Agriculture Reference
In-Depth Information
worm,
Spodoptera exigua
can be a serious pest (Lorbeer
et al.
, 2002). The pest is
protected from contact insecticides when inside the hollow leaves of shallots and
is therefore difficult to control. Beet army worm-resistant shallots that produce
Bt
toxins have been developed by genetic transformation (see Fig. 3.7b).
Shallot aphid
Myzus ascalonicus
, the shallot aphid, is one of 18 species of the order
Hemiptera, plant bugs and aphids, reported as allium pests. It may infest onion
bulbs in store, where it damages fleshy scales and distorts developing leaves and
flower parts. It and other aphids - for example,
M. persicae
- can transmit many
viruses of alliums, including onion yellow dwarf (see Viral Diseases). Quick-
acting insecticides must be used if they are to have any preventative effect
against virus transmission. Fumigation with nicotine or pirimicarb has been
used to control aphids on stored bulbs.
Other pests
Twenty-three beetles, order Coleoptera, were reported as allium pests by Soni
and Ellis (1990). Many affect stored bulbs but some destroy foliage. They also
reported nine species of mites, class Arachnida, order Acarina, as pests. Mites
feed on sap released after piercing plant cells, and some enshroud the plants in a
characteristic web. Allium pests include red spider mites,
Tetranchyus
spp.,
which damage many crop species, and also
Aceria tulipae
, the garlic mite. This
tiny mite, only 0.10-0.25 mm long, can infest stored bulbs of garlic, onion and
shallot, causing shrivelling. Infested growing plants develop yellow-streaked,
twisted leaves. This is termed tangle-top malady in India. The mite is a vector of
garlic mosaic and onion mosaic viruses (see Viral Diseases). Control is difficult,
since the pests lie hidden between leaves in the neck, or are inaccessible in bulbs.
Organophosphorus acaricidal sprays are used for control on growing plants.
Nematodes, or eelworms, are small, unsegmented worms which form an
important constituent of the soil fauna. Sixty-eight species identified as
associated with the roots of crop alliums were listed by TDRI (1986). A small
percentage have been shown to be damaging pests and one species, the stem
and bulb eelworm,
Ditylenchus dipsaci
, is a major pest. Green (1990) wrote a
detailed review and bibliography of the nematode pests of alliums, and Perry
and Moens (2006) include more recent information.
