Yellowing of some soybean plants (IDC) can be seen in a number of soybean fields in the region. Although there is sufficient iron in most of our soils for plant growth, the soybean plants displaying the yellowing have difficulty taking up the iron during this early stage of growth (first and second trifoliate just expanding). Symptoms of IDC are yellowing of interveinal areas of young leaves (Figure 1). Brown and necrotic spots may occur in leaf margins and plants can be severely stressed or killed if the stress is severe.

Research has indicated that IDC has been associated with calcareous soils (pH greater than or equal to 7.4).  If soils are calcareous, testing for soluble salts and calcium carbonate is suggested.
 
In fields with higher plant populations (plants in close contact with each other) IDC symptoms seem to be less severe. Coating the soybean seeds with chelated iron sources has had positive effects on yield. However, only relatively small amounts of iron can be applied as a seed coat and the benefits are not great enough to pay for the additional seed treatment cost.

Correcting IDC with a foliar application of iron has not provided consistent results and is an expensive practice.

Iron chlorosis is more severe when there are other stress factors on the soybean plant. Seedling diseases may result in a weaker plant. Saturated conditions, cool temperatures, soluble salts, calcium carbonate, herbicide stress (conventional beans) are all stress conditions which may aggravate the IDC symptoms.

Warm and dry conditions may allow fields to recover however research showed a negative correlation between IDC score and yield (Figure 2, see Cropping Issues, Vol 2 Issue 5, June 21, 2005 ).

As a management strategy it is suggested to take some soil samples where the soybean plants are yellow, light green, and green to document the soluble salt and calcium carbonate levels in the field. One way to manage salts is through leeching and removal of the salts from the soil. Tile drainage (if enough moisture percolates through the profile) will over time decrease the soluble salt levels.

It is important to make note of the specific soybean variety grown in the fields with higher levels of IDC. Selection of a variety with tolerance to IDC is an important management decision for soybean growers. Not all companies rate IDC in a similar fashion, however most companies do rate and rank their varieties (Table 1).

The U of M chlorosis ratings are based on tests conducted on high-lime (high pH) soil near Foxhome. It is a comparative rating between varieties. Ratings can vary depending on the test site and year of test. NDSU chlorosis field studies were set out at five locations in 2005, to measure the resistance of about 180 soybean varieties to IDC. The scores are posted on the web at:

http://www.yellowsoybeans.com