Commercial Vegetable Recommendations Extension Bulletin £-1437 (Minor Revision) February 1986 Coopererative Extension Service CARROTS Michigan State University

Bernard H. Zandstra, Department of Horticulture Edward J. Grafius, Department of Entomology Darryl D. Warncke, Department of Crop and Soil Sciences Melvyn L. Lacy, Department of Botany and Plant Pathology

Production and maturity than open-pollinated Genetic resistance is the best pro- cultivars, but the seed is much tection against bolting. Approximately 7,000 acres of more expensive. Some growers carrots are planted in Michigan plant open-pollinated cultivars for There are four main types of car- each year. fall harvest because the roots do rots (Figure 1): The average state yield for fresh not oversize as quickly as hybrids, market carrots is 8.8 tons (350 50-lb thus giving the farmer more Imperator—long, small shoulders, bags) of usable carrots per acre. latitude in scheduling harvests. tapered tip; used primarily for Yields on good fields with no Bolting (formation of a flower fresh pack. Most carrots grown for nematode, water, or other limiting stalk the year of planting seed) is a fresh market in Michigan are of problems may exceed 15 tons (600 response to cold temperatures and this type. 50-lb bags) per acre. Minicarrots plant size. Plants that bolt do not Nantes—medium length, uniform yield about 11 tons per acre. form a marketable root. Plants that diameter, blunt tip; used for bun- Processing carrots can yield 35 to have reached sufficient size bolt ching, slicing, and mini carrots. 40 tons per acre on good fields with when exposed to temperatures Although not widely grown in irrigation. below 50°F for an extended period Michigan, Nantes type carrots of time. Although the most suscep- have a good eating quality, and are Use tible cultivars require less than 2 especially suited for local sales. days of cold temperature to induce They normally mature earlier than Approximately 85% of Michigan bolting, most cultivars used in Imperator types. carrot acreage is used to produce Michigan need about 10 to 15 days. Danvers—large, medium long, full size carrots for fresh market. Mini or baby carrot production for Fig 1: Four main types of carrots. fresh pack is increasing, but is still a minor part of total production. Imperator Danvers Nantes Chantenay About 15% of carrot acreage is used to produce processing carrots. Types and Cultivars

The carrot is a biennial plant. During the season in which it is planted, the plant produces a storage root. After a period of cold temperature, the root begins to grow again and produces a seed stalk. Most carrot seed is produced in the western U.S. in areas that have relatively mild winters. Seed is planted in August and produces a small root before winter sets in. The next spring the plant resumes growth, flowers, and sets seed, which is harvested in August. Most carrot cultivars used in Michigan are hybrids. Hybrids tend to be more uniform in quality processing type; used for dicing Climatic Requirements periods of hot, dry weather often and slicing. Danvers cultivars re- and Irrigation cause a strong, unpleasant flavor. quire a long season (120 days) to Alternating periods of slow or develop tonnage and high sugar Carrot is a cool season crop. rapid growth caused by irregular content. Most carrots grown for Seeds germinate at soil temperatures or moisture often processing in Michigan are of this temperatures of 40°F cause rough carrots. Saturated soil type. or higher. Roots and leaves grow conditions after heavy rains often Chantenay—large shoulders, short, best at temperatures of 60° to 70°F. kill the tap roots, resulting in short, usually with a large, distinctly Carrot seedlings grow rapidly dur- stubby carrots. Good drainage is colored core; used for dicing. ing cool growing conditions in the therefore as important as a suffi- These are older cultivars and spring, producing their mature- cient water supply for good carrot usually not of the quality required length tap roots in the first 3 weeks production. by processors. They are now used of growth. primarily by home gardeners. Young carrot seedlings can with- Soil Requirements and stand light frosts, but hard frosts Tillage Qualities of Good Fresh heave the soil and break the tap Market Carrots roots, which results in stubby and Carrots grow best on deep, loose, forked