dahlia has been evaluated with weekly sprays of mineral oil, beta‐pinene emulsion, polydimethylsiloxane emulsions and pyrethroid insecticide. In lily, beta‐pinene in ‘Wilt Prufgave’ 40% reduction of virus spread. In 1995–97 deltamethrin in ‘Decisgave’ 22–58% reduction. Deltamethrin added to sprays of mineral oil ‘Luxan oil H’ and polydimethylsiloxane (PDMS), e.g. in ‘Dow Corning 36’, efficiently improved control efficacy. The latter was also observed in tulip and dahlia. Mineral oil and deltamethrin gave best control by 81–97% reduction of virus spread at standard spray volumes (6.25 litre ha^?1+0.4 litre ha¹). ‘Luxan oil H’ at 3.125 litre ha^?1 with deltamethrin gave 69–91% control. Efficacy of control by polydimethylsiloxane in ‘Dow Corning 36’ was superior to ‘Luxan anti‐foam’. ‘Dow Corning 36’ with deltamethrin (7+0.4 litre ha^?1) gave satisfactory control (68–87%). In tulip, the control by ‘Dow Corning 36’/deltamethrin sprays proved satisfactory compared with ‘Luxan oil H’/‘Decis’‐sprays. In bulbous iris the efficacy of tested PDMS‐brands was clearly different in favour of ‘Dow Corning 36’. In dahlia mineral‐oil and PDMS‐sprays gave some control of semi‐persistent DaMV (16–24%). This ranged at higher level (65–80%) when deltamethrin was added to the spray mixture. Similar trends were observed in the control of persistent TSWV. The effect of polydimethylsiloxane emulsions in the spectrum of virus‐control agents is described for the first time. The effect of PDMS compared with that of mineral oils and synthetic pyrethroid insecticides is discussed with respect to efficacy, mode of action to prevent virus transmission and possible reduction of bulb weights in vegetatively propagated bulb crops.     

Potential for biocontrol of sclerotinia rot of carrot with foliar sprays of Contans® WG (Coniothyrium minitans)

A glasshouse and field trial were conducted to evaluate foliar sprays of Contans® WG (Coniothyrium minitans) conidial suspensions for control of sclerotinia rot of carrot and infection of Sclerotinia sclerotiorum sclerotia by C. minitans. In the glasshouse trial, foliar sprays (1×10⁴–10⁸ conidia mL^?1) decreased the viability of sclerotia recovered from diseased plants and increased infection by C. minitans. In the field trial, three successive foliar sprays applied at 14-day intervals failed to reduce foliage disease severity, but significantly reduced viability of sclerotia recovered from diseased plants/crop debris and increased infection by C. minitans. No significant differences in sclerotial viability or infection were observed between two conidial concentrations (2.4 and 4.8×10⁶ conidia mL^?1). Foliar sprays of Contans® WG have potential for reducing viability of sclerotia produced on diseased foliage.     

Evaluation of the lady beetle,Serangium parcesetosum for control of Bemisia tabaci on greenhouse eggplant in the Mediterranean region

Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is one of the most serious pests of greenhouse crops. It is mainly controlled by chemical means, requiring some 10–12 sprays during the average growing season in Turkey. There is growing interest in finding alternatives to pesticides for control of B. tabaci in greenhouse crops because this heavy pesticide usage disrupts biocontrol and leads to rapid build-up of insecticide resistance in the pest. In our study, the control of B. tabaci on greenhouse eggplants was evaluated following releases of the lady beetle Serangium parcesetosum Sicard (Coleoptera: Coccinellidae). In cage experiments, four adults per plant were introduced and, within 3–4 weeks, resulted in 97 and 98% reductions in whitefly populations in 2004 and 2005, respectively. In a large plot experiment, two adults per plant were released only one time. Beetle larvae were observed through 2–9 weeks after release. The density of whitefly in large plot receiving beetle adults showed fluctuations to a level lower than in control plot receiving no beetle in 2004 and 2006. Further study is needed to develop new managing strategies in biological control of B. tabaci with S. parcesetosum in protected culture.     

Monitoring airborne concentrations of sporangia ofPhytophthora infestans in relation to tomato late blight in Emilia Romagna,Italy

Late blight caused byPhytophthora infestans is one of the most important diseases of tomato crops in Emilia Romagna. In total, 7–8 chemical sprays are applied per season to control the disease without taking into account the risk of infection. An integrated warning service for the prediction of tomato late blight was set up in order to define a more rational disease control strategy. As a part of the warning service, a number of sites monitoringPh. infestans airborne sporangia was set up for a timely disease prediction in the regional tomato growing areas. The results of 3 years monitoring ofPh. infestans sporangia are presented. They suggest that concentrations of airborne sporangia rapidly increase 1–2 weeks prior the blight onset in the field.     

