Controlling Carrot Pests and Diseases

Preventative care for carrots is key when it comes to protecting them from diseases and pests, both starting at planting time with proper soil preparation and continuing throughout the growing season. This may involve crop rotation, keeping weeds out of the garden, using row covers when necessary or even rotating crops within your plot.

Root knot nematodes (Meloidogyne spp) cause extensive root damage in carrot roots, rendering them unmarketable and often leaving a lot of unusable harvest. To combat this problem, preplant soil fumigant treatment and crop rotation are effective ways of combatting it.

Insects

Carrot crops often encounter problems caused by insects. These pests tend to thrive in hot weather and become active sooner in the south than the north, although organic and chemical solutions exist for combatting them.

Carrot roots can become susceptible to several root diseases, including crown and root rot (Rhizoctonia or Pythium), leaf spot and white mold Cercospora Alternaria fungus diseases. Symptoms of such diseases can include soft carrot tops, stunted root growth and general plant wilt. Controlling such ailments begins with crop rotation using nonsusceptible plants as part of your rotation schedule.

The carrot weevil can be an arduous pest to deal with. This worm-like insect overwinters as an adult in soil and garden debris, making control difficult. Crop rotation, cleaning the garden area regularly and planting onions, lettuce or potatoes as nonhost plants for weevils may all help combat its infestation.

Wireworms can also pose a threat to carrot gardens, attacking carrot roots and opening an entry point for secondary pathogens that cause secondary rot-causing pathogens. To combat this pest, it’s best to plant in well-drained organic soils with plenty of drainage holes, while using mulch as moisture retention protection.

Aphids are another of the more widespread umbelliferae pests that threaten carrots and other umbelliferae crops such as parsnips, celery and fennel. These sucking insects damage fine foliage while leaving honeydew behind that forms sooty mold patches on surfaces. Aphids can be controlled organically using natural predators like ladybugs or lacewings, or chemical sprays such as those sold at DIY Tool Supply that contain acetic acid-based insecticidal soaps with an insecticidal action against honeydew excrement.

Preventative measures are the key to controlling most pests of carrots and other cool-season crops, including site selection, weed management and timely fertilization. Row covers such as Reemay or Agribon may help early in the season to shield carrots against aphid eggs from being laid onto them by aphids; later on you may require fencing or wire mesh as barriers against carrot rust fly larvae entering your garden.

Fungi

Carrots are susceptible to various fungal diseases that threaten yield and quality, often due to wet field conditions or airborne spores. Fungicide application and crop rotation are two key management practices to combat such issues.

Powdery mildew is an increasingly prevalent crop disease that often results in yellowing, deformed leaves, and leaf stippling on carrots. Rot, taproot enlargement and heavy infections may reduce marketable yield of the crop. Powdery mildew can remain as an adult on harvested crops for the remainder of its existence and also infect other root vegetables, including celery, parsley and radish roots.

Sclerotinia Rot is an extremely destructive carrot disease that can result in major losses during storage. A fungal pathogen known as Sclerotinia sclerotiorum attacks both roots and leaves of carrot plants, invading both their roots and leaves before colonizing both as it survives for multiple years in soil and crop debris. Wet weather (rain or overhead irrigation) or temperatures above 55degF favor infection with symptoms appearing as water-soaked spots on leaf petioles or crowns – older tissues are especially susceptible.

Infection can be avoided by choosing certified disease-free seeds and applying fungicide prior to planting. Also, rotating with nonhost crops such as legumes and cereals will help break the disease cycle.

Black Rot (Alternaria radicina) and Rubbery Brown Rot (Phytophthora porri) are two sporadic diseases that can threaten carrot crops. Both conditions start on the leaf petiole and move downward to the root. Once affected areas become dark and soft and may even have an unpleasant bitter flavor that makes the carrots unmarketable and potentially unsafe to eat.

To control these diseases, avoid soil that has been contaminated by overwintered carrot plants or other root vegetables. Ensure proper drainage, amend clay or compacted soil with organic matter to improve structure, aeration and health of the soil. When necessary use fungicides either on the surface of soil, or via foliar spray to protect plants against disease; carrot varieties resistant to such ailments are available and stored carrots should be kept at temperatures no higher than 0degF to monitor for signs of disease.

