Diseases in oilseed rape, April 2019

Fungicide sprays targeting light leaf spot will be imminent when conditions dry up and allow field operations again – many crops are now extending away and at green bud stages.

Sclerotinia risk will be important to assess when crops come in to flower. Decisions to protect against sclerotinia should be based on the risk and that includes the presence of other hosts in the farm rotation as the host range for sclerotinia is very broad and includes many valuable cash crops such as peas, beans, potatoes, carrots and vegetable crops like lettuces. The disease is carried over in soil in the form of long-lasting resting bodies (sclerotia) but also as an airborne phase when these germinate so your assessment of risk should be based on the on-farm and local experience and not just on the individual field.

Sclerotinia risk is made up of the risk from previous crops and then the risk that these germinate and spread airborne spores at a time when the crop is flowering.  That risk is then enhanced by wet weather over flowering which makes petals sticking to the stem more likely.  That is a lot of steps in a chain to come together which is why the severity of infection is so erratic between seasons.  Your previous experience of the disease is a key driver – if you have past experience of outbreaks you will have a reservoir of infection and a higher need to treat. If you have other susceptible and high-value crops in the rotation that will be another key reason to protect flowering rape crops.

At the minute our risk is low as spores have yet to be detected, plus humidity and temperature criteria risks are still low.  If warmer temperatures and higher humidity coincide with flowering that will increase the risk, which will be further increased if flowering is prolonged and/or if weather is wet over that period.

In addition to your own on farm assessment, you can check sclerotinia infection risk at two monitored sites in the Borders and Lothians on the AHDB link here: https://ahdb.org.uk/sclerotinia