Getting the word out about rootworm resistance

I'm at the ISU Extension Ag Chem meeting in Ames today. My presentation will review the status of western corn rootworm resistance to Bt corn. There are several tactics farmers can use to delay resistance, and I will encourage people to implement in 2012.

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Entomologists are funny, just ask us!

Us entomologists don't really have that many jokes to tell. I still think "frass happens" is pretty good stuff. But this year at the ESA meeting in Reno, they had an insect-related limerick contest. There were many humorous and creative submissions - perhaps we are a funny society after all? The overall winner was Martha Lutz, who wrote a witty poem about fireflies:

Au Naturel Selection: Photinus meets Photuris
A firefly who was benighted
saw a light and became so excited–
he rushed to his fate
while selecting a mate:
lost his head, lost his heart, was de-lighted.

It's actually about an interaction between two firefly species. I encourage you to visit Bug Girl's blog that gives a bit more detail about insect mimicry and the deceptive nature of some fireflies.

Some female fireflies lure in males with false mating signals.  

Photo by J. E. Lloyd.

Award-winning YouTube Videos

For the last three years, the ESA (Entomological Society of America) conducts a "YouTube Your Entomology" contest for members called the Stinger Award. There are several categories (research, extension and open) to submit 3-minute videos about insects. I have been fortunate enough to have my videos win in 2009 and 2010. My first video was about my young niece, Chloe, and her love of monarchs. Last year, I made an extension video about using a sweep net in soybean. This year, I made an extension video about Japanese beetle management in corn and soybean. I also partnered up with Brian McCornack and Wendy Johnson at Kansas State University, to do a spoof video in the open category. We talked about how Speed Scouting, a sampling plan for soybean aphid, is going paperless with a web-based tool called SoyPod DSS. I ended up winning in both categories this year!

ESA Meeting in Reno

I'm attending the annual entomology meeting in Reno this week. I presented a talk on the Iowa pest survey I conducted in 2010. It was a great discussion on changes in soybean production since the arrival of soybean aphid.

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This is a call…for aphids in corn yield response data

Like the Foo Fighters song, “this is a call” for your assistance with field data. I am interested in strip trials with aphids in corn from 2011. Did you count aphids in corn and make foliar insecticide applications? If you are willing to share data, I am compiling a larger data set to help answer some basic biology and economic questions about aphids in corn. When do aphids start to build up and how high can the populations reach in corn? When were applications made and were previous applications made in the same year? How many aphids does it take to cause a yield response? Is this number different for drought-stressed field? What is the knockdown efficacy of currently labeled products? 

It got pretty bad for corn fields in NE and NW Iowa this year. I saw corn that was grey and covered with aphids, cast skins, and honeydew. Most of the heavy infestations were at the field edge, so scouts could have overestimated populations if they didn't sample throughout the field. This is a difficult task, given it was mid-August!

  Some fields had very heavy aphid infestations in corn this year. Aphids were colonizing the stalk, ears and leaves. Photo by Brian Lang.

All this information feeds into developing an economic threshold and sampling plan for future growing seasons. I would really appreciate hearing about your experiences with aphids in corn this summer. Please email (ewh@iastate.edu) or call (515.294.2847). Thank you!!

Can bugs be good and bad?

Building on my last blog topic, I am still amazed by how insects adapt to cold weather. Most insects seek refuge in the soil or under leaf litter, but some are adapted to finding cracks in rocky hillsides. Well, Iowa isn’t exactly the most diverse landscape and so many insects have to adapt. Unfortunately, that means some insects try to seek shelter in homes and other buildings. When insects are found inside, most people are very frustrated because they are a nuisance. But most people can keep these accidental invaders under control by sealing crevices around the house and removing them with a vacuum. 

There are a couple of fall invaders in Iowa that are especially annoying. But the multicolored Asian lady beetle (Fig. 1) probably tops the list. I think of it as a beneficial predator – a good bug – to have in field crops. The multicolored Asian lady beetle is one of the most abundant predators in corn and soybean. The larvae eat about 25 aphids a day and the adults can eat 15-65 aphids a day. Larvae feed for about two weeks and adults can live up to 90 days. That is a lot of aphids consumed in a lifetime. Egads!

