Agriculture Reference
In-Depth Information
SELECTION CHARACTERISTICS
Cultivated leek varieties differ primarily in leaf color, winter hardi-
ness, length and thickness of leaf sheaths, and the number of bulbils in their root zones. Plant selection
takes place in autumn and again in spring. Potential selection criteria:
• length and thickness of leaf base
• leaf color
• leaf structure and configuration
• flavor
• resistance to bolting (use as summer or overwintering leek)
• resistance to drought, frost, and diseases
• development of underground bulbils (= “false pearl onions”) in second year
• overwintering leek: winter hardiness
• summer leek: rapid growth
DISEASES AND PESTS
As with the common onion, downy mildew can be a problem in leek cultiva-
tion. Purple blotch (pathogen:
Alternaria porri
) is a seed-borne fungus that can also be spread by in-
fected plant debris. Elongated, oval spots appear mainly on the upper halves of leaves. Infected leaves
rip open, contort, and ultimately die. The fungus prefers warm, moist weather. Prevention: mulch,
mulch, mulch. Leek rust is caused by the fungus
Puccinia allii
and is spread by plant debris in the soil
or from plant to plant when plants overwinter outdoors. Symptoms: many small, elongated yellowish
brown to orange spots and rips on the top surfaces of leaves. Round yellow spores in summer quickly
contaminate all surfaces. Bad cases lead to stunted growth. The fungus spreads most in late summer
and early autumn in the form of winter spores. Plants deal with infection better when weather in au-
tumn is cold and wintry. Prevention: sufficiently wide planting distances, not overfertilizing. Treat-
ment: remove infected leaves and plants. Onion flies (
Delia antiqua
) and leek moths (
Acrolepiopsis
assectella
) are pests that are easily controlled the first year with insect netting. The white, shiny eggs
of the leek moth can be washed away by heavy rain or by watering. The gray-green black-headed
caterpillars of the leek moth can eat their way into the hearts of leeks and kill leaves. Plants can be
protected the second year with taller isolation cages, though pollinating insects will need to be intro-
duced. Plants can be affected by all diseases and pests in the second year as well and are especially
susceptible when flowering.
Ripe seeds in leek flower head
