Check infestation level
Aphid influx Thorough inspection beyond the edge of paddock
THE problem of cereal aphids has popped up again in several areas of our winter cereal crops.
There are generally three main species of aphid that may affect our wheat, barley and oats; the oat aphid, the rose grain aphid and the corn aphid.
Their effect can be twofold in impact with their moisture sucking habits the first problem they create.
In a crop unaffected by moisture deficits, invariably you can live with this facet of their presence.
In other times, particularly in the many drier areas, we now have some very moisture stressed cereal crops and taking the option of spraying aphids in them is getting close to the desperate stakes.
You are betting that cleaning out the aphids will prolong your moisture availability levels for a few more days or weeks until rain arrives.
Of course, for these systemic insecticide options to work reasonably effectively, you are going to need cereal plants that have some sign of growth and development.
If it is Roundup or Gramoxone spray time for your crop, then I would suggest your Dimethoate or Pirimicarb insecticide control strategies were due two weeks earlier.
The second problem that aphids can introduce is the disease angle, which also gives the unthrifty look and yellowing of leaves.
Unfortunately nothing as concrete or as visual as Ascochyta Blight or Botrytis Grey mould that occurs in our chickpeas.
The way aphids affect your cereal crops is by infecting the plant with their sap-sucking mouth parts,
Cleaning out the aphids will prolong your moisture levels for a few more days or weeks until rain arrives
–Paul McIntosh
introducing the diseases like Barley Yellow Dwarf Virus or BYDV.
Now this diseases presence is not an absolute death knell for your crop and over many years of research done by some very reputable characters, the long and animated discussions we have had, suggests you do need a fair number of aphids to consider a foliar spray to be cost-effective and produce a positive economic return.
Unfortunately these moisture-sucking and diseasecarrying small green to blackish insects are not that predictable in the damage stakes.
In southern areas of Australia farmers are electing to apply seed dressings containing insecticides to reduce early aphid numbers and so maximise tiller numbers on their cereal crops.
That facet may be moving north, especially if the year before is a massive aphid problem year where headers are gumming up with the aphid secretion of honey dew.
So what are our thresholds for our cereal crops in Queensland?
The most acknowledged numbers are about 10 to 15 aphids per tiller.
You need to compare this threshold mentioned above, along with a thorough paddock inspection and not just on the edge, where aphid populations invariably start.
This will give you a good start to determine whether a foliar insecticide option is warranted.