carrots. Young seedlings are well-drained mineral and organic burned off easily by high soils with good water holding Carrot cultivars for fresh pack in temperatures that occur before the capacity. Most Michigan carrots plastic bags should have the follow- plants are 1 inch high. are grown on deep muck soils. ing qualities: Although mature carrot leaves Sandy and marl mucks can pro- can tolerate several nights of frosts duce good carrots, but require • long (9 to 10 inches), slender, with temperatures in the mid-20°F more careful management. Sandy smooth, with small diameter range, they will be killed when and clay soils crust easily after necks (point of attachment of temperatures fall below 20°F for rains, which reduces seedling leaves) several hours. Because leaves are emergence and air penetration. If • uniform deep orange or gold needed for harvest, recoverable crusting occurs, the soil between color (including the core) yields of roots decrease as leaves rows should be worked with a • mild, sweet flavor are killed by frost. Healthy tops cultivator as soon as possible. • vigorous, blight-resistant leaves resist frost better than blighted Carrot roots are very sensitive to • high percentage of usable yield tops. soil compaction. Rows next to the Carrots require about 90 to 120 wheel track often have more forked Good cultivars should also be days to mature in Michigan, and stubbed carrots than rows in consistent producers regardless of depending on cultivar and season. the center of a bed, and usable weather and season. Unfort- Harvest of early, fresh market car- yields are reduced. Therefore, limit unately, few cultivars meet these rots begins in late July or early movement of equipment in fields qualifications. The following August. Processing carrots are as much as possible. During the cultivars have performed better harvested in September and first 3 weeks of growth, stay off the than average in Michigan trials. October. Mini carrot harvest field completely. begins in early July. Some farmers grow carrots on Carrots should not be exposed to raised beds. This allows the soil to Recommended Cultivars water stress. When irrigating, soak drain better and warm sooner in the soil completely to avoid separa- the spring. It is of most benefit on Fresh market cellopack (Tm- tion between sub-soil and surface heavy and poorly drained soils. perator type): Spartan Fancy 80, moisture. A separation between Spartan Delite 80, Six-Pak, moisture sources with a dry mid- Fertilizer Requirements Chancellor, Debut, Fanci Pak, dle zone can cause differential Grenadier, Paramount, Trophy growth and cracking. Carrots need Add lime to muck soils to main- Nantes type: Pioneer, Nantes, about 10 to 14 inches of water dur- tain a soil pH of 5.5 to 5.8; main- Scarlet Nantes ing the growing season, depending tain pH of mineral soils at 6.2 to Mini carrots: Frantes, Scarlet on the soil type and water table. 6.8. Nantes The water table should be main- It is important to maintain active Processing: Spartan Bonus 80, tained below 30 inches. foliar growth throughout the Danvers 126 Weather has an adverse affect on season to minimize damage from several quality factors. Long leaf blights. Hybrids are less susceptible to cracking caused by banded fertilizer at planting, or 4 cases, up to 50% of the roots are excess fertilizer and water than lb manganese sulfate (1 lb Mn) in undersized and cannot be packed. open-pollinated cultivars. water as a foliar spray in mid-June Seed companies are trying to im- Therefore, it is often advantageous to early July. Include Mn with in- prove uniformity of germination. to increase the nitrogen fertilizer secticide or fungicide sprays 2 or They harvest the seed at an op- rate on hybrids if blight is a 3 times to avoid deficiency later in timum time when most of it is problem. the season. mature, grade it to remove large A good nutrition program main- Boron (B) deficiency causes and small seed, leaving seed of a tains moderate to high nutrient necrosis (plant tissue death) in the relatively uniform size, dry the levels in the soil with annual addi- growing tip or internal breakdown seed, seal it in airtight containers, tions of fertilizer based on a soil in carrot roots. To avoid this prob- and keep it in refrigerated storage. test. Soil should be tested at least lem, apply 10 to 20 lb borax (1 to Some seed companies