Fennel

Description

Fennel, Foeniculum vulgare, is an herbaceous perennial plant in the family Apiaceae grown for use as a herb or flavoring. The fennel plant is an erect herb with 4–5 hollow stems and distinctly divided feathery foliage. The leaves are simple and linear and are 2–15 cm in length. The plant produces flowers on flat umbels which can be 20 cm (7.9 in) in diameter and possess 20-50 tiny yellow flowers. The plant may reach 2 m (6.6 ft) in height. Fennel is a short-lived plant and is almost always grown as an annual. Fennel may also be referred to as wild fennel or sweet fennel depending on variety and originates from southern Europe and the Mediterranean.


Uses

Fennel leaves can be used fresh or dried as a spice in cooking. The bulb of some varieties is also edible and is usually consumed after cooking. The seeds can be dried and used as a spice.


Propagation


Basic requirements
Fennel is a perennial plant which is commonly grown as an annual. It grows best in cool weather at temperatures between 21 and 24°C (70–75°F). Hotter temperatures tend to induce bolting. Fennel will grow best if grown in full sun in a well draining, fertile loam soil with a pH between 6.3 and 8.3.

Planting
Fennel is usually propagated directly from seed and requires and ambient temperature between 15 and 20°C (59–68°F) to germinate. It should be planted in early Spring or Fall when temperatures are suitable. Seed should be sown at a depth of 1–3 cm (0.4–1.2 in) leaving 15–50 cm (5.9–19.7 in) between plants and 60 cm (24 in) between rows.

General care and maintenance
Fennel should be kept free from weeds which will easily out compete the plant for light and nutrients. Plants will benefit from the addition of nitrogen fertilizer but care should be taken not to overfeed the plants as it will result in a disproportionate amount of vegetative mass developing. Fennel should be provided with regular irrigation to prevent the stalks from splitting.

Harvesting
Fennel stalks should be cut just before flowering. Stalks are usually ready for harvest between 5 and 7 months after planting. Seed heads should be collected promptly before they shatter. The seed heads are ready to harvest when they turn brown in color. Once the stalks have been harvested, the bulb can also be cleaned and stored.


References

Anderson, C. R. Fennel. University of Arkansas Division of Agriculture. Avaialble at: http://www.uaex.edu/publications/PDF/.... [Accessed 02 December 14]. Free to access.

CABI Crop Protection Compendium. (2014). Foeniculum vulgare datasheet. Available at: http://www.cabi.org/cpc/datasheet/24271. [Accessed 02 December 14]. Paid subscription required.

Robinson, C. & Myers, C. (1998). Fennel, Sweet Anise. In Specialty and Minor Crops Handbook, 2nd Edition. University of California Agriculture & Natural Resources. Available at: http://www.ctahr.hawaii.edu/sustainag.... [Accessed 02 December 14]. Free to access.


Common Pests and Diseases

Rust
Puccinia spp.
Uromyces spp.
Nyssopsora spp.

Symptoms
Light green discolored lesions on leaves which become chlorotic; yellow-orange pustules on underside of leaves; stems bend and become swollen or distorted; plants may be stunted
Cause
Fungi
Comments
Some species infect only parsley while others have alternative hosts which may provide a reservoir for the disease; disease emergence is favored by high humidity
Management
Plant in well-draining soils to reduce humidity around plants; apply appropriate systemic fungicide

Cercospora leaf blight
Cercosporidium punctum

Symptoms
Small, necrotic flecks on leaves which develop a chlorotic halo and expand into tan brown necrotic spots; lesions coalesce and cause leaves to wither, curl and die
Cause
Fungus
Comments
Disease can be introduced through infested seed and spread by wind or water splash; symptoms usually occur on younger foliage first
Management
Plant only pathogen-free seed; rotate crops; plow crop debris into soil ofter harvest; apply appropriate fungicide sprays

Powdery mildew
Erisyphe heraclei

Symptoms
Powdery growth on leaves, petioles flowers stalks and bracts; leaves becoming chlorotic; severe infections can cause flowers to become distorted
Cause
Fungus
Comments
Fungus can spread long distances in air; disease emergence is favored by high humidity and moderate temperatures; infection is most severe in shaded areas
Management
Plant tolerant varieties; avoid excess fertilization; protective fungicide applications provide adequate protection; sulfur application can be used in infection occurs early in season

Downy mildew
Peronospora umbellifarum

Symptoms
Yellow spots on upper surface of leaves; white fluffy growth on underside of leaves; lesions become darker as the mature
Cause
Fungus
Comments
Disease affects young, tender leaves; disease emergence and spread is favored by prolonged leaf wetness
Management
Plant pathogen-free seed; do not overcrowd plants; rotate crops with non-umbelliferous varieties

Armyworm
Pseudaletia unipuncta

Symptoms
Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside
Cause
Insect
Comments
Insect can go through 3–5 generations a year
Management
Organic methods of controlling armyworms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae

Aphids (Willow-carrot aphid)
Cavariella aegopodii

Symptoms
Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in color; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants
Cause
Insect
Comments
Distinguishing features include the presence of cornicles (tubular structures) which project backwards from the body of the aphid; will generally not move very quickly when disturbed; willow-carrot aphid will also attack parnip, carrot and celery
Management
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use

Cutworms
Agrotis spp.
Peridroma saucia
Nephelodes minians
and others

Symptoms
Stems of young transplants or seedlings may be severed at soil line; if infection occurs later, irregular holes are eaten into the surface of fruits; larvae causing the damage are usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant; larvae are 2.5–5.0 cm (1–2 in) in length; larvae may exhibit a variety of patterns and coloration but will usually curl up into a C-shape when disturbed
Cause
Insects
Comments
Cutworms have a wide host range and attack vegetables including asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato and tomato
Management
Remove all plant residue from soil after harvest or at least two weeks before planting, this is especially important if the previous crop was another host such as alfalfa, beans or a leguminous cover crop; plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants; hand-pick larvae after dark; spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it); apply appropriate insecticides to infested areas of garden or field if not growing organically

Root knot nematode
Meloidogyne spp.

Symptoms
Galls on roots which can be up to 3.3 cm (1 in) in diameter but are usually smaller; reduction in plant vigor; yellowing plants which wilt in hot weather
Cause
Nematode
Comments
Galls can appear as quickly as a month prior to planting; nematodes prefer sandy soils and damage in areas of field or garden with this type of soil is most likely
Management
Plant resistant varieties if nematodes are known to be present in the soil ;check roots of plants mid-season or sooner if symptoms indicate nematodes; solarizing soil can reduce nematode populations in the soil and levels of inoculum of many other pathogens