THE number of native budworm moths making their way into some areas of the Western Australian grainbelt has again increased in the past few weeks.
The higher numbers reported over this period include Southern Cross (423 moths), Dowerin East (129), Wyalkatchem (110), Dalwallinu (104), Mount Walker (104), Muntadgin (102), Dandanning (90), Yandanooka (84), Merredin (50), Bindi Bindi (28), and Maya (26).
Given the quantities of moths encountered in some areas, it is likely that higher numbers of caterpillars will be found in crops in the coming weeks.
Department of Primary Industries and Regional Development (DPIRD) technical officer Alan Lord said although information on moth flights was very useful in alerting growers to potential native budworm risk, there was no substitute for sweep-netting crops to check for native budworm grubs.
"Taking multiples of 10 sweeps within at least five locations in a paddock is recommended to build an accurate picture of the numbers of grubs that may be present in the crop," Mr Lord said.
Recent reports from agronomists on caterpillar numbers varied greatly across the State.
In the Wubin to Koorda area, one to three budworm caterpillars per 10 sweeps were found in lupin crops.
Less than one caterpillar per 10 sweeps have been reported in lupin crops near Eradu and two budworm caterpillars per 10 sweeps were reported in a haying off lupin crop near Dandanning.
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An agronomist found one budworm caterpillar per 10 sweeps in a field pea crop near Grass Patch, while another reported finding about two caterpillars per 10 sweeps in a late flowering field pea crop near Beaumont.
"With many pulse crops in the vulnerable pod development growth stage, it is important to regularly monitor grub numbers and determine whether control measures are required," Mr Lord said.
"The decision to spray for native budworm in canola and lupins, but not other crops, can be left until pods are beginning to mature.
"If caterpillar numbers are below threshold limits, the decision to spray should be delayed and periodic sampling continued."
The feeding behaviour of caterpillars changes according to the type of crop the caterpillars are feeding upon.
Field pea, chickpea, lentil and faba bean crops are very susceptible to all sizes of caterpillars during the development of pods as tiny caterpillars can enter pods and damage developing seed or devour the entire contents of the pod.
Whereas narrow-leafed lupin pods and seeds will not be damaged by native budworm until they are close to maturity and the pods are losing their green colouration.
Canola is similar to narrow-leafed lupin in that canola pods only become attractive to caterpillars as the crop nears maturity and begins to hay-off.
Caterpillars of all sizes will enter pods at this stage, with larger caterpillars doing the most damage.
"The decision to spray a lupin crop should not be made until caterpillars are greater than 15 millimetres in length and the pods are losing their green colour," Mr Lord said.
"Growers who may be contemplating spraying maturing canola, lupins and field peas should be mindful of chemical withholding periods and to check chemical labels before spraying.
"Minimum times required between the spray application date and harvest or windrowing crops can vary from zero to 28 days."
