Prepared: December 2003
Carrots are becoming an important vegetable crop in Georgia. Although Georgia production is dwarfed by the major carrot states like California and Florida, Georgia carrot acreage increased more than 600% between 1996 and 2000 and more than 300% between 1998 and 2000. Georgia soils and climate are well suited for carrot production, and carrot acreage is expected to increase.
Additionally, carrot acreage in Florida has decreased as environmental pressures have eliminated carrot production from one of the principal growing areas around Lake Apopka. Carrot production in Florida fell from 12,000 acres in 1987 to less than 7,000 acres in 1997 Florida Crop/Pest Management Profiles: Carrots. As a result, there may be greater opportunities for carrot production in Georgia.
Because carrots are a relatively new vegetable crop for Georgia, researchers and Extension specialists are still developing information about production parameters and pest management. As a result, this profile will be updated periodically. Much of the information in this profile was taken from http://www.ces.uga.edu/ES-pubs/RR653.html and the Florida crop profile for carrots.
Production Facts
Carrots are direct seeded (transplanting is not recommended) at a rate of 2-4 lbs seed/A. The seeds germinate in seven days at 68°F; cooler temperatures slow germination. Carrot seed is commonly planted along with a fungicide. Carrots are planted from January to April for a spring crop and from July to September for a fall harvested crop.
Carrots are a cool season crop, with optimal growth between 60°-65°F, with a minimum of 45°F and a maximum of 75°F. Fall crops can be started in the heat of late summer to ensure that a substantial period of cool weather exists before frost.
Color development is determined by temperature. Maximum color development occurs in the 60°-75°F optimal growth range. Temperatures over 70°F will also reduce root length, while temperatures below 60°F will produce longer roots.
Carrots are ready to harvest 90 to 150 days after planting. They are machine harvested by mowing the tops and lifting the roots with a modified sweet potato harvester, or by loosening the soil with a specialized plow (carrot lifter) which harvests the crop in one pass.
Potential Worker Exposure
Nearly all growers apply dichloropropene before planting, an herbicide at planting, and herbicides, fungicides, and insecticides during the season. The grower or a farm employee typically makes the applications. The applicator would also mix and load the pesticides. A typical applicator on a large farm (up to 1000 acres) could apply the pesticides several days in a row for about eight hours per day. Carrots are planted sequentially, so the applicator may repeat the application sequence several times. All commercial carrots are machine planted. Most growers have tractors with an enclosed cab; larger farms are more likely to have closed-cab equipment. A typical operation would apply pesticide to their carrot fields up to 15 times per season.
Typically, scouts monitor carrot fields once per week throughout the season. Most growers hire a consultant. A consultant will commonly scout carrots and other crops every day throughout the vegetable season. If the grower or farm employee scouts a single farm, the scout would typically be in the field 3-4 hours per week on a larger farm.
Nearly all carrots are irrigated with a center pivot system. It is not necessary for anyone to enter the field during the season to operate or move irrigation equipment.
Hand weeding is uncommon for commercial carrots. Commercial carrots are not cultivated during the season.
All commercial carrots in Georgia are harvested by machine.
Soil insects (e.g., wireworms, mole crickets, and white grubs) are the most serious insect pests of carrots in Georgia. In 2001, soil insects caused losses (yield loss + cost of control) of nearly $500,000. Foliar pests (e.g., aphids and lepidopteran larvae) were responsible for about $5,000 in losses. For more information, refer to the Summary of Losses from Insect Damage and Costs of Control in Georgia (http://www.ent.uga.edu/online_pubs.htm).
Soil pests including wireworms, mole crickets, and cutworms injure seedlings and cause death and deformation of the developing carrots. They also provide entrance for pathogens. Nearly all growers use insecticides at planting to manage soil pests.
Aphids and various caterpillars can be important foliar pests. Aphid feeding deforms the foliage and makes the plant less thrifty. Their feeding also deposits honeydew that encourages the growth of sooty mold. Aphids can be a problem because they can reproduce very quickly under favorable conditions. Large populations of caterpillars can quickly defoliate carrots. Growers regularly apply foliar insecticide to control these pests.
