Depending upon where you are reading this, you may already be familiar with rosemary beetle pests. Sure, they are beautiful, but they are deadly to aromatic herbs like:
If you live for fresh herbs in your cooking, you’ll want to know about managing rosemary beetles or if you are in a particularly homicidal mood, how to kill rosemary beetles.
What are Rosemary Beetles?
It’s always helpful when dealing with an adversary to read up on your foe. Gather as much knowledge as possible before deciding on your battle strategy. First, you need to know what rosemary beetles are.
Rosemary beetles (Chrysolina americana) are beetle pests that are actually brilliantly colored in metallic hues of green and purple. Although they are fairly small, they are easy to spot with their colorful advertising. They first appeared in the United Kingdom in 1994 brought over no doubt on imported plants from southern Europe… a rather unwelcome import. They have rapidly made themselves at home throughout England and Wales into Scotland and Northern Ireland.
The damage is easy to spot as well, brown, dying plant tips. They and their slug-like young dine on the tender new shoots of the herbs. They also like to eat dinner as a family, so where there is one, there are often several.
In the late spring, the first of these unwelcome visitors can be spotted. Adults do little or no feeding until midsummer but by late summer, they are thinking about expanding the family and begin to eat, mate and lay eggs. The eggs are laid on the underside of the leaves and will hatch in 10 days. The larvae feed for a few weeks and then drop down to the ground to pupate.
A long-living insect, rosemary beetle pests can have some overlap between the new and old generations, which means that adult beetles can be found almost any time of the year. Oh joy.
Rosemary Beetle Control
They can decimate a plant quickly, so managing rosemary beetles, at the very least, is of primary importance. To control rosemary beetles, you can handpick them; they shouldn’t be hard to spot. If your plant is large enough, you can shake it and then pluck them up from the ground and drop them in a bucket of soapy water.
This may be a bit too tedious for some of you, in which case you want to know how to kill rosemary beetles using chemical warfare. Look for products that contain pyrethrum, natural fatty acids, or surfactant-based products. A general insecticide containing bifenthrin or imidacloprid should do the trick. Do not spray when the plant is in flower or you will kill off all your bee friends too. Also, I would be super leery about utilizing the herbs once you have sprayed them.
Unfortunately, there are no known natural enemies commercially available to control rosemary leaf beetles. Netting and fleeces will stop adults from moving between plants, so at least containment might be possible. Check plants weekly for the beetles and remove them before their numbers get out of hand.
Lastly, encourage insectivorous birds by providing nesting boxes in the spring as well as hanging feeders in the winter. Our insect loving avian friends can do all the dirty work for you.
The key differences between the two methods are mainly concerned with frost and the type of soil of you have:
- no variety of rosemary is fully frost hardy and all varieties can be killed by very severe frosts. Some can be killed by light frosts. See the section below on frost hardiness for more specific details. Growing rosemary in pots gives you the ability to move the plants to a frost free position for a few days if a bad frost is predicted.
- rosemary prefers a light soil in full sun, plants grown in standard multi-purpose compost do well and they can always be positioned in full sun. If you are growing in open ground and your soil is heavy then prepare it well to lighten the soil and give good drainage.
- rosemary grown in open ground almost looks after itself. Only in the very driest conditions will it ever require watering. In open ground there is no need to feed the plant, it will extract sufficient nutrients from all but the very lightest of soils.
As you can see from the above if you choose a hardy variety of rosemary, prepare the soil well and position it in mainly full sun, both pots and open ground cultivation work well. If you have problems with heavy soil or want to grow a less frost tolerant variety then it's probably best to grow this herb in pots.
Companion Plants to Attract Beneficial Insects
One compelling reason to practice companion planting is the tendency of certain plants to attract beneficial insects . Beneficials are insects that feed on common garden pests, like aphids and caterpillars. Beneficial insects are considered the good guys and are the best reason not to spray insecticides at random.
These beneficial insects should be welcome in your garden:
- Parasitoid wasps feed on aphids, caterpillars, and grubs.
- Lacewing larvae feed on aphids.
- Ladybug larvae feed on aphids.
- Ground beetles feed on ground-dwelling pests.
- Hoverflies and robber flies feed on many insects, including leafhoppers and caterpillars.
- Mantids feed on flying insects such as cucumber beetles and squash bugs
- Common garden spiders feed on grasshoppers and caterpillar laying moths.
Because insects tend to have different feeding requirements during the various stages of their development, a diversity of plant material is essential to attracting them. Although beneficial insects do feast on pest insects, there may be certain points in their life cycles when their diets are confined to nectar and pollen. To attract these insects to your garden, you will need to provide host plants and even plants for shelter. Planting a small bed of Zinnias in the vegetable garden will bring in pollinators which also helps to increase yields from beans, squash, vine fruits such as melons, and cucumbers. Sunflowers make excellent borders, also attracting pollinators and providing food for songbirds.
Diversity in both plant material and the season of availability is crucial. Hedgerows used to serve this function. The trees, shrubs, and weeds would leaf out sooner in the spring than cultivated crops and provide early food sources.
Hedgerows are rare today, but you could easily plant a mixed border of fruiting and flowering trees, shrubs, and perennials that have something in bloom all season. This patchwork of plants would benefit your ornamentals, and planting it near a vegetable garden will ensure beneficial insects on your vegetable crops.
How to get pests off of Rosemary?
