Insecticide usage survey

A survey of insecticide use on fruit trees and grapevines in the Riverland of South Australia

By P. T. Bailey and G. O. Furness

To assess the areas and crops sprayed with insecticide in the 1977–1978 season in seven irrigation districts between Renmark and Waikerie, South Australia (the Riverland) a survey of 213 fruitgrowers, representing 2 095 ha or 18 per cent of the area of perennial fruit crops, was made. Evidence is presented of a recent decline in the area sprayed with insecticide due to the successful implementation of biological control programmes. The proportion of the area of the various crops not treated with insecticide was: citrus 74 per cent, grapevines 62 per cent, apricots 73 per cent, peaches 22 per cent, apples 0 per cent, pears 8 per cent, almonds 17 per cent, and olives 100 per cent. Petroleum oil was the most widely used insecticide, followed by lead arsenate, and various organophosphate insecticides. Other insecticides were applied to small areas of crops.

Growers also indicated the sources from which they obtained advice on pest management, and these are discussed briefly.

Introduction

In the 1960s, there was widespread use of organophosphate insecticides annually on two of the four major fruit crops in the Riverland. On citrus at this time, an estimated 80 to 90 per cent of orchards were sprayed annually with one organophosphate insecticide, followed by one petroleum oil spray (D. Shaw, personal communication).

Richardson (1970) listed nine basic spray programmes used by Riverland peach growers in 1967–1968; the number of organophosphate sprays applied during the growing season ranged from five to nine. There are few insect pests of grapevines and apricots, and current spray practices have remained unchanged since the 1960s.

Biological and integrated control methods were introduced during the early 1970s on both citrus (Campbell 1976) and peaches (Richardson 1970). In 1972–1973 Davies (1974) surveyed insecticide use in citrus orchards in some Riverland districts, and in Mildura, Victoria. He found that, depending on the district, 20 to 57 per cent of citrus trees were sprayed with orqonophosphate insecticides, that 25 to 71 per cent of growers used chemical control methods, and the remainder biological or integrated control, or oils only. Hence insecticide use had declined on citrus since the 1960s.

Preliminary observations suggested that biological and integrated methods of insect control had become widely adopted by Riverland growers. The main aims of this survey were to estimate the extent of adoption of these methods of insect control on the various crops grown and to establish baseline data on insecticide use for comparison with future surveys.

A secondary aim of the survey was to discover the sources of pest management information used by growers.

Survey methods

The Riverland is a series of irrigation districts along the River Murray in South Australia: for the purpose of this survey it includes the districts of Renmark, Paringa, Berri, Barmera, Loxton, Moorook-Kingston, and Waikerie. The main crops include grapevines and citrus and smaller areas of stonefruit. Minor crops include vegetables and pome fruit. The region is ecologically isolated from other horticultural areas by drylands. The main pests have either been introduced with the crop, or accidentally introduced at a later date. The exceptions are lightbrown apple moth, a native leafroller, and some species of carpophilus beetle.

The orchards sampled were chosen from a complete list in each district. Every orchard of 40 ha and over was included in the sample. Of the remaining orchards (that is between 1 and 39 ha) 5 per cent were randomly chosen in each district. The survey was thus biased to sampling proportionally more large orchards than small. We justify this on the grounds that we were more interested in finding the area covered by insecticides than the number of orchards using insecticides . Details of the number and area of the sampled orchards are shown in table 1. The total area of orchards sampled accounted for approximately 18 per cent of the area planted with perennial tree and vine crops.

Table 1: Number and area of orchards sampled, compared with the total number and area of orchards

The owners or managers of each sample orchard were interviewed either by telephone (133 growers) or were visited (80 growers). A standard interview form (Appendix) was filled out, and all growers were asked the same questions. There were six interviewers. To reduce bias, a standard and rehearsed questioning procedure was used. Those growers visited were those who did not have a telephone, or who proved to be difficult to contact via the telephone. Each grower was asked to name his crops for the 1977-1978 season, the pests against which insecticides were applied, the insecticides used, and the sources of information for pest management. Insecticides were defined to include oils, synthetic insecticides (chlorinated hydrocarbons, organophosphates, and carbametes), lead arsenate, Bacillus thuringiensis and synthetic miticldes, but did not include sulphur because of the difficulty in trying to distinguish between its use as a miticide and as a fungicide. All the pests known to occur on each crop grown were mentioned to the grower during the interview.

