<P> Due to its high level of nutrient requirements, cabbage is prone to nutrient deficiencies, including boron, calcium, phosphorus and potassium . There are several physiological disorders that can affect the postharvest appearance of cabbage . Internal tip burn occurs when the margins of inside leaves turn brown, but the outer leaves look normal . Necrotic spot is where there are oval sunken spots a few millimeters across that are often grouped around the midrib . In pepper spot, tiny black spots occur on the areas between the veins, which can increase during storage . </P> <P> Fungal diseases include wirestem, which causes weak or dying transplants; Fusarium yellows, which result in stunted and twisted plants with yellow leaves; and blackleg (see Leptosphaeria maculans), which leads to sunken areas on stems and gray - brown spotted leaves . The fungi Alternaria brassicae and A. brassicicola cause dark leaf spots in affected plants . They are both seedborne and airborne, and typically propagate from spores in infected plant debris left on the soil surface for up to twelve weeks after harvest . Rhizoctonia solani causes the post-emergence disease wirestem, resulting in killed seedlings ("damping - off"), root rot or stunted growth and smaller heads . </P> <P> One of the most common bacterial diseases to affect cabbage is black rot, caused by Xanthomonas campestris, which causes chlorotic and necrotic lesions that start at the leaf margins, and wilting of plants . Clubroot, caused by the soilborne slime mold - like organism Plasmodiophora brassicae, results in swollen, club - like roots . Downy mildew, a parasitic disease caused by the oomycete Peronospora parasitica, produces pale leaves with white, brownish or olive mildew on the lower leaf surfaces; this is often confused with the fungal disease powdery mildew . </P> <P> Pests include root - knot nematodes and cabbage maggots, which produce stunted and wilted plants with yellow leaves; aphids, which induce stunted plants with curled and yellow leaves; harlequin bugs, which cause white and yellow leaves; thrips, which lead to leaves with white - bronze spots; striped flea beetles, which riddle leaves with small holes; and caterpillars, which leave behind large, ragged holes in leaves . The caterpillar stage of the "small cabbage white butterfly" (Pieris rapae), commonly known in the United States as the "imported cabbage worm", is a major cabbage pest in most countries . The large white butterfly (Pieris brassicae) is prevalent in eastern European countries . The diamondback moth (Plutella xylostella) and the cabbage moth (Mamestra brassicae) thrive in the higher summer temperatures of continental Europe, where they cause considerable damage to cabbage crops . The cabbage looper (Trichoplusia ni) is infamous in North America for its voracious appetite and for producing frass that contaminates plants . In India, the diamondback moth has caused losses up to 90 percent in crops that were not treated with insecticide . Destructive soil insects include the cabbage root fly (Delia radicum) and the cabbage maggot (Hylemya brassicae), whose larvae can burrow into the part of plant consumed by humans . </P>

Name the organic acid present in cabbage and green leafy vegetables