Maggots and armyworms

It is that time of year when I hear about maggots and armyworms in field crops. At least that means people are out there looking for insects! I don't always get great photos of the insect activity or injury, but this week is the exception. Keep 'em coming, everyone!

Brian Lang, ISU Field Agronomist in northeast Iowa, has already found a soybean aphid (actually he almost always finds the first ones every year) AND he found a few prevent plant fields with seed corn maggot in soybean. He seemed to notice more plant feeding in fields that were planted to oats last year compared to radish. He also noted it was a field with mostly naked soybean seed (no insecticidal seed treatment).

Seedcorn maggot and pupae at the base of an emerging soybean plant. Photos by Brian Lang, ISU. 

Tom Hillyer, a crop consultant in Iowa, always sends me interesting photos. He manages to stump me on a regular basis with insect identification. But his recent photos included some developed armyworms feeding on corn. He also found a few bean leaf beetle on soybean despite my earlier prediction for high mortality this year. 

Yellowstriped armyworm. Photo by Tom Hillyer.

Armyworm. Photo by Tom Hillyer.

Bean leaf beetle. Photo by Tom Hillyer. 

Did this winter kill all the corn rootworm eggs?

Insect mortality happens every winter, even under ideal conditions. However, this winter was the 9th coldest in 121 years and I’ve been getting questions about how the harsh conditions may have impacted overwintering corn rootworm eggs. Maybe we don’t need to care rootworms this year if all the eggs froze to death? We’re probably not so lucky. Many factors besides cold air temperatures influence successful overwintering of insects in Iowa, including our most important field crop pest.

Cold temperatures can kill rootworm eggs; temperatures below 18.5°F can be lethal to eggs (Woodson and Gustin 1993). We know the eggs are deposited into soil cracks and crevices and are somewhat protected to air temperatures. Mike Gray (University of Illinois) provided a nice blog summary of research involving soil temperatures, egg depth and survivorship. To see how cold it really was this winter, I was able to extract a graph showing soil temperatures at three depths near Ames (1 November 2013 – 1 May 2014). There were several dates where the temperature was cold enough to kill eggs in the top 12ʺ of the soil in central Iowa and likely other places throughout the state. 

Soil temperature data courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.

Egg deposition is highly variable within and between species, but in general eggs have a better chance of surviving if they are placed deeper in the soil. Western corn rootworms tend to lay most eggs 4-8ʺ below the soil surface, compared to northern corn rootworms that tend to lay most eggs in the top 4ʺ (Gray and Tollefson 1988). So the odds are in favor of more westerns surviving the winter just because of where females put the eggs.

Crop residue and snow cover can significantly improve egg survivorship (Godfrey et al. 1995). However, just how much residue/snow cover is needed is not fully understood. Tillage and tillage timing does not significantly reduce egg populations (Gray and Tollefson 1988). Soil texture did not appear to influence egg mortality in a Nebraska study (Godfrey et al. 1995).

Saturated soils do not kill corn rootworm eggs, but they can negatively impact larvae. When soil is saturated, oxygen can be limited and cause suffocation. About 50% of third instar western corn rootworm larvae die in saturated soils after 24 hours (77°F); survivorship is increased in saturated soil with decreasing temperatures (Hoback et al. 2002). So later this summer, saturated soils could reduce larval populations but don’t count on it for eggs.

The bottom line is all these factors had some impact on overwintering egg mortality. There was probably more egg death this winter compared to more normal winter temperatures. I do think some corn rootworm eggs survived in Iowa. In a recent ICM News article, I estimated corn rootworm egg hatch is happening now if they survived. This prediction is solely based on growing degree days in the soil. Research has demonstrated about 50% of the eggs hatch when they accumulate 684-767 degrees (base 52°F, soil). It makes sense that egg hatch starts in southern Iowa every year, with the average hatching date for the state around 6 June. Predicted egg hatch is important because larvae will feed on corn roots for about 3 weeks. I encourage everyone to assess corn root injury as larvae finish feeding. Remember, one node of injured roots means a 15% yield loss (Tinsley et al. 2012). It's called the billion dollar pest for a reason!

