There is nothing like a potato crop, with its abundance and culinary delights. From mashed potatoes and French fries to roasted and scalloped, there are so many ways to use your harvest. They store for a good, long time, too.
But there’s one pest that can come calling that will ruin your entire crop.
We are going to talk about why you really don’t want the potato tuberworm to find your garden and what to do if it does.
What Are Potato Tuberworms?
Potato tuberworms are the larvae of the potato tuber moth (Phthorimaea operculella) in the Gelechiidae family. This offspring can also be referred to as tobacco splitworm.
The preferred host plants for both larvae and adults are those in the Solanaceae family. This family encompasses potatoes, as well as tomatoes, eggplants, peppers, tobacco, and petunias.
Lifecycle
The larvae’s coloring depends upon its food source. They can be pink, green, grey, or off-white. Although they are called worms, they’re biologically caterpillars.
The adult moth is small. It measures about a half inch in length and has a wingspan of about a half inch.
The wings are fringed with long hairs and have a distinct white spot near the tip. Adult females have an “X” symbol on their backs and the males have three distinctive white dots. Both females and males have cream, tan, dark brown, and white marbling.
The female potato tuber moth lays 30-150 eggs during her life, depending on the environmental conditions and host plant availability. The eggs are hard to see individually, but you can spot the large clusters.
Eggs can be laid anywhere on the plant’s foliage and stems as long as they protect the eggs from predators and adverse weather. The female can also lay eggs in cracks or broken soil where tubers are easily accessible.
Once in place and conditions are right these eggs will hatch in three to seven days.
Potato tuberworms emerge from the eggs and move with the use of prolegs to begin immediately feeding on plant tissue. If eggs are laid in soil, they will burrow in and tunnel into the closest tuber.
This is the biggest eating phase of this pest’s entire lifecycle. It must consume lots of nutrients to mature enough for the next stage. There are four instars until it’s developed enough to metamorphose through the pupa stage.
Next, the potato tuberworm makes a cocoon known as a pupal case. Inside this protective covering the potato tuberworm becomes the moth adult, undergoing significant changes in body structure and developing wings.
They can pupate in soil, plant debris, or on the plant itself.
Once the morphological changes have happened and the reproductive organs fully developed the moth adult will emerge. They will mate shortly after leaving the cocoon and the cycle starts again for the next generation.
In the right climate and if food sources are optimal, several generations of this pest can occur in one growing season. Male moths live for about one week, whereas females can live up to ten days.
Having a short lifespan of the adult moth highlights the importance of rapid reproduction and efficient dispersal for this pests survival.
Characteristics and Habitat
P. operculella can survive in egg, larvae, and pupae stages should conditions be unfavorable for reproduction. They are well equipped to hide out during winter months in plant debris, soils, weeds, and your potato store room.
Global warming has allowed the adult moth to migrate to further northern regions. It prefers tropical and subtropical climates and is common on the east and west coasts of the US. It can also be found in Asia, Africa, Europe, South America, and Oceania.
Because potatoes are its primary host, the potato tuberworm has evolved to survive where potatoes grow indigenously. Its lifecycle requires high temperatures mixed with a good dose of humidity.
The adult isn’t a long-haul flier, but rather a cumbersome one at best. It isn’t flying to new climates but is likely being carried by humans to new regions on plant matter or in the soil.
Signs and Symptoms
The good and bad thing about this pest is they don’t hide their destruction. They’re heavy feeders at the worm stage and rarely contained to the tubers alone. The adults are easy to spot, too.
Pest Presence
The gathering of adult moths during the evening or night and around your potatoesmight be a sign of tuberworm presence. Of course, many moths fly at night, so you’ll need to trap one and confirm the species to be certain.
Pheromone traps will draw in the males so that you can identify the culprit.
You might also spot clumps of tiny white eggs on the underside of potato leaves. Check the growing tubers to confirm an infestation.
Like most caterpillars, the potato tuberworm creates excrement, called frass. Basically, black or brown insect poo may appear on foliage and surface of the tubers.
Unfortunately, a problem may not be obvious until the tuber is cut open unless foliage has also been attacked.
