Protecting early pods is likely to be the key to maximising returns in this year’s large desi chickpea crop. Growers are encouraged to talk to their supplies to ensure they have product on hand when it’s required. Photo credit: G Cumming
Preserve chickpea value with effective grub control
by Cindy Benjamin
Pulse Australia estimates that over half a million hectares have been sown to desi chickpea this year in the northern growing region of Queensland and northern NSW. This is the largest area sown to chickpea in the industry’s history in Australia, double the 5-year average, and brings with it some potential logistical difficulties.
National manager, Gordon Cumming says the key to maximising yields this year will be to retain as many early pods as possible through effective insect and disease management.
“The outlook is for a dry finish, so we expect a shorter effective podding window,” he says. “Hot, dry conditions in spring could potentially limit the number of pods produced later in the season making any losses of early pods to disease or pest damage even more damaging overall.”
With such a large chickpea planting this year, there is considerable supply pressure on Altacor and Steward, the preferred insecticides for grub control.
“Although it is a little early in the season to be controlling insect pests I strongly encourage growers to be talking to their suppliers about likely insecticide needs,” says Mr Cumming. “Supply could be quite tight and it is important that growers are able to respond quickly once insect pressure reaches economic thresholds.”
Dr Melina Miles, Department of Agriculture and Fisheries (DAF) principal entomologist, has led the department’s GRDC-funded research into the best management practices for helicoverpa grub control in chickpea.
“The overall aim of grub control is to preserve yield and grain quality,” says Dr Miles. “Current best practice centres on the control of larvae that are less than 10 mm long and are not yet burrowing into pods.”
Once larvae have burrowed into pods they may be shielded from insecticides and damage to seed has already occurred. Any damage to pods also increases the risk of weathering of intact seeds in the event of rain.
The DAF entomology team have developed dynamic economic thresholds for growers and advisors to use when making management decisions regarding helicoverpa in chickpea. This dynamic, online calculator accounts for variables such as row spacing, costs of control and crop value takes away the need to remember formula or do complex calculations in the field.
“The calculator is built on sound entomology data and has been thoroughly tested in the field,” says Dr Miles. “It can be used to estimate the potential yield loss and subsequently the economic threshold, taking into account all the relevant variables and information available about the crop.”
“The team’s research has shown that if one helicoverpa larva (per square metre) completes its lifecycle on the chickpea crop, the resultant loss is 2 grams of grain. This relationship is the outcome of an interaction between crop damage caused by the larvae and the compensatory response of the crop,” she says. “The calculator uses this yield loss estimate to predict the grain yield loss, based on the number of helicoverpa present.”
The calculator uses beatsheet sampling data and adjusts the predicted yield loss that will be caused by the population while taking into account likely larval mortality (30 per cent mortality of small larvae) and stage of crop growth.
The cost of control (product plus application costs) is entered into the calculator, along with the expected value of the crop. The calculator will offer suggestions about whether control is warranted (an economic proposition) based on the current crop stage, susceptibility to damage, and cost:benefit return.
“For example, spraying pesticide while the crop is vegetative is not warranted, regardless of the pest density, because helicoverpa only do economic damage to chickpea pods,” she says. “An exception to this rule may be if a significant number of small to medium larvae were present late in flowering, where control may be warranted to avoid having to attempt control of medium and large larvae during pod set and pod fill.”
From the information entered by the agronomist or grower, the calculator determines the potential loss (cost) of taking no action. Having an idea of what it would cost in lost production if no action was taken makes it possible to determine whether the cost of control is greater or less than the potential loss of yield.
“In the event of more than one generation or infestation of larvae in a podding crop, it may be economic to control the second population even if it is sub-threshold,” says Dr Miles. “This is particularly relevant where the first infestation may have been sub-threshold, for example 0.6 per m2, based on a threshold of 1.3 per m2, and no control was warranted. Control of the second influx may warrant control even if the population density is again sub-threshold, but cumulatively the two infestations exceed threshold.”
“At present the calculator does not accommodate this kind of calculation so agronomists and growers will have to refer to their records on helicoverpa densities in the crop during flowering and podding.”
Rather than being used for each control decision, the calculator is probably most useful for re-calibrating rules of thumb that growers and agronomists use when there are changes in the costs of control or chickpea grain price. This is particularly relevant this year where higher grain prices may have been secured.
The calculator is available on the Beatsheet website and has the capability to be used off-line if necessary. It will work on the newer operating systems on computers, mobile smart phones and tablets.