Ethephon on cherries in a dry season

Follow these recommendations to avoid injury when applying ethephon to drought-stressed cherry trees.

Ethephon is a plant growth regulator and its uses vary with plant species, chemical concentration and time of application. Ethephon regulates phases of plant growth and development by application to various growth sites. This plant growth regulator has systemic properties where it penetrates the plant tissues and is decomposed to ethylene. This decomposition impacts the plant’s growth processes. In cherry systems, ethephon promotes fruit loosening to facilitate mechanical harvesting. Ethephon, sold under the trade name Ethrel, has been used as a common management practice in both tart and sweet cherry harvest.

Ethephon releases ethylene, which penetrates plant cells and binds to receptors that affect expression of various genes. In the case of cherries, ethephon affects the gene that controls the synthesis or activation of cell wall loosening enzymes such as polygalacturonase and pectin methylesterase, thus dissolving the pectins between cells in the abscission layer. This chain-like reaction leads to cell separation in the developmentally-programmed abscission zone between pedicel and fruit or pedicel and spur. In short, ethephon loosens the cherries from the stem, which results in a gentle “shaking” of the tree to remove the fruit.

One main concern in recent years has been the amount of ethephon-induced damage with the hot, dry weather conditions. Ethephon can have excessive activity under a certain set of conditions that can result in tree injury. Trees under stress, particularly drought stress, become more susceptible to ethephon damage. Damaged trees exhibit excessive gumming, and branches lose their leaves.

Timing the ethephon application is an important factor. A lower rate of ethephon provides adequate loosening if given adequate time for action (10 to 14 days), while higher rates will loosen fruit to the same degree more quickly. Therefore, it is possible to substitute time for rate and obtain the same effect. Secondly, it is important that the chemical not be applied too early in the season. The fruit should be in Stage III of growth, where the fruit is growing rapidly and the grass-green color begins to yellow or take on a tinge of red. If ethephon is applied earlier than Stage III, the fruit may fail to grow further and has the potential to drop off the tree with the stems attached.

As mentioned above, both temperature and tree vigor are associated with the degree of response achieved. At higher temperatures during the 72 hours following application, the magnitude of response is increased, and at lower temperatures it is decreased. Trees low in vigor or under stress respond to a greater extent, and gumming and leaf abscission may result.

The following recommendations should be used when applying ethephon to cherries.

Rate. Vary the rate depending on anticipated temperatures for 72 hours after application, days before harvest, tree stress and past experience. Lower rates decrease the likelihood of tree injury.

  • Light sweets. When applied concentrate (80 gals. water/acre or less), 1 to 2 pts/acre applied 10 to 14 days before anticipated harvest should provide adequate loosening. Rates up to 2.5 pts/acre may be necessary for harvesting in less than 10 days. When applied dilute, use no more than 0.75 pt/100 gals or 3 pts/acre.
  • Dark sweets. When applied concentrate, use 1.5 to 2.5 pts/acre applied 10 to 14 days prior to anticipated harvest. Rates up to 3 pts/acre may be necessary for harvesting in less than10 days. When applied dilute, use no more than 1 pt/100 gals. or 4 pts/acre.
  • Tart cherries. When applied concentrate, use 0.5 to 1 pt/acre applied 7 to 14 days prior to anticipated harvest. When applied dilute, apply no more than 1/3 pt/100 gals or 1 pt/acre.

Time of application. Apply approximately 7 to 14 days before anticipated harvest. Do not harvest within seven days of application (seven-day PHI).

Temperature. Avoid application when high temperatures are expected to exceed 85°F or remain below 60°F for the 72-hour period after application. Use relatively high rates when high temperatures are expected to be in the 60s and lower than normal rates when highs are expected in the lower 80s.

Tree stress. Do not spray trees that are low in vigor or under stress conditions.

Do not spray trees that had serious gumming the previous year.

Crop load. Heavy crop load, such as low leaf to fruit ratio, is more difficult to loosen, so use relatively higher rates or expect a longer time to achieve desired loosening.

Concentrate spraying. Applying ethephon with concentrate sprayers, such as 80 gallons of water per acre or less, achieves the same level of loosening at lower rates per acre than does dilute applications. Uniform coverage is important.

Tree size. Suggested rates per acre are based on full-sized trees. Adjust rates downward when treating blocks with smaller trees.

Growers should pay particular attention to the temperatures. As evident from the last three seasons, hot temperatures can really do damage to cherry trees. Growers that have had problems in the past years should avoid ethephon, especially if the trees showed serious gumming and leaf loss.

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