Keep a lookout for phytoplasma in mungbeans and other summer legumes

Common brown leaf hopper, Orosius orientalis

Com­mon brown leaf hop­per (3 mm). This is the most like­ly vec­tor and has been wide­ly observed in sum­mer and win­ter puls­es infect­ed with phy­to­plas­ma. Note the dis­tinc­tive dark retic­u­lat­ed pat­terns on the wings and body.

Last sum­mer saw unprece­dent­ed lev­els of phy­to­plas­ma in sum­mer pulses/legumes (includ­ing chick­peas, mung­beans and pigeon peas) in all crop­ping regions in east­ern and north­ern Aus­tralia from the Ord Irri­ga­tion area (WA), Burdekin/Atherton Table­lands (NQ), to cen­tral NSW. The most like­ly insect vec­tor is the brown leafhop­per Oro­sius ori­en­tal­is, which has been detect­ed in recent (2017) spring crops. While plant­i­ngs of spring mung­beans have been lim­it­ed by dry weath­er in many regions, phy­to­plas­ma has been observed in spring 2017 Bur­dekin crops, but at low­er lev­els than in the spring of 2016.  Phy­to­plas­ma has also been observed in most­ly low lev­els in many chick­pea crops in Queens­land and NSW.

phytoplasma-earlyinfection

Ear­ly infec­tion show­ing mass­es of tiny leaves. Pho­to by Kathi Her­tel (NSW DPI)

Phy­to­plas­mas are restrict­ed to the plant host’s phloem tis­sue and are trans­mit­ted by phloem-feed­ing insect vec­tors. Oro­sius sp. leafhop­pers have been doc­u­ment­ed as trans­mit­ting phy­to­plas­ma in Aus­tralia and over­seas, and feed on the plant’s phloem tis­sue,  In con­trast, oth­er bugs such as the green veg­etable jas­sid (Aus­troas­ca viridi­grisea) and Ruther­glen bugs (Nysius vin­i­tor) are not phloem feed­ers and are there­fore most unlike­ly to have been respon­si­ble for the cur­rent out­breaks.  Indeed, major pre­vi­ous out­breaks of veg­etable jas­sids and Ruther­glen bug have not coin­cid­ed with phy­to­plas­ma out­breaks of the mag­ni­tude expe­ri­enced in recent years.

Last sum­mer, ear­ly out­breaks in pre-flow­er­ing mung­beans were char­ac­terised by ‘lit­tle leaf’ symp­toms, i.e. mass­es of under­sized leaves in dense clumps. In flow­er­ing crops, symp­toms exhib­it­ed include phyl­lody (where flow­ers devel­op abnor­mal­ly into leafy struc­tures) and lit­tle pod (where pods are deformed and remain small and green). Lat­er infec­tions appear to be asso­ci­at­ed with puffy pod symp­toms in mung­beans. Because symp­toms can take at least 2–3 weeks post-infec­tion by leafhop­pers to man­i­fest them­selves, growers/consultants are asked to reg­u­lar­ly sam­ple crops for leafhop­per and oth­er suck­ing bug activ­i­ty.

At this stage, the eas­i­est way to sam­ple is with a sweep net. Take 20 sweeps in 20 paces at walk­ing speed, and invert the catch into a large plas­tic or glass jar for easy obser­va­tion. Take a num­ber of such sam­ples across the pad­dock as leafhop­per num­bers can vary great­ly. Keep the sam­ples to send away for iden­ti­fi­ca­tion if phy­to­plas­ma is detect­ed lat­er in the field.

Sam­pling with a beat sheet is not rec­om­mend­ed, as the leafhop­pers are small (3 mm) and often fly off before being count­ed. Liz Williams will be eval­u­at­ing leafhop­per mon­i­tor­ing meth­ods this sum­mer so watch this space.

Seed trans­mis­sion is high­ly unlike­ly to be respon­si­ble for last season’s out­breaks, as the inci­dence of phy­to­plas­ma in pigeon pea crops in dif­fer­ent pad­docks (plant­ed with the same seed) var­ied from very low to extreme­ly high.

Please report any out­breaks to ento­mol­o­gists Hugh Brier and Liz Williams at DAF Kingaroy, and to plant pathol­o­gist Mur­ray Shar­man at DAF Bris­bane (con­tact details below).

Leafhop­per spec­i­mens should be sent to Hugh and Liz in small con­tain­ers with sam­pling type (sweep net, etc.), date, crop (type and stage) and loca­tion details (includ­ing GPS coor­di­nates). Note also the length of time between the sam­ple and phy­to­plas­ma symp­toms appear­ing (if applic­a­ble)
Infect­ed plant sam­ples should be sent to Mur­ray Shar­man for mol­e­c­u­lar (PCR) test­ing to deter­mine the strain of phy­to­plas­ma in affect­ed crops, dis­tri­b­u­tion and host range. Send plant sam­ples (just the affect­ed parts) in a sealed plas­tic bag with paper tow­el inside to soak up con­den­sa­tion. Keep cool, but not frozen, and dis­patch in an insu­lat­ed con­tain­er (a card­board box with shred­ded paper insu­la­tion will do) via an express couri­er. Please email or call Mur­ray to let him know the sam­ples are com­ing, so that arrange­ments can be made to keep them cool on arrival.

Liz Williams (0476 850 415; [email protected]) or
Hugh Brier (0428 188 069; [email protected])
QDAF
214 Kingaroy-Coo­yar Road
Kingaroy QLD 4610

Mur­ray Shar­man
QDAF, 2C-West
Eco­Sciences Precinct
Base­ment 3 load­ing dock (off Joe Bak­er St)
Dut­ton Park QLD 4102
Ph: 07 3255 4339
Mob: 0405 564 428 or 0467 721 400
[email protected]

Article by: Hugh Brier1, Liz Williams1 and Murray Sharman2, Department of Agriculture and Fisheries
1 J. Bjelke-Petersen Research Station, Kingaroy Q,  2 Eco Sciences Precinct, Dutton Park Q.