Carrots

Land preparation

Lightly aerate the soil by shallow digging before sowing carrots or sow them raised bed of 10 to 20cm height and 1-1.2m width to facilitate weeding, thinning, and to limit soil borne diseases. In addition, this will allow easier penetration by the carrot root and will also improve water holding capacity.

• Manure and Fertilizer application

Nutrient requirements of carrots are particularly high for potassium (100 kg/ha), medium for nitrogen (50kg/ha) and phosphorus  (50 kg/ha). Carrots are sensitive to high Cl concentrations and more susceptible to diseases at very high soil pH.  Liming is recommended when pH is below 5.5. Well-decomposed organic manures are beneficial when applied moderately (20-25 t/ha). Fresh organic matter such as farmyard manure or from a leguminous crop, can result in forked roots, which are difficult to clean and to market.

Seed requirements is 0.6 kg/ha, spacing can  vary (20 x 5-8cm) depending on type of soil and variety.

Carrots are propagated by seeds. Seeds are sown, often mixed with sand, 0.5 – 1 cm deep in drills 20 cm apart in finely prepared soils previously cultivated to a depth of at least 30 cm. Cover the sown seeds with a thin layer of soil and dried rice straw or dry grass and water.

• Mulching

Carrot germinates within two to three weeks after sowing. Once it germinates, remove the dry cover. The best way to keep the moisture in the ground and the carrots from drying out is to use mulch. Spread out a layer of 2 to 4 inches of mulch along the rows of carrots to keep the soil moist. Do not place the mulch on the carrots, but around them. Carrots will not only thrive by keeping the soil moist, but love organic material to keep the soil rich in nutrients. Organic mulch will help to provide the nutrients needed. Mulching can reduce weed competition against vegetable crops, and save fuel and labor costs for weed control.

• Thinning

Seedlings are thinned to 5-8 cm in the rows in order to enable easy growth.

Thinning carrots while removing some of the baby plants in a row to free up space for the rest so that they can grow to full size. Ideally, thin carrots twice during the course of the season.

Begin your first thinning when the plants are 4 inches tall. First look for the smallest and scrawniest plants to remove from the garden, or those that are growing right on top of one another. Thin the plants to about a thumb’s-width apart. Thin the carrots for a second time about a month later to about 1 1/2 to 2 inches apart.

• Earthing up

Seedlings may be earthed-up when roots start swelling to keep them cool and prevent green tops.

Try earthing up around the tops of the carrots and also applying a 2cm layer of grass clippings around the plants. Carrots tend to push themselves up out of the ground a bit and you get green tops. Earthing them up a bit just prevents the green tops.

• Watering

Watering during dry spells is necessary to prevent irregular root development.

About a week after planting the seeds, you should start thinking about watering carrots. Carrots require about an inch of water per week to reach their full potential. If no rain falls in your area, you’ll need to water the carrots yourself. You can use a soaker hose or a drip irrigation system, but these options can be expensive. Before watering carrots, dig down about 4 inches into the soil beside the plants. If the soil is moist, you’re probably in good shape. If it’s dry, it’s time to water.

• Weeding

Young carrot seedlings are weak and grow slowly; therefore, it is essential to keep weeds under control for the first few weeks after germination. Till shallowly with a hoe.

•  Leaf blight (Alternaria dauci)

The disease is caused by the fungus . Dark-grey to brown, angular spots form on leaves. Surrounding tissue yellows and affected leaves eventually die. Older leaves are attacked first and only in very severe cases are younger leaves affected. Large spots can girdle leaf petioles and kill leaves without spots developing on individual leaflets.

During warm moist weather, dying of affected leaves may occur so rapidly that plants appear scorched. This fungus can also cause seedling damping-off. The fungus is seed-borne and survives in the soil crop debris.

Photo. Leaf blight symptoms on carrot

Management:

• Use resistant hybrids where available.
• Use certified disease-free seeds. In case of using own seeds, hot water treat seeds.
•  Practice crop rotation and good field hygiene.
• Enhance aeration of crop field by less dense crops and ridge cultivation.
• No or little N-fertilization.
• Monitor fields regularly to be able to react properly.
• Copper treatments can reduce infection.

• Powdery mildew

The disease is caused by the fungus called Erysiphe polygoni (E. heraclei). It is characterised by the development of white, powdery fungal growth on leaves. Affected leaves become chlorotic and eventually die. The fungus is seed-borne.

Photo. Symptoms of powdery mildew on carrot

Management:

• Use certified disease-free seeds If using own seeds hot water treat the seeds.
• Practice good field hygiene
• Spray with sulphur based products where acceptable

Storage Diseases

Major post-harvest losses in carrots are due to Sclerotinia rot. The Sclerotinia fungus infects the carrot roots in the field through the crown. During storage, the Sclerotinia fungus produces a white, cottony mycelium which covers the roots. Infected roots are usually soft and watery.

Storage losses to Sclerotinia can be minimized by:

(1) pre-harvest application of a registered fungicide such as Bravo 500

(2) rapid removal of field heat from freshly harvested roots

(3) increasing row width to increase ventilation since prolonged periods of leaf wetness induce rot

(4) crop rotation

(5) post-harvest application of a registered antimicrobial such as Dowicide (O- phenylphenol) at a concentration of 98 g/L.

Carrots are mostly harvested manually by pulling up the roots at the leaves as long as the soil is moist and soft. If the soil has dried, it will be necessary to use either a spade or similar tool to loosen the soil and harvest the roots. Carrots are usually ready for harvesting 60-85 days after sowing. Mature roots should be orange-colored internally down to the blunt tip. Average yield is 20-30t/ha.

Freshly harvested carrots must be sorted to remove defective roots; undersized, broken, diseased, green core, split/cracked and sun burnt carrots should also be discarded. Careful handling is necessary to avoid bruising and tip breakage during these grading steps.

Post-harvest management

Harvesting carrots in cool weather will extend their shelf life and maintain post-harvest quality. Low soil temperatures improve the storage potential of carrots by (1) cooling the roots before they are harvested, and (2) creating conditions that are not conducive for the growth of pathogens.

Depending on the market requirements, carrots can be sold as topped or bunched carrots (tops left on). Bunched carrots respire faster, and therefore deteriorate faster, than topped carrots. Carrots being marketed as topped must be properly trimmed such that the length of the tops is approximately 2.5 cm.

During storage, avoid mixing carrots with ethylene- producing commodities such as apples, peppers or melons.

Transport carrots carefully – avoid excessive bouncing and shaking in bins to reduce bruising and splitting. In hot weather, cover the carrots with a tarpaulin during transport.

Never keep harvested carrots in the sun. Shading will reduce dehydration. Heated carrots lose quality and dehydrate more quickly.