As the season gets later, we come into contact with the next wave of insects that have the potential of damaging our crop yields. It is important to know what pests and beneficial insects numbers are in your paddocks so you can make the right decisions with IPM strategies and pest thresholds. Below is an overview of the top 8 insects our agronomist will be checking for in your paddocks that we recommend you keep an eye on too.
1. Native Budworms
There are two species of native budworm in our areas; Helicoverpa punctigera and Helicoverpa armigera. Both will grow to around 40mm long and will vary in colour from brown, green and orange, with lines and bands running the length of the body. They can be told apart by the hairs around their head. The H. armigera budworms have white hairs, as well as a saddle of darker pigment on their back. H. punctigera’s have black hairs and no saddle. You’ll find H. punctigera more commonly in our areas, which is good news. The H. armigera variety is known to have resistance to some chemical groups across Australia. The budworms will attack field peas, faba beans, lentils, chickpeas, lupins, and canola, to name a few crops. They will be found feeding during the formation and development of pods, causing damage by chewing holes in pods or seed heads. If not addressed, their damage can cause downgrading at harvest. You can monitor budworms levels by using sweep nets. However, their economic thresholds will depend on crop variety and grain pricing. Give us a call to help determine these for your crop.
2. Diamondback Moth
Diamondback moth larvae are a pale yellowish-green, tapered at each end and will be around 10mm long when mature. The larvae will feed on canola and other Brassica crops by chewing on leaves resulting in holes or windows, which can cause severe defoliation and reduced yields. Monitor canola throughout late winter until late spring/early summer with sweep nets. Throughout Australia, economic thresholds are: >10 larvae per 10 sweeps for pre-flowering, >50 larvae per 10 sweeps for early-mid flowering through pod formation, and >100 larvae per 10 sweeps for late flowering through to podding (GRDC, 2010). Chemical control can sometimes be tricky as they can evolve insecticide resistance quite readily.
3. Armyworm/Barley Grub
There are several armyworm species commonly found in our areas and can be difficult to distinguish apart. The larvae grow to 40mm in length and are distinctly striped and vary in colour. They are hairless and usually pinkish, brown, or green. The larvae can be distinguished from cutworms and native budworm by three prominent white stripes on the ‘collar’ behind their head which runs the length of their body. Armyworms love to feed on cereal crops. Most of their damage will be caused in spring when they are feeding on the last remaining green material just below the maturing head. This damage will cause heads to be lopped off and will affect barley and oat crops the worst. Monitoring is difficult, but it can be done. Check for chewing marks on leaves, and also by scratching under stubble and the soil surface to find the grubs.
4. Russian Wheat Aphid
Russian wheat aphids are pale green and about 2.5mm long. They can be distinguished from other aphids by their elongated body, their short antennae, and their double tail at the back. These annoying pests cause a lot of damage when they feed. When feeding, they inject toxins into the plant, which leads to the yellow striping of the leaf, as well as stunted growth and loss of plant vigour. They are primarily found feeding on wheat and barley crops, but can also be present in oats, rye, and triticale. Keep an eye out for their trademark yellow-striped, curled leaves in stunted areas of the crops. By unrolling the leaf you will be able to see if aphids are present. Luckily, they have not developed any resistance, and most sprays will be effective.
5. Green Peach Aphid
The green peach aphid is pale yellow-green, green, orange or pink in colour, and around 3mm long and oval-shaped. They will feed on lupin and canola as well as some other pulse crops. They are mainly found on the underside of plant leaves and will be sparsely distributed throughout a crop. As a bonus, they can spread the Cucumber Mosaic Virus and Bean Yellow Mosaic Virus in lupins, as well as the Beet Western Yellows Virus in canola. They are difficult to control due to their resistance to several chemical groups.
6. Cowpea Aphid
Cowpea aphids are shiny black insects and grow up to 2mm long. They will form dense colonies on the growing points of a single plant before moving onto other surrounding plants. They are found widespread in legume crops commonly in patches of heavy infestations. They feed by removing sap, which deforms leaves, growing points, and will stunt plants. Along with the green peach aphid, cowpea aphids can be a vector for many plant diseases. Monitoring of vulnerable crops should begin at bud formation until late flowering.
7. Pea Weevil
The pea weevil is brownish and flecked with white, grey, and black patches, and will grow up to 5mm long. It is not a true ‘weevil’ as it lacks the typical weevil snout. During spring the weevil flies to the nearest pea crop when temperatures warm to the ’20s and will lay its eggs on green pods. When the eggs hatch, the larvae bore into the pods and feed on the seed, where they complete development before emerging as adults later in spring. The damage they cause to the seeds can cause downgrading as well as rejection. Monitor with a sweep net on calm days. Count the number of weevils per 25 sweeps at 5 -10 sites in the crop. A well-timed spray is recommended if the average densities exceed 2 or more weevils per 25 sweeps.
8. Etiella (Lucerne Seed Web Moth)
The Etiella moth is around 10-15mm long and a greyish-brown colour. They have a tan coloured line that runs across the forewings and a white stripe that runs the full length along the outer edge of the forewings. When disturbed, the adults can be seen making short flights and landing on the underside of foliage. You’ll mainly find them in lentil and Lucerne crops. However, they can also infiltrate peas, lupins, vetch, medic, and clovers. Their larvae cause damage when they hatch and bore into seedpods for feed. Then, as they develop, they feed on the seeds inside. They have the ability to web seedpods together to continue their feeding regime and will cause seed damage and yield losses, as well as downgrading of loads. Thankfully, we can use a degree-day model produced by SARDI to help identify the predicted onset of moth flights. This also alerts us of when critical crop monitoring is by sweeping. The threshold for lentils is 2 or more adult moths per 20 sweeps, averaged across a minimum of three lots of sweeps.
If you have any questions about these pests or others, economic thresholds, or IPM strategies, get in contact with our agronomist team today.
For more info on identifying pests, visit: www.cesaraustralia.com