Map data courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.

References

Godfrey, L.D., L.J. Meinke, R.J. Wright, and G.L. Hein. 1995. Environmental and edaphic effects on western corn rootworm overwintering egg survival. Journal of Economic Entomology 88: 1445-1454.

Gray, M.E., and J.J. Tollefson. 1988. Influence of tillage systems on egg populations of western and northern corn rootworms. Journal of the Kansas Entomological Society 61: 186-194.

Hoback, W.W., T.L. Clark, L.J. Meinke, L.G. Higley, and J.M. Scalzitti. 2002. Immersion survival differs among three Diabrotica species. Entomologia Experimentalis et Applicata 105: 29-34.

Tinsley, N.A., R.E. Estes, and M.E. Gray. 2012. Validation of a nested error component model to estimate damage caused by corn rootworm larvae. Journal of Applied Entomology 137: 161-169.

Woodson, W.D., and R.D. Gustin. 1993. Low temperature effects on hatch of western corn rootworm eggs. Journal of the Kansas Entomological Society 66: 104-107.

Where are corn rootworm eggs right now?

I am "all done" with winter and I'm probably not alone. I'm looking forward to buds bursting, better vegetables and sandals. Insect-related questions coming my way have all been focused on cold winter temperatures that could be killing pests. The main pests of concern are corn rootworms (really, what else is there to talk about in Iowa?). I had to do a little digging in old literature, but found some interesting research on survivorship of corn rootworm eggs (the overwintering life stage).

Western corn rootworm eggs. Photo by Purdue Extension.

In lab tests, Gustin (1981) showed significant egg mortality at soil depths of 3-6 inches with four constant weeks at -7.5 degrees. But I wonder how often those harsh temperatures might happen in the field? Is that where the majority of eggs are even deposited? And even if those temperatures and depths are realistic, rootworms have survived over 50 years in Iowa and must be relatively cold hardy.

One method for measuring "how cold does it have to be before it kills rootworm eggs" is finding the supercooling point. The supercooling point is defined as the process of lowering the body temperature below its freezing point without becoming solid. I briefly talked about how insects might do this in a previous article. This lower lethal temperature would be species specific. Western and northern corn rootworm both had a supercooling point of -27 degrees, but most eggs did not hatch if they experience -21.5 degrees (Ellsbury and Lee 2004).

Gray and Tollefson (1988) examined the differences of four tillage regimes and corn rootworm egg mortality. In the end, egg density wasn't different in fields that experienced no-till, chisel plowing or moldboard plowing. The timing of cultivation (fall or spring) did not matter either. They also looked at egg deposition, or how deep females might be laying eggs. There was a surprising difference between northern corn rootworm and western corn rootworm. Northern corn rootworm eggs tend to be located closer to the soil surface, while over a third of western corn rootworm eggs were found in the lower 4 inches of the soil.  Insects that overwinter deeper in the soil may be further insulated from cold air temperatures. 

Some other things that influence corn rootworm egg (and all other soil-dwelling insects) survivorship over the winter include plant residue, snow cover, and soil moisture (Godfrey et al. 1995). Northern corn rootworm tend to handle dry conditions better than the westerns (Ellsbury and Lee 2004).

High residue in cornfields can protect soil-dwelling insects from extreme cold temperatures. Photo by Lori Abendroth, Iowa State University. 

The bottom line is this cold winter probably had a negative impact on corn rootworm eggs. I expect there to be higher egg mortality compared to normal winter temperatures. But egg survival is increased if they are deeper in the soil and if the field had snow cover and residue. Egg sampling is difficult and tedious, and not recommended. But I still encourage root injury assessments this summer; that will be the true test of egg mortality in corn. 

References:

Ellsbury, M. M. and R. E. Lee Jr. 2004. Supercooling and cold hardiness in eggs of western and northern corn rootworms. Entomologia Experimentalis et Applicata 111: 159-163. 