Other sporadic pests include carrot weevil, aster leafhopper leafminers, armyworms, mites, and plant bugs. Growers rarely have to use insecticides to control these insects.
Insecticides. Nearly all commercial carrots are treated with insecticides.
Nonchemical alternatives and IPM. Insecticide applications are based on scouting information, and naturally occurring biological controls are one of the factors that determine if an in-season pesticide application is warranted. However, there are no nonchemical strategies that can replace insecticide applications for control of damaging insect populations.
Review recommended insecticides in the Georgia Pest Management Handbook.
Weed control in carrots is an essential component of producing a high-yield, high-quality crop. Weeds compete with carrots for light, water, nutrients, and physical space. In addition, many weeds impair the harvesting process, either through improper digging or contamination of the harvested crop. Weeds also harbor pest insects and diseases. The presence of plant residue from weeds or other plants during fumigation can also decrease the effectiveness of most soil fumigation materials and increase nematode problems.
Carrot growers face a multitude of weed problems including both summer and winter annual broadleaf weeds and grasses. These may include sicklepod (Cassia obtusifolia), crabgrass (Digitaria spp.), pigweeds (Amaranthus spp.), carpetweed (Mollugo verticillata), lambsquarters (Chenopodium album), wild radish (Raphanus raphinistrum), cutleaf evening primrose (Oenthera lanceolata), and several others.
Nutsedge is one of the worst weeds in carrots. Most infestations are limited to yellow nutsedge (Cyperus esculentus), which is found throughout Georgia. Nutsedge causes the greatest problem in the early fall, during carrot emergence and seedling growth.
Carrot growers typically apply herbicides at planting and during the season to control weeds.
Herbicides.
Review herbicides recommended for weed control in carrots in the Georgia Pest Management Handbook.
Nonchemical alternatives and IPM. Growers incorporate other techniques in an IPM program for weeds, but nonchemical methods cannot replace the critical role of herbicides in carrot production. Growers try to avoid fields with heavy infestations of perennial weeds like bermudagrass and nutsedge. Cultural techniques that ensure optimum carrot growth and density help control weeds. Growers plant carrots at a density that helps control weeds. Hand weeding and cultivation during the season are uncommon.
Crop rotation is an important aspect of controlling some persistent weed species and problem weeds such as sicklepod, nutsedge and cocklebur.
Georgia carrots have a number of disease problems. This first group of diseases is responsible for nearly all applications of fungicides and nematicides to Georgia carrots.
Pythium rot can blight seedlings if plants are infected early, but the disease is more commonly a root disease. The root tips are primarily affected; typically excessive root branching occurs. Plants may also be wilted or stunted. Yield and yield quality can be greatly reduced by Pythium infection.
High soil moisture and excessive nitrogen favor development of Pythium infection. Plants that are not growing at optimum conditions (e.g., undesirable soil temperature) are more susceptible to Pythium. Finally, the disease is more likely in fields that have been planted to carrots or another host for several consecutive seasons.
Growers commonly use at-planting fungicide to control Pythium.
Southern blight (Sclerotium rolfsii) is a warm weather disease that attacks a variety of vegetable crops. Infected seedlings often die. The first symptom in older plants is yellowed or wilted leaves. Infection occurs at or near the soil line. A white mass of mycelium advances up the stem and down to the roots. The mycelium can move across the soil and infect other plants. The fungus can also survive in the soil; it is spread in water, soil, and infected plant parts. With warm temperatures and high moisture, southern blight can spread rapidly. Southern blight is best controlled by deep turning and following a rotational program that decreases the amount of southern blight in the soil. It is also suppressed by fungicide applied to control Pythium.
Sclerotinia (Sclerotina sclerotiorum) is a cool weather disease that attacks a variety of vegetables. Carrot injury usually occurs along the soil line, and the foliage rapidly collapses. Most growers use rotation and deep turning to manage this disease. In cool, wet weather, growers typically use fungicides to manage losses from this disease.