are every 2 to 3 years. Soil test levels 2 lb B) per acre in the broadcast fer- developing a seed treatment ser- for good carrot production should tilizer each year. Boron deficiency vice called priming to improve be maintained at 150 lb phosphate occurs on both sandy and muck uniformity of germination of carrot (P2O5) and 350 lb potash (K2O) per soils. seed. This process includes soak- acre. Nitrogen (N) does not ac- Copper (Cu) deficiency ing the seed in an aerated salt solu- cumulate in soil over time, so it sometimes occurs on new muck. It tion, which brings it to a uniform should be applied annually for each results in poor orange-color level of pregermination. The seed crop planted. development in carrot roots. If Cu is then dried to an optimum A 20-ton carrot crop removes levels are below 20 ppm by soil test, moisture level and sealed and about 100 lb N, 25 lb P2O5, and 100 apply 12 lb copper sulfate or 4 lb stored like unprimed seed. lb K2O per acre. Annual sup- copper oxide (3 lb Cu) per acre per Theoretically, priming improves plemental nutrients can be applied year, until a total of 20 lb actual Cu uniformity of germination and in a combination of broadcast band has been applied. Since Cu remains seedling emergence, which should and sidedress applications. In available in the soil system and result in more uniformity at years between soil tests, apply does not leach, additional applica- harvest. Results have been variable, about 75 lb N (up to 120 lb on sandy tions should not be necessary. but refinements in the technique or marl muck), 100 lb P2O5 and 200 may improve the effectiveness of lb K2O per acre for carrrots grown the process. on good muck soil. For example, Carrot Seed Carrot seed loses viability rapidly broadcast and plow down 300 lb when stored under damp and 18-45-0 and 400 lb 0-0-60 per acre To obtain a high percentage of moderate to warm temperature (54 lb N, 138 lb P2O5, and 240 lb marketable carrots at harvest, car- conditions. To maintain viability, K2O). Sidedress when carrots are 5 rots must be uniformly spaced in store seed in a cool, dry place in a to 6 inches high and have 6 to 9 the row. Precision seeders place sealed container or air-tight bag. fern leaves with 60 lb 45-0-0 or 80 seeds accurately and can be used Check seed for germination before lb 34-0-0 per acre (27 lb N). Increase successfully for carrots. However, planting. the sidedress N rate to 50 lb per because carrot seed is very small, acre on sandy and marl mucks. If most precision seeders can plant heavy rains occur, apply a second the seed only if it has been pelleted Spacing and Planting sidedressing of N. On mineral or coated. To obtain maximum soils, apply 120 lb N, 75 lb P2O5,and benefit from precision seeding, Chisel-plow land to a depth of 18 150 lb K2O per acre if soil test in- almost every seed has to germinate to 24 inches in the fall. Plow 12 formation is not available. and form a usable carrot root. inches deep and then follow with Manganese (Mn) is commonly The flowering habit of carrots a roller to form a firm seedbed im- deficient in organic soils in results in differences in size and mediately before planting. Michigan. In carrots the deficiency maturity of the seed at harvest. Planting of fresh market carrots appears as interveinal chlorosis These differences result in non- begins about April 15 and con- (yellowing between veins of the uniform germination and tinues through June 15. Schedule leaves) uniformly over the whole emergence when the seed is plantings to provide a continuous plant. Since it is very immobile planted in the field. Early-emerging supply of carrots to the packing- (does not move) in the soil, apply seedlings dominate later-emerging shed throughout the season. Car- Mn in a band at planting. If all fer- seedlings and out-compete them rots planted in mid-April mature in tilizer is broadcast before planting, for water, nutrients, and light. Con- about 110 days. Carrots planted Mn can be foliar-applied. Apply 8 sequently, at harvest, there is wide during warmer weather mature in lb manganese sulfate (2 lb Mn) in variability in root size. In many 80 to 100 days. Hybrid carrots reach maturity and become over- tends into November. Maximum and can be stored for 4 to 5 months sized in about one week. Open- marketable yield of fresh market under proper conditions (32°F and pollinated cultivars