Gardening Harmful insects Plant diseases

Insects That Spread Plant Diseases

Some pretty innocent-looking insects can transmit some pretty powerful plant diseases. Ill.: laidbackgardener.blog

Insects that feed on the sap or scrape or munch on the leaves of our garden plants sometimes have much more serious consequences than just a bit of leaf damage. They may well be carrying an incurable plant disease that will cause more damage than the insect itself ever did.

This isn’t so surprisingly, really. It’s well known that mosquitoes transmit malaria, dengue fever and Zika virus to people. That other insects do the same to plants is a similar process.

Plant viruses and their relatives, viroids and phytoplasmas, are mostly transmitted by insects that inject them into plant tissues as they eat. However, there is no treatment for viruses in the home garden except to pull out and destroy infected plants. That’s why it’s important to act quickly when a plant is attacked by any insect in the hopes of removing the pest before it has time to spread its deadly cargo.

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Spittlebugs look fairly innocuous, but are a major vector of plant diseases. Photo: extension.entm.purdue.edu

Among the insects that commonly transmit viruses are aphids, flea beetles, leafhoppers, whiteflies, thrips and spittlebugs (froghoppers).

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Mosaic virus is one of the more visible viruses. Photo: DieterO, Wikimedia Commons

Viruses (and other related diseases) sometimes have visible symptoms: for example, a specific discoloration of the leaf (mosaic or marbling) or deformed foliage or flowers, but most often not … except the plant weakens and becomes less productive. The two classic cases are strawberries and raspberries. Both are very productive for 2 to 5 years, then go so far downhill due to multiple viral infections that the only logical solution is to destroy them and start anew with “indexed” plants (plants confirmed to be free of viruses).

A good way of reducing the attacks of virus-carrying insects in the home garden is to maintain a good biodiversity in your plantings. Monocultures, where a single plant species is grown over a large area, attract and retain predatory insects of the crop being grown. When plants are grown in mixed plantings, though, these insects have a harder time finding their favorite host and your plants are therefore less often infested with debilitating diseases.

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Nasturtium used as a trap crop. Photo: http://www.nature-and-garden.com

If you add a trap crop to your garden, that is, a plant the insect pest likes even better than the crop you want to protect, such as the nasturtium (Tropaeolum majus), an excellent trap crop for aphids, prevention can be even more effective: just yank out the trap crop at the first signs of infestation, before the insect can spread to neighboring plants.

Garden writer and blogger, author of more than 60 gardening books, the laidback gardener, Larry Hodgson, lives and gardens in Quebec City, Canada. The Laidback Gardener blog offers more than 2,500 articles to passionate home gardeners, always with the goal of demystifying gardening and making it easier for even novice gardeners. If you have a gardening question, enter it in Search: the answer is probably already there!

1 comment on “Insects That Spread Plant Diseases

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