Rutherglen bug in canola stubble – potential to damage establishing summer crops.

Canola stems with adult and nymphs clustered on the base after harvest.

Mul­ti­ple stems with adult and nymphs clus­tered on base post har­vest.

Ruther­glen bug (RGB) are best known for the dam­age they can cause in sun­flower and sorghum dur­ing grain­fill, but they can also dam­age and even kill seedlings when present in large num­bers.

In 2012 RGB dam­aged estab­lish­ing spring crops in areas of south­ern and north­ern NSW.

This spring, in some crops there are large num­bers of RGB in the canola stub­ble post-har­vest.

As the canola stalks start to dry out and no longer pro­vide a source of food, the RGB start mov­ing out of the can­la stub­ble and into neigh­bour­ing fields, or onto emerg­ing seedlings plant­ed direct­ly into the stub­ble.

All sum­mer crops are sus­cep­ti­ble to direct feed­ing dam­age from RGB, includ­ing grains (sorghum, soy­beans, sun­flower) as well as cot­ton. Dam­age to seedlings in neigh­bour­ing fields tends to be along the crop mar­gin clos­est to the canola stub­ble.

Symptoms of RGB feeding on a cotton seedling.

Wilt­ing as a result of RGB dam­age to peti­oles of a cot­ton seedling.

Symp­toms of RGB dam­age to canola include wilt­ing, brown­ing of leaves and ter­mi­nals and the death of small seedlings.

Man­ag­ing RGB mov­ing from canola stub­ble

If large num­bers of RGB move into the estab­lish­ing crop, insec­ti­cide seed dress­ings will not pre­vent dam­age to seedlings, as each RGB must feed to get a dose of the insec­ti­cide, and in doing so con­tribute to the plant dam­age.

Some of the tac­tics sug­gest­ed to min­imise crop loss caused by RGB mov­ing from canola stub­ble into neigh­bour­ing crops are:

i) plough a deep fur­row or cul­ti­vate the ground between the sus­cep­ti­ble crop and the canola stub­ble,
ii) apply an insec­ti­cide bare earth bar­ri­er treat­ment
iii) fill chan­nels, tail drains or head ditch­es with water to form a bar­ri­er

Flight­less nymphs are most com­mon­ly move from the stub­ble to the seedling crop, which is why tac­tics that form a bar­ri­er to ground move­ment are effec­tive. The winged adults appear to dis­perse more wide­ly from the stub­ble, rather than mov­ing into near­by crops.

Plant­i­ng into RGB-infest­ed canola stub­ble
Plant­i­ng into canola stub­ble where there are RGB nymphs is high risk as the nymphs can eas­i­ly move from stub­ble to seedlings as they emerge. RGB infes­ta­tions in canola stub­ble is patchy, so dam­age and seedling loss will  occur in patch­es across the field where the RGB den­si­ties are high.

If dam­age to seedling and seedling loss is severe, it may be nec­es­sary to con­trol the RGB by treat­ing the field. High water rates and good cov­er­age will be need­ed to con­trol the nymphs shel­ter­ing on the stub­ble and trash.

Watch a short video on  Ruther­glen bug in canola stub­ble on the Beat­sheet YouTube Chan­nel.