develop slower carrots is usually obtained when 95% to 99% relative humidity). and thus have more flexibility for 20% of the carrots in a field are Remove excess soil and rotten car- harvest. Processing carrots are jumbos (over 1 1/2 inches in rots, but do not wash carrots before planted from late April to early Ju- diameter). Carrots are mechan- storing them. Do not store carrots ly. Processing cultivars mature in ically harvested by undercutting in the same room as apples, pears, 110 to 130 days. the roots and elevating them out of or other fruit, because these fruits Plant carrots with a vegetable the soil and into the machine by give off ethylene gas, which causes seeder (such as Planet Jr.) equipped grasping the leaves. Thus, it is im- a bitter flavor in carrots. with a 2- or 3-inch scatter shoe or portant to maintain healthy leaves multiple-row shoe. The row should until the carrots are harvested. not be more than 4 inches wide Carrots are transported to the Insects because of difficulties passing the packingshed in trucks or trailers leaves through the harvester. Plant and unloaded into water to reduce Consult Extension Bulletin enough seed to obtain about 24 live root abrasion. They then pass E-970, Celery and Carrot Insect seeds per foot of row for fresh through a rotary root washer and Pests, for pictures of pests and market carrots, 30 to 40 seeds for sizer before moving to the packing detailed life history information. mini carrots, and 16 to 18 seeds for line. See Extension Bulletin E-312, Con- Danvers-type processing carrots. The storage life of carrots is im- trol of Insects, Diseases, and Rows should be at least 15 to 20 proved by hydrocooling, preferably Nematodes on Commercial inches apart. Closer spacing makes before packing. The half-cooling Vegetables, for current control harvesting difficult and prevents time for loose carrots is 3.2 recommendations. air movement through the leaf minutes. Cooling after packing is Aster leafhoppers (Macrosteles canopy, which may result in in- not as efficient as cooling before fascifrons) are the most important creased blight infection. Plant car- packing and thus takes more time. insect pests of carrots in Michigan. rot seeds 1/8- to 1/4-inch deep into Carrots cannot be vacuum cooled The leafhoppers do no direct moist soil. If soil is dry, irrigate the efficiently. damage to carrots, but transmit fields immediately after seeding. If U.S. No. 1 grade carrots are 3/4 aster yellows to carrots, celery, let- irrigation is not available, plant to 1 1/2 inches in diameter and at tuce, and weeds such as wild car- seeds 3/8- to 1/2-inch deep. Make least 5 inches long. Jumbos are at rot, marestail (horseweed), and sure that the seed is pressed firmly least 1 inch and no more than 2 1/2 pineappleweed. Aster yellows is into the soil to obtain good soil- inches in diameter. Fresh market caused by a mycoplasma-like seed contact. carrots are usually packed in 1, 2, organism and can be controlled Approximately 2 to 3 lb of carrot 3, or 5-lb plastic bags and then only by controlling the leafhopper seed are needed per acre for fresh packed in 48 or 50 lb master bags. and the weed hosts. market cultivars, 4 to 5 lb for mini Jumbo carrots are packed in 25 or The adult aster leafhopper is light carrots, and 1 to 2 lb for processing 50 lb bulk sacks. gray-green, 1/8 inch long, and is an cultivars. Always plant according Handle carrots as carefully as active flier. The leafhopper over- to desired plant stand count, taking possible during and after harvest to winters in the egg stage on grasses into consideration the germination avoid damaging the roots. Injuries and weeds in Michigan and may rate and number of seeds per reduce shelf life and increase also migrate .into Michigan from pound. chances of decay. Fresh market overwintering areas in Missouri Rye or barley strips are often carrots are especially susceptible to and Arkansas. However, long planted between every 3 to 6 rows injury because they aro harvested distance migrants are probably of carrots to protect young carrots before maturity (i.e., the epidermis rare in Michigan. from wind damage. Remove wind- is not fully developed) to obtain the Check fields for leafhoppers at break strips when carrots are 4 to desired market-size roots. Fresh least 1 or 2 times per week and 5 inches high, either with her- market carrots can be stored for 4 treat if numbers exceed 5 to 10 per bicides or by tilling. to 6 weeks if held at 32°F and 95?