The Online Gardener's Handbook 2010
Chapter 4: Vegetables
Carrot, Celery, Lettuce, Parsnip

Table of Contents

  1. Introduction
  2. Aster Yellows
  3. Carrot Rust Flies
  4. Downy Mildew
  5. Leaf Spots and Blight
  6. Pea Leafminer
  7. Learn More


In this chapter, a description of various carrot, celery, lettuce and parsnip pests will be provided along with suggested management options. These management options will not include the use of pesticides. Some biopesticides and certain reduced risk pesticides are still available to the homeowner for controlling weeds and pests in lawns and gardens. For more information, refer to Chapter 2 of this handbook and the Ministry of the Environment's website. For suggestions on managing specific weeds and pests, consult local horticulturalists, Master Gardeners or your local garden supply centre.

Aster Yellows

Aster Yellows is caused by a mycoplasma-like organism, with symptoms similar to viral diseases. It affects carrot, celery and lettuce, turning leaves yellow and stunting growth. Carrots also develop multiple crowns and many lateral roots. The disease is spread by the aster leafhopper.

Management Options

Prompt removal and destruction of affected plants is of some help. Control weeds in and around the garden. Reduce leafhopper populations - for information on managing leafhoppers, refer to Beans.

Carrot Rust Flies

The first generation adults of carrot rust flies lay eggs near the young carrot and parsnip plants during May; the small yellowish-white maggots that hatch invade the roots. The maggots will feed on root hairs for up to a month before tunnelling into the carrot. A second generation usually occurs in mid-to-late July. Adults are shiny and black and approximately 6 mm in length. The maggots are cream-white and legless with dark mouthhooks. Roots are covered with rust-red burrows and surface scars, but damage is usually limited to the lower two-thirds of the root.

Management Options

Delay seeding until July 1. This usually reduces populations of the second generation in late July, but some damage by the larvae may be expected. Plant these crops away from sheltered areas as this fly avoids windy locations. Remove and destroy infested roots - do not compost. Control weeds in the carrot family (e.g. Queen Anne's Lace) that are in and around gardens.

Downy Mildew

Downy mildew is a fungal disease that affects lettuce and primarily occurs in cool, moist weather in spring and fall. Yellow patches develop on leaves, later becoming brown and faintly netted with dark markings. Undersides of patches may be covered with a downy, white fungus growth under humid conditions. Infected tissue usually dies.

Management Options

Plant resistant varieties, space adequately and follow proper watering practices. Remove and destroy infected tissue. Rotate out of lettuce and celery if possible.

Leaf Spots and Blight

Leaf spots and blight are quite common on carrot and celery and cause leaves to turn brown or black and curl. First symptoms appear on the lower leaves, usually in late July. On carrots, mild symptoms do not need to be treated. On celery, usually older, outer leaves are affected so there is often little impact on plant, unless the blight starts to affect the celery stalks or when a majority of the leaves are infected.

Management Options

Plant disease-free, hot-water treated seed. Follow proper watering procedures. Rotate crops and improve air circulation.

Pea Leafminer

The pea leafminer has been found in the Holland Marsh area of Ontario, on celery, lettuce (especially the head and leaf types) and other leafy vegetables. Adults are small, black to grey flies with yellow markings. Eggs are laid in the leaves, leaving small "bronzed" puncture marks. Females pierce the leaves to feed on plant sap. Larvae feed between the leaves, creating straight mines that follow the veins. The pea leafminer is typically a late season pest with populations peaking anytime from the end of August through the middle of September.

Management Options

Harvesting susceptible crops before the beginning of September may avoid population peaks when the most severe damage occurs.

Learn More


For more information:
Toll Free: 1-877-424-1300
Author: OMAFRA Staff
Creation Date: 21 July 2005
Last Reviewed: 25 June 2010