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Its damage relevance is so devastating that the Colorado potato beetle was even considered as a biological weapon in the mid-20th century. Immigrated from the USA, the adult beetles, young beetles and larvae devastate a potato bed by defecating. Tomatoes are not spared either. It doesn't have to come to that, because there are effective strategies available to combat it. Read here how to get rid of the pests on potatoes.
Characteristics
- Insect family of leaf beetles (Chrysomelidae)
- botanical name: Leptinotarsa decemlineata
- Common names: Colorado potato beetle, Colorado beetle, Ami beetle
- immigrated in 1877 from the United States (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 occurrence of 1 to 3 generations
- Peak mating season: May-June, July and August
- Sleep-wake behavior: diurnal
- Food plants: Potatoes and other nightshade plants such as tomatoes, aubergines, peppers
They are there just in time for the sprouting of potatoes. If the ground temperature exceeds 15 degrees in spring, the Colorado potato beetle crawls out of the ground to multiply explosively. The feeding 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. It's a good thing that in the 200 years since they appeared in Europe, effective strategies for fighting the little monsters have emerged, at least to some extent. Read here how to get rid of the pests on potatoes.
The damage potential of Colorado potato beetles is based primarily on the fact that the pests immigrated from the USA. Therefore, there is still a lack of natural enemies that could restore the ecological balance if they appeared in large numbers. In addition, the leaf beetles are extremely robust and even survived being dropped from an airplane at a height of 8,000 m. Furthermore, the physiology of the pests is so flexibly balanced that they quickly adapt to chemical insecticides and develop resistance.
life cycle
Exact knowledge of the life cycle of Colorado potato beetles significantly optimizes the control strategy. Since it is primarily the larvae and young beetles that devastate your potato bed, egg laying should be prevented. In the third and fourth instar, each hatched larva is able to eat up to 40 square centimeters of leaf surface.
As this phase of destruction extends over a few weeks, the timing of the control is just as important as the control itself. Below we summarize the most important stages of development from the egg to the beetle.
- Colorado potato beetles hibernate up to 60 cm deep in the ground and crawl out from a ground temperature of 15 degrees
- from May the mated females lay up to 1,200 red-yellow eggs in small packets on the underside of the leaves
- Deep red larvae with black spots hatch within 1 to 2 weeks
- thanks to extensive feeding on potato leaves, the larvae are fully grown after 21 days
The fully grown, now orange-colored larvae crawl into the ground for 2 weeks to pupate. They then appear as young beetles, only to attack the leaves of potato plants in turn. After a further 14 days of constant eating, they are sexually mature, so that the second generation is born from July. In mild weather conditions, a third generation appears in the worst case in August.
combat
Ecological control methods
Colorado potato beetles have the unique ability to adapt and develop resistance to chemical control agents within a short period of time. Anyone who wants to get rid of the pests on potatoes with the help of insecticides is therefore in a losing position and ultimately holds a chemically contaminated food in their hands. In contrast, the ecologically oriented strategies of organic farmers have proven to be powerful and long-term. Here we explain proven procedures in the fight against Colorado potato beetles and their larvae.
collect
The consistent collection of the Colorado potato beetle, their larvae and egg packets is still unsurpassed in terms of efficiency. In allotment gardens in particular, 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 in the early morning hours from May and drowning them in water, you prevent egg laying.
If you continue the morning inspection rounds during the summer, you can remove the leaves with egg packets or hatched larvae in good time. Then spray the infested plants with horseradish manure or mint broth to scare off the brood as well.
Bacillus thuringiensis
The bacterium Bacillus thuringiensis, which is non-toxic to humans, vertebrates and plants, is at the top of the list of successful control methods. The crystalline toxin has a deadly effect on Colorado potato beetles and their larvae as well as other insects. Specialist shops have effective preparations that are made on the basis of special strains of the bacterium. These convince with reliable accuracy by destroying the pests, while beneficial insects such as hoverwasps or lacewings are spared if they happen to be in the catchment area.
The Bt control agent works under these conditions:
- the Colorado beetles and larvae have to feed on the bacterium
- at the time of application, temperatures of 15 degrees Celsius and higher prevail
- apply the product in the early morning hours, since the pests take up most of their food at this time
- spray the spray or spray solution directly onto the pests
- in addition, all the upper and lower sides of the affected plant are treated
The remedy causes an immediate feeding stop. In the further course, beetles and larvae die off. Products approved for use in allotment gardens, such as Novodor FC from Biofa, already have an effect on the brood in larval stage 1 and should therefore be applied at an early stage.
neem
The tropical neem tree provides ingredients that are effective against Colorado potato beetles and other harmful insects that bite or suck. With products such as NeemAzal T/S, you can fight pests in your home garden in a way that is safe for your health and the environment.
The remedies are made from the seeds of the tree in the form of an extract that contains a high proportion of azadirachdin. The active ingredient is not immediately fatal. Rather, the life cycle is inhibited in the first stage by a nutrient, followed by the reduced ability to reproduce.
