Usage of paclobutrazol (Cultar)

Mango    India

In one of the episode regarding maintenance of mango trees I learnt about the chemical called paclobutrazol (Cultar) which should be provided to trees during the month of September. However, my research on the internet confuses me on this aspect. While there definitely appears to be a positive impact on flowering and growth of fruits, the chemical apparently inhibits microbial activity which reduces soil quality. Moreover, there are also some articles which say that it may have carcinogenic effects.

I therefore request you to kindly clarify the same. Further, is there any organic substitute for the same.

Posted by: Abhishek (1 point) Abhishek
Posted: May 20, 2018


It would be helpful if you could provide links to the articles you mention

You soil is bare from the photo and you could improve the microbial community through mulching. This would offset any perceived effect of Cultur on the soil. With that said, you havent told me what the effect on the soil so I dont know. Cultar is a plant growth inhibitor belonging to the triazole group so I dont know how it affects microbes (do you mean fungi and bacteria?)

Below is some text from here https://dpir.nt.gov.au/__data/assets/...

(also, check this https://www.ijcmas.com/7-2-2018/Satye...)

How does paclobutrazol act?
Available evidence strongly suggests that flower initiation depends on the presence of an unknown flowerpromoting
factor or factors synthesised in the leaves. At the same time, there are other factors in the shoots
which work against the flowering factor or factors. It is believed that a group of plant hormones called
gibberellins act as inhibitors to flowering. When paclobutrazol is applied to the soil, it moves up through the
roots into the shoots and, due to its anti-gibberellin properties, blocks the synthesis of flowering inhibitors,
thereby allowing the flower-promoting factor(s) to work.
How and when to apply paclobutrazol?
The application of paclobutrazol to soil as a drench around the tree trunk (collar drench) is the most effective
method, as it ensures proper uptake by the tree. The required quantity is mixed in approximately one litre of
water and poured onto the soil around the trunk in a circular band. In the Top End, the ideal time to apply
paclobutrazol is from soon after harvest to early January. In dry conditions, a light irrigation is recommended
after application. Foliar sprays have been ineffective.
At what age should trees be treated and when should treatment be repeated?
The size of trees at first application is important. This depends on the age of the trees and the spacing
between them. Apart from promoting flowering, paclobutrazol also restricts tree vigour. Trees should
therefore be allowed to develop a good canopy before treatment commences. In high tree density situations
with closer spacing, it is recommended to apply paclobutrazol early when trees are about three years old.
However, when trees are spaced farther apart, say 10 m, early application with paclobutrazol will reduce
canopy size and the fruit bearing area. In such a situation, treatment can commence when trees are about
five years old. Tree size and canopy fill are important considerations. Large trees, especially seedling
trees, respond more slowly than young, bearing, grafted trees. The dosage required also varies between
cultivars. Florida cultivars, such as Irwin, Glen and Tommy Atkins require a lower dosage than Kensington
At excessively high dosages, flower and shoot compaction can lead to increased infestation by caterpillars. If
such compaction occurs, the dosage of repeat applications should be reduced., Two sprays of potassium
nitrate at 4 g/L at ten-day intervals, commencing at signs of flower bud burst, were found to minimise panicle
compaction. However, compaction is best prevented by using an optimum dosage. If you are not sure
about dosage and/or if your trees are ready for the treatment, seek expert advice.
It is also important to note that tree size and not age is the key factor for determining dosage. Where there is
considerable variation in tree size, dosage may have to be varied.

Posted by: David Hughes (54 points) David Hughes
Posted: May 20, 2018

You need to log in if you'd like to add an answer or comment.