Figure 1. Multicolored Asian lady beetle forewings range from yellow-orange to red with zero to 19 black spots, or may be black with red spots. Photo by Hedwig Storch, Wikipedia.

One myth about this beetle is that it was intentionally released to control soybean aphid. Not true! It was released in California around 1916, and was kept localized until the early 1980s. Since then, it has spread throughout the United States and Canada, and was confirmed in Iowa in 1994. So it was here before soybean aphid was confirmed in North America. 

Ok, it’s not all sunshine and lollipops. Here is where a good bug can do bad. The multicolored Asian lady beetle is native to China and Japan, and normally overwinters in the south-facing rocks in the mountains. They are especially attracted to prominent, isolated areas on the horizon, and light-colored objects. Adults like to mass on these structures and enter diapause. In areas that lack mountains and rocky hillsides (aka, Iowa), these beetles will attempt to enter human structures.

 Multicolored Asian lady beetles like to mass inside structures to survive the winter. Photo by Robert Koch.

In addition to invading homes, the adults can secrete a defensive chemical from the leg joints that is very offensive (e.g., wet, dead leaves). The chemical can cause stains and become an allergen. It can also taint wine grapes with a rancid peanut butter flavor.

But the biggest problem I have with multicolored Asian lady beetles is that they are too competitive! They are more aggressive and tend to displace our native lady beetles. The lady beetles eat aphids but will also eat other lady beetles. 

Overall, the multicolored Asian lady beetle is a good thing to see in field crops. Even though some may see it as a pest, I think the benefits outweigh the negatives. For more information, Robert Koch wrote an excellent review of multicolored Asian lady beetle biology.

A long winter's nap

This fall, Iowa’s temperatures have fluctuated between freezing and 80 degrees. I started thinking about how insects are adjusting to the temperature swings as they make preparations for winter. My biggest decision the last two weeks was to wear flip flops or fleece. But insects go through a surprisingly complicated process to switch gears from active in the summer to apparently “sleeping" in the winter.

Most insects in Iowa need to go through a period of inactivity or diapause to survive the harsh elements (aka, cold weather and a lack of food). Diapause can be described as having little or no development, greatly reduced activity and metabolism, and increased resistance to environmental stresses. Any life stage can go through diapause, but is usually fixed for a particular insect species. Examples include:

     Egg: grasshoppers, corn rootworm, stalk borer

     Larvae: European corn borer, Japanese beetle, colaspis beetles

     Pupae: seedcorn maggot, fall webworm, sod webworm

     Adults: bean leaf beetle, green stink bug, lady beetles, billbugs

 

Diapause begins with external stimuli that signal upcoming changes in the environment BEFORE they happen. Usually that means colder temperatures in temperate zones. But in other parts of the world, hot and dry weather may trigger diapause. Hormones inside the insect start to change and are not easily reversed. So once the body starts to enter diapause, that behavior is permanent even if the weather improves.

The most important external stimulus is decreasing photoperiod or day length. Shorter days cue insects to start the process of finding suitable shelter. A common trigger for insects is experiencing less than 13 hours of light a day for 1-3 weeks. Another important stimulus in Iowa is cold weather. Insects are motivated to move before it freezes. Usually photoperiod and temperatures go hand-in-hand in nature. And in the case of field crops, their food source is often eliminated and stimulates diapause behavior.

Insect diapause is huge obstacle to overcome! You should see all types of insects starting the overwintering process right now.

Bean leaf beetle adults overwinter in leaf litter. 

Photo by Purdue Cooperative Extension Service.

Another research season comes to an end

Insect sampling efforts the last couple weeks have really tapered off. Our research plots in corn and soybean are drying down and maturing. I've also seen commercial fields being harvested around central Iowa. We plan to start harvesting our plots within the next 2-3 weeks.

