Every spring, hobby gardeners go head-to-head with voracious Colorado potato beetle larvae for the valuable potato plants. Those who can identify the pests by their appearance are clearly ahead. This guide explains with words and pictures how to accurately identify a Colorado potato beetle larva. How to fight the insatiable enemies in the potato patch with natural means.

Colorado potato beetle larvae are red, adult Colorado potato beetles are orange-yellow

Table of Contents

Show all
  1. the essentials in brief
  2. Identify Colorado potato beetle larva
  3. Combat biologically
  4. Combat manually
  5. Use organic spray
  6. Home remedies fight Colorado potato beetle larvae
  7. frequently asked Questions

    8. the essentials in brief

    • A Colorado potato beetle larva is 2-10 mm long, bright red, later reddish-yellow, has 6 short legs, a black head and a black nape shield.
    • A special feature are 2 rows of black dots on each side of the elongated, cylindrical body.
    • Biological control methods are: collect, shake off, organic sprays (neem, vegetable brew, rock flour) and household remedies (coffee grounds, moonmin, wood ash).

    Identify Colorado potato beetle larva

    Colorado potato beetle larvae hardly resemble their parents

    The appearance of a Colorado potato beetle larva is a world away from the yellow and black striped warning color of adult Colorado potato beetles. Nevertheless, specific features characterize the appearance, which enable reliable identification even for the untrained eye. The first appearance of the pests can be expected from the end of May/beginning of June. At this time, the Colorado potato beetle larva hatches from its orange-yellow egg, which its mother placed on the underside of the leaf of a young potato plant two weeks earlier. The larva cannot complain about loneliness, because the eggs are laid in packs in numerous clutches of around 20 eggs each. Within three to four weeks, a Colorado potato beetle larva goes through four larval stages (L1-L4) and changes size and color in the process:

    • Larval stages L1 and L2: 1-3 mm long, bright red to reddish brown
    • Larval stages L3 and L4: 4-10 mm, reddish yellow
    • Appearance L1 to L4: 6 black legs, black head, black neck shield
    • Special identifier: 2 rows of black dots on each side of the elongated-cylindrical body

    By far the most damage is caused by a Colorado potato beetle larva in the fourth stage (L4). Defecation of potato plants is not uncommon in this phase. After the four-week feast in the potato patch, the fully fed larvae drop to the ground, dig in and pupate. Two weeks later, finished young beetles crawl out of the ground with yellow and black stripes and start procreating the second generation. The pictures below show the development of a Colorado potato beetle larva from L1 to L4.

    Fighting Colorado potato beetle larvae - an overview of organic methods

    When natural hobby gardeners cross swords with insatiable Colorado potato beetle larvae, biological methods take precedence. Tons of pesticides that commercial farmers spray in potato fields are not allowed in private allotment gardens and are not permitted anyway. However, ecologically ambitious allotment gardeners do not throw in the towel right away. In fact, the arsenal is well stocked with natural anti-potato beetle weapons, as the following table shows:

    Manual combat Biological sprays home remedies
    collect neem coffee grounds
    Shake off vegetable brew moonmin
    rock flour wood ash

    The ultimate remedy for Colorado potato beetle larvae has yet to be invented. In fact, Colorado potato beetles are masters of adaptation. Since it was introduced at the beginning of the 20th century, the pests have quickly developed resistance to arsenic, DDT and other toxins. Modern pesticides, such as pyrethroids, are losing their effectiveness in commercial potato cultivation. Hobby gardeners who are close to nature transfer this knowledge to the use of natural control agents against Colorado potato beetle larvae. The effectiveness of biological methods depends on a well-considered combination and alternating use, so that the beasts do not have time to adapt.

    In the following video, Professor Dr. Kühne speaks, a luminary in the field of Colorado beetle control. Join the expert on a short journey through time that explains why Colorado potato beetles and their larvae are so difficult to get rid of.

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    Fight Colorado potato beetle larvae manually - this is how it works

    Manual methods undermine the ingenious adaptability of Colorado potato beetle larvae. When collecting and shaking off, target the pests individually.

    • Best time: From mid/end of April continuously every few days until August
    • Half fill the empty PET bottle with water
    • Collect larvae and beetles from the leaves in the morning and throw them in the water bottle
    • Alternatively, spread out a foil, shake the plant and collect any fallen pests

    Finally, please subject all undersides of the sheets to a precise check. Discover orange-yellow eggs here, wipe off the clutches by hand or with kitchen paper.

    digression

    Preventing potato beetles - tips & tricks

    Hobby gardeners who are close to nature act according to the motto: Preventing Colorado potato beetle larvae is better than fighting them. Two effective methods aim to prevent Colorado potato beetles from laying eggs. In early spring, dig the kitchen garden two spades deep. Ideally, you sift through the garden soil using a throw-through sieve. You catch the adult beetles in hibernation and nip the threatening plague in the bud. Because you can never be sure if you've killed the entire population, wet the ground afterwards. A close-meshed protective net intercepts all Colorado potato beetles that crawl out of the ground and prevents them from approaching young potato plants, tomatoes and other nightshade plants.

