Plant hormones and the importance of controlling apical dominance

A natural characteristic of all grasses (which includes cereal crops) is that of apical dominance. The primary or apical shoot is always the strongest and dominates any secondary shoots (known as tillers). If this primary shoot dies or is shortened (eg by being grazed off by an animal), the tillers become stronger and catch up with or replace the primary shoot. The apical dominance can be suppressed by products such as the Mandops PGRs and this allows the plant to produce (on average) a larger number of viable shoots and heads of grain with more grain sites and, therefore, a higher yield of grain.

Gibberellins and auxins are necessary for normal plant growth and development. The gibberellins and auxins are produced in growing stems, and they inhibit the growth of tillers or lateral buds, ie they maintain apical dominance.

The ratio (not absolute amounts) of gibberellins/auxins in relation to cytokinins is the important factor in apical dominance systems. Apical dominance can be suppressed by:

a) applying anti-gibberellins (eg ADJUST, BARLEYQUAT B, BETTAQUAT B, CERAIDE, K2 or MANIPULATOR),

b) applying an anti-auxin or

c) applying a cytokinin (although there is evidence of their rapid degradation and repeated applications are often necessary).

Plant hormone systems also govern photosynthetic capacity (source) and storage capacity (sink) relationships, eg grain filling processes and senescence. In cereals, ethylene and abscisic acid are involved in the process of senescence (maturity) and cytokinins can prolong chlorophyll production, maintain stomatal opening and generally regulate rates of senescence and sink capacity.

During early grain filling, gibberellins and auxins increase and are accompanied by cell growth and dry matter storage. Dry matter storage stops as soon as abscisic acid levels rise appreciably.

Always read the label. Use pesticides safely. Adjust, Barleyquat B, Bettaquat B, Ceraide K2 and Manipulator contain chlormequat.