Senescing plants are not a favorable nutrition source for insects anymore, and so they look for overwintering locations. Plus the shorter days are another indicator to insects that they should protective shelter soon. But some insects are still trying to survive before the cold weather really hits.

Green stink bug nymphs feeding on nearly mature soybean. Photo by Mark Licht.

You may notice other insects attempting to feed on plants or the prey on plants until harvest. Usually those insects can't cause economic damage unless they are clipping pods or damaging corn kernels. But it is something to evaluate if the damage is throughout the field. Also take into consideration the pre-harvest interval of most insecticides is at least 21 days.

Are you seeing any late-season insect activity out there?

Corn aphids explode

Starting last week, I've been seeing and hearing about an aphid explosion - in corn! For the last 3-4 years, certain areas in Iowa have had serious problems with aphids infesting corn in August. The areas having problems right now include the NE/NW corners and west central Iowa. Some of these heavily-infested fields have already been sprayed with an insecticide earlier this year. From my observations this week, I noticed aggregated colonies at the end rows.

In the past, corn leaf aphid could be a problem during tasseling. This species aggregated around the ear and silks, and sometimes their honeydew production interfered with pollination. But natural enemies and the environment rarely let them build up past July. So economic thresholds have only been determined for aphids around tasseling and mostly targeted to fields during drought-stressed summers. Now, it seems aphids are colonizing corn later in the summer and are building up to striking levels. They can be found at the base of the stalk, around the ear and sometimes building up colonies above the ear leaf. 

Aphids in corn can build up large colonies, sometimes exceeding 2,000 per plant. 

Photo by Erin Hodgson.

One important observation I've noticed is that most fields have two aphids species - corn leaf aphid and bird cherry oat aphid. They are closely related and look very similar in size and color. The bird cherry oat aphid had an orange-red saddle between the cornicles. Other aphid species can also be found, including greenbug and English grain aphid, but are not as common in corn this year. Species identification isn't that critical for management at this point (an aphid is an aphid). You can see more than one species in a field and even on a single plant. 

All aphids have a piercing sucking mouthpart and feed on the sap from the plant phloem. They excrete sugar-rich honeydew that can cover the aboveground portion of plants. The honeydew can promote a sooty mold that can interfere with plant photosynthesis. You've probably remember seeing grey-looking soybean leaves when soybean first hit Iowa about 10 years ago. We know soybean plants covered with mold and aphids can have serious yield loss, but we don't know the extent of yield reduction caused by aphids in corn. 

Corn aphids infesting the ear and above the ear leaf. Photo by Erin Hodgson.

Currently, there are no treatment thresholds for aphids in corn past tasseling. But regular sampling will help you make educated decisions about a foliar application at this time. Here are some considerations to make before applying an insecticide for aphids in corn:

1. Are 80% of the plants infested with aphids?

2. Do most of the ears have aphids? What about the ear leaf and above?

3. How long has the field been infested and is the density increasing? Sample field-wide (30 plants for every 50 acres) to determine the average density. 

4. Do you see honeydew or sooty mold on the stalk, leaves or ear?

5. Are you seeing winged aphids or nymphs with wing pads? This may be a sign of migration out of the field. 

6. Is the field under drought stress? Dry weather will make amplify potential feeding damage to corn. 

7. Do you see any bloated, off-color aphids under humid conditions? Natural fungi can quickly wipe out aphids in field crops. 

8. What is the corn growth stage? Fields reaching hard dent may be past the point of a justified foliar insecticide.

9. Some insecticides have a 60-day preharvest interval. Check the label and calender.

10. Get good coverage of the application - ideally droplets should make contact with the aphids for a quick knockdown. Don't expect residual to protect the corn from fluid feeders. 

I strongly encourage you to leave an untreated check strip or two in fields that you spray. Try to leave a strip that is a fair comparison to the majority of the field - not just the stunted corn the field edge. If you decide to treat for aphids in corn, I would like to hear about the yield comparisons. Your pooled data will help me formulate treatment guidelines for the future.

