Its damage relevance is so devastating that the Colorado potato beetle was even considered as a biological weapon in the mid-20th century. Migrating from the USA, the adult beetles, young beetles and larvae devastate a potato bed by eating it bare. Tomatoes are also not spared. It doesn’t have to come to that, because effective strategies for control are available. Read here how to get rid of the pests on potatoes.
- Insect family of leaf beetles (Chrysomelidae)
- botanical name: Leptinotarsa decemlineata
- common names: Colorado potato beetle, Colorado beetle, Ami beetle
- immigrated in 1877 from the USA (Colorado)
- body length of adult Colorado potato beetle from 7 to 15 mm
- yellow elytra with 10 black longitudinal stripes
- reddish larvae, dotted with black on the sides and head
- annual emergence of 1 to 3 generations
- main mating season: May-June, July and August
- sleeping-waking behavior: diurnal
- Food plants: potatoes and other solanaceous plants, such as tomatoes, eggplants, peppers
Just in time for the emergence of potatoes, they are at hand. If the soil temperatures exceed the 15 degree mark in spring, the Colorado potato beetles crawl out of the ground to multiply explosively. The damage caused by the larvae and beetles is devastating, because not only potato plants are eaten bare, but also tomatoes, peppers and other nightshade plants. How fortunate that in the 200 years since their appearance in Europe, at least rudimentary effective strategies for controlling the little monsters have emerged. Read here how to get rid of the pests on potatoes.
The damage potential of Colorado potato beetles is mainly due to the fact that the pests have migrated from the USA. As a result, there is still a lack of natural enemies that could restore the ecological balance in the event of a mass occurrence. In addition, the leaf beetles are extremely robust and even survived a test drop from an airplane from 8,000 m altitude. Furthermore, the physiology of the pests is so flexibly balanced that they adapt to chemical insecticides and develop resistance within a short time.
Precise knowledge of the life cycle of Colorado potato beetles significantly optimizes the control strategy. Since it is primarily the larvae and young beetles that wreak havoc on your potato patch, the egg-laying stage should already be prevented. Each hatched larva is capable of destroying up to 40 square centimeters of leaf area in the third and fourth stages.
Since this destruction phase extends over a few weeks, the timing of control is as important as the control itself. Below we summarize the main stages of development from egg to beetle.
- Colorado potato beetles overwinter up to 60 cm deep in the soil and crawl out when the soil warms up to 15 degrees Celsius
- from May on, the mated females lay up to 1,200 red-yellow eggs in small packets on the undersides of the leaves
- within 1 to 2 weeks deep red, black spotted larvae hatch
- thanks to extensive feeding on potato leaves, the larvae are fully grown after 21 days
The adult larvae, now orange in color, hide in the soil for 2 weeks to pupate. They then emerge as juvenile beetles to again attack potato plant leaves. After another 14 days of continuous feeding, they are sexually mature, so that the second generation emerges from July. In mild weather conditions, a third generation appears in August at worst.
Ecological control methods
Colorado potato beetles have the unique ability to adapt to chemical control agents within a short time and develop resistance. Anyone who tries to get rid of potato pests with the help of insecticides is therefore at a loss and ends up with a chemically contaminated food product. In contrast, the ecologically oriented strategies of organic farmers have proven to be effective and long-term. Tried and tested procedures in the fight against Colorado potato beetles and their larvae are explained here.
The consistent collection of Colorado potato beetles, their larvae and egg packages is still unsurpassed in its effectiveness. Especially in small gardens, this control strategy is more efficient than all other methods. By collecting the overwintered beetles from the upper and lower sides of the potato leaves and drowning them in water in the early morning hours from May onwards, you stop the egg laying.
Continue the morning inspections during the summer, you can timely eliminate the leaves with egg packets or hatched larvae. Spray the infested plants with horseradish liquid manure or mint broth afterwards, additionally scare away the brood.
The bacterium Bacillus thuringiensis, which is non-toxic to humans, vertebrates and plants, ranks right at the top of the list of successful control methods. The crystalline toxin is lethal to Colorado potato beetles and their larvae as well as other insects. The specialized trade has effective preparations available, which are produced on the basis of special strains of the bacterium. These are convincing with reliable accuracy, in that the pests are destroyed, while beneficial insects, such as hover wasps or lacewings, are spared, should they happen to be in the catchment area.
Under these conditions, the Bt pesticide is effective:
- the Colorado potato beetles and larvae must feed on the bacterium
- temperatures of 15 degrees Celsius and higher prevail at the time of application
- apply the product in the early morning hours, as this is the time when the pests feed the most
- spray the spray or the spray solution directly on the pests
- in addition, all the upper and lower sides of the infested plant are treated.
- The agent causes an immediate stop of feeding. In the further course beetles and larvae die off. Products approved for use in allotments, such as Biofa’s Novodor FC, act on the larvae already at larval stage 1 and should therefore be applied at an appropriately early stage.
The tropical neem tree provides ingredients that are effective against Colorado potato beetles and other biting or sucking insect pests. With products such as NeemAzal T/S, you control pests in the home garden in a way that is safe for health and the environment.
The products are made from the seeds of the tree in the form of an extract containing a high proportion of azadirachdine. The active ingredient is not immediately lethal. Rather, the life cycle is inhibited in the first stage by a feeding agent, followed by the reduced ability to reproduce.
