This is a transcript of a presentation given at the Potato Pest Management Workshop put on by Alberta Agriculture & Forestry in Sherwood Park, AB on March 6, 2018 and Lethbridge, AB on March 8, 2018.
Good afternoon everyone. I’m an agronomy consultant based in the irrigated area of Southern Alberta. My specialty is helping people grow plants and build their soil based on sound, agronomic principles. My roots, so to speak, are in conventional agriculture, but they are always exploring new ground. In my leisure time I garden. Most of the plants I grow are for food, but I also love growing ornamental plants in my yard. My garden is the place where I experiment and play with new ideas and techniques.
I’ve put this presentation and links to many of the resources I used in preparing this talk on my [website]. You could go there right now and download them, or just listen in and go back and review later. I’ll put this information up again at the end of my presentation.
General Discussion on Flea Beetles
The tuber flea beetle is very similar to many of the other flea beetles you’ll be familiar with. If you’ve ever grown canola, or anything in the brassica family, you’ll know how destructive this pest can be. In my own garden at home I’ve pretty well given up trying to grow brassicas (like kale, radishes, or brussels sprouts). I could spray them, but I prefer not to. It requires being out there consistently to find them and any of the sprays available can also kill the beneficials in the garden. I’m not against using chemicals. I use RoundUp to tackle perennial weeds in my garden in the fall and Killex in my lawn to spot spray dandelions through the year, but for insects I’ve chosen not to spray them. I have tried the floating row covers but I found them to be a pain. With the winds of southern Alberta, they need to be tied down tight, and on a more aesthetic note – I just didn’t like the look of them in my garden. So, since I wasn’t too attached to having those crops, I just found other ones that I can grow and that can resist pests well.
Now if I really wanted a particular crop, and didn’t mind how it looked, I’d make it work. For you guys, you can’t just deal with the pest by avoiding the crop, so we have to figure out the best way to do this. So, let’s get into the pest to try to learn how best to manage it.
Flea beetles are a group of jumping beetles from the leaf beetle family. They will feed on many different plants, but species have evolved that have adapted to specific plants. I mentioned flea beetles in canola before. You may have heard of them being referred to as crucifer flea beetles and striped flea beetles. The crucifer flea beetle is found throughout the province and the striped one is mainly in the northern areas. Knowing what you have is helpful in how you go about controlling them. The striped ones tend to be harder to kill with insecticides and knowing this helps you to know what you are up against. This is an example of adaptation by a species. The one that can tolerate neonics better, the striped beetle, survives more often, and so we see more of it present.
In potatoes there are three main flea beetles to be concerned about in Alberta. These are the tuber flea beetle, the western potato flea beetle, and the potato flea beetle. All three can cause damage to the foliage but this is usually not a big concern in potatoes. After feeding on the foliage, the females lay eggs in the soil below. The larvae that hatch feed on the roots of the potatoes. While this doesn’t usually cause much damage to the plants, the tuber flea beetle has evolved to feeding on the developing tuber itself.
From the perspective of the plant, this does not cause a lot of damage, at least when compared to other pathogens like fusarium dry rot or pink rot. The tubers can take some damage and still be fine. The problem lies in the fact that the outside of the tuber has a bunch of channels throughout it. It can be peeled and eaten with no health concerns, it just looks unsightly. Consumers like produce to look good, so it generally makes the tubers unmarketable. On the processing side of the industry the potatoes still may be used, but they may require deeper peeling, which is generally not desired. On the seed side, it is still safe to use the potatoes, as the insect is no longer present, but the seed may be more open to pathogen entry.
The Tuber Flea Beetle
I’d now like to drill a little deeper into the life cycle of the tuber flea beetle. Like most flea beetles it is very small. In metric it is 2-4mm in size, and in imperial that’s only 1/16 to 3/16”. There are differences in colour between the different species that attack potatoes, but it would take an expert to look at each one to distinguish them. The potato flea beetle is black, the tuber flea beetle is dull black, and the western potato flea beetle has a bronze colour in bright light. In canola it’s handy that the one that is harder to control, the striped flea beetle, looks very different than all the rest. In potatoes it would be nice if the tuber flea beetle had a distinctive mark, so we could easily tell if we were dealing with it or not, but it doesn’t.
