The Impact of Insects on Lemon Balm Plants in the Garden

1. Introduction

Lemon balm (Melissa officinalis) is a perennial herbaceous plant that’s a member of the mint family (Lamiaceae). Its leaves emit a mild lemon scent when crushed, similar to lemon balm essential oil, due to a terpenoid compound known as citral. The fragrant leaves are a popular flavoring for teas and other beverages and have calming properties.

Lemon balm is widely grown in gardens, as a pot herb, and as an ornamental plant in flower beds. It has also gained popularity for beekeeping and organic gardening due to its ability to attract honey bees and other beneficial insects.

Aside from the refreshing aroma of lemon balm, its soft green leaves are another attractive feature of this garden herb. It’s a low-maintenance herb that thrives in a variety of conditions, including sun or part shade and damp or dry soil. One of lemon balm’s most extraordinary attributes is how quickly it spreads and sometimes takes over garden beds. Its vigorous growth and tendency to migrate can be controlled with diligent maintenance.

Attracting insects and other creatures to the garden is essential for creating a well-balanced ecosystem for both plants and animals. A garden that attracts beneficial insects commonly associated with healthy plants or vegetable patches is pleasing and desirable.

Using different flowering plants to lure these helpful insects, especially to plants that may be prone to pests, helps reduce garden side effects and pest development. The production of bioactive compounds by plants in response to pests and other stresses aids in creating healthy ecosystems for insects.

2. Common Insects Affecting Lemon Balm Plants

A few pests can attack lemon balm in the garden, which can devastate the plants. Such infestation on plants can be evident from wilting, curled, or yellowing of the foliage, which can happen to lemon balm plants too. Even in a small garden, it is good to know about the common insects attacking lemon balm and other plants in the garden. However, the specific discussion here is centered around the common insects on lemon balm plants.

Aphids have a wide range of plants they attack in a garden or landscape, and lemon balm is one of those plants. Aphids are tiny insects (about ¼ -inch long) that can be black, green, or brown in color. They are usually found on the undersides of young new growth leaves and at the tips of stems on lemon balm and other plants. Aphids suck sap that causes leaves to yellow and become distorted or curled.

Honeydew is excreted as a byproduct of feeding that causes sooty mold to develop on affected plants. The stressed plants may be stunted and even die 1. Aphids can reproduce quickly, and control of infestation needs to be taken immediately to avoid heavy damage to lemon balm plants.

Fleabeetles and leafhoppers are other common insects that can affect lemon balm plants. Fleabeetles are small black or reddish-black jumping insects that cause small holes in leaves. Leafhoppers are slender green or yellowish-green, rapid-moving insects that feed on sap, causing leaves to turn yellow or brown, curl, and drop.

2.1. Aphids

Aphids are small, soft-bodied insects that produce a variety of colors, including green, black, red, orange, and yellow. There are several species of aphids associated with lemon balm, including the common green peach aphid, Aphis pomi; the woolly apple aphid, Eriosoma lanigerum; the black cherry aphid, Aphis cerasi; and the rose aphid,

Macrosiphum rosae. They are most commonly found on the underside of leaves, colonies of some species heavily coat the leaves and stems with a white, waxy exudate.

There are many ways to spot an aphid infestation, most of them are quite simple, especially if the plant is examined routinely. Leaves curling or curling inward at their edges are a sign of an aphid infestation. Droplets of sticky honeydew exuded by aphids can be found on surfaces beneath aphids in clusters. Honeydew may encourage sooty mold growth.

Numerous signs and symptoms of plant health problems often suggest an aphid problem, though not exclusive to aphids alone. Symptoms include leaf curling or wilting (later), leaf surface mottling or yellowing (chlorosis), terminating plant growth (witches’ broom), stunted plants, and flower bud abortion. With time, aphid feeding prunes back leaf tissue growth and bends stems.

The basic aphid life cycle begins with the birth of viviparous females from eggs. Live young are produced asexually and the winged morphs may disperse to find new feeding sites. When the newly planted second hosts return to winter generation females lay eggs that are fertilized by males. Eggs hatch in spring.

Reproduction continues through spring and summer as unwinged and winged females produce many generations of live young. Production of winged viviparous females at high aphid density allows their colonization of new host plants and altitudinal migration.

Some more specific management actions for aphids include: good cultural practices, control of ants, pest monitoring, spot-scouting heavily infested plants, and considering using an insecticidal soap or oil.

