Last week some corn fields in Dane, Lafayette, and Rock counties had areas with yellow stunted plants while other areas of the same field ha normal, taller "healthy" looking plants plants. Oftentimes patches of healthy corn would be scattered within the stunted areas. Above-ground plant symptoms included yellow striping and chlorosis with firing along leaf margins. Stunted plants had these symptoms on all leaves, while healthier plants had normal looking leaves near the top of the plant progressing to yellow fired bottom leaves, although leaf yellowing was often seen beginning near the tip of the top leaves. Below-ground plant symptoms included poor root growth with many plants exhibiting root "fanning: where roots were orientated with the seed opener furrow. Often field conditions were wet at planting. Symptoms have been seen on fields with tillage ranging from chisel tillage to no-till. No significant change in soil test levels of potassium were seen between 1994 and 1995.

The plants in these fields are exhibiting classic potassium deficiency symptoms. Although corn might have produced high yields on these fields last year, the wet spring soil conditions this year may have caused compaction contributing to poor root growth and preventing adequate uptake of potassium. Some sidewall compaction is evident when roots exhibit "fanning." Plant symptoms would be more severe on fields with soil tests of low to medium potassium levels. Unfortunately nothing can be done about the deficiencies, except to plan on bringing soil test levels of potassium up this fall and next spring.