What are growth regulators?
Why do we use them?
Why should we use them?
How can we achieve the results other than by chemical inputs?
The significance of plant growth regulators (GRs) was recognised as early as 1932. The application of these compounds to mainly field environments was, and still is to some degree, fairly limited. The upturn in their present day usage has been promoted by major chemical companies worldwide.
Such products have a number of important uses. They can improve the period of time taken for establishment of the plant, thereby reducing the potential of weed ingress. They can also improve vegetative growth, hence better rooting and density of the plant.
The modern approach is to apply these GRs in order to reduce time and labour during mowing operations, while improving rooting, colour and sward density.
So, what are growth regulators? Basically, when a plant has the appropriate environment and conditions for the successful growth, i.e. water, light, air, root room, organic materials within the soil which include nutrition and natural growth factors, the condition is "balanced", hence it is strong, vigorous and healthy.
Under these balanced conditions the disease, stress and wear tolerances may prove to withstand planet earth's environmental pressures. These key issues are further compounded when players, members and officials demand all year round playing standards and facilities.
Natural GRs, or "hormones", act as a chemical messenger within the plant. Today's grass manager utilises chemical developments to change the plant's natural processes by using GRs to significantly effect plant growth. Today's synthetic GRs simulate a similar structure to that of the natural plant's hormones, however, the majority of these bear no relationship to natural plant hormones.
As greenkeepers and groundsmen react to pressure from external factors, we compromise our knowledge and education in order to satisfy demands from our "clients". In doing so we all too often sacrifice good knowledge and practices in order to exert the plant to grow quicker than its normal behaviour pattern, thereby accelerating growth, colour and sward. Whilst this removes the potential for complaint from officials, members and players and allows for an easy life, the natural processes within the plant are severely disrupted.
It has become the natural assumption that, in order to get the green turned around quickly, to get some growth in the grass in the spring and summer, whilst improving rooting and restoring density in the winter, we have to use chemicals.
Applying an artificial fertiliser takes between 7 to 10 days to show signs of uplift. Iron (Fe) is often applied to improve the aesthetics quickly. By this time we are mowing it in order to control the growth, particularly when the temperatures and vigour are favourable. Unfortunately, due to labour or equipment restraints, there is insufficient time to keep on top of this and the grass gets away, so we "manage" it with a growth regulator.
Not only can the GR reduce top growth, it can also improve rooting, create denser sward and improve colour. However, it does mean that we have to put some nitrogen (N) on to offset browning off. It's good, it's effective.
Although the greenstaff can utilise the plant GR to manage aggressive grass behaviour following high N applications, it is vitally important that the application rates and timings are carefully managed.
In most recent times, products affecting the balance of gibberellic acids (GA) are common place. The GAs shows very marked effects on growth, in particular promoting the rapid extension of plant cells. Today's GRs have proven chemical hormonal effects on the GAs, i.e. they suppress them, thus reducing the stem elongation.
When you apply synthetic, non organic nitrogen the plant language changes. Growth cell elongation, stem elongation and cell division are triggered more aggressively. The grass plant sugars are increased but, due to elongation of the leaf, stem and vegetation, you now have to mow more often to control the additional growth. As a result, the plant becomes stressed and the sugars manufactured within the leaves are not able to return food to the brain, i.e. the roots. The plant then becomes more out of balance, roots are starved and root hairs are not replaced or satisfied.
Root hairs only live for seven to ten days, and that is in ideal horticultural soil, not compacted, toxic, shallow rooting rootzone with over applied NPK (nitrogen, phosphorus, potassium) with a thatch organic layer.
So, the spiral continues in a downward motion. More Poa annua (annual meadow grass) is observed. The colour, vigour, rooting, toxicity and disease infested grasses need further intense feeding to keep the decline in check. Now we are really under pressure to achieve.
With water, air, temperature, organic material, light and nutrition all in balance the plant will be satisfied. If all is well, then a plant which has the correct balance of hormones will grow perfectly well. It can withstand the modern stresses that it may encounter from whichever source throughout the growing season.
Once stress of over watering, feeding, drought, frost, snow, play, mechanical operations, over use of chemicals is a key factor, the plant's hormone balance can change dramatically, resulting in negative growth characteristics.
The brain of the turf plant is the roots and is the most important part. If we have continuous root growth then the plant will be able to self regulate the balance of its hormones, resulting in positive growth characteristics.
During stress, ethylene is produced by the plant which encourages gibberellic acids to become dominant. GA can cause excessive top growth which directs plant resources to the top of the plant, often at the expense of the roots.
As a result of the above events, it is the natural assumption that we need a modern plant growth regulator to control the growth of the plant. However, we need to ask whether we can achieve this control without the use of chemicals.
The answer is yes, we can, by balancing the nutritional input to the plant. This requires careful management of nutrition and an understanding how nutrition works.
Nutrients help the plant self regulate its hormone balance in a positive manner, thus allowing us to achieve the same results in colour, vigour, sustainability, better rooting, wear, tear and disease resistance, whilst still satisfying the professional turf manager, the members and officials. However, there are no short cuts and the mechanical operations are vitally important to successful turf culture.
By introducing a complex bond of Amine nitrogen (NH2) and calcium (Ca) with natural bio-stimulants and micro nutrients, which the plant is able to utilise immediately, the turf manager is able to apply much less nitrogen during the course of the season. This mix does not cause plant stress like other forms of nitrogen.
Calcium is an important nutrient which creates many advantages towards hormonal balance, resulting in positive growth characteristics. Growth promoting effects of humic and fulvic acids enter the plant cell membrane, which sensitises physiological functions.
Today's nitrogen disturbs the natural hormonal balance and contributes towards excessive, leggy, lush, soft top growth, which is defenceless against disease, wear and tear and lifeless grass vigour. When this response is initiated by a fertiliser the natural hormone balance needs to be restored.
There are alternatives to using chemicals. If you are receptive to change, there are vital answers for the modern turf manager.
By David H. Bates