Godfrey, L. D., L. J. Meinke, R. J. Wright, and G. L. Hein. 1995. Environmental adn edaphic effects on the western corn rootworm overwintering egg survival. Journal of Economic Entomology 88: 1445-1454.

Gray, M. E. and J. J. Tollefson. 1988. Influence of tillage systems on egg populations of western and northern corn rootworms. Journal of the Kansas Entomological Society 61: 186-194.

Gustin, R. D. 1981. Soil temperature environment of overwintering western corn rootworm eggs. Environmental Entomology 10: 483-487.

Learn more about corn rootworm

For those of you who want to understand more about corn rootworm, I encourage you to view a webinar happening later this month. I was lucky enough to be a co-investigator on an educational grant from the USDA-NIFA North Central IPM Program. We gathered entomologists that focus on corn rootworm from land grant universities. Here is what the the speaker lineup looks like:

• Rootworm biology and behavior, Dr. Joe Spencer, Illinois Natural History Survey
• Resistance evolution and IRM for rootworm, Dr. Aaron Gassmann, Iowa State University
• Adult management options, Dr. Lance Meinke, University of Nebraska-Lincoln
• Larval management options, Dr. Bob Wright, University of Nebraska-Lincoln
• Decision tree for growers management options, Dr. Ken Ostlie, University of Minnesota

This FREE webinar will be on February 20, 2014 at 1pm (CST) and end at 2:30pm. You can join from anywhere you have a computer/tablet, internet and speakers. Start connecting to the session about five minutes before 1pm. Use this URL link to enter the meeting, or copy and paste this link:

https://connect.unl.edu/r9ra3734mey/

Once connected, you will find a login page. You can enter your name, business, etc. and click "enter room." At this point you should be able to make any sound adjustments. You may want to test your computer before February 20 by using this URL link, or copy and paste this link:

http://www.extension.iastate.edu/testconnect/

Please spread the word about this webinar to your family, friends, clients or co-workers. We don't often get the "big dogs" all in one place, so this is a unique opportunity to hear from the experts. This is the most important corn pest in Iowa right now, and it is important to be proactive in rootworm management.

Learn more about rootworms right from work or home!

Learn how to identify Japanese beetle females

Recently, I had a crop consultant ask me to verify his male/female specimens of Japanese beetle. He squished them to look for eggs (which is highly diagnostic of a female!). I thought there might be an easier and less messy way to determine the sex. But after spending some time online and reading through my textbooks, I only found a few external characteristics that were different. I was somewhat disappointed because sometimes beetles have drastically body features. When males and females of the same species look different - that is called sexual dimorphism.

Western hercules beetles on ash; note male horn on top and size difference. Photo by Alex Wild. 

Depending on how good your eyesight is, you will be able to tell male from female Japanese beetle. Look at the first pair of legs and focus on the tibia. The tibia is the late large segment before the tarsus, or "feet." You may need a hand lens to see the tibia. The male will have spikes on the tibia and the female will have more spoon-like paddles. 

Male Japanese beetle. Photo by Tom Hillyer. 

Female Japanese beetle. Photo by Tom Hillyer. 

Or just use the squish test to look for eggs in female Japanese beetle. Photo by Tom Hillyer. 

For more information (with drawings), visit these websites: University of Tennessee Extension and NAPPFAST. 

Thinking about treating corn rootworm adults? Read this first.

Adult corn rootworm emergence is in full swing all around Iowa. Actually seeing adults is a good reminder to assess for larval injury before too much root regrowth obscures feeding. Questions about adult management are popping up from ISU field agronomists, crop consultants, and farmers. My answer is not automatic - it really depends on the field history and ultimate goal for long-term production. Ask yourself:

#1. Are adults interfering with pollination? Adults aren't considered an economically important life stage unless they clip silks and prevent pollination. The late planting of many fields this year is coinciding with adult emergence. Silk feeding is certainly happening around Iowa. They are strongly attracted to green silks and will "chase" silks in neighboring fields. Target late-planted or late-maturing hybrids for your scouting efforts. After pollination is complete, they will feed on corn leaves, but that is considered minimal.

