ProTone Plant Growth Regulator Vs. Ethephon

Compare Modes of Action to See How Both of These Leading PGRs Can Work for You

Bad coloring years can be quite costly for growers of red table grapes. In fact, between 10% and 40% of the fruit can remain unpicked due to poor color. Prior to the introduction of Valent BioSciences’ ProTone, the plant growth regulator ethephon was the only coloring tool growers had available. But now both of these compounds can be used in an integrated program to maximize benefits. How?

Ethephon releases ethylene gas that enhances ripening and turns berries red. But because it enhances ripening, ethephon also begins the process of softening the fruit. The storage life of softened fruit can be shortened considerably, causing big problems for growers, especially those seeking to tap into distant and lucrative export markets.

ProTone overcomes this challenge by increasing an enzyme, UDP-glucose-flavonoid 3-0-glucosyltrans ferase, or UFGT. This enzyme increases anthocyanin, the red coloring agent of the berry. ProTone does not affect ethylene production at all.

It’s also important to note that because ethephon initiates senescence in grapes, growers must wait until veraison to apply. Veraison is a vague term referring to the onset of ripening, typically regarded as the point when 50% of the berries are soft. ProTone can be applied earlier than ethephon can – a significant benefit. In Flame grape production in the Coachella Valley of California, for example, softening to harvest can be only 14 days. Since ethephon’s preharvest interval (PHI) is 14 days, application for coloring can be tight. With ProTone, a grower can come in earlier. ProTone also has a (PHI) of zero days, and the re-entry Interval (REI) is just the bare minimum of 4 hours.

How It Looks In The Field

ProTone is not intended to replace ethephon. In fact, the two work well together in an integrated program designed to increase marketable yield. With ProTone, color will begin on contact. ProTone is not translocatable. It does not work as fast as ethephon because it increases an enzyme which then produces anthocyanin which then must work its way through the fruit.

Flame Seedless Northern Cape - South Africa
Color development 3 weeks after the 1st spray application (1 wk. before harvest 1)
Untreated 200 ppm ethephon
(Veraison & Veraison + 7d)
200 ppm ProTone
& Veraison + 7d)
200 ppm ProTone™ + 200ppm ethephon
(Veraison) & 200 ppm ProTone (Veraison + 7d)

Because ethephon translocates throughout the plant, application to the leaves can help color the fruit. Another point to remember: the ethylene gas that ethephon produces generally works faster at higher temperatures.

Application Techniques Differ

Understanding how ProTone works its way through the fruit is critical to the techniques you use to apply it. Some refer to ProTone application as “painting” the fruit, meaning that if a grower only sprays one side of a cluster, the other side of the cluster won’t color.

To color berries inside clusters, growers can’t just casually spritz the product on the vine. Spray volumes of 80 to 150 gallons per acre are recommended for conventional spray equipment, which is often more than growers are accustomed to applying at this timing. With ethephon, growers might use only 40 to 50 gallons per acre, driving at a high speed. But because of the need for complete and thorough coverage, ProTone applications require a slower application, with product directed at the fruit clusters.