/o 100 sweeps with an insect net. to 99% relative humidity. Weekly field scouting can save 4 to Harvest and Postharvest Harvest of processing carrots 6 sprays per season with no in- usually begins about October 1 and crease in aster yellows incidence. Fresh market carrot harvest extends into late November. The carrot weevil (Listronotus begins when carrots are of suitable Because processing carrots are oregonensis) can be a severe pest of size. In Michigan, harvest usually harvested when they are mature, carrots, celery, and parsley. The begins around August 1 and ex- they are less susceptible to injury weevil overwinters as an adult. It roots—including carrots. fungicides. lays eggs in the petioles and the Where wireworms are observed Bacterial blight (Xanthomonas larvae bore down into the crown during tillage or where problems carotae) symptoms are similar to and eventually into the root of the are suspected, treat with a soil in- those of the fungal blights: dark carrot. Damage is almost always secticide prior to planting. brown, water-soaked spots appear restricted to the upper 1/3 (2 to 3 on leaves; as the lesions age, the inches) of the carrot. centers become brittle and crack; Crop rotation is an excellent con- Nematodes the spots are also surrounded by a trol because the adults rarely fly. yellow margin. Bacterial blight Fields with problem infestations Northern root-knot, carrot cyst, may also cause small brown or can be identified at harvest and root-lesion, and pin nematodes can maroon spots or water-soaked targeted for crop rotation or special be major limiting factors in flecks on roots. Bacterial blight scouting and insecticide Michigan carrot production. The may be partially controlled with treatments. See Extension Bulletin problem is especially severe in fixed copper compounds. E-890, Detection and Control of Car- fields where carrots are grown con- Aster yellows, caused by a rot WeeviJ, for pictures of adults, tinuously. Infected carrot roots mycoplasma, is spread by aster eggs, larvae, and damage, and may be stubbed, forked, or knobby leafhoppers. It causes yellowing, details on monitoring. and have round galls on the secon- twisting, and reddening of leaves. Green peach aphids (Myzus per- dary and tap roots. These Young leaves do not develop fully sicaej are pests of many vegetable nematodes also infect other and form a tight rosette. The tap crops, including carrots. Damage vegetable and field crops; however, root becomes woody, brittle, and to carrots is less serious than other onions, corn, small grains, and bitter with excessive root hairs. crops because carrots are not sub- sorghum appear to be less affected The organism overwinters in ject to virus diseases and the and should be considered as rota- perennial weeds of the aphids do not cause contamination tional crops to reduce soil infesta- Umbelli/erae and Compositae problems as they do in leafy crops. tion levels. families, such as wild carrot, wild The green peach aphid adults are Historically, soil fumigation has lettuce, marestail, and pine- yellowish green and 1/16 inch long; been the most effective means of appleweed. Control these weeds in the winged adults are black with nematode control in carrot produc- and around fields to reduce infec- green markings. They overwinter tion. If nematode problems are tion. Once leafhoppers appear in as eggs on peaches and other stone suspected, have soil and roots fields, apply insecticides on a fruits and migrate to carrots in tested for nematodes (see Exten- regular schedule. early summer. These aphids are all sion Bulletin E-800, Nematode Storage rots are caused by a females and produce live young Detection). If plant parasitic number of organisms. The most without mating. A single female nematodes are present in popula- common is crater rot (Rhizoctonia can produce 100 to 200 young and tion densities above an action carotae). To avoid storage rots, cool populations build rapidly, especial- threshold, an appropriate the carrots after harvest as quickly ly during warm, dry weather. nematode management procedure as possible to 32°F. Avoid Check fields for aphids regularly will be recommended. mechanical damage to roots during and treat, if necessary. Avoid ex- Oxamyl (Vydate 2L and Oxamyl harvest. Do