The Online Gardener's Handbook
Chapter 4: Vegetables
Cucumber, Melon, Pumpkin, Squash, Zucchini
Table of Contents
- Cucumber Beetles
- Cucumber Scab
- Cucurbit downy mildew
- Leaf Spots
- Powdery Mildew
- Seed-corn Maggots
- Squash Bugs
- Squash Vine Borers
- Learn More
Cucurbits are pollinated by bees and some insecticides may be very
harmful to them.
In this chapter, a description of various cucurbit 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.
Cucumber beetles are a common problem. They are striped yellow
and black or yellow with black dots and are about 6 mm long. They
move quickly when disturbed. Young plants are killed by defoliation
and older plants wilt and die from bacterial disease carried by
Remove beetles by hand or, for large numbers, use a portable vacuum
to remove adults in the early evening. Place in a sealed plastic
bag or a bucket of soapy water and dispose of them. Floating row
covers may prevent damage to young seedlings, but need to be removed
when blossoms appear to allow for pollination.
Cucumber scab symptoms appear as grey, sunken spots on the fruit,
darkening and sinking with age, sometimes exuding a gummy substance.
Most of the injury occurs on the fruit but leaves may have water-soaked
spots and stems may have cankers. Cooler night temperatures from
mid-summer on favour this disease.
Remove and destroy all plant residues in fall. Plant resistant
cultivars or consider a long crop rotationrotating out of cucurbit
crops for 2 to 3 years.
Cucurbit Downy Mildew
Downy mildew is a serious fungal disease of cucurbit crops. Infected
leaves develop pale green areas on the upper leaf surface. The lower
leaf surface may be covered with a downy, grey-to-purple mould with
visible black spores. Cucumbers are the most susceptible to infection;
however melons and other vine crops can be affected by certain strains
of this disease. Cucurbit downy mildew will not affect plants from
other crop families. Downy mildew is windborne and highly infectious.
It can destroy a crop in less than 1 week. Downy mildew is favoured
by cool, wet or humid weather conditions. At present downy mildew
spores do not appear to be able to survive Ontario's cold winters.
The disease overwinters in southern regions and spores usually blow
in from the southern U.S. and Mexico, during the spring and early
summer. In recent years, spores have been blowing up in late May
or early June, resulting in early infection of cucumber crops.
Purchase transplants from reliable sources and ensure they are
free from disease. Ensure there is adequate air circulation between
plants. Avoid overwatering and water in the morning so plants have
time to dry. Avoid watering the foliage by directing the water toward
the base of the plant. Cucurbit downy mildew is a devastating disease
and, once it appears in an area, plant loss is generally unavoidable.
In some areas of Ontario it may be very difficult to maintain cucumbers
throughout the growing season.
Leaf spots on cucurbits can be caused by a number of bacterial
or fungal pathogens. Small, circular spots appear on the leaves.
They may be "water-soaked" and angular in appearance,
or dry and reddish brown with a yellow halo, yellow to brown with
concentric rings. The lesions often turn brown and fall out, leaving
holes in the leaf, or grow together, causing the leaves to drop
from the vines and leading to a reduction in crop yield and quality.
Plant resistant varieties. Remove infected leaves and remove and
destroy all plant residue at the end of the season to eliminate
overwintering sites. Do not compost. Avoid wetting the leaves when
watering. For some leaf spot pathogens, it may be necessary to rotate
out of cucurbits for 2-3 years.
Powdery mildew is a fungal disease that appears as a dry talcum
powder-like mass of white spores on upper leaf surfaces during hot,
humid days and cool nights, resulting in the death of the leaf tissue.
When severe, mildew significantly reduces crop yield and causes
the plant to die prematurely.
Plant resistant varieties. Plant in unshaded areas and ensure air
circulation is adequate. If symptoms are limited in extent, remove
and destroy diseased tissue.
For information and management options, see the section on corn
Squash bugs are sap-sucking insects in the plant bug family affecting
mainly pumpkin and squash, but sometimes cucumber and melon. Young
bugs, or nymphs, are grey; adults are dark brown and about 17 mm
long. Affected areas of leaves, stems and vines are lighter in colour
at first and later turn brown and die. For more information see
the Plant Bug section of Chapter
In June, place traps of boards and stones between plants and remove
bugs from under them each morning. Hand pick and destroy any adults,
eggs or immature insects observed on plants. Remove and destroy
all plant residue after harvest to remove possible overwintering
Squash Vine Borers
Squash vine borer adult moths, which have metallic olive-brown
wings and an abdomen ringed with red and black, lay large reddish-brown
eggs on stem near the soil in late June through late July. They
hatch into creamy white, brown-headed insects, enter and feed inside
vine stems for four to six weeks. Coarse greenish-yellow excrement,
pushed out by the borer through holes, can be seen along the sides
of the stem. Plants wilt suddenly and may break or rot from the
point of attack. Fruit is poor and small. The insect overwinters
in the soil and once it is in a garden, the problem occurs every
Destroy eggs before they hatch. When vines wilt and the holes of
the borer are noticed, slit stem lengthwise and remove borer. Mound
soil over injured area and over vines near leaves to promote new
root growth from stems. The Butternut variety is resistant to the
squash vine borer.