Make More Avocado Fruit

As of March 27, 2018, foliar application of GA₃ (ProGibb LV Plus®, Valent BioSciences, Corp.) to ‘Hass' avocado trees in commercial orchards has been approved. Dr. Carol J. Lovatt, emerita professor of plant physiology at the University of California – Riverside, recently completed research concerning the effectiveness of ProGibb LV Plus® on avocado fruit size and yield. A summary of her research — including best practices — follows.

Application Best Practices

ProGibb LV Plus® should be applied as a foliar spray when 50 percent of the trees in a block are at the cauliflower stage of inflorescence. If a grower cannot make an application at this time, it is best to apply the spray later, rather than earlier in order to ensure effectiveness.

The spray should be applied like a pesticide spray — full canopy coverage with a focus on the inflorescences. Those applying the spray should avoid spraying to run-off.

The ideal dilution for ground application is 12.5 fluid ounces of ProGibb LV Plus® (25 grams active ingredient [gai]) per 100 gallons of water/acre. For aerial application, use 12.5 fluid ounces (25 gai) in 75 gallons of water/acre. According to the research, the ideal application rate is 25g GA₃ per acre; higher and lower doses were less effective. The pH of the water used should be adjusted such that the final pH of the spray solution is between pH 5.5 – 6.0.

Dr. Lovatt utilized organosilicone surfactant Silwett L-77® or Widespread Max® at a concentration of 0.05 percent as a wetting agent. Similar pure organosilicone type surfactants would be acceptable as wetting agents. It is important to note that until additional research can be conducted, other materials should not be included in the ProGibb LV Plus® spray solution.

Effect of ProGibb LV Plus® (GA₃)

Dr. Lovatt's research team tested the effect of ProGibb LV Plus® on fruit size and yield for both ground and aerial applications. Overall, the research team noted that GA₃ had no negative effects on ‘Hass' avocado fruit quality.

Ground applications were tested in March at groves located in Corona, Irvine and Somis, California. The tests were run on Duke 7 clonal rootstock trees at the cauliflower stage of inflorescence development. Each of the groves reported net increases in total yield and large/commercially valuable size fruit. The results were as follows:

Table 1. Effect of GA₃ (25 g ai/acre) applied at the cauliflower stage of inflorescence development on yield and fruit size (pounds/tree) of ‘Hass' avocado trees in Corona, CA.

^z Values in a vertical column followed by different letters are significantly different at specified P-values by Duncan's Multiple Range Test at the P-values indicated. (From the work of Salazar-García and Lovatt, 2000).

Table 2. Effect of GA₃ (25 g ai/acre) applied at the cauliflower stage of inflorescence development on yield and fruit size as pounds and number of fruit per tree in an alternate bearing ‘Hass' avocado orchard in Irvine, CA.

^z Values in a vertical column followed by different letters are significantly different at specified P-values by Duncan's Multiple Range Test at the P-values indicated. (From the work of Lovatt and Salazar-García, 2007; Zheng et al., 2011)

Table 3. Effect of GA₃ (25 g ai/acre) applied at the cauliflower stage of inflorescence development at on yield and fruit size of ‘Hass' avocado trees in Somis, CA. Percent net increase reflects the benefit of GA₃ at 25 g ai/acre relative to the untreated control trees.

^z Values in a vertical column followed by different letters are significantly different by Fisher's Protected LSD test at the P-values indicated.

Overall, ground application of GA₃ resulted in a net increase of 3,905 lb/acre, with a net increase of 4,851 lb/acre of commercially valuable size fruit (packing carton sizes 60+48+40; 178-325 g/fruit) and a net increase in large fruit (packing carton sizes 48+40+36; 213-354 g/fruit) of 4,488 lb/acre.

Aerial applications were tested on groves located in Pauma Valley and Carpinteria, California. Together, the aerial applications demonstrated that GA₃ increased fruit set (fruit retention) by 55 percent into the last week of August and fruit size by 6 percent through mid-August.

Ultimately, Dr. Lovatt's research indicates that use of GA₃ could result in substantial increases in net dollar return per acre to the grower due to increase in yield and commercially valuable size fruit. In addition, growers whose avocado groves are not suited to ground applications (groves located on slopes or in high-density formations) can benefit from the efficacy of utilizing aerial applications. In summary, ProGibb LV Plus® is “vital to the California avocado industry to increase grower income per acre to help sustain the California avocado industry.”

N.B.  Remember, only well managed trees are going to respond.  This will not turn around a poor producing orchard. only potentially increase production on an already good producing orchard.  Ben