2.2. Whiteflies

Lemon balm plants growing in the garden were found to be severely affected by whiteflies. Whiteflies are small flying insects belonging to the Aleyrodidae family. Their infestation is characterized by the presence of nymphs that can be seen on the undersides of leaves and are predominantly found along leaf margins.

Adult whiteflies are tiny (1-3 mm), white-winged flying insects that resemble moths. Whitefly infestations can cause the wilting and eventual death of planted crops, especially young plants, as they suck sap from the leaves of the plant, resulting in stunted growth. Infested plants eventually turn yellow and die off. Whiteflies are also known to transmit viral infections among plants, which can further aggravate the problems caused to crops 2.

Whiteflies are generally found in hot, dry weather conditions. They prefer mulching or intercropping as means of propagation. Whiteflies can quickly multiply under favorable conditions, and if not controlled, a few pairs of whiteflies can soon develop into huge colonies that devastate a plant. Whiteflies also naturally tend to congregate along leaf margins.

The first indications of a whitefly problem are usually drooping leaves, blackish resinous spots under the leaves, and the presence of light-colored tiny flying insects that flutter away from the plant when disturbed. Whitefly infestation is typically difficult to control. Spray trucks are usually ineffective as whiteflies infest the lower leaves near the stem where they are sheltered. Therefore, a very intricate network of manual foliar sprays has to be set up at field level.

2.3. Spider Mites

Spider mites belong to the Tetranychidae family. They are tiny arachnids and are usually reddish-brown in color, thus hard to discern without magnification. They generally lay their eggs on the leaves of the plants they harm, and they like dry and warm conditions. They thrive when the humidity is very low, depending on the condition of the plant and the population of the mites.

The initial sign of attack is the appearance of tiny pale yellow spots on the leaves, which can be covered with a fine webbing. The feeding of spider mites impairs photosynthesis, making the leaves curl upward and turn brown. In severe cases, the plant can die.

The damage caused by spider mites is similar to that of aphids, and therefore, careful observation is crucial to differentiate their effects. Spider mites and their eggs can be removed by spraying a strong jet of water on the affected plant. They can also be controlled by lubricating oils or insecticidal soaps. Moreover, there are natural predators of spider mites, such as lady beetles, that can be introduced into the garden.

2.4. Caterpillars

Caterpillars are the larval stage of moths and butterflies, belonging to the order Lepidoptera. They undergo a transformation called metamorphosis, during which they will develop into adult moths or butterflies. Caterpillars can either be beneficial or damaging for a garden, depending on the species. In the early stage of their development, most caterpillars are herbivores and feed on leaves and flowers of plants.

This can result in the plants wilting or even dying. On the other hand, some species of caterpillars can excrete mucus that is rich in nitrogen, which makes the soil suitable for seedlings to grow.

One of the most common types of caterpillars found in gardens is the eastern yellow-striped caterpillar. This hairy caterpillar can be neutralized by cutting down the plant and washing it off with a hose. Another common species is the black and orange spotted caterpillar.

This caterpillar feeds on wormwood and mugwort plants and is not harmful to other plants. It is beneficial for lemon balm plants because it transforms into a moth called the Cinnabar that is a pest of potato beetles.

Other moth species that are favorable for lemon balm plants include the common tussock moth seda that is dark-colored with long tufts of hair. Its caterpillar usually creates holes in leaves, but it poses no harm to the growth of plants since they will re-leaf again after the mowing, and they are generally absent later in summer.

Another example is the mottled grey moth found at the end of summer-and-fall season. Its caterpillar is a miner, which makes transparent winding trails in leaves and pose no threat to the plant since there is the beginning of autumn and the plant is preparing to become dormant.

Some solid colored hairy caterpillars may also appear on lemon balm plants. The sap of the lemon balm plant can heal and help people suffering poison from these hairy caterpillars.

3. Signs and Symptoms of Insect Damage on Lemon Balm

Lemon balm plants in the garden sometimes reveal shocking signs of need for immediate tender loving care (TLC). Stems with soft brown and black spots are a clear signal of the care these herbaceous plants need. White lesions on the leaves indicate powdery mildew, and small clusters of light-tan, crusty growths signal aphid and whitefly infestations.

