Colorado Potato Beetle Control

 

The information below is lifted from the Organic Agriculture Centre of Canada Discussion Forum which can be viewed here http://www.oacc.info/phpbb3/

 

I would like to share my strategies for controlling Colorado Potato beetles. They are a huge problem for us (our number 1 pest problem after weeds of course). We grow about 12-15 varieties of what a friend call "artisanal potatoes" here in eastern Ontario, so their management is a necessity for us.

 

Mike B of Lotusland FarmOrmond ON

 

So, lets start with a definition; "integrated pest management". This involves much more than looking at your beans, seeing a whole ton of black bean aphids and reaching for the SafersSoap instead of diazinon. It involves knowing how much each control methodology costs, and how much damage the pest can cause (setting action thresholds). Then it involves knowing what is there and how many (pest monitoring). Once the insect numbers exceed the action threshold (in other words they are causing more damage than the cost of the control methodology), you employ the first level control strategy (initial control). Then you see whether the control strategy has worked (effectiveness monitoring). If your control strategy has worked, you go back to the pest monitoring step. If you have not achieved control (pest numbers continue to climb), you employ the next level of pest control strategy. This loop cycles through the control strategies until either you achieve control, or the pest happily eats your entire crop. That is integrated pest management...

 

We have four or five strategies in our Colorado Potato Beetle (CPB) control toolbox here; in some cases, we use them simultaneously and in other cases, they are applied in sequence. This is because some of these strategies take some time to be effective. Firstly, we rely quite heavily on naturally occurring predators for some of the lower level controls. They are free, after all, but they do have needs. As soon as the potatoes are hilled, we mulch the aisles quite heavily with straw (20-30 cms deep). This provides habitat for both the Spotted LadyBeetle (Coleomegilla maculata) and our other major predatory beetle, a beautiful bluecarabid (ground) beetle called Lebia grandis. We need to do this regardless of pest levels when the potatoes are hilled. This is because these predators need time to set up shop in your field, and if you wait until there are larvae munching merrily on your leaves, your predator armies will not be there in sufficient numbers to control the Colorados. So, this control strategy is employed simultaneously with some of the other lower-level strategies. It also helps conserve water and control weeds, so this is an important strategy for us to employ regardless of pest numbers.

 

Here is a useful resource for those of us who are entomologically challenged – a fabulous resource for those of us who can't tell a coccinellid (ladybug) from a chrysomelid (CPB). http://bugguide.net/node/view/15740

 

We use in-field monitoring all the time. We use it initially to see what is there and how many, and even where in the field they are (so we can do spot treatments). If we can find action thresholds (or establish them ourselves), we then use monitoring to see if we have passed the action threshold. Then we use it to see if our selected control method has resulted in control or if we have to move to the next strategy. All this sounds like a ton of work but, if we employ appropriate trapping/monitoring methods, it's not too bad.

 

For Colorados, we use mostly physical counts of adults on plants to determine our strategies initially. Our action threshold at this stage is 2 or more adults per 50 feet of row. We walk the rows twice a week starting about June 1, and when we reach our action threshold, we increase the frequency to once a day, every five rows. Of course, we destroy the adults we see, but there are always some that get away. Once there are egg masses found, we step it up to once a day, every other row. When the first instar (the teeny black and orange "worms" that come from the eggs) appear, we go to every row, once a day. When we get to third instars, it's twice a day until there are adults, when we fall back to every other row, once a day. When we see second-generation eggs, we again go to every row.

 

I can see those growers that grow large-scale shaking their heads about how can we possibly afford this intensity of monitoring, but we are small growers (less than one acre in spuds) with a lucrative market to be filled. We can sell our potatoes in the city for more than $2.00a pound, so our economics are different from the larger grower that wholesales most of his/her crop. One of the biggest secrets/strategies in doing your own on-farm research is to take other folks ideas and see how you can adapt/adopt them to your specific situation, so you have to tailor techniques for your own circumstances.

 

So you walk your field, doing physical counts to determine if your action thresholds are reached yet. So what about trapping.

