Bugs on the rise in crops
WELL, many chickpeas are out of the ground and, apart from early ascochyta disease issues, we have varied populations of helicoverpa larvae scattered around the region.
In other words – grubs – and to some of us, there are concerning numbers eating their way through our early foliage and chopping off branches and growing tips in our chickpea crops.
From various paddock reports given to me, people have counted from five to more than 20 grubs per square metre of different sizes in this early vegetative stage.
Now in a podding situation, you could not get the insecticide out quick enough to protect your pods and seed development from these numbers.
So what decisions or considerations need to be thought about in this early vegetative stage where traditionally we have not applied wholesale insecticides to this stage of chickpea crop?
However, you should never say never, because mother nature will prove us wrong for sure.
So counting helicoverpa eggs is challenging and, apart from research practices, it is not reliable nor consistent enough for a commercial paddock.
Even very small larvae have a high mortality and also are very difficult to count, no matter what the size of chickpea bush.
So the main result from counting very smalls is possible potential in a couple
of weeks’ time in our cool conditions.
So we advance to the next few levels of sizing of these helicoverpa grubs.
Smalls, mediums and larges and they can consume plenty of green material as they get bigger.
Even smalls can have a fair percentage of mortalities and are less of a decision hook.
So let us look at mediums and larges for biggest potential economic damage.
The big question you need to ask yourselves is, can the
chickpea plant develop more growth than the grubs are consuming and still have a reasonable size dry matter by a warming springtime to achieve a yield. Also, could there be any plant development stage delays from this insect defoliation.
So moisture and nutrition, plus any soil constraints, will all come into this equation and it really is a self-judgment in the paddock after your complete scouting.
Apologies that there are no easy answers here. Even
predicting future emerging moths will be difficult.
We know that day degrees is a growth curve for chickpeas, so later plantings in cool conditions may need more of a spray consideration than an early planting date in warmer times. These warmer times with higher day degrees really get the plant going.
Notice I have not said it is never just an automatic spray or a no-spray decision at this mid-winter stage, based on a threshold.
Traditionally we have mostly not sprayed in June or July on chickpeas in Queensland for helicoverpa grubs. However after huge moth and larvae numbers in spring of 2016, is it any wonder we are seeing this early pressure in our healthy and attractive chickpea crops?
So the considerations are plenty, and then what product do you spray with?
That is another Rural Weekly column. It is safe to say, take the blinkers off and protect our latest insecticide chemistry from overuse.