Consider a foliar treatment if: 5 or more beetles per ear AND silks have been clipped to less than 1/2 inch AND pollination is not complete. The threshold of 5 beetles is for drought-stressed corn; the threshold can be increased to 15 beetles per ear for fields with adequate moisture. Also keep in mind other silk feeders that may interfering with pollination (e.g., Japanese beetle, corn earworm, etc.).

Corn rootworm prefer to eat corn silks. Photo by John Obermeyer, Purdue University Extension. 

#2. Is pollination complete? If the goal is try and reduce the egg deposition and potential larval damage the next season, then my response gets a little more complicated. First determine if action should be taken by estimating adult density. If scouting reveals 1-2 beetles per plant in continuous corn, it is recommended to take some sort of action; see the table below for more specific numbers. Taking action means targeting adults this year or larvae at planting the following year.

To try and do an effective job of adult control requires an intense scouting effort and well-timed foliar treatments. We must understand adult emergence in order to apply insecticides to gravid females (mated and mature eggs). Plan for at least two applications, about 7-10 days apart.

To estimate more specifically, a biofix is established and is defined as the first adult found in that field. After reaching the biofix, emergence of the remaining population is based on accumulating air temperature (i.e., degree days). Calculating accumulating degree days is easy = [(max daily temp + min daily temp)/2]- 53 (lower developmental threshold). So for example, if the maximum temp for the day was 95 and the minimum temp was 50, the calculation would look like this: [(95 + 50)/2] - 53 = 19.5.

To answer how long adults will emerge depends on the temperatures following the biofix. Warmer days will mean adults emerge faster. It could happen in three weeks or be extended to five weeks during a cooler summer. ISU entomologists studied how long it takes for adult corn rootworm to emerge and in general: males emerge first and westerns develop faster than northerns. Here is a table that more specifically summarizes emergence based on degree days following the biofix:

#3. How do you know when females are gravid? Again, targeting applications to gravid females is critical. But first you have to distinguish the males from the females. Females are typically larger and have three distinct, black lines on the forewings. Males have a smudgy, black marking on the forewings. See if you can spot the male in the photo above. Gravid females will have swollen abdomens that extend past the end of the forewings. Or consider a looking for mature eggs by expressing them from the abdomen. 

Use the "squish" test to look for mature eggs. Photo by Purdue University Extension. 

#4. What are the long-term management goals? If larval root injury is evident and adults are abundant, that should be concerning no matter what management strategy (or strategies) is implemented. Larval root pruning will reduce yield and make plants unstable. I strongly encourage diversifying management to avoid increasing activity during the next growing season. Plus, resistance to Cry3Bb1 and mCry3A is confirmed in Iowa and is a real threat to Iowa's corn production. We need to be more strategic on how we use this technology in order to prolong the efficacy.

Crop rotation is the single, most effective suppression tool. Corn rootworm larvae will not eat soybean (or other non-corn hosts), and starvation is eminent. I've summarized other management ideas in a publication with ISU corn entomologist Aaron Gassmann - read it and pass it on!

Sorry so long, but this is a complicated topic. Hope it helps, Erin

Corn silk feeders are worth scouting right now

I saw my first corn tassels of the season and it got me thinking about silk feeders out and about now. But then again, I saw some corn that was only 18 inches tall and looked a long way from tasseling. It's been a crazy summer!

Of course many of you are noticing Japanese beetles flying around (and maybe hitting your windshields) this week. They are definitely attracted to green silks and can interfere with pollination. Japanese beetles mate and feed in groups. It is not uncommon to see them aggregated on plants, especially along the edge rows. They are highly migratory and are constantly moving around the landscape. Adults have a wide host range (>300 plants) and are likely to find something they like to eat.

