Boron needs for plant growth and development can be supplied as Granubor® 2 applied preplant to the soil or as Solubor foliar sprays during the season.
- Foliar applications of boron generally are more effective than soil applications in supplying sufficient boron for flowering and reproductive development in crops.
- Solubor® is highly water soluble, and is commonly applied in foliar sprays. It is also compatible with most pesticides, so it also can be applied in these sprays.
- Because the season for the most effective foliar application of boron is short, foliar sprays must be prepared quickly and accurately.
- Tables listing the amounts of Solubor to mix in spray tanks to supply several commonly used boron application rates are shown below.
Foliar spray applications generally are more effective per unit of boron than soil applications for most crops. The applied boron is quickly absorbed by the leaves and other tissues and is immediately available for vegetative and reproductive growth.
Foliar sprays are especially important for those plant species in which boron is immobile; boron uptake from the soil is insufficient to supply these plant’s needs at critical periods of growth and reproductive development.
Foliar spray applications generally are more effective per unit of boron than soil applications for most crops.
Research results have shown that foliar sprays of boron applied just prior to and during bud formation and flowering have increased yields of numerous fruit and grain crops. Boron does not readily move from other parts of the plants to buds and flowers when it is needed for pollen tube growth, pollen production, bloom retention and seed development.
Responses to foliar boron sprays may occur even when soil and leaf tissue analyses show adequate boron levels, especially in those plant species in which boron is immobile.
Proper timing of foliar sprays is essential to ensure that boron is applied when the need is most critical. The boron fertilizer must be on site, the sprayer must be ready to go and procedures should be in place to keep the sprayer operating during the busy season. Applying the recommended boron rate is critical to obtaining optimum crop yields.
Solubor is highly water soluble and commonly applied in foliar sprays. It is also compatible with most herbicides and insecticides, so they also can be applied in these sprays. This saves separate application costs. Buffering agents may be needed when Solubor is applied with some pesticides whose effectiveness is pH-sensitive. However, the cost per acre of buffers is minor relative to the cost of the pesticides. The suggested order of mixing foliar sprays containing Solubor alone or in combination with pesticides is shown in the following chart.
The amount of Solubor to mix in the tank to supply a desired boron rate requires knowledge of the spray rate, the tank size of the sprayer, and the boron concentration in the fertilizer. This calculation is: The amount of Solubor to mix in the spray tank = [(tank size ÷ spray rate) x desired boron rate] ÷ boron concentration in Solubor.
How much Solubor (20.5% B) should be mixed in a 400-gallon tank with a spray rate of 20 gallons/acre to supply 0.25 lbs. of B/acre?
Tables 1-3 give the amounts of Solubor (20.5% B) to mix in sprayers with various tank sizes and spray rates to supply three commonly used boron application rates. The data in these tables has been rounded to the nearest pound of Solubor.
- Spray coverage of a full tank: 400 gallons ÷ 20 gallons/acre = 20 acres.
- Amount of boron needed in the spray tank: 20 acres x 0.25 lbs. of B/acre = 5.0 lbs. of boron.
- Amount of Solubor required: 5.0 lb. ÷ 0.205 = 24.4 lbs. of Solubor.
Mixing more precise amounts would require a recalculation using the equation given above. A footnote is included in each table for making calculations when spray tanks are larger than 400 gallons.
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