Mealy Bug Resurgence in Hawke’s Bay Orchards

New Zealand Journal of Agriculture, Volume 99, Issue 5, 16 November 1959, Page 481

Mealy Bug Resurgence in Hawke’s Bay Orchards

DURING the last two or three years there has been a pronounced resurgence of mealy bug in Hawke's Bay orchards. It has become the most serious pest for many growers of pip and stone fruit. Investigations have been carried out on mealy bug biology and control by officers of the Horticulture Division of the Department of Agriculture for the last two seasons. Results of these investigations are given in this article by N. B. Congdon, Horticultural Advisory Officer, Hastings, and L. G. Morrison, Horticultural Advisory Officer (Biology), Wellington, both of the Department of Agriculture.

IOTEALY bug was formerly a prob■L’* lem in pears in certain areas of the district, but with the introduction of DDT it has until recently been kept under control. The introduction of parasitic insects in the early 1920 s may also have contributed toward satisfactory control. However, growers in these areas have always .noticed a small population of mealy bugs, but not, until recent years, sufficient to cause concern. The resurgence of the pest has been put down to various reasons. The main explanation appears to be that mealy bugs have become resistant to DDT, which, in turn has probably killed out any parasites which may have become established. There may be other factors involved. A rapid build-up of the pest is occurring 'not only in pears, but in apples, peaches, plums, and grapes. From a survey carried out last season it appears that at least 90 per cent of

the orchards in the district are affected to varying degrees, Havelock North being by far the worst. Classification Mealy bugs belong to an order of insects known as Homoptera to which belong such sucking insects as aphids, cicadas, leafhoppers, and spittlebugs, and the family coccidae, which include the scale insects. Mealy bugs do not have a shell or hard outer skin but are covered with a . fine white powdery or cottony wax which enables them to withstand severe treatment without bodily injury. Another function of this wax is believed to 1 be the protection of the insect against moisture, for example, excessive water loss or against drowning. Of the Pseudococcus genus of mealy bugs in New Zealand, three, species P. maritimus, P. comstocki, and P. gahani are reported as attacking pears, while these and P. adonidum attack apples. Of these, the grape mealy bug P. maritimus appears to be by far the most prevalent and the following notes apply to it. Distribution and Hosts The bugs are present throughout New Zealand, mostly in small numbers. However, during the last two seasons there has been a phenomenal build-up of mealy bugs in the fruit-producing areas of Hawke’s Bay. In this district the hosts of primary importance are pears, then apples, grapes, peaches, and plums. Of secondary importance are grass, clover, and docks and other, weeds. However, some 400 hosts have been recorded elsewhere. The areas they most commonly infest on fruits are the calyces of pears, the stem ends of apples, and both these areas where fruit lie together.

Damage The main damage caused by the bugs is indirect: (a) The feeding of the insects on tender parts of plants may cause them to curl up and become distorted or stunted. This is particularly true on grape vines. If severe, infestation causes premature defoliation. Vines, for example, will not be able to ripen their wood properly and the result is poor growth and light crops the following year. (b) Honey dew is freely excreted by the insects. Often the honey dew becomes infected by a sooty mould, fungus. Manuka blight shows a severe form of this. Where the sooty mould appears on the fruits it makes them unsightly, even unsaleable. On the leaves it interferes with respiration and carbohydrate formation. This is undesirable, as it affects flower bud development. (c) Disease ; transmission: Every injury caused by feeding bugs is a possible point of infection by fungous diseases. Description The male bug is only J in. long and because of its small size is rarely seen. Males have two well developed wings and at the tail end have two long white filaments. They have a very short life. Young of both sexes look alike and the mature female differs only in size and in the amount of waxy covering secreted over the body. Mature females are regularly oval, flattened, and usually completely covered with a fine white powdery wax which extends along the side as lateral filaments, with often two or more longer ones at the end (called tails). They grow to be about i in. long and i in. wide. All have six legs and are able to move . about freely during their entire existence.