There has been a lot of marketing about controlling Japanese beetles this year. I don't think it is wise to treat for adults BEFORE tasseling. I have preliminary research that shows foliar insecticides do not have a long residual, regardless of the chemistry. Most broad spectrum insecticides will kill adults if the droplets make contact on the body. That application won't have a 7-day residual for immigrating beetles.

But if beetles are actively feeding when silks are present, determine densities to make smart treatment decisions. Consider an insecticide if: 3 or more beetles per ear AND silks have been clipped to less than an inch AND pollination is not complete. Again, do not expect a long residual with any product, so continue to scout until pollination is over. If a second spray is warranted, alternate chemistries to reduce the chance of developing resistance.

The tricky part of managing this pest is if you have sweet corn that may have staggered planting dates or late-maturing hybrids. This summer is a good example of field corn at various growth stages, too. Be aware beetles will continue to move to green silks throughout the summer.

Japanese beetles at the ISU Johnson Research Farm in 2012. 

The second most common type of silk feeder is adult corn rootworm. Emergence has started in southern Iowa and it won't be too long before we see them all over the state. Like Japanese beetle, they are strongly attracted to green silks and like to feed and mate in masses. Silk feeding can interfere with pollination, so it is important to scout during this period to ensure kernel formation later this summer. Consider an insecticide if: 5 or more beetles per ear AND silks have been clipped to less than an inch AND pollination is not complete. The threshold can be bumped up to 15 per plant if the field is under adequate moisture conditions.

Adult corn rootworm can clip silks. Photo by John Obermeyer, Purdue University.

Grasshopper nymphs and adults can also occasionally eat corn silks. They are usually found around field borders first and then can infest the field interior later in the summer. Since grasshoppers are so mobile, it is very difficult to try and estimate densities. So as with the Japanese beetle and corn rootworm, it is important to watch for silk clipping and take action if they are interfering with pollination. Because grasshoppers tend to move short distances and attack border rows first, a border treatment may be a cost effective decision. 

The differential grasshopper is common in Iowa field crops. Photo by David Cappaert, www.ipmimages.org.

The fourth potential corn silk feeder in Iowa is the corn earworm. The larvae have highly variable body color, ranging from yellow, to green or orange, or brown and even purple. There are alternating dark and light stripes running the length of the body. Larvae have a textured appearance, with many spines coming out of small bumps. This is unlike black cutworm or fall armyworm that have smooth bodies. 

Female moths deposit eggs on green silks during the night. First instars will feed on silks and eventually move down inside the tip of the ear. Older larvae will destroy developing kernels. Since trying to kill the larvae once inside the ear is almost impossible, I recommend monitoring adults. The University of Illinois has a nice website that summarizes how to properly time a foliar treatment for corn earworm, depending on the type of corn grown. 

Corn earworm larvae can feed on silks before they enter the ear to feed on kernels. Photo by Frank Peairs, www.ipmimages.org.

Corn rootworm larvae are hungry

Today, I put out an ICM News article on predicted corn rootworm egg hatch in Iowa. It has a map of the soil  degree day accumulation for the year. Entomologists can predict most insect development based on temperature and we estimate about 50% of corn rootworm eggs should hatch between 684-767 soil degree days (base 52F). The Muscatine area is approaching that important benchmark and many other areas in southern Iowa will in the next week. If we continue to have warm days, expect all insect development to speed up quickly.

Soil degree day accumulation as of 14 June 2013. 

This egg hatch prediction is behind the average date of 6 June and way behind numbers for 2012. People that track egg hatch in Indiana and Illinois also reported delayed egg hatch, due in part to the extreme drought in 2012. Mike Gray, Illinois extension entomologist, said sometimes females will lay eggs deeper into the soil profile in drought conditions. The delayed corn planting throughout much of Iowa means larvae will have a smaller root system to feed on and potentially damage. I've also had people ask me about saturated soils killing rootworms this year. It is possible to suffocate the larvae, but the eggs probably survived water-logged soil. 

