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Plantwise Technical Factsheet

slender burnished brass moth (Thysanoplusia orichalcea)

Host plants / species affected
Allium cepa (onion)
Arachis hypogaea (groundnut)
Beta vulgaris var. saccharifera (sugarbeet)
Bidens pilosa (blackjack)
Brassica oleracea (cabbages, cauliflowers)
Brassica oleracea var. capitata (cabbage)
Cajanus cajan (pigeon pea)
Carthamus tinctorius (safflower)
Chromolaena odorata (Siam weed)
Cicer arietinum (chickpea)
Cichorium intybus (chicory)
Coffea (coffee)
Coriandrum sativum (coriander)
Crotalaria juncea (sunn hemp)
Glycine max (soyabean)
Gossypium hirsutum (Bourbon cotton)
Guizotia abyssinica (niger)
Helianthus annuus (sunflower)
Lactuca sativa (lettuce)
Linum usitatissimum (flax)
Melilotus albus (honey clover)
Mentha arvensis (Corn mint)
Mentha piperita (Peppermint)
Mentha spicata (Spear mint)
Mucuna pruriens (velvet bean)
Nicotiana tabacum (tobacco)
Petroselinum crispum (parsley)
Phaseolus vulgaris (common bean)
Pisum sativum (pea)
Raphanus sativus (radish)
Solanum lycopersicum (tomato)
Solanum melongena (aubergine)
Solanum tuberosum (potato)
Trifolium alexandrinum (Berseem clover)
Trifolium resupinatum (Shaftal clover)
Vigna mungo (black gram)
Vigna radiata (mung bean)
Vigna unguiculata (cowpea)
List of symptoms/signs
Fruit  -  external feeding
Leaves  -  external feeding
Leaves  -  frass visible
Symptoms
Semi-loopers are defoliators causing significant losses during the vegetative and reproductive stages. Leguminous crops, such as soyabean, with high infestations during the late vegetative and reproductive growth stages may suffer significant yield loss. Soyabean can withstand a significant amount of foliar damage when in the vegetative stage of growth because it can compensate for defoliation, but once the crop reaches the reproductive stage, loss of leaf area becomes critical (Jensen et al., 1977).

Newly hatched caterpillars tend to feed on the lower surfaces of soyabean leaves which they scarify, being unable to eat through the lamina. This results in the appearance of 'windows', particularly on the top canopy leaves. If sprays are to be applied, a good time would be at the appearance of this symptom, because the smaller caterpillars are much more susceptible than older ones. Older caterpillars feed on the entire leaf tissue between the veins, giving a very lacey appearance. Under severe infestations there is also a tendency for young pods to be eaten, in which case the damage to yield is direct rather than indirect from loss of foliage.
Prevention and control

Introduction

It is important to be aware of semi-looper infestation early if control measures are to be effective. This is not always simple because the damage done by young caterpillars is not very conspicuous; the small larvae are easier to control chemically. Scouting of the crop would ensure early discovery of an infestation.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
T. orichalcea is an economically important pest on legumes, particularly soyabeans and pulses. On these crops, studies have been conducted to assess the impact on yield, and economic/action thresholds are available. For other crops, crop loss assessments have not been performed. Within a few years of introduction into New Zealand, T. orichalcea had assumed pest status on a range of crops and was reported to be more abundant on seven species of plant than the related species Chrysodeixis eriosoma (Hill et al., 1987). In New Zealand, on cabbages an action threshold of 15% infested plants has been established and spray decisions based on this threshold have resulted in a decrease of the number of spray applications by 25-100% (Beck and Cameron, 1990; Beck et al., 1992).

In soyabeans, Taylor and Kunjeku (1983) determined the economic threshold levels as 15.7 larvae per metre of row and 7.6 larvae per metre of row at pod and bean development stages, respectively. They concluded that it was economical to spray as soon as the loopers appeared after the crop had flowered. Lapointe et al. (1995) established that the impact of defoliation of soyabeans is dependent on the growth habit (determinate or indeterminate) and the stage at which attack occurs. They estimated economic thresholds of 45-145 semi-loopers per metre of row, depending on the cultivar, insecticide and method of application. These thresholds equate to between two and seven semi-loopers per soyabean plant. Soyabeans are very capable of compensating for leaf damage, particularly if this is inflicted during the vegetative stages of growth. In addition, the indeterminate cultivars can almost certainly withstand more damage than determinate cultivars in a good growing season. A healthy crop can cope with more than 30% leaf loss without loss of yield (Taylor and Kunjeku, 1983; Lapointe et al., 1995). When the crop has entered its reproductive stage, however, leaf loss can be serious, and sprays should be considered if the semi-loopers have not succumbed to a natural virus disease.
Related treatment support
 
External factsheets
PlantVillage disease guide, PlantVillage, English language
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