 

There are two really basic ways of trapping to getting a feel for how many insects are in your field. There are pitfall traps and sticky traps. Which method you chose to use in the field depends upon how the insect moves in and out of your field. Pitfall traps are designed to get those who walk to work. They can be as simple as an empty plastic beer glass sunk in the row somewhere flush with the surface of the soil. Of course, this takes a bit of work to dig the cup in, so you are welcome to ensure that the glass is empty. If you are going to check the trap every day, put a bit of alcohol (ethanol is the best as methanol can kill any mammal like your dog or cat that might drink it). If you don't put in some alcohol, you may only find bits and pieces of the smallest insects trapped, and one very happy larger bug! If you are going to leave the trap in place for a few days without emptying, be sure to poke a small hole in the bottom so rainwater or irrigation will drain out. These are especially effective for many of the beetles, including one of our allies in the war on bugs, Carabid beetles. Everyone knows these; they are the black shiny beetles who, like all beetles, have hardened forewings (elytra) that cover the membranous hind wings. These guys are the tigers of the night in your vegetable garden; they come out of their daytime refuges and actively roam over the soil surface, looking for a midnight snack. There is one more really common beneficial bug that is commonly caught in these traps. These are another beetle, but belong to the family Staphylinidae, the rove beetles. Although these are classified as beetles, their elytra are small, and don't extend down the abdomen. They look a bit like earwigs, but without the little pincers (cerci) on their rear ends. Rove beetles are ravenous predators, eating all sorts of bugs and other terrestrial thingies (like Collembola, the springtails. Look them up inBugGuide!!). Another common critter caught in pitfall traps are spiders of various sizes, shapes and colours.

 

Another very common method of trapping in the field is to use sticky traps. These come in a variety of sizes and colours. and can either be used with a pheromone (a mating attractant) or a kairomone (another chemical that the insect reacts to). They can be attached to something like a stick to hold them in the crop canopy to trap flying insects, laid on the ground to trap walking insects (same idea as the pit trap), or used on the perimeter of the field. The various colours that you see are designed to be more attractive to one pest versus another. We use yellow traps here, amongst the cucurbits to both monitor and attempt to trap out Cucumber Beetles (AKA Wetern Corn Rootworm, Dibrotica), another Chrysomelid like the Colorado Potato Beetle. We also use white traps, also on sticks, to monitor for Fleabeetles and the blue ones are for thrips. Here in eastern North America, we are seeing more purple sticky traps, hung in trees, looking for Emerald Ash Borer (Agrilus planipennis), a Buprestid beetle that arrived here in 2002 on wood packaging from China. This highly invasive beetle has destroyed millions of ash trees and threatens billions more. The purple traps are an attempt to find the "invasion front" or where the beetle has just moved to. Interestingly, researchers are testing a very novel way of monitoring for this bug. Solitary wasps are encouraged to nest in the back of a pick-up truck. These wasps use EAB as a food source for their developing larvae, and if there are any in the area, these wasps will find them. Once the truck is parked in an area where EAB is suspected to be, in as short as one-half hour onsite, the wasps can return with EAB that they have captured, a quite unusual type of trapping indeed.

 

There are, of course, other types of traps that can be used for special purposes, such as suction traps for aphids and Lindgren Funnel traps used by foresters, but these are usually just for researchers.

 

So, now we have an idea of what traps are available, now we can think a bit about how to use them. Of course, we have already talked about using these traps to monitor bug numbers, (both good and bad), but they have other uses as well. Some of the most useful data we can get from a systematic trapping program is where exactly in the field these bugs are. That can mean vastly reduced application of control chemicals (if that becomes necessary) as we don't have to spray a whole field, only where the traps tell us the bugs are. They can also be used as a control method by themselves. I mentioned that we try to trap out Cucumber beetles with sticky traps, however, this is not usually successful. We can also determine where the bugs are coming from, both by monitoring the edges of fields, and by seeing which side of the trap has the most bugs on it.

 

Mike seems to be getting lonely, so I'm going to pitch in and keep him company. First, an idea for pitfall traps: because they're a pain to set just level with the soil surface (especially if you're using a lot of them), use double cups, one inside the other. When it's time to empty the trap, remove the inner cup and leave the outer one in place. Then all you have to do is slip the inner cup back in and...voila! It's right back at the correct depth.

 

Our best strategy to date for CPB control (on about 1/4 acre) is lightweight row cover (Agribon 15). This stuff is just an insect barrier, with no heat buildup inside. We lay it over the rows right after planting, weighting the edges down with scrap lumber and stones. Once the spuds are well up we pull the cover off, hill and mulch (with rained-on hay), then re-cover immediately. The potato plants lift the row cover as they grow, and really big plants will eventually lift the edges clear of the ground; but by that time the crop is made and some CPB damage doesn't affect yields.

