Lower Stalk Development and Staging of Corn

Hail insurance adjustors determine corn (Zea mays L.) leaf stages after leaf number one has deteriorated and prior to tassel emergence by examining the longitudinal section of the lower stalk. They assume the sheath of leaf five is attached to the node immediately above the first elongated internode and determine leaf stage by" counting the leaves above leaf five. Since the leaf area destroyed vs. grain yield loss chart is based on plants with 18 leaves, adjustors modify the lea~ stage on earlymaturing hybrids which develop fewer than 18 leaves. To test these techniques of plant staging, we conducted field experiments during 1973–75 to determine the effect of hybrid maturity, planting date, plant density, and geographical location on lower stalk morphology and leaf development of hybrids adapted to the northern corn belt. Experiments were conducted at Lamberton, Minn. on a Webster clay loam (Typic Haplaquoll), St. Paul, Minn. on a Waukegan silt loam (Typic Hapludoll), and Staples, Minn. on a Sverdrup sandy loam (Udic Haplaboroll). Leaf number five (counting the leaf with the rounded tip as number one) was spot sprayed with red paint. Subsequently the 10th leaf was similarly identified before leaf number five sloughed from the plant. At tasseling, plants were dug and stalks split to identify and record the leaf number attached to the node immediately above the first elongated internode. The number of leaves developed, number of leaves on the plant at tasseling, and length of the first four elongated internodes were recorded. In 2 of the 3 years, early planted corn had 0.5 to 0.8 more unelongated internodes compared with late planted corn. The number of unelongated internodes was negatively correlated (r = −0.99) with both heat units (base 10 C) and summation of maximum soil temperature (5 cm depth) for the 2nd week after planting. Hybrid maturity, density, and geographical location had no effect on the number of unelongated internodes. Number of developed leaves and number of leaves at tasseling increased as relative maturity increased in 2 of the 3 years. Averaged over entries, the lower 6.4 leaves sloughed as the stem enlarged and aerial adventitious roots developed. Number of developed leaves was greater for early planted compared with late planted corn but was not affected by test location or plant density. Lengths of the four lowest elongated internodes were greatest for early hybrids and decreased as maturity approached full season. The first elongated internode was longer on early planted than on late planted corn in 1974. Our data indicate early planted corn could be “understaged” by approximately one leaf by using the current procedure of splitting the lower stalk and assuming leaf five is attached to the node immediately above the first elongated internode. Understaging would result in underpayment of a hail loss claim. The early maturing hybrids develop fewer than 18 leaves. Therefore, the leaf stage should be modified (as is currently done) when adjusting loss claims on hybrids which develop fewer than 18 leaves. Without stage modification, loss claims would be underpaid.