Non-chemical control of take-all in cereals
Take-all is an important soilborne disease in UK cereals. With varietal resistance and chemical options extremely limited, reduction of disease severity and impact relies heavily on cultural control approaches.
A one-year break from susceptible crops will usually prevent the disease causing problems in the subsequent cereal crop. Any broad-leaved crop will form an effective break, as will oats, unless the rare oat-attacking strain of the fungus is present. However, a one-year break does not eliminate the fungus. Where the preceding cereal crop suffered a lot of disease, significant inoculum may persist through the break, allowing infection of a susceptible crop. Cereal volunteers and grass carriers also undermine the effectiveness of a break.
Preceding a short sequence of cereals with a two-year ryegrass ley encourages antagonistic fungi to develop. This usually delays the onset of severe take-all by a year, allowing an extra wheat crop to be grown with reduced risk of severe take-all. However, a one-year ryegrass cover may increase severity. A catch crop of a nitrogen-demanding crop (e.g. white mustard), sown after wheat volunteers have been destroyed, may further reduce take-all survival
A firm seedbed discourages fungal growth. However, on heavy soils, over-compaction can hinder root growth and exacerbate the damaging effects of the fungus on root function. Ploughing buries most of the take-all inoculum, which is in the top 10 cm of soil at harvest, and brings less infective soil to the surface. This reduces early infection and gives the plant time to establish before its roots reach more infective soil. However, consolidation after ploughing is important to achieve a firm seedbed. Minimum tillage of first wheat stubble leaves highly infective soil near the surface. This allows more rapid infection of a second wheat but leaves a firmer seedbed than ploughing. Tillage method does not consistently affect take-all in longer cereal sequences.
Volunteer cereals and grass weeds
Cereal volunteers (not oats in most of the UK) and some grassweeds, particularly couch and barren brome, carry the take-all fungus through break crops. In first wheats, the risk of take-all increases in proportion to the density of volunteers or weeds. Early destruction of volunteers and grass weeds reduces the risk to first winter wheats. Take-all may, however, survive or even multiply on couch rhizomes after foliage has been killed. Take-all decline, like the fungus itself, diminishes during a break from wheat.
All varieties are susceptible to take-all. However, some are more tolerant. Although not tested in the AHDB Recommended List, second wheat yields can provide some guidance on varieties for second and subsequent sowings. However, yield responses reflect take-all tolerance, eyespot resistance and ability to withstand the stress of root loss associated with the disease. There is evidence of good levels of resistance in some triticale varieties.
Take-all inoculum falls relatively rapidly after harvest. Consequently, delayed drilling reduces the disease in second wheats. However, any benefit from later sowing may be lost if volunteers or susceptible grasses are allowed to grow between crops. Earlier drilling of first wheats increases the risk that damaging take-all will develop in second wheats.
Climatic conditions, before, during and after sowing, affect risk. Soil temperature during the autumn is particularly influential. The pathogen is active when soil temperatures are above 10–12˚C. Ideally, delay sowings of second wheats until soil temperatures are at or below 12˚C. Drilling dates for continuous cereals should be the same as for second wheats. Early drilled crops are particularly prone to severe attacks, so sow first wheat crops first, followed by long-term wheat and third wheat last.
The effect of drilling date on take-all
|Drilling date (second wheat)||6 Oct||18 Oct||31 Oct||13 Nov|
|Final take-all index||52.5||46.0||44.0||21.1|
Take-all can develop more quickly and become more severe at higher seed rates. This allows more primary and secondary infection, because of greater root density. Reducing seed rates can increase yield where take-all is severe. This may not be practical with later-sown at-risk crops.
Take-all destroys roots, reducing a crop's ability to take up nitrogen and other nutrients. Timing of nitrogen applications is important. Apply nitrogen earlier to crops at risk of take-all. An early application (around 60kg N/ha) in February/March followed by the main dressing in April is better than a single dressing or later applications. Because uptake by crops with severe take-all is less efficient, the disease may increase leaching losses. Take-all may be less severe with ammonium sulphate than with ammonium nitrate, urea or ammonium chloride fertilisers. However, in well-buffered UK soils, the effect is small.
Phosphate-deficient soils (less than 15mg/kg of soil – Index 1 or less) favour take-all. Phosphate should be at 20mg/kg soil (Index 2) before the start of a cereal sequence and any deficiency rectified, ideally before the break crop, to reduce take-all risk in the second cereal.
Manganese, potash and sulphur deficiencies are linked to increased take-all severity. Correct manganese and potash deficiencies before sowing. However, severe take-all sometimes occurs even when supplies of these nutrients are adequate.
No foliar applied fungicides control take-all . Seed treatments only provide partial control:
Wheat 1 (first wheat)
Only treat if there is a known risk (e.g. many cereal volunteers or couch and barren brome weed pressures).
Wheat 2 (second wheat)
Only treat if there is a known risk (e.g. take-all regularly occurs on the farm or the crop is drilled very early).
Wheat 3 (third wheat)
Only grow a third wheat if the second wheat appeared healthy during grain filling and yielded well. Where a third wheat is grown, use a seed treatment. However, expect reduced yields.
Wheat 4 (continuous wheat)
Treat at-risk crops. However, treatment may delay the take-all decline phenomenon.
- Extending the rotation is the most effective way to manage take-all
- Seed treatments only give partial control
- Provide good drainage, consolidated seedbeds and adequate nutrition, especially where second, third, or fourth wheats are grown
- Continuous wheats are not affected so much because of take-all decline. However, yields never return to those of first wheats
- Control cereal volunteers and grass weeds in break crops and avoid a green bridge between successive cereal crops
- Avoid very early drilling of first and second wheats. Aim to drill second and subsequent wheats after mid-October
- Varietal resistance and foliar fungicides offer little control