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Caterpillars of many species of moth occur on plum trees, but the majority feed only on the foliage and usually occur in small numbers. However, caterpillars of two species feed on the fruits. These are the plum fruit moth (Cydia funebrana (Treitschke)) and the fruitlet mining tortrix (Pammene rhediella (Clerck)). Both species are widely distributed in Britain; plum fruit moth is the more common pest, whereas fruitlet mining tortrix occurs sporadically and is less often noted attacking plum. Caterpillars of the plum fruit moth normally feed on the fruits of blackthorn (sloe) but are also locally common pests of cultivated plum and damson. They attack the fruits from June to September and often cause considerable losses. Caterpillars of the fruitlet mining tortrix feed on hawthorn berries and sometimes also attack fruits of plum and apple in late May, June and July. For the description of the fruitlet mining tortrix on apple, see page 137.

Several species of aphid (greenfly) infest the foliage and young shoots of currants and gooseberry in Britain and two species live on the roots. The most important species frequently cause much crumpling of the leaves and stunting of the young shoots during spring and early summer. Severe attacks may result in premature leaf-fall and small fruit. Both foliage and fruit may become sticky with honey-dew excreted by the aphids and dirty with sooty moulds that grow on the honeydew.

The willow—carrot aphid (Cavariella aegopodii (Scopoli)) is a widespread pest of carrot and often causes considerable loss of yield in early and mid-season crops. Parsnip, celery, parsley and other cultivated umbellifers such as chervil and fennel can also be attacked by this aphid and the willow—parsnip aphid (Cavariella theobaldi (Gillette & Bragg)). The willow—carrot aphid overwinters in the egg stage on willow trees, especially the crack willow (Salix fragilis) and the white willow (Salix alba), and also as an adult or immature stage on host crops that remain in the ground until spring.

The virus disease known as ‘reversion’ has in Britain. Infected bushes usually grow vigor-been recognized for many years as a wide-ously but their cropping ability becomes seri-spread and prevalent disease of black currant in Britain. Infected bushes usually grow vigorously but their croppin ability becomes seriously impaired. Plantations once affected ously impaired. Plantations once affected usually become uneconomic and have to be grubbed prematurely. The reversion virus is transmitted by a common and widespread pest — the black currant gall mite or ‘big bud’ mite (Cecidophyopsis ribis(Westwood)). Bushes infected with reversion are more prone than healthy bushes to heavy infestations of the gall mite and are, therefore, a menace to other black currants growing in the vicinity.

Stem nematode (Ditylenchus dipsaci (Kuhn) Filipjev) is a common pest of bulbs and is well known to bulb growers in Britain. Because many countries, especially those within the European Community, strictly prohibit its entry, this nematode is of particular concern to those who grow narcissus and tulip bulbs for export. It is also a pest of many other plants, including various farm crops (see page 440), vegetables (page 458) and strawberry (page 413).

Leaf miners are often found on chrysanthemums and related plants. Normally, these leaf miners are native insects, belonging to the species known as the chrysanthemum leaf miner (Phytomyza syngenesiae (Hardy)), which is a common pest widely distributed throughout the British Isles. However, alien leaf miners are sometimes introduced with imported cuttings and these species are described on pages 271–273.

In Britain strawberry is damaged by three species of nematode that live on the plant above ground and several species that feed on the roots.

The chrysanthemum gall midge (Rhopalomyia chrysanthemi (Ahlberg)) was first noticed in 1915 in North America as a serious pest of glasshouse chrysanthemum. The first two outbreaks in England were in 1927 and 1936, and were traced to chrysanthemums imported from the United States. There have been occasional outbreaks — all under glass — since then, but the pest remains uncommon in Britain and has caused little damage since the early 1950s.

The bulb scale mite (Steneotarsonemus laticeps (Halbert)) is occasionally an important pest causing of forced narcissus bulbs and is probably widespread in many stocks. Although rarely causing extensive damage to bulbs growing in the field, it is of concern to those who grow the crop for export. Other plants attacked are hippeastrum, eucharis, Sprekelia and Vallota. The mite belongs to the family Tarsonemidae, which includes other important plant pests, e.g. the cyclamen mite (see page 338) and the strawberry mite (see page 366).

