Potato, like many of the root crops, becomes a quick meal for the wireworm. Untreated this can devastate the farmer’s cash crop in just a few weeks. They often go unnoticed for the most part unless of course your occupation or livelihood comes from crop production then they become one of your well-noted enemies. Potatoes will be the focus plant for this topic on wireworms giving examples of the breeding conditions, prevention of wireworm, and destructiveness.
Wireworm Biology
There are many different species of the wireworm that have similar traits to one another. As larvae, they spend most of their lives in the soil around the roots of plants or in our discussion the potatoes. Spending three to six years in the ground before maturing. Typically the most common wireworm found is reddish-brown in color. There is three pair of legs directly behind their tail segment that is notched. Their average length from one to two inches. They have a tough outer exterior much like armor.
Adult Stage – Click Beetle
Matured wireworm known as click beetles overwinters in the soil emerging in early spring to lay eggs. The click beetle lays eggs in the early spring on the surface of the ground or to the depth of fifteen centimeters or six inches deep in the soil profile. They lay two hundred to four hundred eggs per beetle. The larvae hatch within three to seven weeks. This starts their lifecycle of feeding on roots and germinating seeds.
Click Beetles inherited their name from their ability to flex their abdomen rapidly popping them up in the air several inches as a defensive mechanism or to upright themselves. In the adult stage of their lives, they do not damage crops.
Wireworm Habitat
Soil Conditions: Silty medium-textured well-drained soils are a perfect dwelling. When soils are fallow for extended periods of time breaking open the soil encourages rapid infestations. Heavily tilled soils (plowing) push organic matter down into the soil profile or in the case of a plow flips it under, and increased decomposition brings the wireworm closer to the surface during warmer periods in the weather. Compacted dry soils tend to be more difficult, and they move to a more habitable land.
Temperatures: While temperatures affect the wireworm they will move up and down in the soil profile depending on the ground temperatures allowing them to survive in extreme conditions along with dry or heavily saturated soils.
Moisture: In warmer weather with heavily saturated soils the wireworm will move to the surface usually the top 2-3 centimeters or one to two inches of the ground. With the lack of moisture and higher temperatures, they will migrate slightly deeper in the soil profile.
Vegetation: This significantly impacts the presence of wireworm. Having exposed soils over winter without vegetation will drive them deeper and in some cases kill off some of them. Unworked or heavy sod lands tend to have higher populations of wireworm unlike fields with crop rotation.
New Field Inspection for Wireworm
Before selecting a location for the production of potatoes determining the presence of wireworms is mandatory for successful crop production before planting. Keeping in mind wireworms are not selective as to whether this will be large-scale crop production or a garden.
The "Gawking"
My first step in determining the presence of wireworm I like to call this the “gawking” technique. By this, I like to study the surroundings, vegetation, and bordering crop fields. Several types of grass will encourage or promote the lifecycle of the click beetle. Gathering the information on the weeds or grasses growing in this area will help you determine their presence.
The boundaries of the fields or nearby fields also can indicate problems. As an example, a nearby field with mustard, rye, or crops that have natural toxins that affect the presence of wireworms can force them to migrate into your selected area. Utilizing a drone to get a quality overview of the fields, boundaries, and surroundings is a beneficial tool for this part of the research.
The "Gravedigger"
My favorite part of the process of choosing a site. I call this the “gravedigger” technique. Much like the pesky moles we see invading our yards, digging small holes in various spots throughout the location we are picking is the next step of our process.
Digging test holes is very important as it gives us a vast amount of data for our decision. Your test holes dug to a depth of one meter or thirty-six inches. Pick several areas in the field to give you a good idea of the soil profile in the top meter and should the wireworm be present there you will find them. Make certain after digging the ground up you inspect the tailing pile for their presence.
This type of inspection gives valuable information from soil type, layering, compaction, and the presence of rocks. At this stage, I strongly recommend you take soil samples of the areas for a more in-depth analysis of your soil.
The "Historian"
Gathering this information educates you on possible wireworm problems. Some of the information I will collect, the past tillage practices, crop production, problematics field zones, areas of flooding or poor drainage, and time the field has been fallow or in use.
