The Online Gardener's Handbook 2010
Chapter 4: Vegetables
Cucumber, Melon, Pumpkin, Squash, Zucchini

Table of Contents

  1. Introduction
  2. Cucumber Beetles
  3. Cucumber Scab
  4. Cucurbit downy mildew
  5. Leaf Spots
  6. Powdery Mildew
  7. Seed-corn Maggots
  8. Squash Bugs
  9. Squash Vine Borers
  10. 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

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 beetles.

Management Options

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

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.

Management Options

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.

Management Options

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

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.

Management Options

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

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.

Management Options

Plant resistant varieties. Plant in unshaded areas and ensure air circulation is adequate. If symptoms are limited in extent, remove and destroy diseased tissue.

Seed-corn Maggots

For information and management options, see the section on corn pests.

Squash Bugs

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 1.

Management Options

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 sites.

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 year.

Management Options

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.

Learn More


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