GOOD roots are an essential feature for cereal crops in any season, but this dry spring has really shown up where there are any crop health issues that have limited the roots. 
In the past two weeks in our SRUC Crop Clinic, we have dealt with dozens of problems with poor patches showing up in crops as a result of free living nematode damage. 
In all cases, when we examine the roots, we can see that they are stunted and fanged compared to the good areas of the field. There is a ‘double whammy’ effect this year, because nematodes are more common in light sandy soils and these are the very soils that are driest and where plants will struggle most to draw up water with poor roots.
These key culprits are known as free living nematodes as they can migrate freely through the soil and graze as they go. 
They differ from more static species of nematodes which form cysts and attach themselves permanently to the roots of the host. Free living nematodes can move between plants and up and down in the soil profile. 
At the moment, for example, they have retreated down the soil profile in search of moisture, so numbers in the top soil when we test are often not that high.
There are several different groups involved with names that broadly describe the damage they do – for example the needle nematodes (longidorus) the stubby-root nematodes (trichodorids) and root-lesion nematodes (pratylenchids).
The symptoms usually appear as patches of poor growth that persist in fields from year to year, gradually moving outwards from the points where they were first introduced. 
Roots in these areas will commonly be stubby and fanged and show signs of their grazing. Their old-fashioned name of eelworms described the shape that enables them to wriggle between soil particles wherever there is moisture.
They like light soils where they can move easily and do not enjoy heavy soils, very dry soils or very wet soils. This could be why they are particularly bad this year – the autumn and winter were not as wet as sometimes, so numbers stayed high and now that crops are having to work hard for water, the damage done to their root systems is much more obvious.
Control is limited. They have a wide host range and will graze on any roots in the field including weeds. 
They have become more common over recent years, possibly related to the fact that the use of nematicides in other crops in the rotation has ceased. 
But their advantage in being able to move between soil particles is also their greatest weakness. Rolling cereals crops before stem extension crushes them between the soil particles and can have a marked effect in reducing numbers below damaging thresholds. 
Soil cultivations can also help to reduce numbers also by crushing them between soil particles. 
However, patches of poor growth in crops are always worth investigating, particularly if they reappear from season to season. Testing can eliminate other causes such as patches of low pH or nutrient deficiency and if nematodes are diagnosed then rolling and cultivating can help subsequent crops. 
Sadly, little will help crops currently affected, apart from rain which will help plants with damaged root systems draw up water.