Monitoring emerging crops for insect pests
As crops begin to emerge, along with recent rainfall and changing seasonal conditions, it is likely to trigger a burst of activity from a range of insect pests. With emerging crops being the most susceptible to damage, it is vital to regularly check for pests to ensure your crops get a healthy start. To assist with monitoring, the Smart Agro has put together a list of common insect pests to be on the lookout for.
Redlegged earth mite
Egg hatchings of the redlegged earth mite have occurred recently with the onset of cooler conditions and rainfall across various localised southern cropping regions.
Redlegged earth mite (Halotyudeus destructor, RLEM) activity is predominantly subject to localised environmental conditions. This pest survives between winter-cropping seasons as over-summering eggs, which will only hatch under specific conditions in autumn.
Generally, the process of egg development and autumn hatching requires at least 5mm of rainfall accumulated over five consecutive days or less, followed by 10 days of average daily temperatures remaining below 16°C, which we’ve recently encountered in most areas across the southern cropping region.
Conveniently for the RLEM, this coincides with the establishment of their host crops, which means monitoring early emerging seedling crops is critical to avoid losses and economic damage. This can be further exacerbated in dry conditions or when plants are stressed e.g. herbicide damage, cold conditions, sown too deep, etc.
A warm and dry April has delayed hatchings of RLEM across most of south eastern-Australia, however with cooler conditions and some rain arriving, peak egg hatchings are likely and in some environments, have already occurred.
The relationship between moisture and temperature requirements for RLEM hatchings has been modelled to provide guidance on egg hatch trends. The GRDC funded research business partner, Cesar Pty Ltd have used this prediction model to estimate the date of peak egg hatching across Victoria in Ballarat, Hamilton, and Hopetoun, and Wagga Wagga and Albury in southern NSW.
Some rainfall and reduced daily temperatures in early May fulfilled the requirements for all these locations, with peak egg hatch expected to have occurred on May 14, 2018. Potentially damaging infestations will likely appear within approximately 7-14 days from this date. Since hatchings are likely to have already occurred, ensure you closely monitor emerging crops for RLEM and be vigilant in your monitoring techniques.
With insecticide resistance in the RLEM now present in the southern cropping region, insecticide stewardship should be high on the priority list. That means not using the same insecticide mode of action groups across successive spray windows (on multiple generations of mites) and reserving co-formulations (or chemical mixtures) for situations where damaging levels of pests are present, and a single active ingredient is unlikely to provide adequate control.
Identifying aphids in canola
Distinguishing aphid species in canola is not always that obvious! Here are some features to look for when identifying these aphids in the field:
Green peach aphid (myzus persicae, GPA), cabbage aphid (brevicoryne brassicae), and turnip aphid (lipaphis pseudobrassicae), are the three main insects that feed on and transmit viruses (like turnip mosaic virus) in canola in south-eastern Australia. It’s important to distinguish between these species as unlike cabbage and turnip aphid, GPA has evolved resistance to major chemical groups creating a truly unique management strategy.
It’s not uncommon for multiple species to be present in the one canola crop. GPA can be difficult to find and go under the radar amongst turnip aphid or cabbage aphid which can lead to costly control failures because of incorrect insecticide selection due to current resistance to Synthetic Pyrethroids groups. For example, Pirimicarb will control cabbage aphid and turnip aphid but will not kill GPA, even at high rates. Colonisation habits and appearance are two areas which can assist with correct identification of these canola pests.
Turnip and cabbage aphid are known to colonise upper leaves and form clusters on canola flowering spikes later in the spring months of more advanced crops. However, GPA prefer to inhabit the lower underlying leaves and are more sparsely distributed. It’s extremely important to inspect the underside of the early cabbaging canola leaves to check for GPA distribution and remember to control common summer weeds such as wild radish, wild turnip, marshmallow, nightshade species, fleabane, afghan melons and stinkweed/stinkwort which act as a carryover summer bridge to host GPA survival.
Cabbage aphid colonies have a characteristic blue-grey appearance and are often covered in a whitish powder. Turnip aphid colonies are typically olive to greyish-green and covered with a white wax, although not as obvious as that on the cabbage aphid. Sometimes dark bars are visible on the abdomen of the turnip aphid and cabbage aphid.
Green peach aphid varies in colour from shiny pale yellow-green, green, orange or pink. If viewed closely, GPA has a shimmery appearance, however generally it predominately colonises on the underside of the canola leaf.
The Smart Agro