The Colorado potato beetle is the bug you will see most often on potato plants. You will see it in two forms. In it’s larvae stage it is red and black and looks like a slug. As an adult it is a yellow and black beetle with black stripes down it’s wings.
Potato Beetle Life Cycle
The adult potato bug overwinters in a potato crop or garden by digging down into the soil 3-10 inches. Upon emerging from the soil the adult potato bug finds a suitable food source and will feed for a short time, about 1-5 days, before mating and laying eggs.
The eggs are layed in batches of 20-50 on the underside of the plants leave. They are small orange spheres in a cluster. A female adult potato bug can lay up to 500 eggs in her lifetime of around 4-5 weeks.
The eggs will hatch between 4 and 15 days depending on the temperature. Larva will hatch faster and mature through the larvae stages faster with a higher temperature. When the larvae first hatch they stay in a cluster and can be seen all in a group at the spot they first emerged.
As they grow bigger they spread throughout the plants. It will take around three weeks for the larvae to go through their four stages and mature upon which time they will drop from the plant and burrow into the soil. After 5-10 days the adult beetles will emerge and the cycle begins again.
There can be up to three cycles depending on the location. Even as far north as southern Canada they can have two cycles. The third cycle in the south is usually not cause for concern as most potato crops are done growing.
The Most Damaging Bug Stage
Potato beetle larvae are hump backed and has two rows of black dots one either side. As the larvae gets older and bigger it will turn into a salmon color. More mature potato bug larvae, the bigger sized and more pinkinsh color, are responsible for around 75% of crop damage. Adult beetles do feed on the plants but spend less time doing so.
Colorado potato beetles feed mainly on potato plants but can also feed on other plants of the nightshade family including peppers, tomatoes, and eggplant.
Do Potato Bugs Kill Plants?
Potato bugs can completely defoliate a plant. The more common concern however is that they will stunt a plant and significantly decrease the yield of potatoes.
The potato plants can handle around 30% defoliation early in the season while in the vegetative state but once they reach the potato bulking stage, around the time of flowering, they become more sensitive and can only handle around 10% defoliation without it affecting the plant growth and yield.
How to Get Rid of Colorado Potato Beetle
Because of potato beetles resistance to synthetic pesticides, the difficulty of timing their application, and my personal gravitation towards organic methods, I recommend using neem oil.
Neem oil is 100% natural. It is made from cold pressed seeds of the neem tree and is naturally high in Azadirachtin, an active ingredient. Neem oil will slow and deter the consumption of foliage, and slowly disintegrate eggs and the bugs exoskeleton.
The best way to get rid of the Colorado potato beetle in a garden is a combination of spraying neem oil and manual eradication. In times of heavy pest infestation, spray with neem oil every two or three days. Combine this with aggressive manual eradication as soon as you start to see the beetles until you don’t see them anymore.
You can manually eradicate bugs by carrying a tub of soapy water and placing the bugs in the soapy water or just by squashing them. The main con of this method is the time it takes to manually eradicate.
Rotating Crops – Crop management can be effective for farmers that rotate to fields that are miles away from the previous year’s potato field. For gardeners it’s unlikely you’ll be able to rotate to an area so far away but it is still good practice to rotate your potato patch to get away from soil pests and disease.
Plant Covers & Trenches – Plant covers are simple and effective as they physically prevent bugs from reaching your plants.
Trenches are sometimes used by farmers to trap potato beetles. In the early spring as the emerging adult beetles mostly walk and don’t fly to reach their new food sources. A trench about a foot deep and wide with at least a 45 degree angle up to a vertical slope can be lined with plastic and this is estimated to catch up to 50% of the beetles around a potato crop.
Spinosad Sprays – This is another organic spray option. Spinosad is a bacteria and is the active ingredient in Monterey Garden Insect Spray.
Synthetic Insecticides – If you choose to use a synthetic insecticide try to use it when the young larvae are present as the young larvae are more susceptible and they have plenty of eating ahead of them if they’re not stopped.
If you’re potatoes are starting to flower be careful not to spray the flowers as this will hurt the bees as they try to pollinate the plants. This is not a problem with organic insecticides.
Plant Early or Resistant Potato Varieties – Early potato varieties can possibly get their growth in before you have severe potato bug problems. The Russet Burbank and King Harry varieties are known to be resistant to potato bugs. King Harry is the offspring of Prince Hairy, named for the hairy skin that gives the variety it’s resistance to the bugs.
Benificial Insects – Beneficial nematodes may eat the pupa after they dive into the soil but it’s impossible to tell whether your nematodes wake up when you mix them in water or whether you’d do just as well planting your cash in the soil.
Spined soldier bugs are similar in appearance to stink bugs but will feed on the larval staged potato bugs. Ladybugs will prey on the eggs of the beetles and green lacewings are natural predators of the beetles.
Please comment with your own thoughts or experiences with potato beetles.