How to advance bud break and achieve more uniform flowering: expert advice

In general, cherry trees depend heavily on chill accumulation to initiate bud break and ensure that it occurs uniformly. In recent seasons, difficulties have been recorded in meeting the chilling requirement, as winters are becoming increasingly mild and the accumulated chill is of lower quality.

In this scenario, products for dormancy breaking play an important role in the operations to be carried out at the end of the winter rest period.

The application of these products promotes better vegetative recovery of orchards after the winter rest period. Their main function is to advance and synchronize bud break, promoting tissue opening even when the specific chilling-hour requirement of each variety has not been fully met.

In seasons characterized by a greater accumulation of chilling hours with a base temperature of 7.2 °C, applications should be brought forward. Conversely, when chill accumulation is lower, applications should be delayed, especially in the case of hydrogen cyanamide.

In this way, interference with dormancy and chill accumulation is minimized until July 30.

The use of products for dormancy breaking makes it possible to advance the harvest and, in other cases, to adopt strategies aimed at staggering it. It is undoubtedly necessary to apply a specific product to achieve concentrated and uniform phenology, allowing the treatments included in the phytosanitary program to be carried out more efficiently and, naturally, to produce high-quality fruit.

Insufficient chill and inadequate accumulation of growing degree days compromise flower quality, affecting the quality of pollen and the formation of the ovary. These aspects are directly related to the final quality of the fruit.

It is important to consider that advancing bud break exposes the orchard to a greater risk of cold damage, since any winter frosts may affect more sensitive tissues. In the presence of this risk, applications should therefore be delayed.

If repeated frosts occur on the days scheduled for treatments or after application, it is essential to immediately activate frost protection systems.

The rates of cyanamide and the application dates must be defined according to the variety and geographic area. In any case, treatment must not be carried out before at least 70% of the chilling-hour accumulation required by the specific variety, with a base temperature of 7.2 °C, has been reached.

The application of products for dormancy breaking is even more important when winter chill accumulation is reduced. Milder winters, in fact, cause a loss of reserves and lower flower-bud quality, resulting in reduced viability of pollen and ovules and, consequently, reduced fruit set.

Orchard with heterogeneous bud break and flowering:

Orchard with uniform bud break and flowering thanks to the use of products for dormancy breaking.

Hydrogen cyanamide

The programs for the use of cyanamide and other products for dormancy breaking, differentiated according to varieties, are as follows.

Program 1: use of hydrogen cyanamide to advance bud break

If the winter is characterized by low chill accumulation or insufficient-quality chill, it is recommended to delay the application of hydrogen cyanamide so as not to interrupt the chill accumulation process and to promote adequate overcoming of dormancy.

It is important to remember that Dormex or Cianamida 50, both based on hydrogen cyanamide, do not in any way compensate for missing chilling hours. On the contrary, they advance the accumulation of growing degree days and act through a caustic effect: they burn and separate the bud bracts, exposing the internal green tissue to temperature.

This allows heat accumulation and triggers bud break in the trees.

Considering the mode of action of the cyanamide and nitrate mixture, it is very important to ensure uniform coverage and avoid dripping, in order to prevent phytotoxicity affecting the spurs.

In orchards characterized by a high incidence of bacterial canker, wood fungi, or the presence of very weak trees, DO NOT apply hydrogen cyanamide or any other dormancy-breaking product.

Program 2: use of hydrogen cyanamide and bud-break uniforming agents to advance the harvest of early varieties

Program 3: use of hydrogen cyanamide and bud-break uniforming agents to advance the harvest of mid-season and late varieties

Bud-break uniforming agents.

Program 4: use of ONLY uniforming agents to achieve uniform bud break

Program 5: use of ONLY uniforming agents to achieve uniform bud break in late varieties

Guidelines to consider before application

1. Do not carry out treatments before reaching at least 60-70% of the chilling-hour requirement of the variety concerned.
2. Do not apply dormancy-breaking products in orchards less than four years old, characterized by low vigor or a certain incidence of bacterial canker or wood diseases.
3. Bud fertility analysis is a useful tool for assessing the health status of the spurs and provides objective data on which to base the decision to carry out the treatment.
4. As part of strategies aimed at advancing or staggering the harvest, do not apply cyanamide before July 15 on early varieties.
5. Always carry out the application with average temperatures above 13 °C and with no rainfall for at least five hours after treatment.
6. Do not repeat the treatment in the event of rainfall after application.
7. Comply with the concentrations indicated on the label: from 1.5 to 2.5% in the case of cyanamide; 5% in the case of Siberio, Erger and Light Up; 8% in the case of Prostar Plus; 6% for calcium nitrate. All concentrations indicated refer to 100 liters of water and must be adapted to the commercial product used.
8. Use an adequate spray volume to avoid phytotoxicity damage. It is important to remember that the application must be carried out considering 70% of the VHA, i.e. the tree-row volume.
   
   
   
   
9. It is essential that the spraying equipment be in optimal condition and perfectly calibrated. Product dripping must be avoided and coverage of the wood within the canopy must be as uniform as possible.
10. Use soluble calcium nitrate, dissolving it beforehand in 20 liters of water. The solution must then be added to the mixture containing the uniforming product in the sprayer tank. Due to the chemical reaction between the products, foam formation is completely normal.

Patricio Morales
Agro Asesoria

Opening image source: Stefano Lugli

Cherry Times - All rights reserved