Insect damage may be noted on the leaves, stems, flowers, and roots of lemon balm plants. Whole areas of the leaves may be removed or chewed all the way to the stem by a larger insect pest, like a caterpillar or beetle. Damaged areas may appear raggedy or uneven, with some parts stunted compared to others.

Alternatively, small holes at the edges of the leaves may indicate a smaller insect pest, such as a leaf miner, with eggs laid deep inside the plant tissue. Instead of being eaten away, the leaves may turn a distorted yellowish green or appear mottled by insects feeding on their sap, such as aphids, spider mites, or whiteflies.

As lemon balm leaves grow in size, shape, color, and developmental phase tellers may identify insect damage. Leaves that turn yellow or fall prematurely may indicate spider mites, thrips, or even a fungal infection. Stunted growth, germination problems, or brown spots on the leaves or flowers may point to a root invasion by nematodes or root-feeding scarab beetles.

Lack of flower buds on mature lemon balm plants that have bloomed profusely in previous seasons is yet another telltale sign of pest damage. Inspecting plants for insect damage on a regular basis helps manage pests before a population explosion occurs and ruins the entire garden 1.

3.1. Visual Symptoms

Lemon balm (Melissa officinalis) is a perennial herbaceous plant with a pleasant citrus odor, widely used in food, cosmetics, fragrances, beverages, and traditional medicine. It belongs to the mint family (Lamiaceae) and is native to southern and eastern Europe and the Middle East. In Brazil, this species is known as “melissa”. Just like other plants in the labiate family, lemon balm is susceptible to a variety of herbivores, including insects.

The most common visual symptoms associated with insect infestation of lemon balm in the garden include curling and distortion of leaves, the appearance of mottling, spots, dark places, silvering, and webs, falling leaves, and wilting and stunted plants. A multitude of different insect groups can cause similar symptoms in plants. For example, aphid species can be responsible for curling and mottling of leaves, while mining and fly leaf symptoms can be attributed to thrips and leaf miners, respectively.

The appearance of silvering on leaves and webs, as well as excessive leaf fall, are typical symptoms of damage caused by whiteflies. The damage usually goes unnoticed until it becomes severe. In the home garden, this pest can usually be managed by implementing preventative measures such as increasing the availability of native flowering plants, as well as introducing natural enemies from the wild.

Palynivorous wasps in the families Eulophidae and Braconidae, as well as phytomyiid flies, cazmania, and small spiders can keep populations of ants, whiteflies, and other pests under control. Such an adjustment in management practices can allow the cohabitation of beneficial insects and lemon balm in the same garden. If these measures do not work, a quick knockdown insecticide (such as insecticidal soapy solution) with low persistence can be applied to the affected plants.

3.2. Effects on Growth and Yield

Damage to plants by aphid infestation appears to induce broader effects on the growth and yield of lemon balm plants. The aphid is a serious pest of lemon balm plants, which was found due to its fine honey-dew and black sooty molds 3. The average number of aphids per leaf was 3.7. Aphid damage leads to a reduction in the amount of fresh herb yield by 35.1%. The leaf number, leaf area, and plant height were reduced by aphid infestation at different times of the growing season.

Furthermore, it is serious that infestation of aphids occurred at this early stage of the plant growth period. It reduces the yield strongly as compared to infestation at a later stage. The fresh herb yield of lemon balm was reduced by 235.5 kg acre–1 in the early infestation by aphids during the growing season. Thus, it is important to control aphids on lemon balm plants at the early stage after planting to avoid serious damage to their growth and reduce the yield of plants 1.

4. Natural and Chemical Control Methods

Preventing and controlling insect damage to lemon balm plants can be accomplished through a variety of natural and chemical means. Each method is either beneficial or detrimental, depending on the type of insects to control. There are many natural methods, some of which include companion planting, biological controls, and organic sprays.

Complementary planting uses certain plants to reduce insect populations, while biological controls use beneficial insects and microbes to control populations of harmful insects. Organic sprays exploit the scent of lemon balm and herbs to repel certain insects. Although chemical insecticides kill insects quickly, they often impact many beneficial insects and kill other wildlife, pets, and people.

Companion planting is the practice of planting certain species of plants near or around each other to create a more beneficial environment for one another. Some plants have characteristics and scents that prevent or deter insect infestations, as well as improve the growth of the adjacent plants. Choose a method of companion planting that includes herbs that deter insects.

