Vegetable Production Guide

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Disease Control

This section was updated - 06 January 2021

Alternaria Leaf Spot

This disease occurs after cool, wet spells and causes numerous small, round, dead spots on leaves. It is most prevalent during hot, dry days combined with dewy nights. Leaves and stems may be killed but there is no spotting of fruit.


Beginning when the disease is first observed and at 7 to 14 day intervals thereafter, apply one of the products listed in Table 3, Cucurbits Disease Control. Bravo 500 sprayed for scab and powdery mildew may also control Alternaria leaf spot.

Angular Leaf Spot


This bacterial disease causes angular yellow spots on leaves and fruit which turn tan in colour. Droplets of gummy ooze form on the lower surfaces of leaves under humid conditions.


  1. If possible, buy seed grown in a dry area where angular leaf-spot is not common.
  2. Follow a three-year crop rotation.
  3. If the disease appears after planting, spray with one of the products in Table 3, Cucurbits Disease Control.
  4. Incorporate the vines immediately after harvest.
  5. Seed catalogues list varieties with tolerance to angular leaf-spot.

Cladosporium Scab


Gray, sunken, disfiguring spots on fruits exuding sticky droplets. Spots deepen and turn dark green or blackish.


  1. Sanitation is the key to control. Destroy all crop refuse at the end of the season.
  2. Rotate fields out of cucumbers for at least two years.
  3. Seed catalogues list varieties with tolerance to scab.
  4. If sprays are necessary use one of the products in Table 3, Cucurbits Disease Control.

Fusarium Root Rot and Wilt

Vines gradually wilt and die. The fungus lives in soil and is carried on seed.


  1. Sterilize soil, flats and greenhouse benches (see Planting section of this guide).
  2. Use seed treated with Thiram seed protectant.
  3. Avoid overwatering.
  4. Maintain or build up soil humus.
  5. Do not grow cucurbits continuously in the same field.

Powdery Mildew

Leaves develop a white powdery growth. Under severe conditions plants are completely defoliated by mid-August.


  1. Avoid fields which tend to have heavy dews and prolonged morning mists.
  2. Select resistant varieties when possible. Earlisweet muskmelon has some tolerance.
  3. Bravo is somewhat effective. Applications must commence prior to onset of the disease. Late applications would have to be applied by aircraft due to runnering of the plants. The results may not justify the expense of the spray program. Do not apply Bravo within 1 day of harvest.

Verticillium Wilt

The causal fungus is soil or seed-borne. First, lower leaves wilt and drop, then petioles turn yellow and wither and, finally, the entire plant may wilt. It is usually worse on light, sandy soils in the Interior, and where root lesion nematodes are also present.


  1. Disinfect used seedling trays prior to use (see Planting section of this guide).
  2. Grow seedlings in sterilized soil or soilless mix.
  3. Use seed treated with Thiram seed protectant.
  4. Follow a four-year rotation plan, avoiding crops susceptible to Verticillium wilt (e.g. potatoes, tomatoes, peppers and eggplants).
  5. Choose a soil that is well-drained and not underlain by hardpan.
  6. Do not plant out until soil temperature has reached 14°C or, if possible, 16°C.
  7. Avoid over-watering and maintain a high humus content in the soil.
  8. Select resistant varieties.

White Mould


Fruit becomes covered with white cottony mould, and later small black hard bodies (sclerotia) appear in the rotting tissue. Stems can also be blighted; older vines are more often affected.


  1. Rotate crops and deep plow to bury sclerotia.
  2. If only a few plants are infected, remove them from the field and destroy; do not dump cull fruit back on the field.

Root Rot

RootShield WP (Trichoderma harzianum Rifai strain KRL-AG2) is a biological fungicide for the suppression of Root Rot in greenhouse vegetable transplants.  When applied to transplants, greenhouse planting mix or soil, the product grows into plant roots as they develop to protect roots  against Pythium, Rhizoctonia and Fusarium. 


  1. Suspend RootShield WP using a spray volume of 30 to 45 g/100 L and apply at the rate of 55 to 110 g per cubic metre (loose) of greenhouse potting mix, soil or planting beds. 
  2. Apply using hand-held backpack or ground spray equipment. 
  3. Becomes active when soil temperatures are above 10 degrees C and is not effective while soils remain cold.
  4. More effective at suppression of root rot in neutral or acidic soils.  
  5. Should be used within 12 months of the date of manufacture.  
  6. Contains the allergens wheat and sulfites.
  7. ☺Approved for use in organics.
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