The mouth parts consist of a long thin sucking tube which can penetrate into the plant tissues and withdraw sap. This is important, as mealy bugs cannot be poisoned unless the poison is in the sap stream. Beneath their waxy covering the bugs vary in colour from flesh pink to grey. Life History In Hawke’s Bay mealy bugs emerge from their winter dormancy toward the end of October and start feeding. When the female is about to lay eggs she moves to some part of the . tree where she will be well protected. Early in the season this is likely to be under the bark or in crevices of branches. Later in the season females will also choose to hide beneath the calyx of fruit, particularly on pears. The female deposits her. eggs in a loose cottony sac of waxy, threads. As this egg laying occupies several days and the eggs do not all hatch at once, it is difficult to determine for how long they are incubated. However, under New Zealand summer conditions the period appears to vary between two and three weeks. As each female may deposit up to 500 eggs, mealy bugs can increase rapidly under favourable conditions. / Shortly after hatching, the young bugs or “crawlers” make their way to young shoots, leaves, or fruit, where they settle down and begin to feed on soft tissue. At this stage, when their food reserves are low and: their covering of protective wax is very light, they are most vulnerable to attack. In the next four weeks the crawlers moult twice. Before moulting for the second time the male spins a cocoon, from which it emerges as. a small winged insect. These males have no functional mouth parts and therefore can live for a few days only. During this time they mate with the females, though these are only about one-third grown. Under favourable conditions P. maritimus can complete its life cycle in about 60 days. Later in the season, when the weather is cooler, more time is required, sometimes up to five months. As the time required for development is shorter during summer, the numbers of mealy bugs increase rapidly then and they are usually most abundant in late summer and autumn. Overwintering Overseas the bug is reported as frequently overwintering as eggs which have been deposited in a secluded spot, such as under rough bark, cracks, crevices, or at contact points between branches. Incubation of these eggs takes months. ‘ On hatching, the crawlers may continue under the protection of the ovisacs (egg cases) for some days. Alternatively, partially mature but fertile females may move off the aerial

parts of deciduous trees and overwinter under the protection of stakes, ties, labels, and litter. This is so in New Zealand, but also in Hawke’s Bay all stages from eggs to adults have been found in mid winter on trees and round birds’ nests. Vast numbers could also be found right in the centre of the tree if the old “sprags”, which are common on some pear trees, were broken apart. Where water sprouts are cut back rather than cut off, it takes only a few seasons for these stumps to form a network of crevices providing very good protection for the bugs. No sprays can reach them and as long as this cover is not pruned off a constant source of reinfection remains throughout the year. Spread Mealy bugs may be spread by various methods. One of the most important is the transfer of infested plants, fruits, and containers and on the clothing of workers who brush against infested material. Animals may also spread the bugs through contact. Overseas, birds are considered to be important vectors, as they may pick up the young crawlers on their legs and feet when settling on infested trees. . Insects, especially winged species, may spread the pests in the same way, bees particularly, as they are attracted to the honey dew the bugs secrete. In South Africa wind is thought to be an important factor. Immature stages can be blown about, and a gale will break off and scatter infested leaves and twigs. Floods and irrigation water are other means of spread. Females and ovisacs can float on water for days without damage, as the wax on the eggs and adults protects them. Furthermore, the delicate wax threads round the egg sacs will stick to any object, touching them. When the

object moves, threads and some eggs go with it. Enemies Natural enemies may be placed in two groups according to their method of attacking the host: Internal parasites, those feeding and developing within the body of the host: One, a chalcid wasp, was introduced into New Zealand in 1923-24, but has had little effect. Predacious enemies, those completely devouring the host: The chief of these is the ladybird beetle Cryptolaemus montrouzieri, or mealy bug destroyer. This black and orange-ended beetle, only 1/16 in. long, is a native of Australia. It lays its eggs among the mealy bug eggs. The young of both hatch about the same time; then the ladybird larvae proceed to eat the young bugs. These ladybirds were first liberated in New Zealand in 1897. Four years later - mealy bugs were reported to be under control, but subsequently more beetles had to be imported and were liberated in 1924. The beetles are now scarce, probably because our climate is unsuitable for them. In California these ladybirds are raised under artificial conditions during winter, but that is not practicable here. Minor predators include other beetles, lacewings, and some flies. Control . Control measures fall into three categories, biological, cultural, and chemical. Biological This has been briefly discussed above. Cultural (a) Clean cultivation, especially round the bases of trees: Not only does litter at the base of a tree provide