Tillage practices will indicate some of the problems that may exist for compaction. Again tillage becomes a factor to consider when researching for wireworm presence or future problems.
Crop rotation is another aid in determining the presence of wireworm. Having a complete history of crop rotation and crop production gives indicators of past or foreseeable problems.
Pay close attention to the field zones that look to have possible swamps or poor drainage areas. On the edges of these areas you may find a high presence of wireworms.
Talk with nearby farmers and neighbors about the location. Discussing the history of the site with them often gives insight that may be hard to discover in your research.
Making a quick decision for your location to plant potatoes can result in low yields, poor plant health, fungus, disease, and massive financial losses. It is a great idea to set wireworm traps throughout various locations in the field. There are several ways to set traps and types of traps with different products for drawing the wireworm. Also commonly called bait traps.
Flour Bait Traps
One of the common techniques used in discovering wireworms in the field is known as the flour trap. Flour traps will attract wireworm and millipedes. Throughout the field including areas, you noted that were possible infested areas from your earlier inspection dig holes fifteen cm or six inches wide and deep. Add one cup of all-purpose flour to the bottom of the hole, fill the hole back up with soil, mound the soil slightly higher than the soil surface to avoid filling with water during heavy rain.
Do this with the soil temperature above 10 Celsius. This will help ensure the wireworms are active in the upper part of the soil profile. Avoid doing this procedure in very dry spots on the field. After five days dig up the soil and take count of the wireworms. More than one indicates there is a potential threat of wireworm infestation.
Identifying Wireworm Damage in Potatoes
Completion of tillage and planting within a few days dig the seedlings up and inspect for damage. During seed germination, severely infested fields finding seedlings turned into mush is common to see. At this stage, there is no treatment available that will correct the damage that has occurred. We will discuss preventative measures further along in this blog.
Once you have noticed the damage the wireworm has inflicted on the potatoes it is too late for any treatment saving the crop. Now I have heard of products that may be applied afterward, but most likely the damage to the appearance of the potato has been done, the buyers will not accept them.
We will review various options we can take for prevention of the wireworm.
Preventative Measures
There are several natural and chemical actions we can take against wireworm infestation. As farmers, our responsibility to the environment, soil erosion, and quality of food for the consumer is always best practice to find natural ways to prevent wireworm infestation. As a last resort, we may need to take alternative measures and utilize chemical products suited for this prevention with maximum impact on the insect and minimum effects on our environment.
There are various techniques available for natural ways to handle the wireworm. The natural products or ways tend to take some time and have a higher risk at the beginning of the potatoes being attacked by the wireworm. Plan accordingly depending on your economic outlook.
Crop Rotation
Crop rotation has multiple benefits on top of handling wireworm infestations. We will focus on the benefits for wireworm. When your main production crop is potatoes it is a good idea to rotate the fields out of potato production for three-year intervals. During the seasons' potatoes are not planted; some good cash crops like rye or mustard act as natural toxins to the wireworm. When doing this wireworm will migrate away from these fields while killing some of them.
Intercropping
It’s interesting to know that intercropping has its benefits in natural ways to ward off wireworm. Using natural toxic plants to wireworm make this an unfavorable site for the wireworm. Intercropping adds some challenges during harvest but if managed properly can become an excellent choice for this type of management for infestations and potential added income.
Tillage
Field preparation and tillage is an important part of the process in combating wireworm. Allowing the fields to be overgrown with grasses creates nursery conditions for the click beetle egg laying period. In any soil tillage practice, it is critical to make the correct selection of the best way to handle the soils.
Organic Insecticides
There are several products that are natural insecticides that can be utilized. Most are for a pre-emergence application and can be worked into the top few inches of the soil. Most of them will kill 100% of the insects and should be handled with care. Although this is an organic natural insecticide we must be cautious to make certain this will not impact our beneficial bacteria.
Conclusion
Wireworms can cause serious damage to crops including potatoes. It is always best practice to take preventative measures before finding an infestation.
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