• Ear malformations can be caused by many factors.
• Off label pesticide applications, temperature and moisture stress, diseases and insects and nutrient imbalances can all result in ear malformations.
• Diagnosing the potential causes can help us better understand what could have gone wrong and, if under our control, make adjustments accordingly.

Pinched or “beer bottle” ears are ear malformations attributed to late applications of ALS-inhibiting herbicides, after the V6 growth stage. Non-GMO corn growers may use Accent in the post emergence herbicide tank mix to control annual grasses. When applied late, the active ingredient concentrates in the actively growing whorl causing the whorl to restrict the girth of the ear going forward to resemble the shape of a beer bottle (Image 1 below). The risk of pinched ears can be minimized by scouting early and making those applications before corn reaches V6.

Image 1. Pinched or Beer bottle ear.

Blunt ear syndrome (BES) is another ear malformation that has been researched for decades and no real cause has been determined yet. With BES the kernel rows around will not be affected but the kernel row length will be halted making the ear look like a soda or beer can in size. Initially some post emergence corn herbicides were thought to be the culprit of BES. Later on a cold period around the V8 growth stage, near the ear formation stage, was thought to be a factor contributing to BES.

Moisture stress, too much or too little, can affect corn development and reduce yields. Drought can severely impact crop yields. Considering that the potential number of kernel rows is typically determined around the V7 growth stage, drought stress around the V5-V7 growth stage can greatly impact kernel row number. Additionally drought during pollination will result in reduced pollination and abortion of kernels. Corn that has been severely affected by drought will often have smaller, nubbin type ears, sometimes even having sporadic areas on the cob and even the tips with no kernels, due to the lack of pollination (Image 2 below)

Image 2. Drought effected ear.

Arrested ear syndrome is typically caused by early applications (prior to tasseling-VT) of fungicides with an adjuvant. Because during these vegetative stages the plants are determining ear length, the ears will be about the size of a soda or beer can. Fungicides alone applied during these vegetative stages will not result in crop injury. Adjuvants can certainly aid fungicide distribution on the leaf but when sprayed prior to VT, particularly at V12-V14, injury and ear malformations can result. For this reason it is very important to stage the crop prior to application to determine whether an adjuvant can be added in the tank or not, and if uncertain wait until tassel has emerged.

Another ear malformation that can be found at harvest time is tip dieback. High temperatures, foliar diseases, cloudy weather, nitrogen deficiencies, drought and high planting populations can all contribute to tip dieback. Ears with tip dieback look like unfilled ear tips or little to very minimal kernel development on the tip 1-3 inches of the cob. The “dried and shrunken” kernels are typically due to a lack of ovule fertilization and can become a light yellow to white color or even a brownish color. Tip dieback can be managed to an extent by providing adequate soil fertility, minimizing crop stress as much as possible and selecting hybrids appropriate for your soil type and growing conditions. Yield may not always be limited in the case of tip dieback as some ears may contain a greater number of kernels around than a normal ear would to compensate for the tipback.

Not all of these malformations can be prevented; environmental factors cannot be controlled, except for drought when irrigation is an option. Foliar disease however can be mitigated with the use of fungicides, and compaction can be prevented by staying off of wet soils. Lastly, once the damage is done, we often cannot fix the problem, but we certainly can learn from the issue to help prevent it in years to come. We wish everyone a safe and smooth harvest.