not try to store carrots cessive spraying because extremely 10G) are registered for nematode from poorly drained fields or fields high populations are often found in control in carrots. that have suffered excess water fields that are heavily sprayed with damage during the growing insecticides and fungicides. The season. aphids may develop resistance to Diseases insecticides and flourish where all natural enemies (insect predators, Alternaria leaf spot (Alternaria Weeds parasitoids, and fungal diseases) daucij and Cercospora leaf spot have been eliminated. (Cercospora carotae) cause similar Annual grasses and broadleaf Wireworms are sometimes a symptoms on leaves and are dif- weeds are the major weed pests in problem in fields that recently have ficult to distinguish in the field. carrots. Most can be controlled been planted with sod or have had Spots on leaves have a dark center with herbicides currently grassy weed problems. Adult surrounded by a yellow margin. registered for use on carrots. wireworms (click beetles) are at- The leaves curl when lesions ap- However, a few resistant weeds are tracted to grassy weeds for egg lay- pear on the edges of leaf segments. becoming serious problems. ing, and the larvae live in the soil Both of these diseases can be con- Several weeds in the Compositae for 2 years, feeding on plant trolled by regular applications of family, including marestail (Con- yza canadensis), pineappleweed commonly used preplant incor- E-433 Weed Control Guide for (Matricaria ma- tricarioides), and porated to control weeds in carrots Vegetable Crops groundsel (Senecio vulgaris) are planted on mineral soils. somewhat resistant to both linuron Several additional herbicides are E-486 Secondary and Micro- (LoroxJ and stoddard solvent. Dod- nearing registration on carrots. See nutrients for Vegeta- der [Cuscuta campestris), a parasitic Extension Bulletin E-433, Weed bles and Field Crops weed, is spreading in some areas. ControJ Guide for Vegetable Crops, A good weed control program in- for current recommendations. cludes both pre- and E-550 Fertilizer Recommen- postemergence application of her- dations for Vegetable bicides, crop rotation, and cultiva- Additional Information and Field Crops in tion. Linuron is widely used both Michigan pre- and postemergence on muck More information on carrot pro- soil. Because it can injure ger- duction is contained in the follow- E-800 Nematode Detection minating carrots, apply linuron ing bulletins, available from preemergence at no more than County Cooperative Extension Ser- E-890 Detection and Control 1/2-lb active ingredient per acre. If vice Offices or from the MSU of Carrot Weevil dodder, chickweed, or smartweeds Bulletin Office, P.O. Box 6640, East are major problems, include chlor- Lansing, Michigan 48823-6640. E-970 Celery and Carrot In- propham (FurloeJ in the Some of these bulletins are for sale sect Pests preemergence application. only. Consult your County Stoddard solvent, a petroleum Cooperative Extension Service Of- E-1720 Diseases of Carrots distillate, can be sprayed fice for prices and availability. postemergence over the top of car- E-1751 Identifying Diseases of rots and kills most broadleaf and E-312 Control of Insects, Vegetables grass weeds. However, it is very ex- Diseases, and Nema- pensive and can leave an oily taste todes on Commercial in carrots if applied too close to Vegetables harvest. Trifluralin (Treflan) is

I MSU is an Affirmative Action/Equal Opportunity Institution Cooperative Extension Service programs are open to all without regard to race, color, national | origin, sex, or handicap. Issued in furtherance of Cooperative Extension work in agriculture and home economics, acts of May 8, and June 30, 1914, in cooperation with the U.S. Department of Agriculture. W.J. Moline, Director, Cooperative Extension Service, Michigan State University, E Lansing, Ml 48824. This information is for educational purposes only. Reference to commercial products or trade names does not imply endorsement by the Cooperative Extension Service or bias against those not mentioned. This bulletin becomes public property upon publication and may be reprinted verbatim as a separate or within another publication with credit to MSU. Reprinting cannot be used to endorse or advertise a commercial product or company.

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