Growth Stimulants Retardants and Rooting Hormones Growth regulators

Growth Stimulants, Retardants, and Rooting Hormones

Growth regulators ¡ Hormones ¡ Organic chemicals that act and interact to affect growth rate ¡ Auxins – accelerate growth by stimulating cell enlargement

Gibberellins ¡ Stimulate growth in stem and leaf by cell elongation ¡ Stimulates premature flowering, growth of young fruits and breaking of dormancy

Cytokinins ¡ Stimulate cell division ¡ Work along with auxins ¡ Will not work without auxins present

Inhibitors ¡ Abscisic Acid and Ethylene Gas ¡ inhibits seed germination ¡ Inhibits stem elongation ¡ Hasten ripening of fruit – ethylene gas

¡ Auxins and Gibberellins promote cell enlargement ¡ Cytokinins stimulate cell division

Growth Hormones ¡ Organic chemicals produced by actively growing plant tissue ¡ Shoot tips and young leaves ¡ Move throughout the plant and can be found in most tissues

¡ These chemicals react with one another in a very complex system in the plant ¡ In some cases a concentration of one hormone stimulates growth and a different concentration restricts growth

Apical Dominance ¡ Dominance of the terminal bud ¡ Apical dominance exists there ¡ Terminal bud secretes chemicals that inhibit or prevent the growth of axillary buds on the same shoot

Apical Dominance ¡ Axillary buds are found in the axil – angle between a leaf and the stem. ¡ Causes the plant to grow tall and not branch ¡ Once the plant reaches flowering age and the terminal bud becomes a flower, the chemicals are no longer secreted

Apical Dominance ¡ The plant then starts to send out side branches ¡ This allows the plant to grow above competing plants ¡ Once height and access to sunlight are secured, the plant spreads out over its competitors

Apical Dominance ¡ Pinching off terminal buds removes the hormone and causes branching to happen faster ¡ Common practice in greenhouses and nurseries to produce bushier plants with many flower buds

Stimulants ¡ Allow plants to grow taller ¡ Most common is Gibberellic Acid (GA) ¡ Causes stems of plants to stretch out ¡ Nodes are farther apart

Growth Stimulants ¡ Natural growth stimulants have been found in alfalfa ¡ It causes stimulation of growth ¡ It is the alcohol called Triacontanol ¡ Stimulation is brought about by mulching plants with alfalfa hay

¡ Or watering plants with a “tea” made from soaking alfalfa feed pellets in water ¡ Amount needed is very small ¡ Also sold commercially

Chemical Retardants ¡ Chemicals are used to retard growth of plants causing them to be shorter and more compact ¡ Plants are more attractive and the plants themselves are stronger ¡ Used commercially ¡ B-Nine is commonly used on Azaleas

¡ Newest uses of Plant Growth Retardants (PGR) is the application to lawns ¡ After first mowing in the spring “Limit” is applied and absorbed by the roots ¡ Restricts growth for 6 -8 weeks

¡ “Embark” is absorbed by the leaves and also restricts growth ¡ PGR’s absorbed by the leaves move to the growing point where it interrupts cell division, stem elongation and seed head formation ¡ Roots continue to grow ¡ Applied after first or second mowing

Sumagic ¡ New growth retardant ¡ Reduces height of plants by inhibiting production of GA ¡ Chemical is taken up by leaves and moves through the plant to the terminal bud

¡ Used to control growth of shrubbery and hedges ¡ PGR Atrimmic applied after pruning can last an entire season ¡ Reduces or eliminates the need to prune

Atrimmic ¡ A systemic ¡ Penetrates the plant, enters the plant sap, and moves through the plant ¡ Blocks plant hormones that stimulate growth ¡ Applied as a foliar spray

Rooting Hormones ¡ Important when propagating plants by cutting ¡ Helps cuttings to develop more roots faster than without a rooting hormone ¡ Indoleacetic Acid (IAA) naturally occurring, causes roots to form on plant stems

IBA – Indolebutyric Acid ¡ Most widely used rooting hormone ¡ Most effective rooting hormone

Rooting Hormones ¡ Either mixed with talc and used as a powder or dissolved in water and used as a wet dip ¡ Liquid can be slightly more effective ¡ All rooting hormones should contain a fungicide

Fungicide ¡ Helps prevent cuttings from rotting

Dwarfing Rootstock ¡ Used in fruit trees ¡ Shorter trees enable you to pick fruit without using a ladder ¡ First research done to prevent apple trees from growing very tall ¡ Trees growing from certain types of roots didn’t grow as tall

¡ These trees also bore fruit at an earlier age ¡ Complete series of rootstock known as malling rootstock developed in England ¡ Controls size and rate of growth or apple trees

¡ Stock has also been developed for peach and pear trees as well ¡ Dwarf trees can be purchased commercially

Chemical Blossom Set ¡ Used on tomato blossoms early in the season ¡ Causes earlier development of fruit ¡ Causes seedless tomatoes to set on first blossoms and results in tomatoes ready to eat as much as 10 days earlier than normal

Plant Biostimulants ¡ Natural products ¡ Organic ¡ Work to stimulate soil microbial activity and improve soil cation exchange capacity, stimulate plant growth and promote disease resistance

Humic Acid ¡ Product of rotting organic matte is an example of a soil microbial stimulant

Root growth biostimulants ¡ Improve water and nutrient uptake ¡ Increase number of fibrous roots ¡ High levels found in kelp plants

Biostimulants ¡ Greatly reduce the need for fertilizers, especially N ¡ Saves money, reduces pollution

Methanol ¡ A form of alcohol ¡ Speeds plant growth ¡ Research in California showed an increase in plant yield of 36 -100% ¡ Works by blocking photrespiration ¡ Plants use water for growth rather than transpiring it into the air

Methanol ¡ Works best on plants frown in full summer sun ¡ Water use reduced by as much as 50% in some plants

Allelopathy ¡ Production of a chemical compound in one plant that slows or stops the growth of another plant ¡ Natural herbicide ¡ Black Walnut, Millet