Damaged Tubers
Any infested potato tuber will have brown or black tunnels and holes. These are created by the feeding habits of the tuberworm, which causes bruising and rotting in the flesh of the host plant.
With the burrowing into the tuber flesh, pathogens, oxygen, soil particles, and moisture can get in and speed up the tuber’s decomposition. This breakdown in the tuber’s cellular structure can cause the potato to become mushy and soft to the touch.
Reduced Yield
The presence of this pest can significantly impact the plant’s development, particularly as we tend to grow potatoes in close proximity to one another for ease and to encourage more produce to develop.
With heavy infestations comes the risk of loss of most of the tubers. The tuberworm damage renders the potato home unsellable, unusable, and undesirable.
Stunted Growth
Whether the plant’s foliage or tubers are under attack, this symptom is almost certain if not treated quickly. This is especially true when the roots are also feasted upon.
When the protective membranes and outer layers are damaged, the plant’s ability to maintain its health and vitality is interrupted.
Often, when this is a factor, other diseases and pests contribute to the suffering, as the host plant becomes weakened.
Discoloration of the Foliage
Alongside poor growth and development is the wilting and discoloration of plant parts above the ground.
As the appetite of the tubeworm increases, with its maturing, migration to stems and leaves can cause them to turn yellow to brown, become twisted, and new growth disappears.
Prevention and Pest Management
Using good gardening and growing practices from the outset reduces the risk of the potato tuberworm moving in and damaging your entire crop.
1. Crop Rotation
When growing potatoes or other host plants, consider either intercropping or rotating crops every year or two with non-host plants.
These plants don’t offer a food source to the pest:
Crop rotation can break the pest lifecycle and reduce populations dramatically.
2. Garden Hygiene
First, only purchase certified disease-free and pest-free planting materials and tubers to reduce the risk of introducing potato tuberworm into your growing space. Be cautious when moving tubers or soil from one garden to another.
You should keep weeds away from your garden as these can act as an alternate host.
Implement cultural practices such as proper irrigation systems, plant-specific organic fertilizer, and weed control to promote healthy plants and reduce stress or competition.
3. Timely Harvest and Good Storage
Harvest potatoes as soon as they reach maturity. This will reduce the chances of an infestation. Leaving them in place can attract the adult moths, encouraging them to lay eggs.
Properly store harvested potatoes in a cool, dry place, and use clean containers and fresh materials for storage to prevent re-infestation. Check stored crops regularly for any signs of potential pest presence.
4. Protect
With the assistance of good equipment and prevention techniques, the potato tuber moth and offspring can be deterred from laying on and eating your crop.
Floating row covers are your best defense, but be sure to put them in place early in the year before the adults come around. Buy a six by 50 foot cover at Amazon.
5. Biological Control
Making your growing space a haven for beneficial bugs will improve the health of your garden and help you avoid potato tuberworms and other pest infestations in the future.
Birds and bats will eat the adult moths, and birds will also feast on the eggs and larvae when they can reach them.
Trichogramma wasps, tachinid flies, ladybugs, green lacewings, braconid wasps, and praying mantises will all keep pests under control,
5. Irrigation
In drier climates, irrigation can be an effective way to prevent the females from laying and the eggs from maturing. Keep the soil regularly moist so that cracks don’t develop in the soil. This makes it difficult for the worm to get into the soil.
6. Chemical Treatments
In decades past, people relied on pesticides to control potato tuberworms. Now we know that broad spectrum pesticides create resistant species and kill beneficial insects. Try to avoid pesticides and aim for integrated pest management techniques instead.
Certain organic treatments can help suppress pest populations with less of an impact on the environment than conventional products.
Bacillus thuringiensis (Bt) is a beneficial bacteria that kills all kinds of common pest larvae. It has shown to be effective against potato tuberworms. You can purchase a gallon at Amazon.
Neem granules and oil spray might provide a small measure of control against the adults.
These less impactful remedies should be tried with any infestation first before implementing chemically based treatments. Such applications should be made when this pest is most active in the evening.
This helps you target them effectively and reduce cross-contamination with friendly creatures, which tend to be more prevalent during the day.
