One of the characteristics boron is known for is to facilitate rapid nutrient transport to the sugar sinks. This effect can be very valuable to speed up crop maturity and senescence while also increasing harvest quality.
When an alfalfa crop is growing rapidly and still very vegetative in late fall as we approach winter dormancy it is possible to quickly trigger senescence and rapidly move the sugars contained in the plant down into the crown with a generous foliar application of boron. A treated section can turn brown within a few days to a week (depending on weather and time of year), as all the sugars move down into the crown and the plants begin to senesce. The following spring, the section treated with boron in the fall will emerge from winter dormancy much faster and with many more shoots than an untreated section, because the crowns have much more energy from the stored sugars. Any perennial crop with a similar growth pattern will show this effect.
This effect can also be used to speed up the natural maturity process of other crops. A generous foliar application of boron on fruit such as tomatoes or apples will speed up the natural sugar transport into the fruit. This can help the fruit color and mature quickly and evenly days to weeks earlier than plants without a generous supply of boron.
This effect of boron on speeding up maturity and natural ripening can also be used on small grains in place of a desiccant or harvesting aid. Wheat that receives a foliar application of boron can mature rapidly and dry down as much as five to ten days faster than plants without adequate boron. The upside is that there is often a gain in test wheat and protein content, since boron produces this effect by increasing photosynthate and protein transport into the grain rather than reducing transport to the grain as a desiccant might.
Boron does not produce these effects if the crop is not at the right stage of growth. It can only speed up the plant processes which are occurring naturally. Managed well, boron applications can speed up these natural processes dramatically, and produce a higher quality grain or fruit, with an improved nutritional content.
How much boron is required? It varies based on the existing boron content of the soil and the crop. Many crops and soils are deficient, which is why crops are not maturing well in the first place. Often, the upper end of label rates are required if this is the only application being applied in the season. It is better to supply the crops foundational boron requirements during the growing season, and then top off the requirements with a lighter application a few weeks before maturity to produce the optimal effects we are looking for.