Risk assessment for fusarium mycotoxins in wheat

Some fungal species can grow on crops and foodstuffs and produce toxic chemicals. Of widely varying toxicity to humans and animals, these chemicals are called mycotoxins. To keep mycotoxin levels below set limits, it is important to follow best practice – which includes the completion of a risk assessment.

In cereals, mycotoxins can result from fungi that either develop from field-borne infections (fusarium mycotoxins and ergot alkaloids) or in stored crops (ochratoxin A).

There are legal limits for fusarium mycotoxins deoxynivalenol (DON) and zearalenone (ZON) in wheat intended for human consumption and guidance limits for feed grain.

The owner (farmer, merchant or processor) is legally obliged to ensure grain is safe for human consumption. Depending on end use, processors may require a lower limit at intake than the legal limit for unprocessed cereals to ensure finished products conform to legal limits.

Crop assurance schemes are designed to help farmers comply with food laws. They include an audit of the risk assessment and an AHDB risk assessment score is required on the grain passport.

For traceability purposes, document the actions required when performing a risk assessment.

The final risk assessment score for a field of wheat is calculated by adding together scores for a number of key risk factors:

• Region
• Previous crop
• Cultivation
• Varietal resistance rating to fusarium ear blight
• T3 fungicide application
• Total rainfall during flowering
• Total rainfall pre-harvest

Calculate this score at harvest and enter it on the grain passport.

Check purchaser requirements to determine whether mycotoxin testing is required.

DON and ZON levels in wheat tend to be highest in southern and eastern England. Higher humidity in coastal areas may increase risk.

Crop residue on the soil surface is the major source of inoculum. The greatest risk is after grain maize or forage maize. Rotations should aim to minimise wheat sown after maize.

After maize, sugar beet and grass are potential inoculum sources.

Always aim to remove inoculum sources (e.g. straw).

Complete burial of debris by ploughing is most effective at reducing the risk, while risk is highest with direct drilling. Intensive non-inversion tillage (three or more passes with discs or tines) is more effective at reducing risk than reduced non-inversion tillage (one or two passes).

The risk assessment includes varietal resistance based on the AHDB Recommended List (RL) rating for fusarium ear blight.

• Untreated infected seed*
• Poor seedbeds
• Warm, dry weather from sowing to about GS31 encourages the build-up of fusarium inoculum
• Microdochium is more prevalent in cooler conditions
• Various broad-leaved and grass weeds, crop debris, as well as some insects, can provide a source of fusarium

*Seed treatment is the main method of controlling seedling blight. Information on the effectiveness of seed treatments against fusarium seedling blights is available from the fungicide performance section of the AHDB website.

Using an appropriate dose of an approved T3 ear fungicide with activity against fusarium and/or mycotoxin production reduces the risk.

Wet weather promotes fusarium development. The score is based on total rainfall during flowering (GS59–69 – full ear emergence to end of flowering).

Wet weather promotes fusarium development. The score is based on total rainfall from GS87 (dough development stage/start of ripening stage) to harvest.

• Lodging, resulting in humid conditions conducive to mycotoxin production
• Delays in harvesting by more than two weeks
• Damaged grain

Avoid delays at harvest for crops at high risk of mycotoxins, especially where grain is intended for human consumption.

Set combine, especially the fan speed, to minimise retention of light fusarium-damaged grains and chaff that contain the highest concentrations of mycotoxins. Dry and cool grain as soon as possible.

Harvest and store grain from localised patches of weathered or lodged crops separately.

It is important to understand and manage the quality of your grain. As part of this, accurate sampling is required to guide management and provide a robust record of all the grain that leaves the farm.

When ear blight levels are high nationally, the risk of DON and ZON occurrence in crops will increase.

Although mycotoxin risk in barley is lower than in wheat, it should be considered, especially when it is commonly grown in the rotation with maize with minimum tillage.

Covering thousands of sites across England, Scotland and Wales, our map-based tool shows how much rain has fallen during the critical winter wheat flowering and pre-harvest periods. Use this information to help calculate (DON) risk assessment scores required on the combinable crops grain passport.

Agrochemical residues, mycotoxins and other major contaminants in cereals and co-products have been monitored independently since the mid-1980s. Find out about our research that aims to help ensure the safety of UK grain and its end products.

The following resources will help you assess and manage mycotoxin risk. They will also help you to obtain composite and representative samples for testing for DON and ZON (where required by the end-user).