 

Dave

 

I like the idea of the floating row cover but have a some concerns. When I was growing conventional spuds on the West Coast, our biggest facilitator of Late Blight was the heavy dews, which leave the leaves wet for long enough (I think its four hours) for blight spores to germinate. These can start as early as mid-July. Have you had any issues with late blight or do you take of the row cover after the first generation of CPBs?

 

So, as you may recall, I left off last time threatening to talk a bit more about traps, specifically barrier traps and trap crops. Well, brace yourself, 'cause here it comes. We used barrier traps on the West Coast to exclude Tuber Flea Beetles, a serious concern in that part of the world. In the 80's, when I was working out there, the chemical of choice for controlling flea beetles( Epitrix tuberis) was Temik (aka Aldicarb), a hugely toxic granular that was applied in the seed trench at planting. For those with a technical bent, the L.D. 50 was less than 1.00, making the most toxic pesticide commonly used in veggie production. It has also been implicated in the death of migrating waterfowl that may graze in the harvested fields in the winter. I worked with a guy who was looking for alternatives to Temik, and he found that a simple roll of one-foot wide poly, stapled vertically to posts and dug in about one inch would exclude a large percentage of flea beetles, and enabled him to harvest respectable yields of marketable potatoes without using any pesticide for Tuber Flea Beetles. I have also seen barrier traps for Cabbage Flies (Delia radicum). For CPB, we use a hybrid Pitfall/Barrier trap. The guy I was working for tested using PVC pipe as a perimeter trap. He set it in the ground, buried flush with the soil, and CPB, who walk to work, would fall in and not be able to climb out. It was quite effective, but when he did the costing, he assumed that he would be using 6" PVC irrigation pipe, cut in half, and that was the end of the project. It’s just too expensive. I have also seen photos of these trenches (quite wide (maybe two feet) lined with Poly, but that would take up too much room on our property. So, in the true spirit of on-farm experimentation, we did an experiment! We took a piece of 4" Big O drain pipe (like they bury when they "tile" a field for drainage), cut it in half and put a few CPB in it to see if they could climb out. Well, the first one took about 30 seconds to climb out; the second one took even less time! But, I remembered reading somewhere that the effectiveness of these traps increases if there is dirt in the bottom of the trap. It seems that the dirt clings to the claws (tarsi) of the CPB, and decreased their "grip". We put a bit of soil in the trap, and lo-and-behold, the next beetle couldn't climb out. Nor the one after that, nor even beetle #3.

 

We even took some MPGs of the whole thing! So, we till a two foot wide perimeter strip on the two sides facing last year's potato patch and set the half-pipe in the ground. This whole process takes about 2 hours for two people to "fence off" a quarter acre. Its important to keep anything from bridging the trap, at least until the first generation is finished, as CPB are not averse to walking across on a blade of grass or an appropriately-placed weed stalk. You don't have to be overly concerned after about July 1st (here anyway) as the CPB are pretty much finished large scale inter-plot migration by then.

 

There is one more special type of trap we have yet to talk about. This is a living trap, AKA a trap crop! For conventional growers, this is usually a small portion of your land that is devoted to planting something that your pest of concern really likes, and dosing the heck out of it with something really toxic, so that the bugs are drawn to the trap crop, and are controlled (for the most part) by the pesticide. The crop itself will never be harvested, but it has saved the other crops from infestation, so has earned its keep. Organic guys can't use those toxic pesticides, so use living traps in a couple of ways. We use French marigolds (Tagetes spp.) to repel aphids, Nasturtiums to attract aphids away from our crops, and Rapini as a trap crop for Cabbage Butterfly (Pieris rapae), as they LOVE it!! Our single most effective control measure for CPB works on a different principle. It’s called a "dead end" crop. This is a crop that the pest cannot complete its life cycle on. In our case, we do exactly what you are not supposed to do. We plant potatoes right where our last year's crop was. The CPB think this is great. They don't have to walk more than 50 feet to get to a new place to raise the kids! But, there is no free lunch, and once the Colorados have laid their eggs and died, we destroy the crop, usually around the First of July, long before any eggs that have hatched can grow into mature second-generation (overwintering) adults. And, here is the genius, we dig up the "creamer potatoes" that have formed under the sacrificial vines, and sell them to eager buyers at a $2.00/lb. premium!!

So, that is how we cope with Colorados. It's crucial to remember that there is no silver bullet. Its death by paper cuts.

 

Mike B Lotusland Farm Ormond ON