Thrip damage to early summer crops

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Emerg­ing and veg­e­ta­tive sum­mer crops in close prox­im­i­ty to unhar­vest­ed win­ter crop are at risk of thrip dam­age, but the dam­age is large­ly cos­met­ic and rarely war­rants treat­ing.

Thrips breed up in win­ter cere­als, and par­tic­u­lar­ly after rain, will move out of the win­ter crops in huge num­bers. Most of you will be famil­iar with the joys of thrips bit­ing you, and swarm­ing around white vehi­cles and shirts as you check crops at this time of year.

Whilst thrip dam­age can look dra­mat­ic, it rarely results in any last­ing impact on the crop. Typ­i­cal­ly, a crop that is active­ly grow­ing (ade­quate water, warm weath­er, not water­logged) will rapid­ly out­grow thrip dam­age. Seedlings that are grow­ing more slow­ly because of dry con­di­tions, water­log­ging or dis­ease will accu­mu­late more thrip dam­age, par­tic­u­lar­ly on old­er leaves and look unthrifty.

Key issues to consider in relation to thrip infestations in young summer crops are:

  1. Spray­ing to con­trol thrips will kill thrip, but will not pre­vent rapid rein­fes­ta­tion
    • If you have applied a treat­ment, and are see­ing thrips again soon after, it more like­ly to be rein­fes­ta­tion than sur­vival of insec­ti­cide resis­tant west­ern flower thrip (Franklinel­la occi­den­tal­is).
    • Thrips tabaci (tobac­co thrip) and F. occi­den­tal­is are usu­al­ly the most abun­dant thrip species at this time of year.
    • Thrips will move from win­ter cere­als and weeds into the sum­mer crops in large num­bers and poten­tial­ly over sev­er­al weeks.
  2. There are a num­ber of preda­tors such as pirate bug that feed on thrips, and these will be killed by any treat­ments applied to try and con­trol thrip
  3. Insec­ti­cide seed dress­ings will kill thrips that feed on the plants, but because the thrips must feed to acquire a dose of insec­ti­cide, there will still be plant dam­age.
    • The sys­temic insec­ti­cide will pre­vent thrips estab­lish­ing in the sum­mer crop (lay­ing eggs and pro­duc­ing young).
  4. Thrips are use­ful preda­tors in areas prone to spi­der mites

Thrips typ­i­cal­ly infest the under­sides of leaves, pierc­ing the leaf cells and suck­ing up the cell con­tents. As air enters the cells, they turn sil­very. Some crops will also exhib­it a bronz­ing in response to thrip feed­ing, and the leaf mar­gins will also brown.

The fol­low­ing images show typ­i­cal thrip dam­age symp­toms to sun­flower, maize and cot­ton.

For more infor­ma­tion on thrip dam­age to cot­ton see the Cot­ton Pest and Ben­e­fi­cial Guide

Population of thrips on the underside of a sunflower leaf.

Pop­u­la­tion of thrips on the under­side of a sun­flower leaf.

IMG_1370_sunflower bronzing_thrip

Bronz­ing on the under­side of sun­flower leaf, caused by thrips feed­ing.

IMG_1391-maize seedling_thrip damage

Thrip dam­age to maize plant. Note the dam­age is cumu­la­tive, and there­fore worse on the old­er leaves where the thrip have fed for longer.

IMG_1388_maize thrip damage2

Close-up of thrip dam­age to the under­side of a maize leaf.

 

 

 

 

Thrip damage to seedling cotton. Typical signs are cupping of leaves.

Thrip dam­age to seedling cot­ton. Typ­i­cal signs are cup­ping of leaves.

 

 

 

 

 

 

 

 

 

For more infor­ma­tion on thrip dam­age to cot­ton see the Cot­ton Pest and Ben­e­fi­cial Guide