Look out for Russian wheat aphid – ‘sprinter’ is upon us

The first detections of Russian wheat aphid in NSW have surfaced, but will populations flare as winter-spring conditions warm? In any case, monitoring is a must!  

Russian wheat aphid (Source: cesar).

 

Where have they been reported?

Russian wheat aphid (RWA, Diuraphis noxia) has now been confirmed at two locations in NSW; the first near the town of Barham, and a second in a wheat crop in the Erigolia area, both in the Riverina district. The distribution of RWA in Victoria seems to have stabilised over winter, according to Agriculture Victoria’s Public Information Map. The aphid has been found in the Wimmera, Mallee, Northern Country and Central districts, as far east as Werribee. RWA have not been identified in Tasmania or Queensland.

About RWA

Information on RWA can be found in PestFacts south-eastern Issue No. 3. and Issue No. 4, and at the Plant Health Australia website.

Our advice

Activity of RWA is subdued by the cooler and wetter conditions of winter. Nonetheless, Victorian and South Australian field reports suggest that breeding has continued slowly over winter. Population growth will escalate as temperatures warm. The ’sprinter’ period of August and September, when rapid crop growth commences, is expected to be a high-risk period for crops infested with above-threshold RWA populations.

Consistent with the GRDC RWA F.I.T.E. strategy, we recommend:

1. Find RWA through regular Monitoring. 

Finding symptoms of RWA (pale and reddish streaking on leaves, leaf rolling and curling, tillers collapsing sideways, cereal heads being trapped in a hook in the boot) are easier than finding aphids, but can also be challenging. We suggest first looking:

• on crop edges where aphids first invade,

• in areas of crop stress such as on diseased plants, on water challenged crop rises or areas of compacted soil,

• in areas where cereal volunteers germinated in March/April.

Given the aphids ability to reproduce quickly, we recommend regular monitoring.

2. Identify RWA and distinguish from other cereal aphids.

Seek help through an agronomist or entomologist. The use of a hand lens or other magnification tool is critical for this.

The most obvious diagnostic features include the (almost) absence of the usual aphid cornicles or ‘exhaust pipes’, two tail-end projections or caudate, and the long slender, spindle-like appearance of RWA. In NSW, RWA suspected detections must be reported through the Exotic Plant Pest Hotline 1800 084 881, or in Victoria, through the CropSafe program.

3. Apply economic thresholds.

The beginning of the high-risk period for RWA is approaching. From early booting until soft dough, crops will not need a spray unless the current industry threshold for RWA applies: 10% of tillers with RWA symptoms. This threshold, based on international experiences, will need to be tested under Australian conditions.

4. Enact management strategies

• Consider the role of natural enemies in suppressing aphid and caterpillar populations and avoid the prophylactic use of insecticides. Natural enemies including ground beetles, spiders and predatory mites on the soil surface, and crop canopy beneficials including wasp parasitoids, lady beetles, hoverflies, lacewings, predatory bugs and various pathogenic fungi all attack aphids.

• Use registered products and especially those offering a vapour effect: pirimicarb 500 @250g/ha or chlorpyrifos 500 @600ml/ha (registered under an Emergency Use Permit). Pirimicarb, which is relatively soft on natural enemies, is recommended, especially as day temperatures increase.

• Good spray coverage / penetration is essential as many RWA will be ‘sheltering’ in the tight leaf roles. Use a water volume > 80 L/ha up until canopy closure, and 100-120 L/ha thereafter. Include a non-ionic surfactant with mid-size droplets.

• Crops with moderate damage can recover well after spraying.

• Spraying insecticides can kill foraging bees – advise beekeepers or visit BeeAware: beeaware.org.au before spraying. Bees forage over many kilometres of crop and can be tending weeds in cereals.

While the RWA may appear during spring in many previously unreported areas, the risk of the aphid causing serious crop loss in these areas is untested and probably not great. Nonetheless, regular crop monitoring should be a key management strategy.