Iowa State Observations
In 2006, bouquet ears appeared at a higher-than-normal frequency in corn fields from Iowa to Indiana. Iowa State researchers recorded the following observations that year (Elmore and Abendroth, 2006):
- Incidence reports from fields expressing bouquet ears ranged from 20% to 100% of plants.
- In extreme cases, clusters contained up to eight small ears.
- Different hybrids from different seed companies were affected.
- Several different herbicides (pre and post) were used.
- Some locations were affected by early-season drought.
- Some had mid-season fungicide applications, others did not.
- In the end, no single cause could be identified.
University of Illinois Observations
When bouquet ears occurred in Illinois in 2007, the following observations were made (Nafziger, 2007):
- Some hybrids were more likely than others to produce “side” ears. In some fields, up to 5 or 6 ears developed.
- The side ears were well developed, though many likely failed to form kernels due to late silking and lack of pollen.
- In general, the larger and more numerous the side ears, the more likely that the main ear was damaged in some way or had low kernel number.
Nafziger concluded that secondary ears were likely able to grow faster when the primary ear either showed less dominance or just used less plant sugar, leaving more for the other ears. He also surmised that the causes of damage to the main ear might have been different in different fields.
Corteva Agriscience Observations
Corteva Agrisicence corn breeders place an ear shoot bag over the small ear shoot of a corn plant prior to silk emergence to protect silks from pollen contamination prior to making a controlled pollination. These researchers have long noted that when such plants are not pollinated, multiple ears often develop at the same stalk node as the non-pollinated ear. This suggests that the failure of the primary ear is the stimulus for the development of the secondary ears. Other observations by Corteva Agriscience researchers and agronomists confirm this conclusion. When extreme silk feeding by corn rootworm beetles or Japanese beetles prevents or limits pollination of some ears, the formation of multiple ears often results.
Multiple ears on the same shank may also result from stress to the plant earlier in its development. Stress during primary ear formation around the V6 stage can cause disruption of ear development and the loss of apical dominance. Pioneer agronomists have observed multiple ears on the same shank associated with stress caused by high winds, extreme temperatures, and wide swings in temperature during ear development.
Pioneer agronomists have observed bouquet ears resulting from a specific disease commonly referred to as crazy top. This disease is caused by a fungal pathogen (Sclerophthora macrospora) spread by flooding. Crazy top may result not only in a proliferation of leaves in the tassel of the plant (from which it draws its name), but also a proliferation of ears at a single node (Figure 8). Other diseases have been implicated in expression of bouquet ears, but a direct cause and effect relationship has not been conclusively established. Likewise, no conclusive relationship has been established between herbicide, fungicide, or insecticide application and bouquet ears.