Native budworm and diamond back moth

Growers are encouraged to keep a close eye on canola and pulse crops over the coming weeks for the presence of caterpillars, especially native budworm and diamondback moths (DBM). We have recently received reports of adult DBM flying around Skipton and Derrinallum, in the western district of Victoria. Depending on weather conditions, caterpillars will likely hatch in these localities within 1-2 weeks. Early infestations of DBM have already caused issues for canola growers in parts of South Australia this season.

The first major native budworm flights have now been confirmed following the run of northerly winds between 8^th and 9^th September. Consultant, Bill Gardiner (West Vic Ag services), says large numbers of moths have recently been observed around house lights in the central region of the Victorian Wimmera. It is predicted that caterpillars will hatch by late September in these parts, but is likely to be sooner in northern localities.

Diamondback moths

DBM (Plutella xylostella) can be found throughout the year, but are most abundant during spring and summer. DBM can have a significant impact on canola yields and current control measures are variable. DBM develop more rapidly with rising temperatures. At 25°C the complete life cycle takes only 17 days.

Sampling crops at several locations is important to determine whether numbers are increasing or decreasing before any spray decision is made. Threshold guidelines in canola range from >30 caterpillars per 10 sweeps for pre-flowering stressed crops to 100-200 caterpillars per 10 sweeps in full flowering unstressed crops. Heavy rainfall events >10mm can cause high mortality of caterpillars due to dislodgement and drowning, therefore it is worthwhile re-assessing spray decisions after rainfall.

Affirm^® and Success Neo^® are effective insecticide options registered to control DBM in canola. Bt products applied late in the evening (to reduce UV degradation) are an option to control small caterpillars <5mm in length. Synthetic pyrethroids and organophosphates are generally not recommended for control, as many DBM populations are known to have moderate to high levels of resistance to these chemical groups. In years when DBM populations are large, a two-spray strategy is recommended. 

Native budworm

Native budworm breed in inland regions of Australia before migrating to southern and eastern cropping regions in late August and September. The number and timing of these migratory flights can be hard to predict as the moths often travel hundreds of kilometres on north-westerly winds. When moths arrive and lay eggs in crops the resulting caterpillars can cause serious damage if left uncontrolled. Given the good growing conditions in northern Australia this year, it is reasonable to expect some issues with native budworm this season.

Native budworm (Helicoverpa punctigera) is a pest of a variety of crops. The caterpillars feed on buds, flowers, fruiting parts and seeds and will attack field peas, faba beans, lentils, chickpeas, lupins and canola crops, as well as pasture seed crops of lucerne, annual medic and clover. When caterpillars are detected, it is important to sample representative parts of the entire crop prior to making a control decision. Eggs laid by moths will take at least 2 weeks before they hatch into caterpillars and grow to a size of approximately 5 mm where they can be detected whilst sweep netting crops. It typically takes about 7 weeks from the time of egg-laying until caterpillars are fully-grown.

Moth numbers, and the subsequent generation of caterpillars, will vary between regions and paddocks and under different weather conditions, so monitoring remains the best way to determine the risk they pose to individual crops. For example, large numbers of moths may lay prolifically in a crop, but significant rainfall within a week of egg-lay can dislodge and kill most eggs and even young larvae. Crops should be monitored using a sweep net from early flowering and throughout podding in pulse crops. Pod inspections are also essential in order to detect small caterpillars and accurately determine numbers. Canola and lupin crops differ from pulse crops in that native budworm will only cause damage to pods close to plant maturity when these crops are starting to dry off.

Click here for further information on native budworm management.