Lupin growers are being encouraged to assess their crops for manganese (Mn) deficiency. This has re-emerged as a problem in recent seasons, causing split seed disorder. The GRDC’s Western Lupin GrowNotes says this can result in yield penalties of up to 70%.
According to Jeremy Lemon from WA’s Department of Primary Industries and Regional Development, Mn deficiency can be induced in areas with histories of heavy lime application.
“We see it on lime dumps in paddocks and I have seen it in lupins in the Esperance region.”
The residual value of fertiliser Mn declines over time. Heavy liming and dry seasons can further reduce Mn availability. Common symptoms of Mn deficiency in narrow leafed lupins include plants with straggly growth, delayed maturity, dropped leaves and leaves reshooting as a tufty growth on the branches.
But as Jeremy points out, narrow-leaved lupins often don’t show more obvious, visible symptoms of Mn deficiency until seeds are split through the seed coat, discoloured or malformed. At this point, it is too late to address the issue.
“The main message is not to over-lime paddocks and to be on the lookout for Mn deficiency.”
Monitoring should include sampling the main stems. Collect them from ground level to the flower at mid-flowering, strip them of all leaves and laterals and send them to a laboratory for analysis.
Split seed disorder can be treated by applying Mn fertiliser to soil or as a foliar spray to lupin crops. The soil-applied fertiliser is residual and can last for several years, whereas the foliar spray will only act on the target crop in the season of application.
When retaining seed for sowing, test lupin seed for Mn concentrations to ensure adequate levels for germination and crop establishment. Ideally only keep and sow seed from crops that have had Mn applied or that have been grown in soils with adequate Mn levels.
Primary Industries and Regional Development WA: