A Description of Silk Cut, a Stress-Related Loss of Kernel Integrity in Preharvest Maize

Silk cut is an important recurring problem of many commercial maize (Zea mays) hybrids exposed to late-season drought stress in southern Texas. Silk cut is the preharvest occurrence of one or more lateral splits in the kernel pericarp that expose the kernel tissues and embryo to either pre- or postharvest attack by fungi and insects. It can occur as multiple lateral splits anywhere on the seed surface but its primary and most common occurrence is as a single, lateral split at the kernel edge on either side or both sides of the embryo. Individual splits range from nearly microscopic to those that almost encircle the seed. Silk cut can be initiated at kernel moistures as high as 50% but is more commonly initiated and observed at kernel moistures of 28% and lower. In yearly observations from 1986 to 1994, silk cut was highest in incidence and severity on normal-yield-potential maize crops exposed to rapidly increasing environmental stress (decreasing soil moisture and high soil and air temperatures) during the latter stages of maturity but especially after black-layer formation. Hybrids with open ear tips and loose husks were among those most vulnerable to silk cut but incidence and severity varied widely across years, sites, and stress environments. Incidence also varied widely between adjacent plants. Total silk cut (kernels with silk cut colonized by fungi and noncolonized) on 105 and 110 ears from consecutive plants of two vulnerable hybrids averaged 23 and 31% but ranged from 0 to 94 and 0 to 97%, respectively. Average difference in silk cut incidence between ears of adjacent plants of these hybrids was 28 and 29% and individual differences ranged from 0 to 93 and <1 to 97%, respectively. Kernels on the top one-third of the ear had a higher average incidence of silk cut (44%) than those in the middle (38%) or bottom (shank end) (31%) positions.