I encourage all you scouts and farmers to check your corn roots mid July to assess any corn rootworm injury. It will help determine the ongoing strategies for this unruly beast. Unexpected corn rootworm is possible with all Bt traits in continuous corn production. To read more about corn rootworm management, read this short ISU publication Aaron Gassmann and I wrote over the winter. 

Aphids in corn?!

I saw something new for the first time today - aphids on V4 corn. Actually, my summer crew found them while scouting for early-season pest activity in a small plot trial at the ISU Johnson Farm just south of Ames, Iowa. Nice job scouting today - way to go!

Meet part of the 2013 crew. I hope to post something just about our lab personnel soon. 

This find is exceptional for three reasons. First, Iowa corn doesn't always get infested with grain aphids. The overwintering potential in Iowa isn't fully understood, but most people think they have to migrate here from the southern U.S. every year (kinda like potato leafhopper and many other insects). So it can be hit or miss if they land here and establish at all. But grain aphids would rather live on small grains, like wheat sorghum, barely, oats, rye, etc. However, some of these aphids will feed on corn and have been known to build up to extremely high populations after tasseling. There was an corn aphid outbreak in much of northern Iowa in 2011. But finding them in mid-June is very interesting (to an entomologist!).

The second curious part of finding aphids in corn this early is that all conventional corn contains an insecticidal seed treatment. My general thinking is aphids shouldn't like to feed on that or stick around long enough to produce nymphs. But it wasn't hard to find alates (winged adults) and nymphs in this small plot trial.

While looking for cutworms and stalk borers, we found aphids instead!

Alates and first instars were easy to find on V4 corn today. 

 The alate was gone, but left behind at least four nymphs on this plant. 

The third thing that was surprising is I identified them as English grain aphids. Of the many species we can potentially find in Iowa, the two most common species are corn leaf aphid and bird cherry oat aphid. English grains aphids are a little larger than either of them, but not as big as a pea aphid. Adults have dark cornicles (tailpipes on the sides of the abdomen), "knees," and "feet" with a pale cauda (little appendage at the very tip of the abdomen). This species does not alternate between a primary, woody host and secondary perennial host (like with soybean aphid). It is capable of vectoring barley yellow dwarf virus in small grains. It can overwintering on true grasses within the Poaceae family. 

English grain aphid, note the dark knees and feet. Photo by Rothamsted Insect Survey.

I should note we didn't see large colonies on any plant. The alates are migrating to these plots and dropping off a few nymphs. We don't know if they will survive or succumb to the insecticidal seed treatment. Of course we are monitoring these plots weekly and I will post an update if they survive. But in general it means that aphids are around in central Iowa. If colonies persist and are allowed to develop over the growing season, it could be significant feeding that results in yield loss. 

Live brown marmorated stink bugs in Iowa

The first specimen of brown marmorated stink bug (BMSB)  in Iowa was confirmed last February in Cedar Rapids. Since then, several other dead BMSB have been confirmed by our ISU Insect Diagnostician, Laura Jesse. Recently, there have been some live detections near Davenport and Bettendorf, Iowa.

Brown marmorated stink bugs have a marbled coloration, and white-banded antennae. Photo by Laura Jesse, ISU. 

These stink bugs are established along the east coast for about a decade. They have been migrating westward in the U.S. When they invade a new area, they are typically considered an urban pest. They attempt to overwinter in human structures similar to boxelder bugs and multicolored Asian lady beetle. But they eventually become a pest of fruit and field crops. Adults and nymphs will probe fruit and leaves, causing necrotic spots. BMSB feeding can severely deform soybean, and cause "stay green" along soybean field edges. 

Stink bug feeding during the seed fill stage can cause deformation, shrinkage and discoloration in soybean. Photo by Galen Dively, University of Maryland. 

At this time, we don't know if BMSB is established in Iowa, or if a few individuals have hitchhiked here. If you suspect BMSB around your home or buildings, submit samples to the ISU Plant and Insect Diagnostic Clinic. Instructions for submitting samples can be found here.

Harvest begins!

