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Corn Rootworm - Part 1: Description of Corn Rootworm and Other Early Season Corn Pests

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Rating Corn Root Damage

Corn roots are rated for the amount of damage inflicted by corn rootworm larvae. This rating will assess the level of damage from mild to severe. There are two scales that can be used when rating root injury. The first scale is referred to as the traditional Iowa 1-6 scale. In this scale, one represents no damage to the roots and six corresponds to a root with three nodes of roots eaten (Table 1).


Table 1 - Iowa 1-6 Scale


Iowa Scale
No damage to only a few feeding scars
Feeding scars but no roots eaten within 1.5 inches of stalk
Less than one node of roots eaten but not within 1.5 inches of stalk
One node or equivalent eaten within 1.5 inches of stalk
Two nodes or equivalent eaten within 1.5 inches of stalk
Three nodes or equivalent eaten within 1.5 inches of stalk


 The second scale is the Node-Injury scale (Table 2). This scale uses a range of zero to three, with zero representing no damage and three representing severe damage.

Table 2 - Node Injury Scale
Node Injury Scale
No damage
One node or the equivalent of one node eaten within two inches of stalk
Two nodes eaten within two inches of stalk
Three nodes eaten within two inches of stalk
Note:  Damage can also be recorded as a percentage of a node removed, i.e. 1.75 = 1 ¾ nodes eaten.

For more information on these two scales and to view associated pictures of corn roots, see the Iowa State University Entomology interactive node-injury scale at



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