protective cover for bugs, but grass, clover, and weeds may be alternate hosts and a source of reinfection. (b) Scraping trunks of pear trees so that all excess bark is removed from older trees is particularly useful in removing overwintering sites and also allows more effective spray coverage. This suggestion may be rejected on grounds of. cost of the operation and possible damage, but it would undoubtedly assist control. (c) Clean pruning: By this is meant the removal of all old, spent, or dead fruiting spurs, and twigs and water sprouts from inside the pear leaders. These parts provide ample shelter for mealy bugs and if present are nearly always infested. Chemical Recent experiments carried out in 1 Hawke’s Bay orchards show that with the large range of insecticides available only the organo-phosphate materials are effective. In particular two materials, parathion and diazinon, have given good control. However, fairly high rates of application at frequent intervals and with good coverage are essential. Of the two, parathion appears a little more effective, than diazinon, but is extremely dangerous to operators, who must wear the recommended protective clothing. Diazinon is safer to the operator, but is more expensive (almost double the price of parathion when used at a strength to give equal control). Trial on Pears A brief description of last season’s trial on 1 acre of Winter Cole pears at Havelock North is given below. Treatments were as follows: Per 100 gallons Parathion (31 per cent) . . 10 oz Parathion (31 per cent) . . 15 oz Diazinon (20 per cent emulsion) .... i pint Diazinon (20 per cent emulsion) .. .. 1 p i n t “Phosdrin” (25 per cent emulsion) . . . . i i n t “Phosdrin” (25 per cent emulsion) • . . ... 1 pint Preceding these treatments was an overall combined application during the dormant season of winter oil 1 in 20 4- lime sulphur 1 in 15. There was a heavy carry-over of mealy bugs (eggs and adults) from the previous season and infestation was considered to be uniform throughout the pear block.

* Permissible residues on food at time of sale of some of the materials mentioned are specified in Amendment No. 12 to the Food and Drug Regulations 1946 as follows: Parathion, not greater than 1 part per million; “Phosdrin”’ nil. The Systemic Pesticides Notice 1959 prohibits application of "Phosdrin” to pip and stone fruits within one week of harvesting and of ‘Roger 40” within tw« weeks of harvesting.

Treatments were in single rows of eight trees each separated by guard . rows. Spraying was done with the grower’s air blast machine, about 6 gallons per. tree being applied, and was carried out in a system to eliminate drift to adjacent trees as far as possible. The trial block received four applications. The first was applied on 12 November when a heavy infestation of all stages from crawlers to adults was collecting, mainly round the bases of young lateral growth, particularly in centres and tops of trees. To obtain the greatest possible kill, spraying, was delayed a few days from when first emergence was noted. Bugs appear to feed at the base of young growth for a week or two before moving out to leaves and fruit spurs. Before the second application all trees were summer pruned (all surplus lateral growth was pulled but (not cut) from the centres of the trees, and as far as one could reach along the fruiting arms). This was done to allow better penetration of sprays and .to reduce protection for the bugs. Many bugs adhering to the bases of the laterals were removed on the growth pulled out. The second application with all treatments was made on 6 December. Spraying was done at a time when it was considered there was a predominance of young crawlers round laterals and spurs from a recent , second hatching. It was obvious from this stage onward that there was an overlapping in stages between eggs and adult bugs. This was probably due to the fact that bugs emerge from wintering places both as young crawlers and as adults. As a result of the first two applications very few had managed to reach the calyx in the most effective treatments. On 17 January a third application was made as for the earlier treatments except that “Phosdrin” j pint, which was giving poor control, was replaced by parathion. i On 17 February the fourth and final sprays were applied, being similar to those of the third application. Before this final spray it was evident that re-infestation from a late hatching had occurred during early February from eggs laid within the actual spur, crawlers having only a short distance to travel to infest fruit. They quickly collected at the point of contact between pears in the bunch and some moved into the calyx to become firmly embedded under the calyx leaves.

