When feeding damage is found in an establishing broadacre crop, the species or type of pest responsible is not always immediately obvious for several reasons.
One reason is their behaviour; many common pests of broadacre crops are nocturnal, actively feeding at night and seeking shelter during the day.
A second reason is habitat: some pests live below ground in the soil or are hidden by heavy stubble loads.
A third reason is size; some pests are tiny and are difficult to see with the naked eye.
Conversely, spying an invertebrate in proximity to crop feeding damage is not a direct indication of the species to blame.
Best management practices always start with identifying the cause of the damage.
It pays to have knowledge of pest feeding symptoms and understand how they can provide clues to narrow down the pool of suspects.
As there are very few pests that produce unique feeding symptoms, it is not recommended to enact a pest management strategy based on plant damage alone.
Chewed leaves, holes in leaves, severed plant stems or missing seedlings are caused by pests with 'chewing' or 'rasping' mouthparts.
Pests with chewing mouthparts (jaws and associated feeding appendages) are capable of chomping and grinding plant tissue when feeding.
Some typical chewing broadacre pests includes armyworm, cutworm, the European earwig, and adult weevils.
Belowground pruning or severing of roots is typical of chewing pests that are soil dwelling, such as certain species of wireworms, immature weevils and scarabs.
Slugs and snails create similar damage to chewing species, except they have a rasp-like mouthpart (a radula), which they use to scrape the soft tissue from leaves during feeding, often resulting in a shredded appearance or irregular-shaped holes in leaves.
However, some other broadacre crop pest species have mouthparts designed for 'piercing and sucking', which generally creates a different set of feeding symptoms.
For example, aphids pierce plants and extract nutrients and moisture with their needle-like mouthparts, and can cause wilting, distortion, discolouration and/or yellowing.
The mouthparts of some mite pests, such as the redlegged earth mite and Bryobia mites, are also adapted to pierce and suck, often causing silver patches or stippling, leaf-cupping, and shrivelling.
Once it has been determined whether crop damage is from a piercing and sucking species or a chewing/rasping species, monitoring tactics can help to further identify the pest responsible.
A magnification tool such as a hand lens or a smartphone with clip-on macro lens, can help detect small species such as mites on foliage or the soil surface, or aphids on the undersides of leaves or close to the plant's crown.
It is beneficial and time saving to understand when you are most likely to catch sight of suspected pests.
For above ground chewing or rasping damage, tactics to catch nocturnal species are often required.
Cutworm and armyworm shelter during the day and can be found curled up at the base of the plant, just beneath the soil.
Refuge traps are an effective tool in luring and detecting slugs, earwigs, slaters and millipedes.
Refuge traps can be tiles, wet carpet, hessian squares or drums that are placed on the soil surface in multiple locations across the paddock.
Night inspections with a torch can also be very useful for revealing the pest and their densities.
To detect soil dwelling root-feeders, it's necessary to dig up some soil with a shovel to reveal their presence.
However, the most abundant invertebrate found is not always the cause of crop damage.
Farm paddocks are also home to beneficial species and other invertebrates that play important ecological functions, and they can be mistaken for pests when found near damaged plants.
For example, springtails are often found on farm paddocks, around plants in extraordinarily large numbers, and while these numbers can at first seem 'alarming', the majority of species likely feed on decaying organic matter, not living plants.
For information on identifying key pests of broadacre crops in south-eastern Australia, visit the PestNotes southern series, http://cesaraustralia.com/sustainable-agriculture/pestnotes/.
About the author: Julia Severi is an extension scientist at cesar.
Have you signed up to Stock & Land's daily newsletter and breaking news emails? Register below to make sure you are up to date with everything that's important to Victorian agriculture.