This is how development proceeds:
- best time for application is on the fifth day after egg laying
- prepare the necessary amount of spray broth only on the day of application
- neem inhibits egg hatching, so that no development takes place beyond the first larval stage
You optimize the control success of neem-containing products by applying the bacterium Bacillus thuringiensis 2 to 3 days later, as the two biological agents complement each other.
Pyrethrins and canola oil
Under high infestation pressure, troubled amateur gardeners opt to use a combination product of pyrethrins and canola oil, such as Spruzid Neu. For years, the pyrethrum it contains was considered a bright spot in the fight against the disastrous Colorado potato beetles. However, the pests developed resistance, so that efficacy dropped to below 20 percent.
Thanks to intensive research, effectiveness has been optimized by adding natural canola oil. Although the pesticide is not completely harmless to the environment and health, it is currently still approved for use in allotments. The European Federal Office of Consumer Protection and Food Safety (BVL) maintains a database that lists all approved pesticides, including the date of the end of approval.
Approved for organic farming by the European Union is the active ingredient spinosad, which has also proven effective against Colorado potato beetle. If all purely natural control strategies fail, this alternative is available to get rid of the pests on potatoes. The agent is obtained from special strains of bacteria and amino sugar.
The insecticide may only be applied in compliance with special protective precautions, such as wearing protective clothing and gloves. In addition, it is dangerous to bees and other beneficial insects, so they must not apply it to flowering plants.
Since the forecast calculation works with a lead time of one week, you have sufficient time to choose the control method and procure the appropriate agent. This service is available free of charge on the Internet and can be fully used by both commercial farmers and private gardeners.
In a naturally managed garden, you can prevent an infestation by Colorado potato beetle in advance with the help of purely natural means or nip it in the bud at the first signs. In the following, we present tried and tested methods in more detail. To ensure that the clever pests do not adapt to one agent and develop a resistance, please keep changing the group of active ingredients.
Horseradish liquid manure
In spring, repeatedly apply a horseradish (Armoracia rusticana) slurry to your beds of potatoes and other nightshade crops. This plant liquid manure keeps the potato beetles crawling out of the soil from laying their eggs on the leaves in advance. Furthermore, horseradish liquid manure serves as a natural control agent in the first larval stage.
This is how you prepare the liquid manure:
- in a wooden barrel pile up 1 kg of fresh or 300 g of dried horseradish.
- pour over it 10 liters of collected, filtered rainwater or stale tap water
- place in a sunny, warm, out-of-the-way location in the garden
- cover the container with wire mesh and do not close it with a lid
- Stir the liquid several times a day to allow oxygen to enter.
Already after 2 to 3 days, the solution has a certain degree of effectiveness against the Colorado potato beetle. However, the slurry develops its full potential only after 2 weeks, when the liquid is completely fermented. Strain the plant parts and pour the horseradish liquid manure into a watering can or pressure sprayer. As a preventive measure, wet the plants weekly. If Colorado potato beetles or their larvae are already on the foliage, get rid of the pests by applying the natural remedy every 3 days.
As a natural soil additive, rock flour has made a good name for itself in organic farming. The fine material also makes a valuable contribution in repelling Colorado potato beetles and other pests that want to eat the foliage of your crops. If you regularly powder the dew-wet potato plants with rock flour on the upper and lower sides of the leaves in the early morning hours, the voracious pests will lose their appetite.
This applies to both the adult beetles and the larvae. Although rock flour is not suitable as the sole control agent, it is still valuable as a component in the strategy. At the same time, the natural remedy strengthens the resistance of your plants in an environmentally friendly way.
Among the home remedies against Colorado potato beetle, coffee grounds enjoy the best experience in private kitchen gardens. If the young plants have reached a growth height of 10 cm, sprinkle the dried coffee grounds every 4 weeks on the still damp leaves in the morning. In shorter intervals you should not use the coffee grounds, because it lowers the pH value.
The ingredients found in a thuja have the potential to permanently scare away Colorado potato beetles and their brood. After pruning the conifer, you have enough material in your hands to prepare a tea from it. To do this, pour boiling water over the cuttings and let it steep for 24 hours. The next day, strain the plant material, pour the liquid into a hand sprayer and treat the potato plants. Especially for prevention, as well as in the early stages of infestation, this approach complements perfectly with other ecological methods.
Potato beetles are not at all fond of peppermint. This fact was found out by clever organic gardeners, so repeated spraying with mint broth makes a valuable contribution in the defense against these pests. Unlike liquid manure, the broth is prepared within a short time. To do this, put the fresh parts of the plant with water and let everything simmer gently for 30 minutes. After the broth has cooled down, you can immediately spray it on the potato plants.
Defensive plant neighbors
One of the many benefits of mixed cropping is that compatible plant neighbors protect each other from disease and pests. If you associate your potato plants with the following ornamental and cultivated plants, approaching Colorado potato beetles will be repelled or so irritated that they will seek another area for their nursery.
At the same time, if you regularly mulch with bracken, the pests will find it too uncomfortable in your potato patch.
I have 30 years of experience and i started this website to see if i could try and share my knowledge to help you.
With a degree a Horticulture BSc (Hons)
I have worked as a horticulture specialist lead gardener, garden landscaper, and of course i am a hobby gardener at home in my own garden.
Please if you have any questions leave them on the article and i will get back to you personally.