Source: Rutgers Cooperative Extension
 
Boron-deficiency symptoms compiled from Rutgers Cooperative Extension and University of Missouri Extension are in a simple chart.

Boron-Deficiency Symptoms

Field Crops
Alfalfa: Death of terminal bud, rosetting, yellow top, little flowering, and poor seed set.

Clover; red, white: Poor stands, growth, and color.Reduced flowering and seed set.

Corn: Short, bent cobs, barren ears, blank stalks, poor kernel development.

Cotton: Dark rings on leaf petioles and shortened internodes, also boll shedding and "hard locks."

Soybean: Reduced yield and poor quality.

Vegetables
Beets: External spotting, cracking, and canker.

Broccoli: Hollow stems or internal discoloration,brown curds.

Cabbage: Hollow stem, watery areas, heads yellow, stunted.

Carrots: Reddening of leaves, splitting of roots.

Cauliflower: Leaves curled, hollow stem, curds dwarfed, brown.

Celery: Stem cracked with brown stripes, heart blackened.

Lettuce: Stunted growth, discoloration of leaves, brittle.

Tomato: Thickened leaves, brittle leaves, fruit fails to set.

Radish: Pale roots, brittle stems, watery flesh, flecked.

Spinach: Roots dry and dark, leaves small and yellowish.

Fruits
Apple: Pitting, skin discolored, cracking, corking.

Pear: Blossom blast, pitting, internal corking, bark cankers.

Grape: "Hen & Chick" symptom, dead main shoots.

Apricot: Twigs die back, fruit fails to set.

Plum: Fruit cracked, beads of gum internally/on skin.

Walnut: Die back from shoot tips, leafless branches.

Strawberry: Pale chlorotic skin of fruit, cracking, die back.