Rutherglen bug damage in mungbeans

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Rutherglen bugs were seen at high densities in many 2017 summer crops.

Ruther­glen bugs were seen at high den­si­ties in many 2017 sum­mer crops.

Although typ­i­cal­ly only in low num­bers in the North­ern Grains region, Ruther­glen bugs (RGB; Nysius vin­i­tor) were observed at very high den­si­ties (e.g. 50 RGB per pod) in many crops last year.

A glasshouse study was con­duct­ed to deter­mine at what plant stage mung­beans were most sus­cep­ti­ble to RGB dam­age, in terms of both yield and seed qual­i­ty. To do this, we caged dif­fer­ent den­si­ties of RGBs on plants of dif­fer­ent growth and repro­duc­tive stages (or indi­vid­ual pods at the late pod­ding stage) for one week (the approx­i­mate time the plants were in that stage).

RGB-closeup

Ruther­glen bugs are small insects (~4 mm), that are brown/grey in appear­ance with clear wings.

Due to the high tem­per­a­tures expe­ri­enced last sum­mer, plant growth and yield were more vari­able than antic­i­pat­ed. How­ev­er, results from this study sug­gest:

  • Short expo­sure of plants to RGB dur­ing veg­e­ta­tive or ear­ly repro­duc­tive stages—even at high densities—did not reduce seed weight, num­ber of filled seeds, or number/proportion of filled pods.
  • While there is some evi­dence that RGB at flow­er­ing can cause abor­tion of all flow­ers, plants com­pen­sat­ed with­in two weeks of RGB removal with no sub­se­quent impact on yield or seed qual­i­ty.
  • Seed qual­i­ty was some­what reduced in small (~5 cm) pods at high RGB den­si­ties (50 and 100 RGB per plant).
  • When green pods with con­stric­tions were infest­ed, seed weight was sig­nif­i­cant­ly less and the major­i­ty of seeds were classed as defec­tive by AMA stan­dards (due to wrin­kling and vis­i­ble sting marks), com­pared to unin­fest­ed pods.
RGBtrial-cages

Whole plants were caged (secured at bot­tom dur­ing test­ing) for the veg­e­ta­tive and ear­ly repro­duc­tive stages. For late pod­ding, Ruther­glen bugs were caged on indi­vid­ual pods.

A more tar­get­ed tri­al will be con­duct­ed this year (hope­ful­ly with bet­ter weath­er con­di­tions) look­ing at the repro­duc­tive stages only, as this was when most dam­age to yield and/or seed qual­i­ty occurred.

  • In the mean­time, man­age­ment options for RGB include:
  • Keep crops and mar­gins weed free, par­tic­u­lar­ly from flea­bane
  • Mon­i­tor crops reg­u­lar­ly for RGB infes­ta­tion
  • If chem­i­cal con­trol is required, organophos­phates (e.g. half rate dimethoate with 0.5% v:v salt) have been shown to give some resid­ual activ­i­ty (up to 7 days), where­as oth­er pes­ti­cides act as a knock­down only and rein­fes­ta­tion can occur with­in hours.

For more infor­ma­tion, con­tact Liz Williams on (07) 4182 1818 or 0476 850 415.