Posts Tagged ‘boron’

Boron Deficiencies in Cole Crops

Friday, September 7th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Long time growers of cole crops know that the micronutrient boron is critical for production. However, newer growers may be unaware of these requirements. Boron is also subject to leaching with rainfall, particularly in our sandy soils, so available soil boron declines over time.

Cole crops have a moderate to high boron requirement. Symptoms of boron deficiency vary with crop type. Most boron deficient cole crops develop cracked and corky stems, petioles and midribs. The stems of broccoli, cabbage and cauliflower can be hollow and are sometimes discolored. Cauliflower curds become brown and leaves may roll and curl, while cabbage heads may be small and yellow. Of all the cole crops, cauliflower is the most sensitive to boron deficiencies.

It is recommended in broccoli and kale to apply 1.5-3 pounds of boron (B) per acre in mixed fertilizer prior to planting. In Brussels sprouts, cabbage, collards and cauliflower, boron and molybdenum are recommended. Apply 1.5-3 pounds of boron (B) per acre and 0.2 pound molybdenum (Mo) applied as 0.5 pound sodium molybdate per acre with broadcast fertilizer.

Boron may also be applied as a foliar treatment to cole crops if soil applications were not made. The recommended rate is 0.2-0.3 lb/acre of actual boron (1.0 to 1.5 lbs of Solubor 20.5%) in sufficient water (30 or more gallons) for coverage. Apply foliar boron prior to heading of cole crops.

Other fall crops such as beets, radishes, and turnips are also susceptible to boron deficiencies in sandy soils with limited boron fertilizer additions.

Boron Toxicity in Beans

Friday, July 8th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

We recently had a suspected case of boron toxicity in snap beans. Boron toxicity is common in western states where boron levels in soils or irrigation water are high. In the east, we do not have high boron soils or high levels in irrigation water. In addition, boron leaches readily from soils. Boron toxicities therefore occur only when excess boron is applied in fertilizers.

Boron is a micronutrient needed by plants. It is closely associated with calcium and calcium transport, cell wall production, cell division in plant growing points, sugar transport in plants, flower and fruit development, and plant hormone regulation. Vegetables vary in their boron requirements. Cole crops, turnips, and beets have the highest demands. Even so, recommended rates of application in low boron soils for these high demand crops is only 3 lbs/acre. More commonly, 1-2 lbs of boron per acre is applied to vegetables as a broadcast. Margin of safety for boron application is small and excess application or improper blending in fertilizers may lead to toxicities – deficiencies show up at 1 ppm and toxicities appear at 5 ppm of available boron in the soil.

The vegetable crops most sensitive to excess boron are beans, particularly snap beans. Boron is generally not recommended for snap bean production and boron should never be included in starter fertilizer for snap beans. Boron toxicity often occurs where starter fertilizer containing boron for other crops, such as corn, is applied to snap beans.

Boron toxicity in beans commonly appears as yellowing in unifoliate leaves with burning of leaf edges and yellowing of leaf edges of the older trifoliate leaves that can progress to edge burn. In severe cases, plants will develop a scorched appearance and leaves may prematurely drop off.