In 2012, we worked at several ISU Research Farms, including: Northwest, Northeast, Southeast, Southwest, and Johnson Farms. We were working mostly in soybean but also had several corn trials this year. Plots are drying down quickly and we are preparing for the last step in our summer research - harvest! Usually it goes pretty slow for us because we have to stop often to weigh grain in every plot. Some of the farms have automatic scales on the combine - otherwise we have to weigh grain by hand. 

2012 Insect Field Clinic a success

Yesterday, I hosted an all-day clinic for insects at FEEL just west of Ames. I don't think there has been an ISU insect-focused field day in over 15 years. I planned a combination of inside and outside presentations and some hands-on demonstrations. There were even 3 guys from Hawaii attending the meeting! I thought you might like to see some photos of the clinic.

Bob Wright, Professor of Entomology at the University of Nebraska-Lincoln, came out and helped with a few of the classes. Photo by Adam Sission, ISU IPM Program.

We reviewed identification and management of common corn and soybean pests. Much of the conversation was around corn rootworm. Photo by Adam Sission, ISU IPM Program.

Everyone got a chance to use Bt tissue testing kits for corn rootworm. These tests are an important first step when visiting potential problem fields in Iowa.  Photo by Adam Sission, ISU IPM Program.

The guys from Hawaii really enjoyed their trip to Iowa. They learned a lot about intensive row crop agriculture!  Photo by Adam Sission, ISU IPM Program.

Finding an orange bug in corn?

This week, I had a couple of questions about "orange bugs in corn." I scoured through my reference materials and also on the web. I didn't see anything that quite matched up to the descriptions over the phone. But someone actually sent a picture to me and that really helped. It was none other than the very common boxelder bug! Donald Lewis, ISU Horticulture Entomologist, recently reported exceptionally high numbers of boxelder bugs in Iowa this year. Our warm winter and spring was ideal for boxelder bugs to survive and then boom in numbers.

Boxelder bug adult. Note the red-orange wing margins and red eyes. Photo by Joseph Berger, www.ipmimages.org.

Most people can easily recognize boxelder bug adults in urban areas, particularly on maple and ash trees. But the nymphs are bright orange or red, and can be confused with other insects.

 

Boxelder bug nymphs sort of look like big, red aphids. Eventually the nymphs will develop dark wing pads. Photo by Whitney Cranshaw, www.ipmimages.org.

Boxelder bug nymphs and adults prefer to feed on boxelder seed pods, but they have been found on many different plants this year. They rarely damage ornamental trees and are not a concern to field crops. Sometimes the adults can become nuisance pests in the fall when they try to overwinter in human structures. I suspect they will be an issue this fall based on our summer numbers.

 Here is a mixture of boxelder bug life stages. Photo by William M. Ciesla, Forest Health Management, www.ipmimages.org.

Finding mites or something else in soybean?

This month, I've really stressed the importance of scouting for spider mites in corn and soybean. Some farmers have starting treating both crops for field-wide infestations. Many people don't have a lot of practice looking for this tiny pest (does 1988 ring a bell?). But with a little practice, most people can easily recognize these little specks moving on leaves, especially if accompanied by webbing and leaf discoloration. A hand lens may be required to see the eggs, nymphs and adults if your vision isn't great.

As more people are actually looking for tiny pests, they are noticing other things moving around at the same time. I've had LOTS of questions about these "long, fast moving insects" on soybean leaves in combination with spider mites. I am fairly certain people are seeing thrips [side note: thrips is singular and plural, kinda like moose]. They are fairly common to see every year, with soybean thrips the main species in Iowa. We have predatory thrips and other plant-feeding species here, too. I can try to point out body descriptions to distinguish the two pests.

Mites would be smaller (less than a millimeter or 1/20 inch) than thrips and round. They are light brown in color with two dark spots on the body. Mites are arachnids and are wingless as adults. Mites live in colonies and will produce a dirty webbing on the underside of leaves. In hot temperatures, spider mites can produce >15 overlapping generations each summer. See a previous ICM News article for management recommendations.

