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Native budworm

Native budworm (Helicoverpa punctigera) moths are still being observed in some regions of northern Victoria and southern New South Wales. Egg-laying by these moths (which will largely be in weeds at this point of the season) will not pose any risk to crops which are rapidly maturing and nearing harvest. Similarly, the risk posed by smaller budworm caterpillars to crops is now rapidly reducing.

In the last few weeks, there have been several reports of small-sized caterpillars being found in a variety of crops. In Victoria, these have come from Horsham, Donald and Charlton, in the Wimmera district of Victoria, near Swan Hill, in the Mallee district, and Elmore, in the Northern Country district. In New South Wales, there have been reports received from Griffith, in the Riverina district, and Temora, in the South West Slopes.

Although there are many paddocks that have been sprayed with insecticides to control native budworm, it is likely that in some cases these sprays are unwarranted. Native budworm caterpillars typically complete their development in 4-6 weeks (closer to 4 weeks with warm weather conditions). The caterpillars eat increasing quantities of seed and plant material as they grow, with the amount of damage caused by small-medium sized caterpillars being minimal. The last two growth stages (5th & 6th instars; 25-35 mm long) are responsible for eating over 90% of their total grain consumption. Younger caterpillars will also surface graze in preference to eating into pods. Thus in situations where crops are 2-3 weeks away from windrowing/harvest and small caterpillars (<15 mm in length) are found, there may not be any economic benefit of spraying. The possible exception may be in circumstances where mild conditions suddenly shift to a series of particularly hot days, which can force young caterpillars to burrow into pods.

Another important consideration prior to spraying is to ensure you accurately identify the pest species. We have received reports of caterpillars surviving sprays of synthetic pyrethroids in canola and faba beans in parts of the Wimmera district, in Victoria. This could be due to application issues or due to misidentification with the cotton bollworm (Helicoverpa armigera). The cotton bollworm is very similar in appearance to native budworm, and field identification is difficult. When fully grown, cotton bollworm caterpillars have white coloured hairs around the head region, while native budworm larvae have black hairs around the head. The reason that accurate identification is so important is that the cotton bollworm has developed high levels of resistance to a range of insecticides, including synthetic pyrethroids. Although predominantly a pest in Queensland and northern New South Wales, the cotton bollworm will occasionally appear in Victoria and southern New South Wales where they can cause similar damage to native budworm. Larvae of cotton bollworm are best targeted when smaller than 7 mm in length.

When applying chemicals, growers also need to be mindful of insecticide withholding periods close to harvest and remember that windrowing is classified as harvest. Some insecticide products registered against native budworm have quite long withholding periods (e.g. alpha-cypermethrin in canola, 21 days).

For more information on native budworm, refer to PestFacts Issue No. 10. Click here for further information on cotton bollworm.

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