Right now, as I speak, these tiny insects are over wintering in fields and shelterbelts. These are the adults that were produced the previous season. When the ground thaws and warms up to about 10C or 50F these adults will start to emerge from the soil. This is generally right around the time the potatoes are emerging from the soil in late May. Clever, right? They’ve evolved to come up when the food is available. If they are not in a potato field and they can’t find any suitable plants nearby, they’ll go looking for potatoes. They can fly long distances until they do find some. Once found they don’t go deep into the field. This is important. They’ll start on the edge of a field and only fly further in if needed.
Once they find the potato plants they will start eating. At this point their sole purpose is to mate and continue the next generation. Over wintering as adults means there is very little time needed from emergence to egg laying. Once egg laying is complete these adults die. The eggs are laid in soil near where they were feeding. The larvae emerge and begin feeding on roots and the developing tubers. This is generally in the later part of June and into early July.
In Alberta, we are fortunate in that we usually only have one generation per year. In warmer, longer seasons, like Washington & Oregon, they can have 3 generations per year. It’s possible that this past year we had 2 generations because of how hot the summer was and how early the heat came. Damage to tubers will increase as the season progresses if you get 2nd and 3rd generations. Early tuber damage will be shallower, but as the skin develops the larvae will go deeper inside the tuber and will tend to tunnel just underneath the skin rather than just munch in a little way and then pull out.
Managing the Damage In-Season
So now that we know more about the pest and what it can do, let’s move onto how to manage it. Once you see the damage to the tubers, it’s too late. You need to prevent the adults from feeding on the plants and laying eggs. In an area with multiple generations, you may be able to prevent further damage by stopping the next generation. However, remember that here in Alberta there is usually only one generation.
So, what if you do find damaged tubers in the field? In this case, your best management is mapping out your problem. I’m from the irrigated areas of southern Alberta, so I think in standard quarter sections with a centre pivot. The irrigated area of the field is about 130 acres. On a field this size it’s likely that the pest is mainly on the edges, but the scouting is going to have to confirm this. For the areas where it has caused damage, you’d need to have graders ready, and you’d want to plan extra time to help get those potatoes sorted out. If possible, they should be shipped direct to processor or to market. Digging early may limit some of the damage if they are still active. If you need to store them, then ideally they go to a separate bin, or they are kept in a part of the bin that is easy to unload. For the areas where it’s at the ends of the rows, it will get diluted in the truck as it is harvested up and down the field. You’ll just need graders looking for it and trying to get it out.
This seems bad, but worse is finding it later in the bin. You’ll have to manage the bin to keep the potatoes the best you can. The damage itself won’t cause storage issues, and the insect is not present in the tuber, but they may not keep as long due to other pathogen entry and water loss. Your best bet at this point is to try to ship the bin early and keep a close eye on it. You’ll also need to recognize you’re going to need extra graders when shipping, and shipping may go slower.
If you have found yourself in this situation, you’ll now want to plan for next year. Since you know the adults are out there, you know you’ll have a problem. Any field nearby will be susceptible to them since they can fly in when they emerge. You already know to never plant potatoes on last year’s potato land, so I don’t even need to mention that, right?
Preventative Chemical Control
The best control is to prevent the adults from laying the eggs in the first place. With that in mind, stopping the adults from feeding is going be your best control. Since they start feeding early in the year, when the plants are emerging, the best control is going to be a systemic insecticide applied as a seed treatment or in furrow at planting.
For seed treatment options there is only Titan from Bayer. It is a Group 4 neonic. It comes co-packed with their fungicide, Emesto. It’s been out on the market for nearly 10 years now and I’ve seen the change in the processing industry from dust to liquid. Though there is still some dust being used, most have switched to liquid.
At the beginning, most people were skeptical of liquid, but once you’ve seen it work you won’t want to go back. And you won’t have a choice in the future - the PMRA is not registering any new dusts. They all must be liquid. The main reason is worker safety. The added benefit is product handling. With dusts you’d need 4-5kg per ton of seed, and with liquids it’s 1-1.4L. It’s best to have a high-quality applicator, which can be pricey, but if you can get a fine spray in a tumbler and get good coverage, it will work for you. The chemical has a drying agent, so although it goes in the truck wet, it’s dry by the time it is unloaded and into the planter.