Results and discussion

Grapevines

Vines occupy the largest area of any crop in the Riverland. An average of 62 per cent of the sample area in all districts was not sprayed with insecticides. A variety of synthetic insecticides was sprayed onto an average of only 5 per cent of the area sampled; the most common of these were aminocarb and methomyl, used against lightbrown apple moth and long tailed mealybug, and dicofol against grapevine mites. Lead arsenate was the most commonly used insecticide on vines. Because it has a comparatively high toxicity when ingested and low contact toxicity, it is useful for controlling chewing insects without harming other insects in the vineyard. The biological insecticide, Bacillus thuringiensis, was used on 3 per cent of the area sampled. This insecticide is specific against larvae of moths and is harmless to beneficial insects and mammals. The results for the different districts are summarised in table 2.

Table 2: Insecticide use on grapevines in the Riverland in the 1977–1978 season.

Note: Some areas were sprayed with more than one type of insecticide

Table 3: Insecticide use on citrus in the Riverland in the 1977–1978 season.

Citrus

Of the citrus plantings, 74 per cent received no insecticide sprays and a further 18 per cent received only an oil spray (table 3). An average of 8 per cent of plantings received an organophosphate Insecticide (one spray only). Methidathion was the most commonly used insecticide.

Low insecticide use on citrus may be attributed to the effectiveness of the red scale parasite. Aphytis melinus De Bach, in the biological, or integrated (parasites and oil sprays) control of red scale, Aonidiella eurentii (Mask.). Citrus orchards are supplied with parasites regularly on a contract basis by two insectaries . The Biological Services insectary at Loxton services 750 ha of citrus throughout the Riverland (R. George, personal communication), and the Waikerie Red Scale Committee services 300 ha at Waikerie (E. J. Harnmerton, personal communication). Parasites from the serviced orchards have dispersed to surrounding areas and provide adequate control of red scale in most years.

Organophosphate insecticides were generally used only at Waikerie. The main reason for the use of more organophosphates in the Waikerie district is probably the nature of the plantings. In several areas in Waikerie there are many orchards in which stonefruit trees are interplanted with citrus trees. Sprays for a pest on one crop are necessarily applied to the interplanted crop. The establishment of natural enemies under these conditions is difficult and attempts to introduce integrated control in many of these, and neighbouring orchards, have proved unsuccessful, so growers have continued to rely on chemicals.

The use of oils is likely to vary somewhat between years, because in some years the parasite does not appear able to adequately control red scale, and growers are recommended to use oil sprays.

Comparison of current spraying practices with those of the late 1960s, before the adoption of integrated control, indicates a substantial  reduction in insecticide use on citrus in the Riverland. The 1962 Red Scale Control Act empowered committees to enforce control. Local red scale committees were set up in each settlement and the secretaries had the task of visiting all citrus orchards several times a year to assess  populations of red scale. Any un-sprayed orchards developed heavy infestations within one or two years, to the extent that some trees were killed. Red scale committees had the power to bring spray contractors to spray any orchard where red scale control was deemed inadequate (D. Shaw, Berri-Barmera Red Scale Committee, personal communication). Shaw's experience combined with unpublished survey data showed that in excess of 90 per cent of citrus orchards were sprayed every year and that in excess of 80 per cent were regularly treated with an organophosphate (usually malathion) in October or November, followed by an oil spray in January or February. The situation in the Renmark and Waikerie districts was similar to that in Berri-Barmera. However. in the Loxton district red scale did not reach all areas until the 1970s, by which time parasites had been introduced. Release of the red scale parasite Aphytis melinus began in the early 1970s and the parasite had spread to all areas by the mid 1970s.