Nematodes

Nematodes are microscopic organisms that influence plant growth in numerous ways, both beneficially and detrimentally, including disease problems in carrot crops. Researchers called nematologists study these organisms, working closely with farmers to devise preventive strategies against any detrimental nematodes from harming important crops like carrots.

Roots of many vegetables and legumes are susceptible to attack from parasitic nematodes, with needle-like mouthparts that penetrate plant tissue to siphon out water and nutrients, leaving crops stunted or sickly. Furthermore, some nematodes release toxic saliva that damages leaves or stems of carrots so much so that their color changes to yellow or brown.

Root-knot nematode (Meloidogyne incognita) is one of the most damaging nematodes to carrots, with other harmful ones including lesion nematodes and root-lesion nematodes also present. Unfortunately, controlling these pests in the field can be challenging because they move around rapidly while some species are resistant to chemicals used against them.

Nematologists have discovered that certain soil conditions can impede the spread of plant parasitic nematodes on carrots. Their research suggests that selecting plant-parasitic nematode-resistant cultivars requires taking account of soil texture when choosing suitable cultivars.

Nematodes consist of an assembly of cuticle, hypodermis and muscular layers that serve as an anisometric skeleton. Their somatic musculature is supported by rigid cuticle support while enclosing a fluid-like cavity known as the pseudocoelom or pseudocele (Harris and Crofton 1957). This flexible framework permits them to exert force against root surfaces similar to muscles.

Nematode cuticles can range from smooth and plain, to those decorated with rings, longitudinal striations or spikes. Certain species possess wings-like structures called lateral alae which project from their anterior end; cervical and caudal alae may also be present (Fig. 2).

Alternative chemical controls for carrot-damaging nematodes are being researched. In Western Australia, Telone and Telone C35 nematicide mixtures have proven highly effective at managing root-knot nematode infestation and lesion nematode activity in carrot fields, while using tyned injection rigs requires injection into soil using these products; approval for their use must first be sought from Australian Pesticides and Veterinary Medicines Authority website or speak to a trained horticultural agronomist about current registration/permit information or consult trained horticultural agronomist for guidance or visit their website for current registration/permit information.

Diseases

Carrots are susceptible to numerous diseases that reduce yields and crop quality when consumed fresh or stored, including foliar diseases that reduce photosynthetic area and make harvest more challenging, or limit marketability if foliage weakens or dies off altogether. Root diseases also pose threats, leading to yield reduction both during cultivation and storage as well as altering their health and nutritional benefits.

Diseases that target carrot roots include rot, crown rot and dry rot. Crown and dry rot can be caused by soil-borne pathogens which remain active in the soil for eight years or more; typically occurring when weather conditions create conditions conducive to high moisture levels in dense canopy soil conditions; symptoms include yellowed leaf margins before eventually death of all leaves in that row – also occurring on their tops! Low temperature storage containers, resistant cultivars and foliar fungicides help manage this problem successfully.

Other root diseases infect carrots through both their tops and roots, eventually leading to the thinning of foliage and eventual death of the entire plant. Fungus diseases usually spread by wet weather conditions are marked by dark brown spots that gradually expand over time, leaving carrots susceptible to dying out entirely. Fungicide seed treatments, row covers and crop rotation are effective strategies for combatting this threat.

Alternaria leaf blight (Alternaria dauci), another fungal disease which attacks carrot tops, also attacks celery and parsley crops and can last up to eight years in soil. Most severe during wet periods in summer months when rainwater pools on top of leaves. Younger leaves are more prone to infection than their older counterparts – to manage this threat use Fungicidal seed treatment, rotation and foliar fungicides for optimal control methods.

CIOA is also contributing to the emerging science of beneficial microbes that interact with crops, with research showing certain carrot genotypes can attract these beneficial organisms more readily than others. Knowing about and recognizing these beneficial organisms will allow growers to manage carrot plants for maximum performance.