Beet cyst nematode (Heterodera schachtii Schmidt) can cause ‘sickness’ in sugar beet, mangels and red beet where host crops of the nematode have been grown too frequently in the rotation. Beet cyst nematode occurs, and is a potential threat to intensive sugar beet crop­ping, in all temperate countries. Where the nematode is established it is important to lessen the risk of crop damage by adopting suitable crop rotations.

The pear and cherry slugworm, which is the larva of the pear slug sawfly (Caliroa cerasi (L.)),occurs in many parts of Britain, particularly the south. It is sometimes a pest in private gardens but is infrequently recorded in commercial plantations. Pear and cherry trees are most commonly attacked, but apple and plum are also attacked occasionally as well as ornamentals such as almond, flowering cherry, hawthorn and rowan.

Pea cyst nematode (Heterodera goettingiana Liebscher) is a serious pest of peas and probably the most difficult to control. It was reported in Germany in 1890 and was first found in Britain in 1912. Since that time it has appeared in widely scattered localities, especially in gardens and allotments.

Raspberry cane midge (Resseliella theobaldi midge was unknown in Britain until 1920 when (Barnes)) is mainly a pest of cultivated rasp-it was reported in Kent and Surrey. It spread berry but occasionally attacks loganberry. This midge was unknown in Britain until 1920 when it was reported in Kent and Surrey. It spread througrout England and by 1973 had reached throughout England and by 1973 had reached Scotland, where it became established in the raspberry-growing areas.

There are two distinct species of potato cyst nematode (Globodera rostochiensis (Wollen-weber) Behrens and Globodera pallida (Stone) Behrens) and both are major pests of the potato crop in temperate regions of the world. One or both species have been well established for many years in the main ware-potato growing districts of England and infestations are common in gardens and allotments throughout the country. As the cysts of these pests are easily spread, it is unlikely that any cultivated area in the arable districts of Britain is entirely free from them, although in the absence of potato crops the cysts would remain undetected and gradually lose their viability.

Apple sucker (Psylla mali (Schmidberger)) used to be one of the more serious pests of apple, but nowadays it is so well controlled by routine sprays that infestations are rarely seen except in gardens or unsprayed cider orchards.

Brassica seed crops are attacked by a succession of insect pests from the early seedling stage until the pods begin to ripen in summer. Yields of seed can be very seriously reduced by any one or a combination of these pests. The most common are pollen (or blossom) beetles (Meligethes spp.) the cabbage seed weevil (Ceutorhynchus assimilis (Paykull)) and the cabbage stem weevil (Ceutorhynchus quadridens (Panzer)); each causes specific and easily recognizable damage. These and other pests frequently found on brassica seed crops are listed in the table on pages 180–181. Those also occurring on oilseed rape are included on pages 182–189.

Caterpillars of several insect species feed on the foliage of currants and gooseberry. Described here are the caterpillars of the magpie moth (Abraxas grossulariata (L.)) and three species of sawfly, i.e. the common gooseberry sawfly (Nematus ribesii (Scopoli)), the black currant sawfly (Nematus olfaciens Benson) and the pale spotted gooseberry saw-fly (Nematus leucotrochus Hartig).

Before the introduction of DDT in 1946, the apple blossom weevil (Anthonomus pomorum (L.)) was a common and troublesome pest of apple and, occasionally, pear. Until recently, damage had not occurred in orchards in which sprays of either DDT or HCH had been used. However, following the withdrawal of DDT and the less frequent use of HCH, the pest has reappeared in a few places. Fruit trees near woodland are more likely to be attacked.

Docking disorder of sugar beet is characterized by irregularly stunted plants, frequently with fangy roots, on light, often structureless, sandy soils. Seedling emergence is normal and uni­form but, as early as the two rough-leaf stage, differences in growth rate appear in areas of irregular shape and extent. Stunted plants (‘chicks’) commonly occur haphazardly — sin­gly, in groups or in lengths of row — among the large plants (‘hens’) (Fig. 80.1). The large plants appear extremely vigorous in compari­son, becoming ten or twenty times bigger than the small ones, which may show symptoms of nitrogen, magnesium or other deficiencies. The stunted plants may appear to grow nor­mally from July onwards, but root yield is less than from unaffected plants. If a large propor­tion of plants are affected and recovery does not occur or is delayed until September, root yield may be only about 8 tonnes/ha. Many of the stunted plants cannot be harvested and the yield is derived mainly from the scattered large ones. Open image in new window Fig.80.1 Sugar beet crop affected by Docking disorder