Apricots

No insecticide was applied to an average of 73 per cent of the apricot plantings surveyed, and on a further 1 per cent of the area only ground applications of insecticide (mainly lindane dust) were made (table 4).

Of the remaining 26 per cent of the area, the fruit was sprayed with Insecticides, mainly aminocarb against light brown apple moth and mevinphos against carpophilus beetles. These are the main insect pests of apricots in the Riverland, and all though they are not important in most years, they sometimes cause economic damage. Thus, the use of insecticides on apricots is likely to vary somewhat with the season.

Peaches

A total of 65 per cent of the peach area sampled was not sprayed during the growing season; of this 22 percent was untreated, while 43 per cent was treated only when the tree was dormant (table 5). Treatment during dormancy is mainly against green peach aphid, Myzus persicee (Sulzsr) and San Jose scale, Comstockespis perniciosis (Corn st.).

Avoidance of spraying during the growing season prevents contamination of fruit with insecticides, and conserves beneficial insects, which are most active during the growing season. The remaining 35 per cent of the peach area was sprayed with organophosphate insecticides, mainly azinphos-rnethvl and parathion, against oriental fruit moth, Cydia molesta (Busck.). Some of this area (5 per cent of the total) was also sprayed with miticides against two-spotted mites, Tetrsnvchus urticse Koch.

The area of peaches receiving sprays during the growing season seems to have declined steadily since 1970, when the first attempts at integrated control of peach pests were made. This decline has coincided with the apparent decline in abundance of the main pest of peaches, oriental fruit moth. Prior to 1970 the provisions of the Oriental Fruit Moth Eradication Act (1962) were enforced in a number of districts, including Renmark. Between 1960 and 1970 most orchards in the Renmark, Lyrup, Barri and Waikerie areas were sprayed in an effort to eradicate the moth.

Table 4: Insecticide use on apricots in the Riverland in the 1977–1978 season.

Table 5: Insecticide use on peaches in the Riverland in the 1977-1978 season.

Apples and pears

Virtually all the ara planted with apples and pears received insecticidal treatment (table 6), to control the main pest, codling moth. Cydia pomonella (Linn.). Small areas of pears were not sprayed, because in the 1967-1968 season, there was excess production of pears and some orchards were temporarily abandoned. The area (30 per cent) of apples not treated with miticides is unusual, because miticides are usually required to control mites on apples. This figure represented only one orchard – a reflection of the small sample size of this crop.

Table 6: Insecticide use on minor tree crops in the Riverland in the 1977–1978 season – all districts combined.

Almonds

A total of 19 per cent of almonds were un-sprayed (Table 6); the remaining 81 per cent were sprayed with a miticide against bryobia mite, Bryobie rubr ioculus (Scheut.) and some of this area was also sprayed with a dormant oil to eliminate the over-wintering eggs of bryobia.

Control of bryobia is unlikely to vary markedly between years 50 the future use of miticides can be expected to be similar to that in 1977–1978.

Olives

Olives in the sampled orchards were not sprayed since no primary pests of olives have been recorded in the Riverland. Scale insects, which are one of the main pests of olives overseas. seem to be under biological control in the Riverland, so any spraying with synthetic insecticides would be expected to induce a scale problem.

Comparative use of insecticides

The areas sprayed with the more common insecticides used in the Riverland are shown in table 7, ranked in order of decreasing area. The area sprayed in each district was calculated as being:

The areas for all districts were then summed for each insecticide. The results are expressed in area covered, and may not directly relate to the volume of insecticide used because a number of sprays may be applied to the same sample area. For example. parathion and azinphosmethyl were used up to six times a year on the same area for pears and apples.

The most widely used insecticide was petroleum oil, used against red scale on citrus. Oil is not known to leave harmful residues in the environment, and is thought to have little effect on beneficial insects. In integrated control programmes (parasites and oil) it reduces red scale numbers to densities that can be controlled by parasitic wasps.

