These results underscore the importance of field testing corn hybrids for susceptibility to Blunt Ear Syndrome (BES).  Corn hybrids found to be susceptible to BES, should be marketed carefully to minimize the possibility of growing susceptible hybrids in areas where damaging levels of BES are known to occur.  As with other agronomic studies, evaluating corn hybrids over several years will provide a more complete understanding of hybrid response to BES.   These results also indicate irrigation water management affects the development of BES.  Additional research on the effect of irrigation on BES is warranted.

Blunt ear syndrome, also called “beer-can ears”, “hand-grenade ears,” and “stunted ears,” is a disorder of corn that is characterized by normal-appearing corn plants having reduced ear lengths and fewer kernels per row (Pearson and Fithian, 1993).  A portion of the ear tip is barren in an otherwise normal-looking husk (Fig. 1).  Yield losses from BES have ranged from minor amounts to as much as 75%, and farmers have reported that BES is often most severe on productive soils (Pearson and Golus, 1990).  Previous research has shown that corn hybrids differ in their susceptibility to BES (Fithian, 1999; Pearson and Golus, 1990).  Identifying corn hybrids that are susceptible to BES allows seed companies to more accurately market their seed.  We have conducted various studies on BES in the Grand Valley for many years.  The occurrence of BES from year to year in the Grand Valley of western Colorado has been more consistent than any other place in the country, making it the ideal location in the U.S. to study BES.   The objectives of this research were: 1) to evaluate Golden Harvest corn hybrids for their susceptibility to BES, and 2) to determine the effect of irrigation on BES development.  Previous research conducted in 1997 and 1999 at the Fruita Research Center indicated that irrigation may affect BES development.

Fig. 1. Typical ear symptoms for Blunt Ear Syndrome showing the lack of kernels at the top of the ear and the sharp, pointed ear tip.

Twenty Golden Harvest and three Pioneer brand corn hybrids were evaluated for BES at the Colorado State University Western Colorado Research Center at Fruita in 2000.  The experiment was a randomized complete block with four replications.  Two sets of plots containing all hybrids and the four replications each were planted- one set on the west side of the field and another set on the east side of the field.  Plot size was 5-feet wide and 50-feet long.  The previous crop was corn and the soil type was a Youngston clay loam.  The seedbed was prepared using clean tillage.  Planting occurred on May 4, 2000 with an air planter that had been modified for planting small plots.  Seeding rate was 35,890 seeds/acre.  Both corn rows of each plot were counted the length of the plot on July 12, 2000 to determine plant populations.

Bladex 4L herbicide was applied PPI at 2 qts/acre on April 28, 2000.  Fertilizer applied was 22 lbs N/acre and 104 lbs P2O5/acre preplant of 11-52-0 on April 27, 2000, and 180 lbs N/acre of 32-0-0 was applied side-dress on June 13, 2000.  Comite II (2.75 pt/acre) was applied in mid-July just prior to tasseling. 

The irrigation schedules used for Treatment 1 and Treatment 2 are shown in Table 1.  The set of hybrids on the west side of the field were Treatment 1 and the set of hybrids on the east side of the field were Treatment 2. 

Corn in each plot was evaluated for BES symptoms on Nov. 1, 2000 using our 1 to 9 rating scale (Fig. 2; Table 2).  Harvest occurred on November 17, 2000 using a small plot combine.  Grain yields were corrected to 15.5% moisture content.  Grain moisture contents and test weights were determined with a Seedburo GMA128 Grain Moisture Analyzer.

Fig 2. Numerical scale for rating Blunt Ear Syndrome symptoms in corn.

The 2000 growing season was favorable for corn growth, although spider mites were a problem in some areas of western Colorado.  At the Research Center, spider mite problems were confined to the edges of the field.  Spider mites did not have a damaging effect on this research.  Weed control in the field was excellent.

Golden Harvest Corn Hybrids

The main effects of hybrid and irrigation treatment for plant population were significant (Table 3).   The hybrid x irrigation treatment interaction for plant population was not significant.  Averaged across hybrid and irrigation treatment, plant population was 36,495 plants/acre.  The planter was set to plant 35,890 seeds/acre.  If small corn seed is used in the planter, the planter plate cell often picks up more than one seed, resulting in seeding rates that are higher than the rate set on the planter.  This situation apparently occurred in this study.  Fifteen of the twenty hybrids had plant populations that exceed 36,000 plants/acre and only two hybrids had plant populations lower than 35,000 plant/acre.  The hybrid with the lowest plant population of 32,316 plants/acre was H-9401Bt.

The main effects of hybrid and irrigation treatment for grain moisture content were statistically significant (Table 3).  The hybrid x irrigation treatment interaction for grain moisture content was not significant. Grain moisture content averaged across corn hybrid and irrigation treatment was 16.8%.   Grain moisture content of Treatment 1 was 0.8 percentage points lower than the grain moisture content of Treatment 2.  Grain moisture content of the hybrids ranged from a high of 19.5% for H-9403 to a low of 14.6% for H-7476RR. Four hybrids (H-9403, H-9533Bt, H-9230Bt, H-9481Bt) had moisture contents greater than 19% and three hybrids (H-6551Bt, H-6800Bt, H-7476RR) had moisture contents below 15.5%.

The main effects of hybrid and irrigation treatment for grain yield were statistically significant (Table 3).  The hybrid x irrigation treatment interaction for grain yield was not significant.  Grain yield averaged across corn hybrid and irrigation treatment was 11,021 lbs/acre (196.8 bushel/acre).  Grain yield in Treatment 1 was 25% lower than the grain yield of Treatment 2 (225.4 bushel/acre for Treatment 2 versus 168.2 bushel/acre for Treatment 1).  Grain yields of hybrids ranged from a high of 13,950 lbs/acre (249.1 bushel/acre) for H-9403 to a low of 6,770 lbs/acre (120.9 bushel/acre) for H-6573.  Three hybrids (H-9403, H-9230Bt, H-9533Bt) were high yielding and six hybrids (H-8123, H-6800Bt, EX 07704RR, H-6551Bt, H-7265Bt/RR, H-7272, H-6573) had yields lower than 10,000 lbs/acre (178 bushel/acre).

