Rutherglen bug in sorghum and sunflower

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 pose a threat to nearby establishing summer crops.

In addition to local weed sources, migratory populations can move from inland Australia to eastern cropping regions, in some cases travelling 200-300 km in a single night.

  Pre-plant & Seedling Vegetative Flowering/Ripening
Insects and damage

RGB nymph

RGB nymph

Sorghum: Consider open-headed type hybrids to deter RGB.

RGB moves into crops at margins from roadsides & adjacent weeds.

Summer crops planted into canola stubble may be at risk of damage from nymphs.

Sunflower: Feeding during budding can cause the head to wilt, become malformed or die. Sunflower:

  • RGB lay eggs between individual flowers – emerging nymphs feed on developing seed
  • Reduce yield, oil content and oil quality

Sorghum:

  • Grain with dark spots and reddening (feeding wounds)
  • Affected grain may be small, shrivelled and does not continue to fill beyond the point it was damaged.
  • Damaged seed is subject to fungal and bacterial infection through feeding wounds, particularly in wet seasons.
Monitoring Monitor from flowering to harvest at weekly intervals. Distribution is typically patchy with some heads having extremely high numbers and others with none. More samples provide a greater level of confidence of overall infestations

Sunflower:

  • Monitor from budding to harvest at least once per week. Inspect flower heads visually, or shake the head into a bucket or zip-lock bag.
  • At budding RGB congregate on stems/buds.
  • Examine 20 heads at 5-10 locations within the crop

Sorghum:

  • Start monitoring at early flowering
  • Shake heads into a bucket or ziplock bag.
  • Sample 1m of row a number of times across the field.

RGB can start to build up at any stage of crop maturity and impact on seed set during flowering and early seed development.

Beneficials
  • Egg parasitoids are the most commonly recorded. Their potential contribution to population control will be limited in seasons when there are large influxes of adults.
  • Predation has rarely been recorded, but spiders may play a role.
  • To improve the abundance and diversity of beneficial insects – consider native vegetation or farmscaping as a part of a pest management strategy.
Cultural control
  • Control weeds around crop edges before RGB move off them into crops as the weeds dry off.
  • Ploughing a deep furrow around the crop can preventing wingless nymphs from walking into crops from weeds.
Store grain with live RGB for a period to kill insects or allow them to escape (open bins).
Thresholds  Sunflower (adults/plant)

  • Spring sown at budding: 10-15
  • Spring sown at seed fill: 20-25
  • Autumn crop at budding: 20-25
  • Autumn crop at seed fill: 50
  • Confectionary market: 5 adults/plant throughout growing season

Sorghum

  • 20-25 bugs/head at flowering and milky dough stage
  • 30-50 bugs/head during the soft dough stage
  • Research shows no impact on yield/quality once the crop is in ‘hard dough’ stage.
Pesticides Repeated influxes of migrating adults can make repeat applications necessary. There are no soft chemical options for the control of RGB.

  • Sorghum: Control RGB when above threshold between flowering and soft dough stages. Later infestations (result of breeding) that typically build up prior to harvest do not contribute to yield loss and do not warrant control unless there are concerns about contamination at harvest.
  • Sunflower: Insecticides are applied at the end of flowering when adults begin to lay eggs. This timing prevents subsequent nymphal populations developing. Treatment must be applied before heads turn down. Spray late afternoon when bees are less active.
Multi-pest considerations
  • There are no soft chemical options for the control of RGB. Insecticides for controlling RGB will kil beneficials that can suppress pests such as helicoverpa, loopers and whitefly.
  • Consider the use of insecticides when other pests are present. These other pest e.g. Helicoverpa armigera may have resistance to chemicals used to control RGB, and exposure of H. armigera to SPs used to control RGB will exert selection pressure for resistance.
Communication Discuss a coordinated approach to the control of weeds and volunteers through an Area Wide strategy. This may also provide early alert for infestations.

Industry publications provide up to date information about regional pest issues.

 

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