Lead arsenate is widely sprayed on vines to control light brown apple moth. This chemical selectively kills chewing insects, leaving beneficial insects unharmed. However. there is some fear that its use may result in residues in wines and its future use is likely to be discouraged. It is also cheaper than most other insecticides. Many growers had previously tried the biological insecticide Bacillus thuririqiensis but because of its high cost and variable results they had returned to using lead arsenate.

Most of the remaining chemicals used were organophosphate or carbomate insecticides. Little of the area was treated with chlorinated hydrocarbon insecticides. Chlordane was used on the ground only on an estimated 90 ha of citrus orchards to control ants which may cause blockages to irrigation systems. Small areas of peach trees were sprayed during dormancy with a mixture of lindane in oil to control green peach aphid.

Decline in insecticide use

The decline in insecticide use on citrus and peaches is attributed to the successful implementation of biological and integrated control. A number of factors have encouraged the adoption of biological and integrated control:

1. The.use of biological control results in greater profit margins in most cases.
2. The damage threshold for some crops has been reduced. In Citrus, increased processing for juice has meant that external quality (which is reduced by the presence of red scale on fruit) has become less important.
3. The low insecticide use on all major fruit crops has probably meant that chemical control measures no longer interfere with biological control in neighbouring orchards.

The only crops requiring large amounts of insecticide were apples and pears. However, these are only minor isolated crops. The main pest, codling moth. cannot yet be controlled biologically, so growers of these crops have continued to use synthetic insecticides.

Comparison with other fruit growing areas

A notable feature of this survey was the area of crop which was not sprayed (table 7), or in which spraying was avoided during the growing season. Comparison with other fruitgrowing areas is difficult because of the lack of published survey results. Most citrus grown in Queensland, South Africa, and California appears to be sprayed with one to six organopbosphate sprays each season.

Peaches and apricots in most parts of the world are sprayed several times a year for fruit fly or caterpillar pests. Survey reports in the United Kingdom by Sly (1965–1977) show that pesticide usage in horticulture in that country is much higher than in the Riverland, although the crops and pest complexes in the two places are different.

The impression that insecticide use in the Riverland and Sunraysia in Victoria is lower than in other comparable fruitgrowing areas, if true, maybe attributed 10 the success of biological and integrated control programmes, the ecological isolation of the area and the effectiveness of quarantine.

Table 7: Estimated area of orchards to which various insecticides were applied.

Importance of natural enemies

Naturally occurring parasites and predators are thought to be responsible for the natural control of a large range of potential pests on all crops (table 8) . Evidence in support of this comes from the rapid increase of twospotted mite which occurs when multiple organophosphate sprays are used to control oriental fruit moth on peaches (Richardson 1972). Insecticides are not toxic to this mite, but are toxic to its natural enemies; hence, after spraying the mites increase rapidly in numbers in the absence of their natural enemies. Growers  have observed that a similar effect occurs with some other secondary pests such as mealybugs, following the use of insecticides. There is also evidence that the incidence of oriental fruit moth has declined in some areas after spraying ceased (Bailey, 1980), indicating that this pest may be controlled by natural enemies in un-sprayed orchards.

Table 8: Major insect pests of fruit crops grown in the Riverland and their most important natural enemies.

Sources of pest management information

The numbers of growers using each of the sources of information about pest Management as their main source are given in table 9. The first ranking source of information was the district horticultural adviser of the Department of Agriculture.

Own experience was cited by 17 per cent of the growers but it is likely that many of these growers obtained their original advice on identification, life cycles and control of pests at some time in the past, and have proceeded to modify this. In most cases it was not possible to ascertain the source of the original information. Publications of the Department of Agriculture provided primary information for only 2 per cent of the growers interviewed. In view of the expense involved in preparing these publications this may appear a disappointing result.

However, it may be that the publications are used as general background information by the grower since 63 per cent were found 10 possess a recent copy of the Department of Agriculture spray guide. Perhaps they rely on specific sources of information to solve specific problems.

Table 9: Main sources of pest management information.

Acknowledgements

We wish to thank Messrs G. Botting, A. DeLaine. R.George, E. Harnrnerton. A. Possingham, M. Richards, D.Shaw and J. Steed tor their help and advice in conducting this survey.