  Adult twospotted spider mites have 8 legs and two dark spots on the body. Photo by Frank Peairs, Colorado State University.

Thrips are cigar-shaped insects, ranging from 1-5 millimeters long (up to 1/5 inch). They are varible in color, including dark or light brown, orange and translucent. Adults can have small, fringed wings. Thrips' have unique mouthparts; they rasp (stab) and puncture plant cells then suck up the sap. Thrips can produce 3-4 generations per year. They can be found anywhere on the plant but don't usually form colonies, and are very fast-moving insects. Thrips rarely cause economic damage in Iowa, but their feeding damage can be more noticeable in drought-stressed fields. Consider a foliar insecticide if 75% of leaves show discoloration and there is an average of 8 thrips per leaf. See Purdue University's website for more info.

Soybean thrips adult and nymphs. Photo by John Obermeyer, Purdue University.

Is your "spider sense" tingling for mites this year?

Do things seem a little too quite in your fields this summer? Maybe you've been out looking for plant pests, but haven't seen any major activity? I would strongly encourage everyone to get out and start looking for twospotted spider mites in soybean and corn, especially if your fields are under drought stress. Finding spider mites takes a little extra time, but you don't want to wait until it is too late to make a treatment decision.

Twospotted spider mites are often surrounded in webbing as they build colonies. Heavily infested plants look dirty and covered in webs. Look on lower leaves for initial infestations. Photo by David Cappaert, Michigan State University.

Leaves with heavy stippling is an indication spider mites have been feeding for a long time. Eventually the leaves will turn yellow, then die and fall off the plant prematurely. Photo by Whitney Cranshaw, Colorado State University.

Spider mites have many overlapping generations of adults, nymphs and eggs. Photo by Brian Lang, ISU Field Agronomist.

This photo was taken in Richardson County, Nebraska on 6 July 2012 by Tracy Cameron. He has been monitoring this field for over a month. Spider mites have spread throughout this soybean field and caused discoloration and leaf drop. 

Some of you may remember the dreadful summer of 1988, when hot and dry weather ravaged the midwest. Our field crops suffered from a horrible spider mite outbreak and farmers lost a lot of yield. I hope spider mite infestations don't get that bad this year. But it is important to be proactive with this pest and not wait for a field-wide disaster. Read this ICM News article for management information. 

Beetles: here, there and everywhere

Just like the Beatles song said, "Nobody can deny that there's something there." Many of you probably noticed a lot of little shiny black beetles around your home and even out in the field. I've seen a few different beetles actively moving around. The sap beetle, or sometimes called the picnic beetle, can be found in high numbers in urban areas now. As the common name suggests, they are attracted to human food, like fruit and vegetables. But they are normally seen  feeding on overripe fruit and decaying organic matter. In a few weeks you may see them feeding on corn silks. They are also secondary invaders and will feed in corn husks infested by corn earworm. Most literature suggests they aren't an economic pest.

Sap beetles are black and shiny with four irregular spots on the forewings. Note the antennae are clubbed and the wings don't fully cover the abdomen. Photo by Joyce Gross, UC-Berkeley.

In addition, I've got reports of a few different flea beetles in corn. Corn flea beetles are common to see early in the season. Corn is the preferred host plant where the adults scrape along upper and lower corn leaves. They will also feed on grasses. The feeding itself isn't an economic problem, but they can vector a bacteria that causes Stewart's wilt. Foliar insecticides are not economically justified after V5.

Corn flea beetles are small, shiny and black. Note the enlarged hindleg femurs used for jumping. Photo by Mike Quinn, TexasEnto.net.

Another flea beetle out and about lately is the redheaded flea beetle. They are similar in size to the corn flea beetle, but more oval in shape and have a red head (funny how entomologists come up with common names!). They can feed a several weeds, corn and alfalfa.

 

The redheaded flea beetle also has enlarged hindleg femurs for jumping. Photo by Lewis Veith.