Sudden Death Syndrome

Foliar symptoms usually appear around or after flowering as scattered yellow spots between the leaf veins that enlarge and merge, so the tissue between the veins turns yellow and then brown while the veins themselves remain green. Severely affected leaflets may drop, leaving the stalks attached. Splitting the lower stem shows a discoloured outer layer but a firm white pith, and roots are rotted and may carry bluish fungal growth in wet conditions.

Fusarium virguliforme survives in soil and on crop residue and infects soybean roots early in the season, often soon after planting into cool, wet soils. The fungus remains in the roots and produces a toxin that is transported to the leaves, where it causes the characteristic interveinal symptoms later in the season. The severity of foliar symptoms depends on how much root infection occurred and on subsequent weather.

• The fungus survives in soil and on residue between crops
• Root infection occurs early, favoured by cool, wet soils
• A toxin produced in the roots is carried to the leaves
• Foliar symptoms appear later and reflect the extent of root infection

Soybean is the primary host of concern. Cool, wet soils at and after planting, soil compaction, and poor drainage all increase root infection and later disease. Early planting into cold soils and the presence of soybean cyst nematode tend to raise risk, as does a field history of the disease.

• Cool, wet soils at planting and early establishment
• Compacted or poorly drained soils that stress roots
• Fields with soybean cyst nematode present
• A previous history of the disease in the field

Because the disease is soil-borne and tied to root health and soil conditions, management combines resistant varieties with practices that improve soil structure and drainage and reduce early-season stress. Managing associated nematodes is also part of an integrated approach.

• Grow varieties with better sudden-death-syndrome tolerance ratings
• Improve drainage and reduce soil compaction to support root health
• Consider planting timing to avoid the coldest, wettest soils where feasible
• Manage soybean cyst nematode, which can worsen the disease
• Track field history and prioritise higher-risk fields