Protecting WA crops

Green bridge - diseases and pests

The green bridge will act as host for many different insects and diseases and will result in population build-ups. Growers and consultants are urged to survey weeds and plant volunteers to identify what insects and diseases are present.

Subscribe to the DAFWA PestFax newsletter to receive weekly news updates, risk alerts and management advice throughout the growing season on pests and diseases threatening crops and pastures throughout the grain belt of WA. The first issue for the season will be distributed soon. The PestFax service is an interactive reporting service that also provides a map of reported pests and disease, a PestFax Reporter app and free insect diagnoses. For more information visit the PestFax webpage on the DAFWA website.

Cereal rust and mildew

Barley leaf rust

The presence of volunteer crop hosts can provide opportunity for cereal rusts and mildews to establish infection and provide early season sources of airborne inoculum. Cereal rusts can only survive on living plants so in seasons where volunteer hosts die before new crops are established outbreaks are more sporadic and less intense.

In 2015, it was wet in the northern cropping areas with a green bridge. This was associated with high levels of powdery mildew and leaf rust plus the first significant amount of stripe rust for several years. With significant summer rainfall across most of the grainbelt in 2017, it’s expected that these diseases could again be problematic. The frosts of 2016 could also have implications where there is more spilled grain than usual resulting in more regrowth.

Soil borne pathogens

Fusarium crown rot white heads in barley

Summer rainfall can have significant impact on the level of soilborne pathogens (root lesion nematodes, rhizoctonia and crown rot) in a paddock, with the common theme that control of green bridge volunteer hosts well before the start of the season providing best management of disease carryover and build-up.

Insects, slugs and snails

Aphids (and some mites) need a living host to survive and when present in very high numbers they can inflict considerable feeding damage if they are not effectively managed and disperse onto emerging crops.

Insects, primarily aphids in WA crops, also transmit viruses to crop plants. Grass weeds and cereal volunteers provide a reservoir for barley yellow dwarf virus (BYDV) and wheat steak mosaic virus (WSMV) (vectored by the wheat curl mite), while wild radish, other broadleaf weeds and volunteer canola host beet western yellows virus (BWYV) and turnip mosaic virus (TuMV).

This year's cool, wet conditions and an abundance of stubble, weeds and volunteer crop growth have provided ideal conditions for slugs. They are actively moving and feeding right now.

Reticulated and black keeled slug

It is recommended to monitor regularly, ideally before seeding as there are more control options available, including burning, grazing and tillage. Before seeding is a good time to put out slug traps, for example hessian bags or carpet squares. This applies not only on the heavy country but also on the lighter soil types especially in long term no till paddocks. If one or more slugs are found under the hessian sacks they can damage emerging canola crops leading to re-seeding becoming necessary.

Other insect pests to be on the lookout for in a green bridge include pest mites such as balaustium mite and bryobia (clover) mite and diamond back moth which may all impact on this year’s crop.

Disease and insect surveys by DAFWA

Volunteer cereal plants with wheat curl mites present in the heads

DAFWA is currently undertaking (or will be undertaking later this year) a number of surveys to provide information on a range of pests.

• DAFWA’s new Regional Research Agronomy team (funding supported by GRDC and Royalties for Regions) is currently conducting surveys of existing green bridge vegetation across the grainbelt and are sending samples to be tested for diseases, aphid viruses and soil borne pathogens.
• DAFWA’s virology team is also currently conducting surveillance work by sampling over-summering hosts and trapping of migrant aphids. This work (funded by Royalties for Regions) is being used to validate new loop-mediated isothermal amplification (LAMP) technology that allows rapid on-farm diagnosis of plant pathogens. DAFWA Research Officer Benjamin Congdon who is working in the virology project says they are developing the protocol using the turnip yellows virus/canola pathosystem. This project and a similar activity at the Centre for Crop and Disease Management (CCDM) at Curtin University are exploring how this technology could be extended to a range of crop pathogens. Detecting pathogens with the user-friendly LAMP machine can be a relatively simple and rapid procedure meaning, once developed, an agronomist could have a diagnosis for the grower in a single meeting in under an hour.
• DAFWA plant virologist Roger Jones advises that a damaging new resistance-breaking strain of TuMV is spreading in canola crops in eastern Australian and the WA oilseeds industry needs to be on the lookout for it because it overcomes all four TuMV resistance genes that currently suppress spread of this virus in Australian canola cultivars. Wild radish and volunteer canola are reservoirs of this virus from which many aphid species can spread it to canola crops. The team is conducting surveillance to find whether this new strain of TuMV has reached WA yet from the eastern states. It is mostly symptomless in wild radish, but this virus can cause yield losses up to 80% in canola.
• DAFWA will also conduct an insecticide resistance testing survey for red-legged earth mites (RLEM) this year through the GRDC supported project Insecticide resistance management in RLEM and chemical sensitivities of other grain pests, given the rise in resistant populations discovered in WA over the past decade.
• DAFWA is part of a national GRDC supported project Biology and management of snails and slugs in grain crops (DAS00160), looking to model what the micro climatic conditions are that initiate slug and snail movement and egg laying, so baits can be timed to kill the pest before crops are damaged. Remote cameras and weather stations have been set up in trials at Mount Barker, Gairdner and Esperance.

More information

• Control of green bridge
• Summer weeds
• MyCrop

You can also search the DAFWA website for more information on individual weeds pests and diseases, or use the MyCrop tool to help with diagnostics in your paddock.