Applying in-furrow with the planter is the other option. You’ll need a good liquid applicator that can spray in the open furrow as the seed is dropping. You can apply Admire or any of the other generics. This is a good option if you are wanting to use a different seed treatment fungicide, whether dry or liquid. You can also use a new option from Syngenta called Minecto Duo. It contains Syngenta’s Group 4 neonic, Actara. In it is also mixed a Dupont chemical called Verimark, which is from a new class of chemicals called the diamines (Group 28). This is a good option to help slow resistance to the Groups 4’s since there is a new mode of action mixed in.
Using any of these options will not be cheap but they will work well. The chemical lasts for about 3 months, which is enough to control the tuber flea beetle. It also targets any sucking or chewing insect such as the Colorado potato beetle, aphids, and psyllids. Because of the long-lasting nature of this option and to help slow the development of resistance, you cannot spray chemicals from these groups, Groups 4 & 28, in-season. Regular scouting should still be performed for this pest, and all other insects, to ensure there are no misses or signs of resistance.
Although these options are approved for Canada, some countries do not have MRL’s and can block potatoes and products. Check with the buyer of your potatoes before using to be sure they are going to be accepted.
Chemical Control In-Season
If you are not using anything at planting, then you will need to plan on extensive scouting. The threshold for action is very low due to the damage this pest can do. If you see the shot-hole damage to the foliage you should still be trying to find the insect before spraying. For effective scouting you start along the edge of the field once the plants are emerged and inspect 10 plants at a time. It can be tricky because they move fast. If you don’t find any, walk for 40 paces and check 10 plants again. If none are found after examining 60 plants, you are below threshold. This should be repeated on a few more edges and within the field. If they are only on the edges you should be able to spray just those areas and continue monitoring. As the plants get larger you may switch to a sweep net. The threshold for sweep nets is 1 beetle per 10 sweeps.
There are many chemical control options and they are all listed in the Alberta Blue book. There are many factors that need to be weighed before choosing a chemical, so every case needs to be judged separately. Some of the factors include the effect on beneficials, pre-harvest intervals, and any restrictions on chemicals that your buyer may have.
The best option to start with is Concept as it has a neonic (Admire) for residual control plus a contact (Decis) mixed together. For an entirely contact option consider any of the synthetic pyrethroids such as Decis, Mako, Matador, Silencer, Pounce, Perm Up, & Ambush. These can also be used if you used a seed treatment or in-furrow chemical at planting time, and have found the tuber flea beetle or any of the other insects. If found, you will want to get them tested for resistance before spraying. Contact your agronomist, input dealer, or chemical rep to find out how. Catching resistance before it develops is huge advantage in planning controls in the future.
The Blue Book also lists the carbamates (Group 1A), the organophosphates, (Group 1B), and the chlorinated cyclodienes (Group 2A). The names you’d recognize from these are Lorsban, Dibrom, Imidan, Monitor, Orthene, Sevin, & Thionex. They also go under a lot of generic names. I would only use these if there was a specific reason that a qualified agronomist thought they were worth using. They are all from the older chemistries which are much more highly toxic to bees, the environment, and workers applying them.
The drawback to using any of these sprays in season – synthetic pyrethroids, carbamates, organophosphates, or chlorinated cyclodienes – is that you may kill the beneficials that are doing a good job on the other potential pests. A common problem is flaring spider mite populations when spraying insecticides for other pests.
To end my presentation, I’d like to go over some cultural control measures that you can use if you have a small field – maybe only a few acres – or are growing them in your garden. This is the most exciting part for me. I love learning how plants interact with other plants and with the soil and soil organisms. This is part of the reason I love gardening so much. I can play around with so many combinations of things and try things out. There have been many failures but there have also been successes.
So, when it comes to things you can do to manage the tuber flea beetle before going to chemicals, well, there isn’t much. They are tough little insects and they seem to get by a lot of our attempts to stop them from getting to our crops. They also don’t seem to have many natural enemies or predators. It’s still worth doing things in your garden or field to encourage beneficials but don’t count on them taking the tuber flea beetle down to manageable numbers.
