Prediction of coumestrol content in unirrigated lucerne crops using weather variables

Elevated coumestrol levels in lucerne (<i>Medicago sativa</i> L.) can reduce the reproductive performance of ewes. A model to predict coumestrol content of lucerne between summer and late autumn was developed to assess the risk of a crop having elevated levels. Data from previous studies have shown fungal damage to be the major contributor to coumestrol levels, but the fungal infestation levels that can cause a risk to reproduction in sheep are difficult to quantify. A number of variables were tested and the sum of rainfall and days where relative humidity was over 95% at 0900 h was found to have the best fit with coumestrol content of lucerne crops. The model was then tested with independent data from the literature and field. A decision tree is proposed as a practical user-friendly guide to predict whether coumestrol content is above or below a risk threshold of 25 mg/kg DM.