Natural Pest Control Series– Take a Hike, Thrips!
As a garden coach, one of the main problems that I have to solve for my clients is pest identification and elimination. From insects to mammals, there are plenty of pests out there that can disrupt your garden’s natural beauty. Each month, I will share a blog post featuring a pest and natural ways to rid your garden of it. This garden advice will be invaluable if you apply it and are persistent. This month’s feature is on those minute suckers, thrips.
What in the Heck are Thrips?
Thrips are miniscule flying insects that are so tiny that you may never spot them, but you will spot the damage after it is done! These small bugs live in the soil under the affected tree or shrub, and attack said plant starting at the bottom and working their way up. If you are diligent about checking the shaded leaves on certain plant species, chances are you will be able to stop the infestation before too much damage has been inflicted.
Thrips suck the life out of a plant a little bit at a time, and can make that plant very unsightly but rarely does it actually kill a plant. If the infested plant does die, most likely, there were also other factors at play. You can identify thrips activity by the affected leaves– the tops of the leaves will have a silvery sheen while the underside of the leaves will be covered with tiny brown or black dots (their feces!) If you hold the leaf up to the light, the veins will be prominent as the leaf has been close to skeletonized.
Thrips are an elongated, slender insect similar-looking to a pincer bug, but on a much smaller scale, measuring one millimeter long, about the size of a tip of a pencil. They can be yellow, brown, black, white, or red, and lay microscopic clear eggs on the foliage, but chances are you will never see them or their eggs, only the damage they inflict. They tend to eat while the leaf is still curled up in bud form; when the leaf unfurls, the damage is revealed but by then the thrips are long gone.
Thrips tend to affect the same species of plants, attacking the new leaves, but have been known to eat just about any plant, including vegetable plants and fruiting trees, and they will eat any part off of the plant, including the flowers and the fruit. Their favorite leaf meals include the ornamental genii Rhododendron, Azalea, Pieres, Hydrangea, Fuchsia, most ferns, and specific species Prunus laurocerasus (English laurel hedge). They are also carriers of certain diseases that they can pass on to plants, such as tomato spotted wilt virus (Tospovirus) and impatiens necrotic spot virus (another strain of the tomato spotted wilt virus.)
Nasty! How To Get Rid of Thrips
Thrips will attack plants that are already suffering another ailment, such as dehydration, compacted soil, nutrient deficiency, oxygen deprivation to the roots, or the wrong type of light exposure. I see them most affecting low-light, moist corners where drainage and air flow is poor. The first step in thrips management is prevention– if your plants are being regularly fed, given the proper amount of water and light, and are pruned in a way that air flows through the plant, chances are that thrips will pass them by. As a rule of thumb, most insect infestation can be prevented through good pruning practices, proper watering, and regular composting, which will both aerate the soil and fertilize.
If prevention didn’t work, and you have a thrips problem, it is time to attack it in the bud, literally! Spray the affected plants and it’s neighbors once a week until you see that the fresh, new growth unfurls healthy and green, not silvery and skeletonized. Spray with neem oil or with mineral oil. Both mineral oil and neem oil are safe enough for a human to ingest– mineral oil in large doses is used in humans as a laxative, and neem oil was used traditionally in Ayruvedic medicine for many applications in humans, including as a parasitic. Neem oil comes from the Neem Tree in India and is a biopesticide used as both as a repellent and a larvicide, while mineral oil’s action is to kill insects by smothering them. Personally, I have found the neem oil to be more useful in the fight against thrips, but using either one will yield results as long as you are adamant about keeping up on the weekly spray schedule.
Even after you see positive results of the spraying, (ie: new growth unaffected,) keep up a monthly spray schedule for a while until you are quite sure your infestation has been eliminated. Since thrips have a life cycle that includes eggs and larvae, once you have killed all of the adult insects, round two and round three are right around the corner! Also, when spraying, be sure to spray under the leaves and in the body of the plant– it may be useless to just spray the top of the leaves on the outside of the plant.
Another natural method of removing thrips from your garden would be to use beneficial insects, although this is a difficult way to control thrips due to the fast turnover in their life cycle, and their very small size. Some beneficial insects that have been known to work are aphid wasps, anthocorid bugs, and phytoseiid mites. Predator nematodes, minute pirate bugs, ladybugs, lacewings, and thrips predators have also been known to make an impact. Just remember– if you are using beneficial insects, DO NOT spray or you will potentially also kill your good bugs!!!
A third method would be using sticky traps, which are pieces of cardboard covered in an extremely sticky solution that traps the bugs. Hang the sticky trap in the affected plant. Use of sticky traps could also be a year-round way of monitoring thrips activity in the garden, and catching them before they become a nuisance.
Only diligence will allow you to win in your fight against thrips, so keep it up and before you know it you will be saying ‘sayonara’ to those little buggers!