Skip to main content

Thrip control: peppermint and clove

Here's a question: how many natural plant scents do you find repellent? The one that comes to the top of my mind is the scent of the newly blossomed corpse flower, Amorphophallus titanum. It smells very much like the name implies. If I could produce a scratch-and-sniff blog post, I would be tempted. The odor is horrible to humans, but sweet to some flying insects which are also attracted to rotting flesh. But perhaps you cannot tolerate the scent of clove, or eucalyptus? Insect pests are like us in this respect.

Pests in the garden and greenhouse

Insects, arachnids, fungi, and viruses. Their numbers are legion. The battle is constant. The most effective weapon is vigilance. In addition to vigilance, there are biological controls made from natural compounds which are generally non-toxic to humans. Included in this category are essential oils. For example cinnamon, rosemary, sage, neem, clove, peppermint and many others. These oils are repellent, and even toxic, to many of the pests in the garden.

It's thrips (singular) and thrips (pleural)

My task in the garden today was to monitor and treat plants for thrips insects. There are more than 6000 different species of thrips, most of them tiny in size measuring about 1 mm. They evolved to feed on fungi, but some feed on plants. The largest thrips feed on other insects. There are thrips species that are beneficial in the sense that some tropical plants (cycads) require specific species of thrips to pollinate their seed cones.

Of those thrips that feed on plants, they are particularly attracted to the blossoms and soft parts of the new growth. Thrips use their mouthparts to slice into the plant and suck out the cell liquid, leaving a scar on the surface. Damage from thrips typically looks like silvery gray spots and curled leaves and petals. They also cause damage by spreading plant viruses between host plants.

Insect repellent of peppermint and clove oil; 6 drops of essential oil per liter of water.

When I found thrips today, I was instructed to give them a good soaking spray with a dilute solution of peppermint and clove oil. There are scientific articles which show this combination is effective to repel and kill some insect pests.

Common thrips (photo from the provincial govt. of Ontario, CA). Adult and two larval (nymph) stages.

Cancer bush (Lessertia frutescens), S. Africa. This plant was noted to have thrips feeding on the orange blossoms. They're attracted to red and yellow colors.

I found a few thrips on this cancer bush, from South Africa. The plant has attractive orange blossoms in the spring. They morph into attractive papery seed-containing sacks. The plant has been used in traditional tribal medicine to treat some forms of cancer, hence the nick-name cancer bush. But, I couldn't find any scientific articles to back up the practice. That doesn't mean it is not useful, just not validated in Western literature.

We also found thrips on a gloxinia, Sinningia macrostachya. Sinningia is a genus of plants from S. America that features a tuberous stem and a preference for growth on stony surfaces. They generally have very attractive blossoms. This particular plant is infested with hundreds of little thrips, although the damage is relatively minor at this point.

Gloxinia leaf infested with tiny white larvae

Bench in 3C, the subtropical room

My work for the day was spent mostly on the collection side of the fence, but also on the display side of the subtropical room. I found most of the infested plants on the collection side, where there are more plants in flower. I used a spray bottle to treat all of the plants on this bench, whether I found thrips or not.

Subtropical collection room, lime tree in the foreground (with one lime fruit way at the top)

Solitary remaining lime on this small tree


Labels:

Comments

Post a Comment

Popular posts from this blog

A Sensitive Plant and Common Weed

Mimosa pudica, also commonly called the sensitive plant  was a popular houseplant when I was growing up in the 1970s. It was popular for its ability to quicky change shape by folding up its leaves to protect them from herbivore predators. At the slightest touch the plant is able to expell water from special cells in the leaves, changing the shape from frond-like to a stick-form. The plant creeps along the ground, never for than a foot or so in height. In tropical parts of the world this plant is considered and invasive weed. Today, as I was treating plants to remove pests I happened to touch the leaves of a Mimosa pudica , one with a pretty puff-like flower. Sure enough, the leaves all folded up to almost nothing. Mimosa pudica , the sensitive plant Other more routine chores during my four-hour shift at the U of M Conservatory included cleaning three plants of Hibiscus clayi, native to Hawaii. These three plants in particular have suffered repeated infestations with a variety of in...
Post a Comment
Read more

Bog Monsters

As a layman of botany the idea of carnivorous plants has perplexed me. The capturing and eating of other creatures seems like it ought to be limited to animals, since animals are mobile and plants are not. Almost all plants survive and thrive in the world through photosynthesis. They do not need to feed on animals to survive. But, what about the group of plants that are carnivorous? As stationary plants, why and how do they eat critters? This topic was stimulated by my assignment today at the Conservatory Greenhouse of the University of Minnesota. My task was to clean several large tanks of water filled with aquatic plants. While cleaning the tanks I realized many of the plants were classified as carnivorous . What is it about the aquatic environment that causes plants to eat - in effect - other creatures? The short answer is carnivorous plants evolved in nutrient-poor settings such as pond water which is naturally low in the amount of nitrogen needed to synthesize proteins. To compens...
Post a Comment
Read more

The Beauty of Decay on the Superior Hiking Trail

If you want to have a rotting good time then what could be better than the Superior Hiking Trail in October? As I walked the trails this year, I - now in my seventh decade - couldn't help thinking of the phrase "there are more days behind me than in front of me." The forest too has very few days of non-dormant life remaining in the year 2024. Much of the trail was obscured by the fallen leaves of various textures, yellowed and soft, or desiccated and brown. The birch trees stand as silent and bare witnesses to the passing of the summer. But along the path, there is beauty too, in the soft carpet of dead leaves, and the rotting logs extravagantly decorated with moss and mushrooms. Adding much more significance to the mere visual beauty of fallen logs is their ecological contribution to the forest long after they've fallen. Hundreds of species inhabit the logs on top, on the inside hollows, underneath, and along the sides. And, the collective biomass of downed trees and...
Post a Comment
Read more