It is important when checking your crops to not only have a good understanding of how to identify insect pests, but also how to identify the beneficial insects that are present in the crop working hard on your behalf.
In addition an understanding is needed of monitoring techniques and economic thresholds to make an informed decision on whether to control an insect pest outbreak.
Many of the traditional insecticides used are extremely toxic to both the insect pest but also the good beneficial insects.
So make sure you are targeting the insect pest only with your product selection so that beneficial insects are maintained to help with subsequent pest outbreaks.
When you are deciding whether or not to spray for insect pests, it is important to take into account the number of insect pests, the crops ability to tolerate the pest, economic thresholds and the number of predators present. If in doubt talk to your agronomist.
There are many great resources available to assist you in identifying pest and beneficial insects in field crops:
Download the factsheet of pesticides registered in NSW for the control of insect pests of cucumber PDF, 415.06 KB.
For more information on the chemical control options download a copy of the NSW DPI Insect & Mite Control in Field Crops Guide
Common insect pests in NSW
Large populations of mites can breed on green bridges. Mites species such as the clover mite (Bryobia spp.) and balaustium mite (Balaustium medicagoense) are capable of maintaining populations throughout the year when habitat is available. Populations can skyrocket if green bridges of clover are nearby and there is a warm start to the growing season. In contrast blue oat mites (BOM) (Penthaleus spp.) and red legged earth mites (RLEM) (Halotydeus destructor) require 5 consecutive days of temperatures less than 20°C to hatch.
RLEM is commonly associated with capeweed so monitor the emergence of this weed as temperatures cool and early season rain appears. Mites can also be vectors of viruses, such as the wheat curl mite (Aceria tosichella, WCM) which is the primary source of the Wheat Streak Mosaic Virus (WSMV). WCM breeds very quickly between 24°C and 27°C, making early sown crops an ideal target.
Mites are often found on volunteer cereals, broadleaf and grass weeds. WCM, in particular, is known to be carried by barley grass, great brome, annual ryegrass, couch grass, liverseed grass, pigeon grass and rats tail fescue. Having an available green bridge to survive on will greatly increase the likelihood of a large population getting a head start to then be able to transfer to a nearby crop.
Aphids pose a threat to cereals, pulses, canola and pastures. Damage can occur when large populations feed on plants or when they act as vectors for various plant viruses. For example, oat aphids (Rhopalosiphum padi), corn aphids ( (Rhopalosiphum maidis) and rose grain aphids (Metopolophium dirhodum) are known vectors of Barley Yellow Dwarf Virus (BYDV). The Russian Wheat Aphid (Diuraphis noxia, RWA) can also be limited if green bridges are controlled effectively.
As part of a GRDC investment, RWA populations were monitored on various grass species in November 2018 to see which species are preferred as a habitat over summer. Large numbers were identified in barley grass, brome grasses and volunteer wheat and barley. Monitoring during the warmer months in January and February noticed that RWA populations significantly decreased as these preferred hosts became rarer.
Broadleaf weeds need to also be managed as they are a green bridge for significant pests like the Green Peach Aphid (Myzus persicae, GPA). This insect is known to be found in turnip weed, marshmallow, Lincoln weed and other cruciferous plants. Over the summer period aphids can also survive in perennial grass such as perennial ryegrass, kikuyu, couch and African love grass. It may also be required to control perennial grasses which are near to or surrounding paddocks where cereals will be sown.
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