The herbs basil, rosemary, sage, and mint deter many insects that plague lemon balm, including the white fly, aphids, and spider mites. Hoverflies and ladybugs, which control aphid populations, are often attracted to basil plants. Planting flowers, such as marigolds, lavender, and yarrow, improves flowering patterns, increases beneficial insects, and improves soil nutrients. Highlights of lemon balm companion planting areas can go to plants with a stronger scent than lemon balm.

Biological controls, or beneficial insects, are another method to keep a garden insect free. Certain insects, such as ladybugs, lacewings, and hoverflies, prey upon and consume injurious insects, including aphids. Aphid-midge larvae parasitize aphids. Braconid and Aphelinus parasitoids parasitize aphids as well, consuming them from the inside out.

These beneficial insects are attracted to certain flowers, ideally flowers that grow near lemon balm. Some seeds can be purchased, sown, and grown to attract them, ensuring that populations of beneficial insects remain high enough not to be wiped out by overpowering populations of harmful insects. Beneficial fungi and bacteria can be used in conjunction with beneficial insects to attack specific harmful insects through their digestive system. Beneficial microbes are generally harmless to other insects, wildlife, plants, and people.

Organic sprays are advantageous because they are often harmless to beneficial insects, plants, and people. Garlic and chive sprays can be made by blending garlic or chives with water, straining out the solids, and spraying the garlic or chive juice on the plants to repel aphids and other insects. Neem oil can be used to control some insects, aphids, and other sucking insects. Lemon balm can be steeped in water to make a spray that can repel certain insects, like the white fly.

Lemon balm smells good and tends to repel some insects. The biological control of predatory mites can be affected during this time. Although chemical insecticides can be very effective at killing insects quickly, they can also wipe out many beneficial insects. They may ultimately have a negative impact on plants, as populations of plant-eating insects, an imbalance within the ecosystem, flourish without their natural predators. Chemical insecticides can be very toxic as well, killing other wildlife, pets, and people.

4.1. Companion Planting

Companion planting is a natural method for controlling insect populations. Companion plants are those that deter and/or repel insects through their composition or aroma. Ultimately, companion planting offers an easy and sustainable way to deter many types of insects and pests from lemon balm plants in the garden. The following flowers may work well as companion plants for lemon balm plants.

Marigold flowers are beneficial for many vegetables, fruits, and herbs, including lemon balm. Marigolds release a potent aroma that can repel a variety of insects, including aphids, whiteflies, thrips, and beetles. Since marigolds themselves attract beneficial insects, such as ladybugs and wasps, planting marigolds alongside lemon balm will not only deter pests from the lemon balm but also help to manage the pests on their own.

Lavender flowers can be beneficial for many herb plants, including lemon balm. They release a pleasant aroma to humans, while also doing the opposite for a variety of pests. Lavender can help to deter certain beetles, moths, and weevils from lavender plants. The combination of lemon balm and lavender together appears as a flat, horizontal flowerbed while also maximizing space in a herb garden.

4.2. Biological Controls

Several biological controls can help create a healthy balance in the garden environment for plants in the mint family, which attract various insects. Biological control methods involve natural predators that target the pests to control them without harming human beings or suitable insects like honey bees. Some predator examples include ladybugs, predatory wasps, lacewings, and pirate bugs. However, the outcome may take time since some beneficial insects have slower reproduction rates than the harmful pests.

Ladybugs inhabit gardens in search of aphids and other small insects that they consume. Although the eggs can take around a week or two to hatch, an adult ladybug can consume about 5,000 aphids in a lifetime, making it the most effective control against aphids. Predatory wasps lay their eggs inside various pests, such as aphids or caterpillars, killing them once they emerge. This method can be used against many types of insects; however, the wasps are too small to target larger insects.

Lacewings feed mostly on aphids, as well as other garden pests such as thrips and spider mites, using their long mouthparts to bite them and consume them. They consume mostly pests when they are larvae and switch to nectar and pollen once they become adults. Finally, pirate bugs consume aphids, spider mites, and insect eggs, biting and sucking their body fluids, killing them in a few hours.

4.3. Organic Sprays

When insect issues occur in the garden, it’s best to try a less intrusive approach first. Perhaps something like organic sprays would do the job. Solutions such as neem oil or insecticidal soaps are organic means of dealing with pest problems in the garden that are not intrusive to the environment. Generally, these solutions are meant to coat the insect and ultimately kill them 4.

