HOME / FACTSHEETS / VEGETABLES / VEGETABLE CROP GUIDES / PARSNIP PRODUCTION GUIDE /
Parsnip Pests and Pest Control
Weeds
Perennial weeds should be controlled prior to planting. Preemergence herbicides usually provide good weed control. Carrots can be severely injured by preemergence herbicides when heavy rainfall or a high water table coincides with carrot emergence. Post-emergence treatments are also available for annual broadleaf weeds and grasses. However the stage of crop and weed growth is critical for good control with no crop injury.
Remove by hand small numbers of weeds that may escape herbicide treatment to reduce future weed potential. Also, carry out a good crop rotation to reduce the general reservoir of weed seed in the soil.
Diseases
Leaf Spots and Blight (fungi)
Characteristics: Cercospora leaf spots are brown to gray and circular. Alternaria blotches are irregularly shaped brown to black and more prevalent on older foliage. Both are seed and soil borne, can be spread by wind, rain splash and farm implements but will only infect leaves when they are wet.
Control: Apply sprays at 7 to 10 day intervals starting the first week of July or if fields are checked regularly then when disease is first detected. Continue spraying until 3 weeks of harvest. Spray intervals can be increased if there is no rainfall and night temperatures are cool(minimum temperature below 15°C). Processing carrot growers usually try to minimize spray applications to minimize costs. Follow a 2 to 3 year rotation and plow down carrot debris promptly following harvest. Storages and crates should be disinfected. Poorly timed irrigation can aggravate these diseases.
Gray Mold (Botrytis) and Sclerotinia White Mold (fungi)
Characteristics: Both fungi produce decay on stored carrots. The former has a gray, "fuzzy" appearance while the latter produces white cushions of mycelium which may contain hard black pea-sized fungal structures.
Control: Plant on a well-drained soil not recently used for soybeans, alfalfa, beans, lettuce, peas, tomatoes, carrots or cabbage. Practice a 3 year rotation. Store carrots at 0°C with a relative humidity of 95 to 98%. Control weeds and "bolters" as they may spread white mold and Botrytis by means of infected flower parts falling on healthy carrot plants.
Root Knot (nematodes)
Characteristics: Carrots may have forked roots, irregular round galls and spindle-shaped enlargements on tap and side roots.
Control: Where root-knot nematodes are a problem soil can be fumigated. Rotation or summer fallowing will reduce nematode numbers considerably.
Aster Yellows (mycoplasma)
Characteristics: Yellowish, dwarfed leaves, usually forming a tight rosette. Older leaves may develop reddish margins. The root at the crown may bulge up into a cone and many hairlike roots develop on the root. The mycoplasma overwinters in many perennial weeds and is spread by leafhoppers.
Control: Destroy weeds in fields, headlands, ditch banks, fence rows, etc. Avoid planting near susceptible crops. See leafhopper control.
Parsnip Diseases
(Itersonilia) Canker or Blight (fungus)
Characteristics: Leaf spots appear as small silvery areas which later enlarge to brown irregular shapes with indistinct dark borders. Cankers are most prevalent near the shoulder of the root; they begin where rootlets are attached to the taproot. Affected areas are first brown to reddish-brown, later becoming black as cankers develop and as affected areas become depressed. The fungus overwinters in diseased plant residue. Disease is worst in cool wet conditions.
Control: Apply five sprays at 7 to 10 day intervals beginning the first of August. In addition to spraying, beneficial results are obtained by gradually hilling the rows. Every 10 to 14 days add a small amount of soil to the ridge until the rows are well covered.
Insects
Carrot Rust Fly
Characteristics: The adult is shiny black, with pale yellow head and legs. It is less than 5 mm in length. Damage is caused in feeding by yellowish-white, legless maggots which are 8 mm long when fully grown. Attacks result in stunting of carrot and parsnip plants. Roots may be reduced in size or distorted, scarred and riddled with rust-red burrows of the larvae. Seedlings may be killed if the growing tips are severely injured. Adult flies appear twice, in early summer and mid August, and lays eggs, which hatch 6 to 12 days later into larvae. Adults start at field margins increasing risk of damage in these areas. Small sheltered fields and poor rotational practices increase the chances of rust fly injury. This insect is a weak flier and does not do well in a windswept field.
Control: Follow a good crop rotation. Do not plant in fields adjacent to last years carrot crop. Where a known population exists chemical controls should be applied at planting. Planting may also be delayed until after mid-June to avoid the first generation of flies. Carrots may be harvested early (in late August or early September) before the maggot leaves the hair roots and enters the main tap root. Individual fields should be monitored using orange sticky traps to determine if control measures are necessary. Place traps in sheltered areas of the field, along the field edge. Apply spray when adult flies are first caught in the traps. Polyester or other fabric covers that exclude this fly could be applied on small fields. Do not allow holes to develop in the material or control will not be obtained. Row covers have not been researched in this area and may aggravate foliar and root diseases.
Aster (Six-spotted) Leafhopper
Characteristics: They are small (4 mm long), slender, wedge-shaped insects. They are greenish-yellow in colour. They feed on many other crops such as potatoes, tomatoes, celery, spinach, lettuce, onion and squash. Adult leafhoppers winter in weedy areas along the margins of fields. They generally move into carrot fields early in July. Leafhoppers can carry aster yellows from plant to plant as they feed Once a leafhopper feeds on an aster yellows infected plant, it can spread the disease to all the other plants it feeds on.
Control: Foliar sprays are required beginning the first week of July and repeated at 10 day intervals until the end of August. Spray field boundaries also. Fields can be monitored using a 30 cm diameter sweep net. Five samples of 25 sweeps along the row are taken and the average number of leafhoppers determined. The threshold for applying a spray is 5 leafhoppers per sample. It is important to control leafhoppers early in the season to prevent the build up of aster yellows.
Carrot Weevil
Characteristics: Adult carrot weevils are dark brown with three light stripes on the thorax. They are about 6 mm long. The head is prolonged into a beak or snout. The adults overwinter in the sheltered margins of fields. They lay their eggs in carrots when the plants are at the second true leaf stage. The larvae are white legless grubs. They feed on the carrot tap root. Usually damage is restricted to the upper third of the root. There is only one generation per year known to occur in this area.
Control: Follow a good crop rotation. Do not plant in fields adjacent to last years carrot crop. Carrot weevil traps can be used to determine the need to apply a control measure. The threshold for a single spray at the second true leaf stage is 1.5 to 5.0 weevils per trap. If the cumulative number per trap exceeds 5.0 then a second application is needed at the four leaf stage.
Damage from this insect has not generally been significant. Good rotation may keep it from becoming a major problem.
This information has been taken from www.gov.pe.ca