Causes of pests and diseases

Pests and diseases are usually the symptoms of an underlying problem. Generally, healthy plants are insect- and disease-free, so look at the basics first.

Leafhoppers arc minute sapsuckers that damage plants and also spread plant pathogens.
Female mealybugs are sapsuckers and protect themselves with an unsightly powdery wax.


Possible cause

Irregular holes, chewed leaves; black droppings

Caterpillars or loopers

Meandering silver lines across distorted leaves


Discolored or distorted leaves

Thrips; lack of nutrients

Speckled dots on leaves and "cobwebbing"

Two-spotted mite

Flowers dropping off before blooming;

brownish marks on petals

Petal blight (fungus)

Stunted, wilted plant

Soil-borne fungus

Stunted plants; yellow, mottled leaves

Mosaic virus

Orange/brown powdery pustules underneath leaves

Rust, a fungal disease

Sticky leaves, black "soot" and ants

Sooty mold (a fungus) growing on a

secretion produced by aphids, scale

insects or mealybugs. The insects are

the problem, the fungus is a by-product.

Buds not opening; leaves twisted and distorted Aphids

Buds not opening; leaves twisted and distorted Aphids

• Does the herb have sufficient light? If not, you have three options: Thin out the surrounding plants, move the troubled herb or plant something more suitable. Herbs that have become leggy and straggly are often reaching for more light.

To treat mildew, remove any affected foliage and also use a fungal spray.

• Is it being overwatered? Many herbs like to dry out between waterings.

• Is underwatering the problem? Watering can require a fine balancing act. Stick a finger a few centimetres into the soil or potting mix to check on its moisture content.

• Is the herb being neglected? Move it to a more accessible position, remove it or write yourself reminder notes.

• How often is fertilizer applied? Giving plants access to the right nutrients will produce growth and vigour when and where it's needed. Check to see if the herbs need an all-purpose feed or one that is specifically for leaf or flower and fruit production and apply accordingly. Remember that more is not better, so overfertilizing won't produce faster-growing or healthier plants. Always remember to follow the manufacturer's recommendations.

Continue reading here: Insecticides and fungicides

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