These data reinforce the importance of field testing corn hybrids for susceptibility to BES. Corn hybrids found to be susceptible to BES, can be marketed more precisely to minimize the possibility of growing susceptible hybrids in areas where a significant potential for BES exits. As with other agronomic studies, evaluating corn hybrids over several years will provide a more complete picture of hybrid response to BES. These data also indicate irrigation water management may affect the development of BES. Additional research on the effect of irrigation on BES is warranted.

Blunt ear syndrome (BES), 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. A portion of the ear tip is barren in an otherwise normal-looking husk. 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 eight 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 best location in the U.S. to study BES. The objectives of this research were: 1) to determine the effect of methyl bromide on BES symptom development. Previous research has shown methyl bromide used as a soil fumigant reduces BES symptoms in corn, 2) to evaluate Golden Harvest corn hybrids for their susceptibility to BES, and 3) to determine the effect of irrigation on BES development. Previous research conducted in 1997 at the Fruita Research Center indicated that irrigation may affect BES development.

Methyl bromide application

Methyl bromide was applied at the Colorado State University, Western Colorado Research Center at Fruita to determine if soil fumigation would affect the development of BES. The experiment was a randomized complete block with three replications. Plot size was 10 feet wide and 30 feet long. Methyl bromide was applied at the rate of 1 lb of methyl bromide per 300 ft² on April 21, 1999. Plastic tents covered the treated area until they were removed on April 26, 1999. Planting occurred on May 14, 1999 with Pioneer brand hybrid 3522. Corn plants were sampled (roots and 6-inch stalk length) on August 4, 1999 and were evaluated for internal bacterial and fungal hosts.

Bladex 4L herbicide was applied PPI at 2 qts/acre on May 11, 1999. Fertilizer applied was 36 lbs N/acre and 112 lbs P2O5/acre preplant of 18-46-0 on May 6, 1999, and 180 lbs N/acre of 32-0-0 was applied side-dress on June 22, 1999. Dimethoate insecticide (1pt/acre) was applied on June 21, 1999. Also, Comite II (2.25 pt/acre) was applied on July 18, 1999 and Capture 2EC (6.4 fl oz/acre) was applied on August 15, 1999.

Grain yields were not obtained in this study. Just prior to the scheduled harvest date strong winds caused extensive lodging and ear drop. Yield losses were so severe that harvesting to determine yield was not possible.

Evaluation of Golden Harvest and Pioneer Hybrids for BES

Twenty Golden Harvest brand corn hybrids were evaluated for BES at the Colorado State University Western Colorado Research Center at Fruita in 1999. The experiment was a randomized complete block with four replications. Plot size was 5 feet wide and 50 feet long. The previous crop was corn and the soil type was a Glenton very fine sandy loam. The seedbed was prepared using clean tillage. Bladex 4L was applied preplant incorporated at 2.0 qts/acre on May 11, 1999. Planting occurred on May 14, 1999 with a white air planter that had been modified for planting small plots. Both corn rows of each plot were counted the length of the plot on June 15, 1999 to determine plant populations

Bladex 4L herbicide was applied PPI at 2 qts/acre on May 11, 1999. Fertilizer applied was 36 lbs N/acre and 112 lbs P2O5/acre preplant of 18-46-0 on May 6, 1999, and 180 lbs N/acre of 32-0-0 was applied side-dress on June 22, 1999. Dimethoate insecticide (1pt/acre) was applied on June 21, 1999. Also, Comite II (2.25 pt/acre) was applied on July 18, 1999 and Capture 2EC (6.4 fl oz/acre) was applied on August 15, 1999. .

Corn in each plot was evaluated for BES symptoms on Nov. 19, 1999 using our 1 to 9 rating scale (Table 1). Grain yields were not obtained in this study. Just prior to the scheduled harvest date strong winds caused extensive lodging and ear drop. Yield losses were so severe that harvesting to determine yield was not possible.

The 1999 growing season was favorable for corn production in western Colorado. Weed control in the field was excellent.

Application of methyl bromide did not affect BES in 1999 (Table 2). Previous studies showed BES severity was reduced by applying methyl bromide (Fithian, 1999). This was not the case in the study at Fruita in 1999. Furthermore, no internal fungal or bacterial hosts were found in corn plants.

Plant populations were significantly different among corn hybrids (Table 3). Average plant population was 37,188 plants/acre. The planter was set to plant 35,890 seeds/acre. If small corn seed is used in the planter, the planter plate cells often pick up more than one seed, resulting in seeding rates that are higher than the seeding rate set on the planter. This situation apparently occurred in this study. Six hybrids had high populations greater than 37, 800 plants/acre and ten hybrids had low plant populations of less than 37,100 plants/acre, as compared to other hybrids. The hybrid with the lowest plant population of 35,680 was EX97735RR.

Blunt ear syndrome symptoms in 1999 at the Fruita Research Center were not as severe as 1997 or 1998. Nevertheless, BES rating scores among corn hybrids were statistically different (Table 3). Hybrid H-7773Bt had the highest BES score of 8.3, which means this hybrid had little to no BES symptoms. Hybrid H-2581 had the lowest BES score of 4.9, and thus, had the highest expression of BES symptoms. BES scores for 16 out of the 20 hybrids were not statistically different. Hybrids with comparatively low scores, 7.0 and lower, were, H-2515, H-2551IMI, and H-2581.

A previous study conducted at Fruita in 1997 indicated that irrigation may affect BES development. In 1999, over irrigation, accomplished by irrigating every 30-inch furrow for 24 hours, decreased BES score by an average of a one numerical score compared to irrigating every other 30-inch furrow for 24 hours (Table 4). In the over-irrigation treatment, BES scores were not significantly different among the three hybrids, but in the normal irrigation the BES-tolerant hybrid (P3514) had the highest score, the moderately susceptible hybrid (P3461) had an intermediate BES score, and the susceptible hybrid (P3522) had the lowest BES score.

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 and Fred Judson (Wester Colorado Research Center staff), and Sara Albertson and Daniel Dawson (part time hourly employees) 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 BES.