Efficacy of soil application of Metarhizium anisopliae and the use of GF-120 spinosad bait spray for suppression of Bactrocera invadens (Diptera: Tephritidae) in mango orchards

Field trials were conducted for two seasons in mango orchards at Nthagaiya, Kenya, to evaluate the efficacy of soil inoculation with Metarhizium anisopliae (Hypocreales: Clavicipitaceae) and GF-120 spinosad bait sprays, applied either alone or in combination, for suppression of the invasive fruit fly, Bactrocera invadens (Diptera: Tephritidae). During the 2006/2007 season, average post-treatment samples showed that B. invadens catches from the control orchards were four times higher than the number of flies captured in the plots receiving M. anisopliae+GF-120. Fruit infestation was 16, 45, 30 and 60% in the M. anisopliae+GF-120, M. anisopliae alone, GF-120 alone and control orchards, respectively. In the 2007/2008 season, average B. invadens post-treatment samples in the control orchards were seven times higher than the treatment with M. anisopliae+GF-120; and fruit infestation was 11, 38, 28, and 52% in the orchards assigned to M. anisopliae+GF-120, M. anisopliae alone, GF-120 alone and control treatments, respectively. Enumeration of conidial densities from soil samples on agar plates showed initial densities of 1.1–2.1×10⁵ colony forming units (cfu)/g of dry weight of soil but decreased to 1.0–1.4×10³ cfu/g at the end of the experimental period. Exposure of laboratory-reared pupariating larvae to soil samples taken from fungus-treated fields showed significant reduction in B. invadens adult emergence (25–36%) compared with the control (80–82%). Our results suggest that the combined use of soil application of M. anisopliae and GF-120 spinosad bait spray is an effective IPM strategy for field suppression of B. invadens on mango.     

An assessment of some new treatments for the control of rotting of stored apples

Benomyl (0.025% a.i.) and thiabendazole (0.05 % a.i.) applied in July, August and September to apple trees cvs. Sunset and Cox's Orange Pippin gave slightly better control of Gloeosporium spp. rots in stored fruit than captan (0.1% a.i.) applied at similar intervals. On Cox's Orange Pippin, treatment with captan at 0.1 % a.i. in July and at 0.2% a.i. in August was as effective as three sprays at 0.1 % a.i. in July, August and September in controlling both Gloeosporium spp. and Nectria galligena rots. Benomyl applied in the spring and early summer to control apple scab on orchard trees reduced the incidence of Gloeosporium spp. and Monilia fructigena in stored fruit. Pre-harvest sprays of benomyl and captan gave good control of rotting caused by N. galligena but thiabendazole was ineffective. Post-harvest dips of thiabendazole controlled rotting by Gloeosporium spp. butnot byN. galligena.     

Report of the Council of the Association of Applied Biologists for the year 1968

Bock (1963) showed that in the years 1956-60 early season sprays achieved good control of coffee berry disease (CBD) in East Rift areas of Kenya. In recent years, however, this spray programme has given erratic and often very poor results. In field experiments in 1966 yields of main (late) crop were increased from 151 to 652 kg/ha by early season sprays but in 1967 practically no control of the disease was achieved. Of the fungicides examined captafol was superior to copper; ‘Tuzet’, the best antisporulant, gave the poorest control. Analysis of the data indicates that this large seasonal variation depends on the very different inter-relationships between rainfall, cropping pattern and timing of sprays which obtained in the 2 years. The hypothesis that early-season sprays achieve control of CBD mainly by reducing the sporulating capacity of the maturing bark is questioned. The view is put forward that the protectant action of these sprays has been underestimated.     

Insecticidal control of aphids and the spread of potato leafroll virus in potato crops in eastern Scotland

Field experiments were carried out in eastern Scotland in 1976-78 to test the ability of granular insecticides, applied to soil at planting, and of insecticide sprays applied to the foliage, to control aphids and spread of potato leafroll virus (PLRV) in potatoes. The three years provided contrasting opportunities for virus spread. In 1976, the main vector of PLRV, Myzus persicae, arrived in early June and multiplied rapidly in untreated plots, and PLRV spread extensively. In 1977, M. persicae arrived 4–6 wk later than in 1976 and most spread of PLRV, which was less than in 1976, occurred after the end of July. In 1978, few M. persicae were recorded but the potato aphid, Macrosiphum euphorbiae, arrived early and very large populations developed in untreated plots. However, little spread of PLRV occurred in 1978, supporting other evidence that M. euphorbiae is an inefficient vector of PLRV in field conditions. In each year, granular insecticides decreased PLRV spread to a quarter or less of that in control plots. Thiofanox gave somewhat better and longer-lasting control of aphid populations than disulfoton, especially of M. persicae, but did not give greater control of PLRV spread. Application of three (1976) or five (1977) sprays of demeton-S-methyl to plots treated with granular insecticides further improved the control of M. euphorbiae but had less or no effect on M. persicae, especially where organophosphorus resistant aphids (R1 strain) were found. These supplementary sprays of insecticide did not further improve the control of PLRV but, in 1978, four sprays of demephion or pirimicarb to plots not treated with granular insecticide decreased PLRV spread. These data, together with previous findings, indicate that the amount of virus spread depends on the date of arrival and rate of multiplication of M. persicae in relation to the timing and effectiveness of removal of PLRV sources in crops. It is concluded that in Scotland insecticide granules should be used routinely only in crops of the highest grade of seed potato. Their use for other grades need be considered only in years following mild winters, when aphids can be expected to enter crops earlier and in larger numbers.