This is how the development works:
- the best time for application is on the fifth day after egg laying
- only prepare the required amount of spray mixture on the day of use
- the neem inhibits egg hatching so that development beyond the first larval stage does not occur
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, plagued hobby gardeners decide to use a combination product made of pyrethrins and rapeseed oil, such as Spruzid Neu. For years, the pyrethrum it contained was seen as a ray of hope in the fight against the disastrous Colorado potato beetle. However, the pests developed resistance, so that the effectiveness dropped to less than 20 percent.
Thanks to intensive research, the effectiveness has been optimized by adding natural rapeseed oil. Although the control agent is not completely harmless to the environment and health, it is currently still approved for use in allotment gardens. The Federal Office for Consumer Protection and Food Safety (BVL) maintains a database that lists all permitted pesticides, including the end of approval date.
spinosad
The active ingredient spinosad, which has also proven effective against Colorado potato beetles, is approved for organic farming by the European Union. If all purely natural control strategies come to nothing, this alternative is available to you to get rid of the pests on potatoes. The remedy is obtained from special bacterial strains and amino sugars.
The insecticide may only be used if special protective measures are observed, such as wearing protective clothing and gloves. In addition, it is dangerous for bees and other beneficial insects, so they must not apply it to flowering plants.
Internet Alert Service
Since the effectiveness of ecological pesticides depends crucially on their being applied at the right time, the state agricultural institutes offer an information service that you as a hobby gardener can also use. A prediction system based on local infestation surveys is available for each region. Taking into account weather data and the course of development from the egg to the larva, the optimum time at which you should use the selected preparation is calculated.
Since the forecast calculation works with a lead time of one week, you have enough time to choose the control method and to procure the appropriate means. This service is available on the Internet free of charge and can be used to the full by both commercial farmers and private gardeners.
prevention
In a garden that is managed in a way that is close to nature, you can use purely natural means to prevent an infestation by Colorado potato beetles in advance or nip them in the bud at the first sign. In the following, we present tried and tested methods in more detail. So that the clever pests don't adjust to one agent and develop resistance, please change the active ingredient group again and again.
Horseradish manure
In the spring, apply a horseradish (Armoracia rusticana) manure repeatedly in your beds with potatoes and other nightshade plants. This plant manure prevents the Colorado potato beetle crawling out of the ground from laying their eggs on the leaves. Furthermore, horseradish manure serves as a natural control agent in the first larval stage.
How to prepare the liquid manure:
- Place 1 kg of fresh horseradish or 300 g of dried horseradish in a wooden barrel
- Pour 10 liters of collected, filtered rainwater or stagnant tap water over it
- place in a sunny, warm, secluded spot in the garden
- cover the container with chicken wire and do not cover with a lid
- stir the liquid several times a day to allow oxygen to enter
After only 2 to 3 days, the solution has a certain degree of effectiveness against Colorado potato beetles. However, the liquid manure only develops its full potential after 2 weeks, when the liquid has completely fermented. Strain off the plant parts and pour the horseradish manure into a watering can or pressure sprayer. As a preventative, water the plants weekly. If the Colorado potato beetle or its larvae are already on the leaves, get rid of the pests by applying the natural product every 3 days.
rock flour
Rock dust has made a good name for itself as a natural soil additive in organic farming. The fine material also makes a valuable contribution to repelling Colorado potato beetles and other pests that want to eat the leaves of your crops. If you regularly powder the dewy potato plants on the top and bottom of the leaves with rock flour in the early morning hours, the voracious pests will lose their appetite.
This applies to both the adult beetles and the larvae. Prehistoric rock flour is not suitable as the sole control agent; as a component in the strategy, it is nonetheless of value. At the same time, the natural product strengthens the resistance of your plants in an environmentally friendly way.
coffee grounds
Among the household remedies against Colorado potato beetles, coffee grounds enjoy the best experience in private kitchen gardens. When the young plants have reached a height of 10 cm, sprinkle the dried coffee grounds on the still damp leaves every 4 weeks in the morning. You should not use the coffee powder at shorter intervals, as it lowers the pH value.
Thuja tea
The ingredients contained in a thuja have the potential to permanently scare off Colorado potato beetles and their brood. After pruning the conifer, you will have enough material in your hands to prepare a tea from it. To do this, pour boiling water over the clippings and leave to soak for 24 hours. The next day, sift off the plant matter, pour the liquid into a hand sprayer, and treat the potato plants. In particular for prevention and in the early stages of infestation, this approach is an excellent complement to other ecological methods.
mint broth
Potato beetles don’t like peppermint at all. Clever organic gardeners discovered this fact, so repeated spraying with mint broth makes a valuable contribution to the defense against these pests. In contrast to manure, the broth is made within a short time. To do this, put the fresh plant parts in water and let everything simmer gently for 30 minutes. After the broth has cooled, you can immediately spray it on the potato plants.
Defensive plant neighbors
One of the many advantages of a mixed culture is that compatible plant neighbors protect each other from diseases and pests. If you keep your potato plants with the following ornamental and cultivated plants, approaching Colorado potato beetles will be repelled or so irritated that they will look for another area for their nursery.
- Nasturtium
- linen
- peppermint
- tagetes
If you mulch regularly with ferns at the same time, the pests in your potato patch will find it too uncomfortable.