35 IREC Farmers' Newsletter No. 199 — Autumn 2018 Damage to crops Aphids are usually a problem for crop plants as they suck sap from leaves and can be a vector for transmitting viral diseases. Russian wheat aphid, however, has another feature that leads to excessive damage in winter cereals — its saliva is toxic and causes significant damage to the plant. Attack by this aphid causes characteristic streaking of the leaf, with red, white or yellow streaks, which is readily observed following aphid feeding. It also causes a ‘cupping’ of infested leaves, somewhat protecting it from predators and insecticide sprays. The characteristic ‘colour streaking’ that Russian wheat aphid produces on winter cereals was not observed on rice crops in the region. Leaves of heavily infested seedlings tended to have damage that more closely resembled typical sucking insect damage, not unlike the symptoms of red-legged earth mites on winter cereals. Most rice crops where aphids were observed were not overly affected; but there are some notable exceptions. Crops that experienced some other significant stress, such as herbicide damage (usually clomazone), were more prone to damage by the aphids. Often aphid populations in these crops were excessive (more than 10 per small rice seedling) and the plants did not appear to be able to withstand the sucking pressure. Several crops were sprayed with an insecticide already registered for use in rice and known to control the aphids. The crops recovered relatively quickly once the aphids were controlled. Overseas, Russian wheat aphid is a serious pest of cereal crops, especially wheat and barley, but there is almost no record of it infesting rice. It has been observed in the rice-growing Gulf States of the USA for several decades but there are no public reports of it causing economic damage to rice crops. Where did they come from? The spring infestation of Russian wheat aphid was very widespread. Probably every drill-sown crop in the Murray Valley (and possibly the Murrumbidgee Valley) had Russian wheat aphid present. It was also amazing how quickly the aphids found the rice crops. They were observed on seedlings within a week of emergence. Russian wheat aphid was detected in the Murray Valley last winter but not in big numbers, and only a few winter crops were actually treated. The widespread and rapid infestation this spring implies that the aphids blew into the district, probably from infestations further to the west. As conditions dried off over winter and early spring, winged aphids became airborne and were blown in our direction. Whether this will be an annual occurrence is as yet unknown. Keep on the lookout Growers are encouraged to remain on the lookout for Russian wheat aphid into the winter cropping season. It is expected that weeds in particular, and volunteer cereals, may host the pest over summer, therefore paddock preparation for winter cereals should remove potential host plants (the green bridge) for a month before sowing. While Russian wheat aphid is a relatively new pest of winter cereals in Australia, the population build-up in the NSW irrigation districts last spring was both surprising and alarming. It puts winter cereal growers ‘on notice’ to take precautions against the pest this autumn. Growers should discuss the benefits of using a systemic insecticide treatment with their crop protection agronomist. They should also familiarise themselves with the symptoms of Russian wheat aphid on wheat and barley seedlings, and regularly monitor crops for the aphid. Further information John Fowler T: 03 5881 9933 M: 0427 079 138 E: [email protected] W: www.murray.lls.nsw.gov.au Further reading Pest description and management Russian wheat aphid (NSW DPI Primefact 1489) Tips & Tactics: Russian Wheat Aphid (GRDC) Russian Wheat Aphid: Tactics for Future Control (GRDC) Green bridge management a must for RWA control (GroundCover GRDC) Pest status Russian wheat aphid - recent pest arrival (NSW DPI) Russian wheat aphid – national priority plant pest (Department of Agriculture and Water Resources) Russian wheat aphid - pest information (Plant Health Australia)