    Organic spray against Colorado potato beetle larvae

    As a biological spray against the destructive Colorado potato beetle larvae, an extract from neem seeds is attested to have the best effectiveness. Hobby gardeners who are close to nature swear by plant suds as a liquid and rock powder (14.13€) as a dry spray against the eaten larvae. The following quick guides explain the details:

    Neem versus Colorado potato beetle larva

    Neem preparations result in a feeding and multiplication stop

    The biological insecticide organic pest-free neem from Naturen is a liquid azadirachtin extract from neem seeds. Applied to the young potato plants, the agent stops them eating within a few hours. In addition, the entire propagation process comes to a standstill. The preparation is bee-friendly, biodegradable and also approved for use in home gardens and small gardens.

    vegetable brew

    If you regularly spray potato plants with plant decoction, Colorado potato beetle larvae will lose their appetite for defecating and females who are eager to reproduce will turn away in disgust as soon as they approach. Various herbs can be considered as ingredients for the organic spray. Production and use in the home garden are extremely easy. How to do it right:

    1. Collect 1000 grams of leaves from stinging nettles, mint, ferns or thuja (green needled shoot tips)
    2. Place green collectibles in a large cauldron
    3. Pour 10 liters of water over it and bring to the boil
    4. Simmer gently for 20 to 30 minutes, stirring occasionally
    5. Remove the pot from the fire and set aside
    6. Leave for 24-48 hours
    7. Sieve the vegetable stock and fill it into a spray bottle or a pressure sprayer
    8. Spray potato plants and other nightshade plants every 3 to 4 days (don't forget the underside of the leaves).

    The natural remedy is most effective before and during egg laying (beginning/mid-April) and shortly after the first larvae hatch (L1).

    rock flour

    Rock flour prevents Colorado potato beetles from laying eggs

    If mildew or other fungal infections are rampant in the home garden, liquid pesticides are unsuitable. Permanently moist leaves provide ideal living conditions for fungal spores. That doesn't mean that you have to give up on Colorado potato beetle larvae. With a wafer-thin layer of rock flour, you prevent egg laying and spoil the appetite of any larvae that are already present. Alternatively, sprinkle the agent on by hand. The use of a powder syringe is more suitable.

    tips

    A border of perennial flax (Linum perenne), nasturtium (Tropaeolum) or horseradish (Armoracia rusticana) forms a green bulwark against Colorado potato beetles. These plants exude special scents above and below ground, which drive away females laden with eggs.

    Home remedies fight Colorado potato beetle larvae

    Home remedies are not a panacea against Colorado potato beetle larvae. At least they can enhance the effectiveness of other biological methods. How to do it right:

    • coffee grounds: Scatter dried coffee grounds in the bed every 4 weeks, spread thinly on plant leaves
    • moonmin: Use as an inexpensive alternative to rock flour
    • wood ash: Apply pure ash (without toxic combustion residues) to the upper and lower sides of the leaves using a powder sprayer

    These home remedies with plant brews achieve a powerful synergy effect. If the potato leaves are still slightly damp from the organic spray, sprinkle on the coffee grounds, Mondamin or wood ash.

    frequently asked Questions

    What do adult Colorado potato beetles look like?

    Adult Colorado potato beetles are orange-yellow with black stripes

    Adult Colorado potato beetles have a distinctive appearance. The rounded-oval body is 7 to 15 mm long and has black and yellow stripes. Each of the light yellow, shiny elytra is adorned with 5 black vertical stripes. Black spots on the yellow-orange pronotum are characteristic. There are no special features on the red-brown underside of an adult Colorado potato beetle. Black feelers and 6 thin legs complete the visual appearance.

    Is the Colorado potato beetle larva only harmful to potato plants?

    No, unfortunately the food spectrum of Colorado potato beetle larvae extends to numerous nightshade plants. Tomato plants, peppers, chillies, aubergines and even tobacco plants are also eaten with great appetite. Not growing potatoes in your own garden is therefore no guarantee that you will be spared a plague of Colorado potato beetles.

    Can Colorado potato beetle larvae bite?

    Like most beetles, Colorado potato beetles and their larvae also have a chewing and biting tool for feeding. Of course, this mouthpart is only sufficient to eat tender plant leaves. The so-called mandibles are far too weak to bite human skin.

    Are there beneficial insects against Colorado potato beetle larvae?

    The Colorado potato beetle is a pest introduced from North America. This circumstance plays into the hands of the invaders, because there are no predators in Europe. Birds, ground beetles, assassin bugs and other beneficial insects spurn both the adult beetles and the reddish larvae. It remains to be seen whether, in the course of evolution, parasitoids such as lacewings or parasitic wasps (€22.99) will recognize the Colorado potato beetle larva as potential prey.

    tips

    The high expectations of the biocide Novodor FC as a control agent against Colorado potato beetles have not been met. The non-toxic bacilli contained in the remedy called Bacillus thuringiensis subspecies tenebrionis should cause the Colorado potato beetle larvae to stop eating immediately. At the request of the authorization holder, the authorization as a plant protection product was revoked on April 30, 2022. This does not apply to Bacillus thuringiensis israelensis. This strain of bacilli is still available to combat mosquito larvae.

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Vegetable garden