Bruchids infesting pulse crops in the field

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There have been two reports recent­ly of cow­pea bruchid activ­i­ty, with these pests infest­ing pulse crops in the field pri­or to har­vest. The first report con­cerned the cow­pea bruchid (wee­vil) Cal­loso­bruchus mac­u­la­tus in field peas from Goondi­win­di. The bruchids were noticed at intake and con­tin­ued to breed in an untreat­ed grain sam­ple post-har­vest. This clear­ly indi­cat­ed they were not pea wee­vils (bruchids) Bruchus piso­rum, which do not breed in stored grain.

Cowpea bruchid (weevil) adults (3mm) in field peas, harvested 16/10 Goondiwindi and noticed at intake on 17/10. They continued to breed in the seed sample.

Cow­pea bruchid (wee­vil) adults (3mm) in field peas, har­vest­ed 16/10 Goondi­win­di and noticed at intake on 17/10. They con­tin­ued to breed in the seed sam­ple.

The sec­ond report was of the close­ly relat­ed Cal­loso­bruchus phase­oli, also known as cow­pea bruchids, in chick­peas at Moura. This is the first time this par­tic­u­lar species has been found in chick­peas in Queens­land although C. mac­u­la­tus has been fre­quent­ly report­ed in this crop. The bruchids in chick­peas were dead at intake, most like­ly because the crop was frost­ed pri­or to har­vest in Sept 2014.

Bruchid damage in chickpeas from Moura, Central Qld.

Bruchid dam­age in chick­peas from Moura, Cen­tral Qld.

In view of these reports, it is rec­om­mend­ed that grow­ers check their pulse crops in the field for seed dam­age and dur­ing har­vest by siev­ing grain. A sub sam­ple of grain at har­vest time should be kept in a con­tain­er as a ref­er­ence sam­ple. Keep this in a warm ‘place’ to check for post-har­vest breed­ing from unde­tect­ed bruchid eggs or oth­er life cycle stages. If the sam­ple is kept at around 30 °C and is still bruchid free after 30 days, it is almost cer­tain­ly clear of insects. This sam­ple serves as an ear­ly post-har­vest warn­ing of bruchids present, but not detectable at harvest/intake. In all cas­es, always ensure insects are cor­rect­ly iden­ti­fied.

If a bruchid prob­lem is evi­dent, store grain in an aer­at­ed, seal­able silo. For spring and sum­mer pulse har­vest times, when bruchid detec­tions indi­cate a low lev­el infes­ta­tion, under­take stan­dard aer­a­tion cool­ing pro­ce­dures for the first two weeks of stor­age to cre­ate uni­form mois­ture con­di­tions in the fresh­ly har­vest grain. This puts the grain in a safe con­di­tion pri­or to seal­ing up the silo for fumi­ga­tion.

Grain tem­per­a­tures should come down from 30 to 35°C at har­vest, to 20 to 23°C fol­low­ing aer­a­tion. Hav­ing used a pres­sure test to check the silo is gas tight, now con­duct a 10 day phos­phine fumi­ga­tion to kill all life stages of the bruchid infes­ta­tion.

For more infor­ma­tion:

Arti­cle by Hugh Brier and Philip Bur­rill
Images by Joe Wes­sels