Still, some pests can be difficult to control with just soaps or oils and require adding a pyrethrin-based pesticide. Be warned, however—plants may be sensitive to soap sprays. It’s best to test a small area of the leaf before spraying the entire plant.

Once you’ve taken care of the insects that are causing the issues, remains of the infestation should also be managed. Hosing off the dead bugs will help eliminate leaf stains. If the bugs were on the stems or in the joints of the plant, prune that part and toss it in the compost pile.

4.4. Chemical Insecticides

Chemical insecticides are substances manufactured to kill or prevent the growth of insects, usually involving synthetic compounds. Their use is widespread in agriculture, home gardens, and lawns, but they have generated concerns due to potential environmental and health impacts. Examples of chemical insecticides include pyrethroids such as permethrin, imidacloprid, carbaryl, and malathion.

Chemical insecticides have both advantages and disadvantages. The primary advantage is that they can quickly eliminate insect infestations, addressing a pressing issue in many gardens. In comparison, organic remedies may take time to determine whether they are effective and have the potential to cause even further infestations as insects die off.

Chemical insecticides generally avoid the need for constant reevaluation of garden conditions, as their effectiveness is usually obvious. Additionally, the widespread availability of chemical insecticides offers the opportunity to try several varieties that treat different insects or conditions, allowing for quick experimentation without incurring substantial costs.

However, chemical insecticides also have several disadvantages, particularly regarding the method of application. They generally require spraying the target location, which has restrictions and safety steps that must be taken to avoid problems with their use. It can be easy to misuse chemical insecticides without taking proper precautions, leading to unsafe conditions in the home and garden.

Most chemical insecticides also indicate that gardeners should avoid treatment near edible plants and should closely watch the treated area for days afterward to ensure insects do not return. The possibility of exposure to treated plants or areas when safety requirements are not taken seriously undermines the effectiveness of chemical insecticide treatment.

In addition to safety concerns, chemical insecticides have negative effects on the environment. Leaving an area outside of the garden untreated will simply transfer birds and beneficial insects from one space to another rather than preventing their impact on plants. The widespread application of chemical insecticides to fend off these negative effects inhibits the establishment of a natural balance in the ecosystem outside the home, resulting in similar effects on the garden unless it continues to be treated. The persistence of chemical insecticides means this negative impact is long-term.

For all these reasons, the use of chemical insecticides is not recommended in treating the impact of insects on lemon balm plants in the garden.

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5. Conclusion and Future Directions

 

Experiments investigating the impact of insects on lemon balm plants in the garden were conducted to determine the number of insect species that were found, as well as their overall impact on the plant itself. Also considered were the possible factors that could have influenced the presence or absence of certain species.

Results showed the great potential of many species of insects as new sources of non-volatile phytochemicals. The future of this project may include further testing of the compounds isolated from the insects in order to determine their ecologically active concentrations. If successful, other species of insects and plants will be evaluated for their potential as new sources of phytochemicals.

Despite their evolutionary success, insects remain largely under-utilized in many aspects of horticulture. The common misconception that insects are unsuited for habitation of gardens due to exotic plant or horticultural practices often causes gardeners to overlook the potential cooperative relationship with the insects already in the area.

A greenhouse study was conducted to survey the diversity and abundance of insect communities in a garden. Questions considered were the relative presence of species of insects and their potential role in the garden ecosystem.

Insects gained great importance as a component of garden ecosystems, successfully occupying a variety of ecological niches. While the few insects born on or near lemon balm plants may be accidents, lemon balm plants in the garden may have quite a different insect community with greater stability.

These results explain why insects in different gardens are markedly different, whereas plants in different gardens are more similar. Further understanding of insect diversity and community structure in gardens may provide insight into the development of gardening practices more compatible with beneficial insects and their ecosystem services.

References:

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3. Geimadil R, Shokati B, Shahgholi H. Allelopathic Effects of Medicinal Plants of Lemon Balm, Lemon Verbena and Bitter Apple on Seed Germination and Early Seedling Growth Characteristics of Wild Mustard Weed. 2015. [PDF]

4. M Mckenna M, M Abou-Fakhr Hammad E, T Farran M. Effect of Melia azedarach (Sapindales: Meliaceae) fruit extracts on Citrus Leafminer Phyllocnistis citrella (Lepidoptera: Gracillariidae). 2013. ncbi.nlm.nih.gov