Tech note – getting the best results from ethephon

The pH of your spray tank water impacts results when you use ethephon plant growth regulator for seedhead suppression?

In this tech note, we discuss how you can save time and money by managing your spray tank water.

What is ethephon used for?

Ethephon [i.e., Incognito (480g/L active ingredient) or intercept (480g/L active ingredient)] is used to suppress Poa annua (Wintergrass) seedhead emergence in turfgrass. When ethephon [(2-chloroethyl) phosphonic acid] breaks down it releases ethylene gas. Several factors influence PGR efficacy, and in this Tech note, we discuss how spray water alkalinity affects ethephon plant growth regulator.

The graph below is courtesy of Greenhouse product news magazine1Walters K and Lopez RG, Enhancing Your PGR Applications — Part 1. Greenhouse Product News, November 2017, 10L/Ha of ethephon in 400L equates to 250ppm.


Water Alkalinity and pH.

The pH of your tank water influences many turf chemicals. For example, we are all aware that water pH affects iprodione, but are you aware that it also impacts ethephon performance?

When you use ethephon for seedhead suppression, it converts into the active gas ethylene. At an acidic pH of 4.5 or less, ethephon is stable and doesn’t break down to ethylene.

However, as the pH increases, this conversion to ethylene occurs more quickly. The key to getting the best performance from ethephon is to keep it in the liquid form as long as possible before it enters the turfgrass.

Managing the water pH keeps ethephon in the liquid form for much longer. So the aim is to keep the water pH below 4.5.

Ethephon is acidic, and when you add it to the tank it lowers the water pH. However, if the spray water has a high alkalinity (CaCO₃), the pH may not fall enough to drop below 4.5.

Once it is taken up by the plant, the plant’s more neutral pH causes the chemical to convert to ethylene over several hours.

The bottom line is if you use this chemical, test your water alkalinity before you mix it. This can be done with a handheld alkalinity metre.

If the alkalinity is too high, then add the spray adjuvant Proforce Manta Ray to lower the pH and alkalinity. Then add the chemical and recheck the spray solution to make sure it is still below 4.5.

Hand held alkalinity metre for use with ethephon
Manta Ray tank adjuvant and spray tank buffer


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    Walters K and Lopez RG, Enhancing Your PGR Applications — Part 1. Greenhouse Product News, November 2017,
Jerry Spencer senior turf agronomist and soil scientist
Senior Turf Agronomist at Gilba Solutions Pty Ltd | 0499975819 | Website

Graduated from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) as a turf agronomist before emigrating to Australia in 1993.

He followed this by gaining a Grad Dip in Business Management from UTS. He has worked in a number of management roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.

He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions as an independent sports turf consultancy in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.