Identifying Insect Damage

Identifying Insect Damage

Nothing ruins a day more than finding crop damage. Particularly when you see fresh emerging plants slaughtered by bugs. Which is why it is recommended to frequently check emerging crops during the first 3-5 weeks. Regular checks give us a higher chance of early detection of any pest issues, boosting our shot at intervention, to ensure crops thrive. But how to do you check for damage? Sometimes insect damage can be visible and easy to identify, and other times it’s not. So, to help you determine what bugs are causing your crop grief, here are our top 5 tips for identifying insect damage and what may have caused it.

1. Check along rows for missing plants or areas that are visibly suffering. Look to find plants that have been chewed off near the base, or with visible damage from chewing.
2. When you’ve found affected plants, try looking for insects. Check in, around and under them, as well as under stubble in the inter-rows and under clods or stones.
3. Take note of the damage on the plant. Is it chewing, windowing, rasping, or sucking damage? Understanding the preferred feeding methods and mouthparts of insects can help narrow down what is likely causing the damage. See below for more information on how to identify.
4. Try trapping them yourself. Set up a pitfall trap near where the damage is being caused. You can do this by placing a plastic cup (or something similar) into the ground, so that is the top is flush with the soil surface. Put about 10mL of water or oil in the bottom and check after 24 hours. 
5. If you come across an insect that you can’t identify, take photos and send to us, or, you can always bring it in the shop for us to have a look. It’ll save you trying to describe it. If you bring in an insect and we can’t figure out what it is, we can have it sent off to be identified. 

To be able to make better decisions and have more accurate control, it’s key to figure out what insects are in your paddock, and more importantly, which of them is causing the damage. Remember, there are also some beneficial bugs out there we want to keep. (Check out our article here on the good guys: www.awvater.com.au/blogs/beneficial-bugs)

Now to identify the different types of damage, and what may have caused it. 

Chewing Damage 

This one is pretty straightforward – pests with well-developed ‘chewing’ mouthparts cause chewing damage. Symptoms for this type of damage include missing portions of plants, serrated or scalloped leaf edges, chewed stems and removal of entire leaves, cotyledons or whole seedlings. Untreated, this can cause a lack of vigour and plant death. 

Insects Include – Weevils, true & false wireworms, cockchafers, cutworms, armyworms, budworms, earwigs, slaters & millipedes. 

Windowing Damage 

Pests that cause this type of damage surface graze plant tissue, leaving a thin transparent membrane.  

Insects Include – Lucerne flea (the usual culprit in the early season, feeding on the underside of the leaf.) also, the Diamondback moth (later in the season). 

Rasping Damage 

This type of damage is caused by molluscs. These species, such as snails, have mouthparts known as a ‘radula’, and their damage is usually identified by shredded edges, irregularly shaped holes in leaves, and removal of plant parts or entire seedlings. 

Insects Include – Snails & Slugs – snails are usually easy to spot during the day, but check at night to find slugs in action. Also, sometimes Slaters.

Sucking Damage 

There are two ways this type of damage occurs:

Firstly, by insects that have long needle-like mouthparts known as stylets. This type of sucking damage happens when the stylet is inserted into the plant tissue, and the insect sucks out the sap, which also removes plant nutrients. Plants wilt and yellow, and you’ll also see a distortion of leaves, stunted growth, and in some cases plant death.  

The second way sucking damage is caused by mites feeding. Their scissor-like mouthparts, known as ‘chelicerae’, lacerate plant tissue and suck up the discharged sap. Affected plants display silvering or whitening of leaves, or distorted, shrivelled leaves.  

Insects Include – 

First Type: Aphids and Rutherglen bugs. 

Second Type: Mites 

If you’ve got damage and you’re still not sure about what may have caused it, give one of our agronomists a call.

For more information head over to PIRSA: pir.sa.gov.au

And if you really want to nerd out, check out the I SPY manual: grdc.com.au/ispy.pdf