The Effect of Two Growth Regulators on Dry-Bulb Onion Production

Lynn Jensen
Malheur County Extension Office
Ontario, OR, 1998


There have been reports in trade magazines about the positive response of growth regulators in dry-bulb onion production. Reports claim greater yields and larger size bulbs from treated fields. This project examined the effect of two growth regulators on onion bulb yield and size.

Materials and Methods

The growth regulators evaluated were Triggrr, manufactured by Westbridge, and Propel, manufactured by Entek. Trials were established on four grower fields in three locations, Ontario, Vale, and Oregon Slope, OR. Plots were 4-beds wide by 50-ft long. The first Triggrr application was made at planting by injecting the material into the soil through the planter shoe so that it was in close proximity to the germinating seed. The second application was made at the early bulbing stage by sidedressing the material into the bed approximately 2 inches to the side of the row. Propel was applied as a foliar spray at about mid-bulbing. The at planting Triggrr (soil) was applied at a rate of 23.9 oz/acre. The sidedressed Triggrr (foliar) was applied at 24.6 oz/acre and the Propel was applied at 23.9 oz/acre. The carrier was water at 30.7, 90.1, and 30.7 gal/acre respectively.

The application sites and varieties were as follows:

Table 1. Application of growth regulators on three onion varieties by sites and dates, OR, 1998.

      Planting Triggrr sidedress Propel application
Site Location Variety date application date date
1 Ontario Viper 3/19/98 6/10/98 7/10/98
2 Ontario Blanco Duro 3/30/98 6/10/98 7/10/98
3 Vale Viper 3/30/98 6/11/98 7/20/98
4 Oregon Slope Vision 4/20/98 6/11/98 -------

Results and Discussion

During the growing season no visible differences were noted in any of the plots. The two Ontario sites were decimated by a hail storm on July 4, which affected total size and yield. Twenty feet of the two center rows of each plot was harvested, and the onions were graded and weighed (Table 2).

Only one of the four trials had a significant response (P< 0.05) to the growth regulator. This was the Vale site (site 3) where the total yield was much less than at the Ontario site where the same variety was grown. The Ontario site also received hail, which reduced yields on all of the farms within the hail zone. Two of the sites had the untreated check as the highest yield, although this was not significantly different from the treatments. It is possible that the onions at site 3 were under stress during the growing season, and that stress may have enabled the growth regulators to stimulate additional growth. There may be some environmental conditions under which these materials enhance growth, but, if so, these conditions were not identified in these trials.

Table 2. The effects of Triggrr and Propel growth regulators on onion bulb yield and grade, 1998.

            Jumbo & Total 
Location Variety Treatment Medium Jumbo Colossal Colossal yield
Site 1 Viper Triggrr at planting / sidedressed 111 551 41 592 704
(Ontario)   Triggrr as sidedress only 90 538 36 574 665
    Propel 125 513 32 545 671
    Untreated check 98 561 48 609 707
    LSD (0.05) NS NS NS NS NS
Site 2 Blanco Duro Triggrr at planting and sidedressed 184 342 0 342 526
(Ontario)   Triggrr as sidedress only 172 316 0 316 488
    Propel 180 323 0 323 503
    Untreated check 196 269 0 269 466
    LSD (0.05) NS NS NS NS NS
Site 3 Viper Triggrr at planting and sidedressed 74 343 148 491 566
(Vale)   Triggrr as sidedress only 65 404 145 549 614
    Propel 67 376 142 518 585
    Untreated check 84 316 152 468 552
    LSD (0.05) NS 53.5 NS NS NS
Site 4 Vision Triggrr at planting and sidedressed 53 490 277 767 820
(Oregon Slope) Triggrr as sidedress only 58 578 236 814 871
    Untreated check 42 602 214 816 858
    LSD (0.05) NS NS NS NS NS