Harvesting of the trial block was carried out between 11 and 14 March, fruit being picked into bulk trailers. Samples of five cases of pears from each treatment were examined for presence of bugs in the calyx. Percentages of infested fruit from each treatment at harvest were as follows:

Per cent Diazinon: 4 pint . . . . 61.9 1 pint . . . . 19.9 Parathion: 10 oz . . . . 26.2 15 oz .. ... 14.5 “Phosdrin”: 4 pint (2 sprays) followed by parathion . 15 oz (2 sprays) .. .. . 76.2 1 pint . . . . . . 75.5

Fruit with even one crawler was classed as . infested, and it should be noted that figures for diazinon 1 pint and parathion 15 oz treatments were mainly very slightly infested fruit (three crawlers or fewer per pear). When this trial was laid down it was intended to keep applications as far as possible to a minimum in view of likely grower practice and cost of materials. Until the end of January satisfactory control had been obtained with parathion and diazinon at the interval used. With the heavy crawler emergence in early February and the difficulty in getting spray to penetrate it appears that at least two closely spaced sprays would have checked this late infestation better than the one application in mid February. Percentages of infested fruit at harvest appear high' from the figures. However, with parathion 15 oz and to a less extent diazinon 1 pint reasonable control was obtained with only four sprays when it is considered that unsprayed trees (which of course could not be included in a grower trial) would undoubtedly have had 100 per cent of infested fruit. Trial results suggest that growers in bad mealy bug areas should apply sprays at regular intervals (say every three weeks) rather than attempt to time applications to crawler emergence. For Winter Cole pears this would mean about six applications, the first in early November and the last 14 days before picking. A further application might be required on Winter Nelis. Earlier varieties of pears would require proportionately fewer applications unless it was seen

that infestations continued to build up after harvesting. Other Trial Work *New chemicals: New spray materials, mainly organo-phosphates,

are continually, becoming available for trial, and these are being included in experiments where considered worth while. One of these, “Rogor 40”, from a preliminary trial at the end of last season appears particularly promising as an alternative to diazinon and parathion. It will be included in larger trials this season. Tree banding: Small-scale trials are being carried out to investigate the possibility of trapping mealy bugs migrating from the ground on to the trees by placing a sticky band round the . trunks. There is little evidence to date to suggest anything of practical value. The difficulty is to find a material which will retain its sticky surface for long. One or two promising compounds will be investigated this year. Trial work this season will be based on an investigation of the effectiveness of promising and recommended sprays in relation to timing, interval between applications, and dose rates. It is also proposed to compare dilute and semiconcentrate methods of application. Growers are themselves doing a certain amount of trial work on their own properties that is providing useful information. Acknowledgment The cooperation of Mr J. W. Jones, Napier Road, Havelock . North, on whose property trial work was carried out in the 1958-59 season is acknowledged.

Control Recommendations PH From first or second week . in November and at threeweekly .intervals until 14 days before harvesting apply: Per 100 gallons Parathion (31 per cent) 15 oz or Parathion (25 per cent) 184 oz or Diazinon (20 per cent) 1 pint Ensure best possible coverage to reach bugs in sheltered places on the tree and include a wetting agent in the spray. An autumn application as soon as possible after harvest will reduce carryover to the next season. (The above strengths could be reduced with closer-interval spraying.) ED Remove all surplus lateral growth from the insides of leaders and fruiting arms during early summer. At this period before growth has hardened laterals can be pulled out by hand and this is preferable to cutting, which leaves stubs that provide additional shelter for bugs. fig - ] To reduce migration of crawlers from weeds and grasses under trees maintain a clean zone round butts during spring and summer. □□ On old pear trees the removal of “sprags” (old gnarled and knobbly growths on leaders and fruiting arms) and scraping off of loose bark from trunks and leaders will greatly reduce the main sheltering places for mealy bugs and assist control. Growers are strongly recommended to take appropriate action where mealy bug is either well established or beginning to appear. There is no point in applying contact insecticides where bugs are not to be seen, but once they appear in a block, infestation is rapid if control is neglected. Eradication is then a far more difficult and costly •business.

* See footnote on page 485