Iron deficiency chlorosis symptoms usually appear in early June, whereas yellowing due to SCN will more likely occur in July and August. The yellowing caused by iron deficiency chlorosis typically affects the areas between the veins of the upper leaves. Yellowing due to SCN usually starts at the edges of the leaves, and can affect leaves on the entire plant. Iron deficiency chlorosis and SCN may occur in the same field and even on the same plant. An area of SCN damage often will appear elongated in the direction of tillage operations.
Most severe damage is often in the center of the area, with damage decreasing towards the margins.
Such areas frequently develop near a field gate, entrance, wherever equipment enters a field, or near fences where wind-blown soil may accumulate. The above-ground symptoms of SCN damage do not always occur consistently. Symptoms range from nonexistent to severe depending on the age and vigor of the soybean plants, SCN numbers, soil fertility, moisture levels, and other environmental conditions. Injury usually is more severe in light, sandy soils, but it also occurs in heavier soils. SCN damage is not always confined to smaller areas within a field.