Insects That Spread Plant Diseases

Standard

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.

20190109B extension.entm.purdue.edu

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).

20190109C DieterO, Wikimedia Commons.JPG

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.

20190109E www.nature-and-garden.com.jpg

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.

Advertisements

Foam on Your Plants? It’s Just Frog Spit!

Standard
20170627A MuPaily, WC

This strange bubbly froth is called frog spit. Photo: MuPaily, Wikimedia Commons

No, not real spit from a frog, but the cluster of small transparent bubbles in a whitish foam is instead caused by an insect called a spittlebug or froghopper, in the Cecropidae family (also in the newly created families Aphrophoridae and Clastopteridae), and goes by the name of frog spit, cuckoo spit or snake spit.

A generation ago, most curious children were in contact enough with nature to have examined the spittle and would have discovered on their own that there is a small pale green to yellow insect inside, but nowadays many children don’t venture far from the asphalt and concrete of the city. When they become young adult gardeners (and gardening has never been as fashionable among the younger generation as it is today!), they can be mystified by this weird froth. What is it and what to do about it?

20160627F treegrow, Flickr.jpg

This spittlebug nymph is feeling quite naked with its bubble shelter removed. Photo: treegrow, Flickr

The insect found in the bubble shelter is the nymph of a spittlebug. Soon its birth, it pierces the stem of its host plant and uses the sap that flows from it to make the bubbles in question, inflating them with air from a special opening on its underside. Not only does this spittle conceal the nymph from predators, it insulates it from sudden temperature changes and prevents it from drying out. Moreover, the foam has an acrid taste, enough to keep even the most stubborn predators at bay.

There are over 850 species of spittlebugs throughout the world. In fact, if there are plants nearby, there are probably spittlebugs! Some are quite ubiquitous and will settle on almost any plant, either woody or herbaceous, but there are species that are exclusive to certain plant groups. In the average garden, you’ll most often see them on small fruits and such ornamental flowers as chrysanthemums, dahlias, mallows, roses, fuchsias and lavenders.

20170627C Charlesjsharp, WB

Adult spittlebug. Photo: Charlesjsharp, Wikimedia Commons

The adult is a small hopping insect, often brown or beige. It is seldom seen, for not only does its color help conceal it, but it leaps to other plants when people approach. When a spittlebug is ready to jump, it crouches down and takes on a froglike posture, whence the name “froghopper.”

The adult spends its summer feeding on the sap of plants. At the end of the season, the female pierces holes in a stem and deposits its eggs. They hatch in the spring and, with the return of favorable temperatures, form a bubble home. The nymphs feed on the plant for several weeks, molt a few times, then emerge as adults. The foam is then washed from the plant by the next hard rain. There is only one generation a year. Given the pest’s life cycle, the appearance of frog spit is often considered a sign of the arrival of summer.

Legends

20170627D carlswebgraphics.com

Just add a bit of frog spit to the pot the next time you get the coven together to make a bit of brew! Illus.: carlswebgraphics.com

Our ancestors found frog spit a very mysterious product indeed, believing it was produced by frogs, cuckoos, snakes or even witches. In fact, frog spit has been a popular ingredient in witches’ brews over the centuries!

Damage Caused

A single spittlebug nymph causes little immediate damage. However, when there are several bubble shelters on the same plant, the growth and vigor of the plant may be affected and the leaves and stems may be deformed.

The real problem, though, is that spittlebugs can transport viruses from one plant to another and that the holes they pierce can leave an open wound on the plant that will be prone to microbial infestations.

It is, however, the adults who cause the most damage and their great mobility makes control difficult. The effect of a single nymph on a plant is minimal.

What to Do?

What to do when you see frog spit on one of your plants? You can simply ignore it if you want to, as it causes little damage. Or you can remove the nymph with your fingers or wash the spittle off with a strong stream of water, thus exposing the creature to the drying sun. When there is more than one patch of frog spit on the same plant, however, it’s best to remove them, as an accumulation of nymphs could damage the plant’s health.

Frog spit: a disgusting name, but it hides a most interesting little insect!20170627A MuPaily, WC

Bugs that Spread Plant Diseases

Standard
20150111

Spittlebug larvae live in a mass of bubbles commonly known as frog spit or snake spit.

Insects that feed on the sap or grate or eat the leaves of our plants sometimes have much more serious consequences: they may well be carrying an incurable plant disease that will cause more damage that the insect itself ever did. 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 the plant. This is why it is important to act quickly when a plant is attacked by any insect. Among the insects that transmit viruses are aphids, flea beetles, leafhoppers, whiteflies, thrips and spittlebugs (froghoppers).

20150111-2

Grass infected with a mosaic virus… but few plant viruses are this visible.

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 becomes weak and less productive. The two classic cases are strawberries and raspberries. Both are very productive for 2 or 3 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.