Root-knot nematode (Meloidogyne spp.) feeding causes stunting, excessive root production, and deformation of the developing carrot. If carrot seedlings are infected, yield losses can be severe.
In some cases, growers can manage root-knot nematode populations by rotating to a nonhost crop. If rotation is not a feasible option, nearly all growers apply a nematicide.
Leaf blight (Alternaria spp. and Cercospora carotae). Alternaria is a fungus appearing later in the season on older tissue; C. carotae appears earlier on younger tissue. They are noticeable on the foliage as yellowing and small dark brown elongated to round lesions; entire leaves may be destroyed. Leaf blight can also cause root decay.
The fungi overwinter on crop debris and seed. Planting disease-free seeds helps prevent the initial introduction into the field. The disease may also be introduced from other infected crop plants or weed hosts by wind or water. Disease development is favored by warmer weather. Growers commonly use foliar fungicides to control leaf blight.
Fungicides. Fungicides are critical for carrot production in Georgia. Growers typically apply fungicides on a 7-14 day schedule, depending on disease pressure and weather conditions favoring disease outbreaks. A typical spray schedule would include 9-13 applications.
Nonchemical alternatives and IPM. Disease management in carrots is based on a combination of tactics. Effective fungicides are a critical component. Chlorothalonil is particularly important because of its role in resistance management. Other products, with a more targeted mode of action, are much more susceptible to resistance problems. The availability of chlorothalonil will prolong the effective life of many other fungicides.
Rotations with unrelated plants are commonly used to manage diseases. Proper handling and storage helps to reduce storage losses. Growers try to avoid overfertilization and suboptimum growing conditions. Deep cultivation is also a common practice for disease management in carrots.
To control Pythium, it is important to maintain proper growing conditions for the plants. Growers choose planting locations that are well drained. Rotation to nonhosts will also help control this disease.
Violet root rot (Alternaria radicina [fungus] and Erwinia carotovora [bacterial]). Root rots are more serious as storage diseases than field. This fungus attacks the roots and foliage. Root lesions appear as irregular to circular dark green to black cavitations showing some surface sporulation . Rots caused by E. carotovora have a characteristic odor and slime that develop rapidly under certain storage conditions. Proper storage conditions (temperature and relative humidity) minimize storage rotting.
Aster yellows is a mycoplasm spread by leafhoppers. Initial symptoms include yellowing and occasional vein clearing. Witches brooming effect is present at the crown characterized by increasing formation of petioles. Roots become woody and form many adventitious roots.
Leafhopper control is critical for control of yellows. Removal of nearby plants and infield weeds helps reduce inoculum. Disease resistant carrot varieties are available, but they may lack other desirable attributes. Crop rotation also helps to reduce disease pressure. Planting of ridges may also improve air circulation and reduce disease development.
Review materials recommended for disease control in the Georgia Pest Management Handbook.
Stormy Sparks (Extension) asparks@uga.edu and
David Riley (Research) dgr@tifton.cpes.peachnet.edu, UGA Vegetable Entomologists
David Langston, UGA Vegetable Pathologist dlangsto@arches.uga.edu
Stanley Culpepper, UGA Vegetable Weed Scientist stanley@arches.uga.edu
George E. Boyhan gboyhan@arches.uga.edu
Darbie M. Granberry granber@arches.uga.eduand
W. Terry Kelley wtkelley@uga.edu, UGA Horticulturists
William C. Hurst, UGA Food Scientist bhurst@fst.uga.edu
The Georgia Pest Management Handbook. [Paul Guillebeau, ed.]. Published annually. Special Bulletin 28. The University of Georgia.
Some information in this profile was taken from Florida Crop/Pest Management Profiles: Carrots
Prepared by Paul Guillebeau, IPM/Pesticide Coordinator, Department of Entomology, University of Georgia, Athens GA 30602 pguillebeau@bugs.ent.uga.edu