Rutherglen bug in canola - IPM Guidelines For Grains

Rutherglen bug (Nysius vinitor) is best known as a seed-feeding pest, attacking grain as it develops and fills. However, in some seasons, large numbers of nymphs and adults can cause damage to establishing winter or summer crops. RGB populations can build up in summer weeds, and move from these into establishing winter crop, feeding on and killing small seedlings. Large numbers of RGB moving out of canola stubble poses a threat to nearby establishing summer crop.

Objectives	Pre-plant – Establishment	Flowering – harvest
Insects and damage RGB adult	Seedlings can be damaged by RGB nymphs in seasons where large numbers of nymphs survive in weeds over summer (mild summer with rainfall to promote weed hosts e.g. wireweed/ common knotgrass). Seedlings can be killed by feeding pressure caused by nymphs moving from weeds on field edges. Seed treatment will not protect seedlings against this extreme pressure. Damage is usually confined to field margins.	RGB adults migrate into fields from local weed hosts, or more distant sources in spring. Infestations can be large and the period of invasion prolonged. Adults and nymphs feed on growing tips, buds, flowers, pods/seed causing flower abortion, reduced pod set and seed development. RGB feeding directly on developing seed affects oil quantity/quality and seed viability. RGB can persist into windrows, and at harvest cause problems with seed flow through harvesters, and by raising the moisture content of the grain to above acceptable standard.
Monitor and record	Check the crop from flowering to harvest at weekly intervals. Inspect flower heads visually or shake heads into a bucket. Examine 20 heads at 5-10 locations within the crop. Distribution is typically patchy across the field which means that the more samples taken, the greater the level of confidence in estimating the size of the infestation. In seasons with wet, mild summer and abundant weed growth, check weeds around the paddock that may be hosting RGB. In particular, Polygonum aviculare (Common Knotweed, Wireweed) is known to be a summer host. Capeweed (Arctotheca calendula) is a common autumn-summer host for RGB Record: Number of RGB adults and nymphs in each sample. Average counts from across the paddock to get a field estimate of density. Presence of other pests and beneficials. Crop stage, proximity to maturity.
Natural enemies	The most commonly recorded beneficial attacking RGB are egg parasitoids. Their major impact on RGB is in reducing population size. They may have some impact on populations over summer or during winter, but have little capacity to control infestations in crops; particularly where infestations are driven by large influxes of adults. Little is known about the impact of predators, but spiders may be a predator of RGB.
Cultural control	Control summer-autumn weeds around field edges and in fallows that may host RGB (e.g. common knotweed/wireweed) Invasion of RGB nymphs from weeds in autumn can be slowed by ploughing a deep furrow between the weeds and the crop. At harvest, allow RGB to escape from open bins to reduce numbers in deliveries. RGB will not survive in storage, or do any damage to harvested grain.
Provisional thresholds	10 adults or 20 nymphs per raceme at flowering/early podding. Higher numbers can be tolerated if moisture is not limiting.
Pesticides	There are no soft chemical options for the control of RGB. Repeated influxes of migrating adults can make repeat applications necessary. If spraying windrowed canola to control RGB – consider withholding period or chemical restrictions on spraying this late in the season. The application of broad-spectrum insecticides in a strategic and targeted manner (e.g. spot or border spraying rather than whole paddock applications), will help to minimise detrimental effects on natural enemies and maintain their contribution to the management of other species e.g. aphids, DBM, Helicoverpa.
Multi-pest considerations	Control of RGB is highly disruptive to beneficial insects because there are no soft options. Spraying for RGB may have direct impact on Helicoverpa, aphid and DBM populations in the crop; and the beneficials that may contribute to the control of these species.
Communication	Maintain communication with neighbours and local agronomists re influxes of RGB to ensure that these are not overlooked. Industry publications provide up to date regional information about pest activity in crops.