The main effects of hybrid and irrigation treatment for test weight were significant (Table 3).  The hybrid  x irrigation treatment interaction for grain test weight was also significant, indicating that the test weights of corn hybrids responded differently to the irrigation treatments.  Test weight averaged across corn hybrid and irrigation treatment was 57.6 lbs/bushel.  Test weight between Treatment 1 and Treatment 2 only differed by only 0.45 lbs/bushel, but this difference was significant.   

Blunt ear syndrome symptoms in 2000 at the Fruita Research Center were not as severe as in many other years.  The main effects of hybrid and irrigation treatment for BES score were significant (Table 3).   The hybrid x irrigation treatment interaction for BES score was also significant in 2000.  BES score averaged across corn hybrid and irrigation treatment was 7.6.  BES score ranged from a high of 8.6 for H-8562 in Treatment 2 to a low of 6.0 for H-2581 in the Treatment 1.

A previous study conducted at Fruita in 1999 showed that irrigation affected BES.  In 1999, over irrigation, accomplished by irrigating every 30-inch furrow for 24 hours, decreased BES score by an average of a one numerical BES score compared to irrigating every other 30-inch furrow for 24 hours.  In 2000, BES score in Treatment 1 was 0.5 BES score lower than in Treatment 2.  

Pioneer Corn Hybrids

The main effects of hybrid and irrigation treatment for plant population were significant (Table 4).  The hybrid x irrigation treatment interaction for plant population was also significant.  Average plant population was 34,902 plants/acre.   Treatment 2 had a significantly lower plant population than Treatment 1.  The plant population in Treatment 2 was 6.6% lower than in Treatment 1.  

The main effects of hybrid and irrigation treatment for grain moisture content were statistically significant (Table 4).  The hybrid x irrigation treatment interaction for grain moisture content was not significant.  Grain moisture content averaged across corn hybrid and irrigation treatment was 16.7%.   Grain moisture content in Treatment 1 was 0.4 percentage points lower than the grain moisture content in Treatment 2.  Grain moisture content of the P3522 was significantly lower than P3461 and P3514.   Differences in grain moisture content between P3461 and P3514 were not statistically significant. 

The main effect of  irrigation treatment and the hybrid x irrigation treatment interaction for grain yield were not statistically significant (Table 4).  The main effect of hybrid for grain yield was statistically significant.  Grain yield averaged across corn hybrid and irrigation treatment was 11,826 lbs/acre (211.2 bushel/acre).  P3461 had a significantly higher grain yield than P3522 and P3514.  Grain yield of P3461 averaged 17.5% higher than P3522 and P3514.  Differences in grain yield between P3522 and P3514 were not statistically significant. 

The main effect of  irrigation treatment and the hybrid x irrigation treatment interaction for test weight were not statistically significant (Table 4).  The main effect of hybrid for test weight was statistically significant.  Test weight averaged across corn hybrid and irrigation treatment was 59.6 lbs/bushel.  P3514 had the highest test weight at 60.6 lbs/bushel and P3461 had the lowest test weight at 58.9 lbs/bushel, while the test weight of P3522 at 59.5 lbs/bushel was intermediate between P3522 and P4561. 

The main effects of hybrid and irrigation treatment for BES score were significant in this study (Table 4).  BES score averaged across corn hybrid and irrigation treatment was 6.8.  Treatment 2 had a significantly lower BES score than Treatment 1.  BES score for the Treatment 2 was 6.4 versus 7.3 for Treatment 1, a difference of nearly 1.0 BES score.  The hybrid x irrigation treatment interaction for BES score was also significant. In Treatment 1, differences in BES scores among the three hybrids were not as great as they were in the Treatment 2.  BES score of P3514 was not affected by irrigation treatment. BES score of P3461 was significantly lower than P3514 in Treatment 2, but P3461 responded similarly in both irrigation treatments.  BES score of P3522 was significantly lower in Treatment 2 than the BES score of P3522 in Treatment 1.

In previous studies BES scores of the susceptible corn hybrids were also affected by irrigation.   Considering the data from 2000 and other years it appears that water application has an effect on BES development.  More research is needed to obtain an increased understanding of how irrigation water management affects BES development.

Fithian, Wayne A.  1999.  Etiology and management of blunt ear syndrome of corn.  M.S. Thesis. Colorado State University.  Fort Collins, Colorado.
 
Pearson, C. H., and W. A. Fithian.  1993.  Blunt ear syndrome - a new disease phenomenon in corn.  Agron. Abst.  85:143-144.

Pearson, C.H., and H.M. Golus.  1990.  Ear stunting in Western Colorado.  Technical Report TR90-7.  Agricultural Experiment Station.  Colorado State University, Fort Collins, Colorado.

Appreciation is expressed to Lot Robinson, Fred Judson (Wester Colorado Research Center staff), and Daniel Dawson (part-time hourly employee) who assisted with the fieldwork for this study.  We appreciate the funding provided by Wayne Fithian and Golden Harvest, and the interest and support of Golden Harvest and Pioneer Hi-Bred in our efforts to better understand Blunt Ear Syndrome.  Thanks to Carroll Bennett for digitizing and manipulating the pictures used in this report.  Thanks to Dr. Abdel Berrada and Bob Hammon for their reviews of the report.