Management in horticulture - vegetables and fruit
Damage
Grass type crops are the most commonly damaged by fall armyworm but the range of horticultural crops reported as hosts is extensive and includes fruit and nut crops, vegetables, various herbs, floriculture and turf. Whether fall armyworm causes damage to any horticultural crop may be a result of seasonal abundance or proximity to more preferred host plants. The pest status of fall armyworm on horticultural crops in Western Australia will become more clear with time.
Among vegetable crops in the south-eastern states of the United States, only sweet corn is regularly damaged. For information about management of fall armyworm in sweet corn, please see the Management in maize and sweet corn page.
In some years, fall armyworm is a major pest of tomatoes and capsicums in south-eastern United States. Fruit can be attacked, leading to premature drop and fruit rot. Fall armyworm is also encountered as a quarantine pest in capsicums exported from the United States to Europe. Other vegetables affected by fall armyworm include crucifer crops, melons and sweet potatoes.
The young larvae first feed on leaves near the ground where the damage may go unnoticed. Leaf damage by young larvae appears in the form of ‘windowing’ where only the epidermis remains. By the second or third instar, larvae begin to make holes in leaves, and eat along leaf edges. Older larvae cause extensive defoliation, often leaving the plant with a ragged, torn appearance. The number of larvae are usually reduced due to cannibalistic behaviour.
Because horticultural crops are used for human consumption, there are generally low damage thresholds for produce or pest presence. This market requirement demands regular monitoring to protect crops from the adverse effects of fall armyworm.
Monitoring
The spread of fall armyworm in Western Australia is being monitored by the use of pheromone traps. This surveillance will clarify the distribution of fall armyworm across the WA’s agricultural regions. In addition, experience with the insect should clarify the time of year crops are most likely to be infested.
If fall armyworm becomes an important or consistent pest in a particular region, a pheromone trap can be deployed to check on the presence of moths as a warning of a potential pest situation.
Early detection is essential. Young seedlings in trays should be checked for egg masses and larvae before they are transplanted in the field. Regularly check crops in the field and record the presence of egg masses and larvae that may be recognised by their characteristic damage to leaves – “windowing” indicates the start of an infestation and gross leaf damage points to the presence of older larvae. Regular, timed searches across crops will ensure the start of an infestation or hot spots early are not missed.
Be sure to clearly identify fall armyworm where damage is thought to be caused by the pest.
When to take action
No action thresholds are available for the range of horticultural crops listed as hosts of fall armyworm. Experience with similar pests, such as cutworms, armyworms and budworms (Helicoverpa, heliothis), will help decide whether infestation levels of fall armyworm require intervention.
Management
An integrated pest management (IPM) approach should be considered for protecting horticultural crops from infestations of fall armyworm.
Fall armyworm has entered an existing suite of pests and associated natural enemies, systems of production and pest management programs. Careful consideration needs to be given to any actions taken for fall armyworm control that may have adverse effects on management options already in place for other pests of horticultural crops, especially where natural control agents are used.
Natural enemies of other insects in the same group as fall armyworms are already present in many horticultural crops and these may also attack fall armyworm. There is already evidence of wasps parasitising fall armyworms in Kununurra. However, the effect of natural enemies with fall armyworm will become clearer as our experience with the pest accumulates.
An important management practice is to maintain farm biosecurity measures and implement good farm hygiene, and to remove alternative hosts such as weeds and volunteer crop plants, especially during periods, and in places, where fall armyworm would not easily be able to survive year-round.
Other cultural practices, such as trap cropping, may reduce fall armyworm numbers. Planting maize or sorghum as an attractive trap crop has led to reductions of fall armyworm in horticultural crops. Understanding the value of the various cultural practices for fall armyworm management that have been tested overseas will require further study under Australian conditions.
In the Americas, Spodoptera frugiperda nuclear polyhedrosis virus (SfNPV) has been successful in significantly reducing the damage caused to maize crops, but this product is not available in Australia. The NPV that controls Helicoverpa larvae is not considered to be effective against fall armyworm. This approach to management may also be used in horticulture if the product became available in Australia.
Insecticides that contain the bacterium Bacillus thuringiensis (Bt) would most likely kill larvae of fall armyworm, especially if applied when larvae are small. However, considering they need to be ingested and larvae feed in concealed areas, foliar applications of Bt products are recommended with caution for use in horticultural crops.
In the short term, insecticides will be relied upon to protect crops from fall armyworm. This insect has a reputation for developing resistance to insecticides. Resistance management strategies will be required to maintain effectiveness of insecticides for controlling fall armyworm.
Application of insecticide will be most effective if applied late in the day and into the night, when the larvae become more active and emerge from protected areas of the plant.
Insecticides available for use against fall armyworms include those available under recently approved APVMA minor use permits. There are numerous permits for horticultural crops. Where required, APVMA permits should be read in conjunction with the relevant product label for information on withholding periods and other critical comments.
Also available for use in WA, are any insecticides registered for use on crops for control of other insects if those products are considered effective on fall armyworm and provided they are applied according to label details. See section 87 ‘Use in accordance with label’, page 53 of Western Australia’s Health (Pesticides) Regulations 2011.
More detail on the permits is available from the information sheets found on the APVMA Portal. A direct link to each minor use permit PDF is provided in the tables below.
Note: New permits are regularly issued for fall armyworm control. Check the APVMA Portal for the most current information.
Important disclaimer
The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.