Healthy clover plants with healthy white root systems (left) compared with diseased plants with pruning of the tap roots with brown lesions (right).

There are many foliar and root diseases which can result in significant production loss or plant death in sub‑clover. Often these problems occur in the roots, so the damage is hidden. Some cultivars may have evolved local tolerance, but the majority of older sub‑clover cultivars will have little resistance.

The main indication of disease impact is poor autumn to winter growth, with a reduction in the density and vigour of plants even when soil nutrient conditions are not limiting and few insects are present.

The impact of a disease outbreak varies depending on when it occurs and the severity of the infection. Plant death early in the season has a much greater effect on animal production than later in the year, when other feed is plentiful.

Plants only hampered by disease early in the season often recover in spring, but autumn–winter production is lost.

It could be expected susceptible cultivars would die out due to disease. However, the intermittent presence of these diseases means if even susceptible cultivars will die in high disease years, they can still have enough seed left in the seed bank to regenerate in following years.

PREDICTA® B testing of soil can be used to confirm the presence of disease. Alternatively, confirmation of fungal diseases and their impact can be achieved through applying fungicides (see Figure 1).

Figure 1: Test strips showing the sub-clover response (healthy green, denser clover with longer and better-branching roots) to the treatment containing fungicide (Metalaxyl) where an additional 800kg DM/ha was grown through winter (Image: Lisa Warn Ag Consulting, 2017)

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