Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
This wet year has brought many problems for sweet corn growers. The biggest issue has been flooding and excess soil moisture. For processing corn growers, this has meant reduced field yields with smaller ears or no ears in field bottoms and poorly drained areas. For fresh market growers, wet field areas are producing unmarketable, small, or poorly filled ears. We are also seeing heavy leaf disease/blight pressure in some varieties. To add insult to injury, as fields dry out, irrigation decisions have to be based on water needs in better drained field areas, often keeping bottoms wet, further stressing corn in these areas. We have also seen unusual problems in sweet corn this year such as fungus developing on silks in storage or shipping, split kernels, and small diameter “skinny” corn.
Reduced Ear Size
Ear size in corn is a function of the number of rows and the number of seeds per row. The number of kernel rows that a corn plant produces in the upper most ear (the main harvest ear) is set between the 5-8 leaf stages in corn (V5-V8). This is strongly determined by genetics. The number of potential seeds per row is determined by the 12-15 leaf stages (V12-V15) and is very much influenced by the environment and plant stress. Stresses during ear initiation and early formation will reduce ear diameter and ear length. In particular, inadequate nitrogen during this period (V6-V15) has been shown to reduce ear diameter and ear length. Poorly drained areas in fields will lose significant amounts of nitrogen due to denitrification. Excess water will also limit root function or cause root death if prolonged thus limiting nutrient uptake. Both these factors have resulted in reduced ear size in sweet corn in 2013. It should be noted that final ear size and seed number will be determined after pollination and seed set.
Skinny Ears in 2013
Small diameter ears can occur where there is reduced row number. Because row number is largely genetically determined, only severe stress at the 5-8 leaf stage will cause a reduction in rows. This occurs with loss of leaf area such as hail injury, defoliation by wildlife or pests, herbicide damage, or other major injuries where photosynthesis is reduced. In contrast, this year we are seeing smaller diameter “skinny” ears where row numbers have not been reduced (see pictures below). This is most pronounced in field areas that were wet during early ear development and where nitrogen was limited during that period (due to denitrification losses and delays in sidedressing because of wet field conditions). This caused smaller cobs to develop in some varieties while pollination and seed set was minimally affected resulting in small diameter ears of similar length to unaffected ears.
Small diameter ear (left) and normal ear (right) from variety trials at the UD Georgetown research farm. Note that both ears have 16 rows and that kernel depth is similar.
Looking closely at the smaller diameter ears, we see that kernel depth is similar; however, the attachment between the seed and the vascular system in the cob core is shorter and that the accessory tissues (the cob “chaff”) at the seed base are reduced or compressed. This smaller cob has caused seeds to be compressed together and slightly deformed. These small diameter ears, while having similar seed counts, are less attractive to consumers resulting in poorer sales. For wholesalers, small diameter corn will pack more per crate or bin but may not be accepted by buyers.
Small diameter ears on the left compared to larger diameter ears on the right. Tip fill is slightly reduced but length is similar.
“Skinny” ear appearance in husk (left) versus normal ears (right). Note that ear length is similar.