The Online Gardener's Handbook
Chapter 4: Vegetables
Carrot, Celery, Lettuce, Parsnip
Table of Contents
- Aster Yellows
- Carrot Rust Flies
- Downy Mildew
- Leaf Spots and Blight
- Pea Leafminer
- 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 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.
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.
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 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
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.
Plant disease-free, hot-water treated seed. Follow proper watering
procedures. Rotate crops and improve air circulation.
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
Harvesting susceptible crops before the beginning of September
may avoid population peaks when the most severe damage occurs.