When talking about a quarter section of potatoes, rotation plays a big role in preventing them from infesting the entire area. Because they are flying in and tend to start on the edge, they can be managed easier by catching them early, and preventing them from moving into the field. In small fields or gardens there isn’t the edge to protect you. The area of potatoes is so small they’ll just take it over on the first flight. Crop rotation is still very important. You never plant where potatoes were the previous year, and ideally you want to wait 4 years to plant them or any solanaceous crop, like tomatoes, in the same area again. It’s just not going to help much if you have a population of them living in your garden.
The most effective method I came across was that you have to put up a physical barrier. I already talked about this for my garden when dealing with brassica flea beetles. Its unsightly (at least to me) and takes some work to put it up, but it can be very effective. It won’t need to stay season long, just long enough to prevent the adults from eating and laying eggs. And remember what I said about crop rotation? What’s going to happen if you plant your potatoes on the same ground as last year and then put up a row cover? The beetles will come out of the ground, under the cover, and start eating and laying eggs without any effort in looking for potatoes.
Trap Crops & Inter-planting
When dealing with flea beetles that attack the brassica vegetable crops there has been some success with trap crops. The idea is to lure them to the trap crop so that they leave the cash crop alone. The trap crop needs to be very attractive and ideally needs to be well ahead of the cash crop. Controls measures can be applied to the trap crop that may not be permitted on the cash crop to try to bring down their numbers. I didn’t find any examples in the potato world, but on the brassica side mustard can be grown between broccoli.
If it were found that a variety of potato, or maybe another plant in the solanaceae family, was very attractive to the flea beetles, it could be used to lure them and kill them before getting to your main crop. Ten years ago, I read about a tomato plant that attracted Colorado potato beetles so well that they’d go to it instead of other tomatoes or potatoes in a field. The tomato plant grew lots of foliage and kept supplying the beetles with food while the cash crop grew. The company that accidently bred it – they were looking for winning tomato hybrids – named it Bugbait. I contacted the company and they said it never went anywhere but offered to send me some seeds to try out this year. I start all my own seedlings for my garden, so I’ll just add them in this year and try them out. It will be fascinating to see if it attracts the Colorado potato beetles and if other potato insects are attracted to this plant
Another option is interplanting. Again, the only example I found was on the brassica side, but it involved planting onions between broccoli to disguise the brassica. Some have tried combining this with a trap crop so that the flea beetles still have a place to go and the main crop is hidden. It seems like a lot of work but if you can use most of the plants it could be beneficial.
Organic chemical control
If you are not wanting, or able, to use the chemical controls that I talked about previously, most of the resources listed insecticidal soaps. It was the most commonly recommended on university gardening sites and as an organic solution. If you are growing organic and you are marketing your produce that way you would need to check what is permitted and what is not before using this method.
It’s possible to make your own soap but you can’t just use the soap from your kitchen. It needs to be the pure soap from natural oils and fats. The problem with most soaps in your kitchen is that they have additives and degreasers. There are many commercial options available with good recommendations from university master gardener sources. The mode of action is still unknown, but it could be suffocation, breaking down the exterior of the insect leading to dehydration, or ingestion that breaks down cells. It may be a combination of all or it may be something else.
It’s completely contact – you must cover the insect. It has no residual effect, but it can build up on plants and harm them. Some people suggest rinsing the foliage a few hours after application. It will take repeated applications. Beetles are tough to get because they move fast and have a hard shell protecting them, but it can work. One site warned that although it’s safe for most beneficials, it can kill the predators of spider mites and you may flare the population of them using insecticidal soap.
With that I’ll end my talk here. Don’t forget that I’ve put my presentation and a list of the references that I used in preparing the talk on my [website]. I’ve went through a lot of information today and I hope that you’ve learned a few things about dealing with this pest and have some new tools in your toolbox. I’ll take some questions now if time permits. Otherwise feel free to catch me at a break or contact me later.
Flea Beetles and Potatoes - Frequently Asked Questions
Potato, Irish-Flea beetle
Tuber Flea Beetle
Flea Beetles on Vegetables
The Battle Against Flea Beetles
Shift in flea beetle species composition
Alberta Blue Book 2017
Dish Soaps Can Damage Your Plants
Insecticidal Soaps for Garden Pest Control
Control Houseplant Insect Pests Safely With Insecticidal Soap
Insect Control: Soaps and Detergents
Trapping Pests With Bugbait
A Short History of Pest Management