How do you keep pests off from Rosemary? I bought a small Rosmarinus officinalis at a local nursery last summer, and it was healthy and bug-free, but after a few months of sitting on my porch, it acquired aphids, spider mites, and some sort of small winged pest I can't identify. So I sprayed it with an organic insecticidal soap advertised as being able to kill exactly those types of bugs. I've used it on almost all my other outdoor plants, and it's worked very well. However, it seems to only partially work on Rosemary due to its leaves, which curl down and inwards, greatly lessening the effectiveness of spray. Even when I try to spray "up" into the underside of the leaves, I found it very difficult to get the spray into these sheltered areas, allowing the bugs to flourish there while dying everywhere else.
My Rosemary's still alive, but almost all the leaves are now partially dead and pock-marked from the punctures of insects. What can I do to help it?
While pests are being confused by rosemary, beneficial insects and animals, such as hummingbirds and bees are attracted to rosemary when it is in bloom. Rosemary flowers in late winter/early spring, which means it provides pollen when not many other plants are. This makes it attractive to wildlife looking for an early start.
Rosemary is native to the Mediterranean climate, which is why we find it so often in Italian food, but as gardeners, this tells us that it is able to sustain itself in a climate without an abundance of rain. It grows very well in Southern California, but for those of us not in this climate or one’s like it, it can make a low-maintenance pot plant or easily cared for garden addition.
Inspiration > Lawn & Garden
Like many gardeners out there, I’m learning about the frustrations of keeping an organic garden. Flies, beetles and other annoying pests destroyed most of the vegetables I grew last year. Chemical pesticides are a big “no-no” in organic gardening, so what’s a girl to do? I can’t just let this massacre continue to reign in my garden.
After some research, I discovered that some herbs are natural bug deterrents. Not only that, but some also allow pollenating insects, such as bees and butterflies, to access your plants without being killed by chemical mixes… SCORE!
Watch out, pests! I’m ready for you this year. The employees at Country Harmony helped me immensely in picking out my herbaceous weapons. They told me which herbs are best to plant and how to care for each type. Here is a list of some herbs and which type of bugs they deter:
Basil – Flies, Mosquitos, Thrips. Plant some near tomato plants for more flavorful tomatoes. Basil is weak against aphids, so plant near some garlic.
Catnip – Mosquitos. When you’re done for the season, dry the leaves to make a catnip toy for your cat.
Chives – ants, aphids, fleas, nematodes. Chives are actually a small species of onion. You use the stems for cooking. Plant this herb with carrots. Chives can also be planted amongst rose bushes to defend against the disease Blackspot.
Mint – Cabbage Moths, flies, flees, ants. This herb can grow out of control rather quickly. If you’re more concerned about repelling flying insects, try planting mint in a pot near your vegetables.
Oregano – Mosquitos (can you tell I really don’t like this pest?), Cucumber beetle, Cabbage butterfly. While oregano repels many types of insects, they are susceptible to aphids, spider mites, and leafhoopers. Plant oregano near garlic, onions or chives to protect them from these insects.
Rosemary – I don’t like cooking with rosemary, but they work well in a garden with cucumbers. Carrot Fly, Mexican bean beetle, Mosquitos, Cabbage Moths
Sage – This is an excellent one, because it repels many types of insects. Plus they look nice and don’t have a strong odor, in case you want to place some around the house. Sage can take a long time to grow. I suggest not starting from a seed. Mosquitos, Cabbage Moths, Carrot Fly
Thyme – Cabbage Moth, whiteflies. Thyme oil helps with respiratory and digestive problems in people.
I stocked up on basil, oregano and sage for my garden. I suppose I’ll get some catnip too, for DeeDee Ramone. She’s been doing a good job of keeping the mice away lately. She deserves a good reward.
For the gardener with limited space to work with, having to add more plants to your garden isn’t easy. Instead of picking herbs based solely on the type of bug they repel, plan which vegetables you want to grow and pair them with herbs and other plants that benefit each other. If you want the benefits of an herb but don’t want to grow it, you can buy oils from the store. Spray these oils onto your vegetables once a week, or more after a big rain storm.
During the spring of 2012, I had the urge to start a vegetable garden. From my first bean plant, which perished prematurely when I was six, to my little pine tree, which didn’t survive the first three months in my college dorm room, I’ve wanted to prove that I inherited my Grandpa Mount’s green thumb. Even though I chose to start my garden during the longest drought in Indiana history in decades, my plants managed to produce a few tomatoes and radishes. This gave me the motivational drive to do what I can to learn gardening.
Rosemary leaf beetle Chrysolina americana
If the shoots tips of rosemary and lavender are turning brown and dying back it could be the sign of an infestation of rosemary leaf beetle. These small beetles feed on the new shoot tips causing them to die back. They're easy to spot because they have metallic green and purple stripes across their backs. Their larvae, which are slug-like and pale grey in colour with a dark stripe down the side, also cause damage by feeding on the shoots as they grow.
- Rosemary leaf beetles only feed on a small number of plant species which includes rosemary, lavender, sage and thyme.
About Rosemary leaf beetle
- These attractive leaf beetles are an invasive species that first appeared in the UK in 1994.
- Since their introduction, they've been spreading steadily throughout the southern counties of England.
- The adult beetles are around 1cm long with metallic green and purple stripes down their wing cases.
- They're usually found in groups on stems, or feeding on the new growth of plants.
- The larvae are small slug-like grubs which are usually found on the underside of leaves. They are light grey with horizontal dark stripes along their body.
- Adult beetles are usually first seen in late spring, although they remain largely stationary on plants until later in the year.
- In late summer they'll begin to mate and lay eggs.
- Eggs are usually laid on the underside of leaves and are around 2mm in length.
- Larvae will hatch in about ten day's time and feed for a few weeks before dropping down to pupate below the soil surface.
- Adults may continue to mate during warmer winter periods, although this is rare.