It's our big soybean aphid spray day

My lab has the nation's largest soybean aphid efficacy trial. It originally started with Matt O'Neal, but he kindly gave me the program when I started at ISU in 2009. The program has typically focused on foliar insecticides, but last year we also incorporated some seed treatments and the Rag1 host plant resistance gene. This year, we even expanded to three locations (Northwest Farm, Northeast Farm, and the Johnson Farm). Last week the Northwest Farm hit threshold and applications were made. Even though aphids haven't exceeded threshold at the other two farms, we are spraying them this week. The Northeast Farm has all our treatments, 35 this year, so spraying all the plots takes some serious planning with a large crew.

The 2009 crew is all suited up in Tyvek, getting ready to start spraying. 

Photo by Erin Hodgson.

At all our locations, we are definitely seeing a visual difference between susceptible and resistant soybean. Aphids are present, but at low levels in Rag1 plots. I will update the blog on yield data once the beans are cut. If you are curious about what products we used in the past, go to our soybean aphid website. We are trying out some new spray equipment this year, so I will also recap how it worked (or didn't!).

Learn how to use Speed Scouting for Soybean Aphid

Now is critical time to scout and make treatment decisions for soybean aphid in Iowa. But sampling whole plants during pod set and seed fill can be very time consuming! I created a sampling plan in 2005 called Speed Scouting for Soybean Aphid. It's a binomial sequential sampling plan that should save growers and crop consultants a lot of time out in the beans.

The Plant Management Network is offering a FREE webinar about how to use Speed Scouting. Visit the Focus on Soybean section under the Resources tab to view open access webinars, or simply click here. I spend about 15 minutes going over the sampling plan and show a few examples of how it works.

Go to my ISU faculty website to get blank Speed Scouting forms. I am interested in hearing about your experience with Speed Scouting. Tell me if you like it or even if you don't. There will be a tablet/smartphone app with Speed Scouting available for next summer.

 

Scouting for aphids is a difficult task in August - try Speed Scouting to make your life easier! Photo by Brent Pringnitz.

Corn rootworm damage is noticable

I've been traveling around the state with our corn entomologist, Aaron Gassmann, the last two weeks. We've been collecting corn rootworm adults and assessing root injury in commercial corn fields. We are visiting fields that seem to have extreme rootworm pressure, even though the corn is expressing Bt. 

  Severe corn rootworm feeding can lead to root pruning which makes plant unstable 

and interferes with nutrient uptake. Photo by Erin Hodgson.

 

Aaron has been looking at problem fields for three years and evaluating the susceptibility of corn rootworm to different Bt proteins. He is finding a few fields with increased beetle survivorship compared to the general population. Does this mean corn rootworm are becoming resistant to Bt? Well, according to his recently published article - yes. He is finding fields that have more larvae surviving, or tolerating, the Bt proteins. Although his research showed incomplete resistance in just a few fields in Iowa. This is not a widespread problem at this time and has not been reported from other states. 

There are a couple of common scenarios to these problem fields. Most are planted with continuous corn and use the same Bt protein for 2-3 years. The vast majority of beetles are Western corn rootworm. Aaron strongly encourages people to use crop rotation with soybean to knock down the beetle population. He also suggests mixing up the Bt proteins used to delay genetic resistance of the beetles. Also consider using an in-furrow insecticide application for those fields with persistent corn rootworm damage. Of course incorporating the recommended refuge corn will help delay resistance as well.

 Western corn rootworm beetle. Photo by Natasha Wright.

During our travels, we saw a few fields with extremely heavy adult emergence and feeding. I would estimate the density of two fields we sampled to be around 10-14 adults per plant. The adults had destroyed the silks and were infesting the ears. Leaf feeding was also very apparent. Some of the fields were sprayed with a foliar insecticide to kill the adults. Corn rootworm had delayed development this year, and adults are emerging over a gradual period. The residual from the insecticide does not appear to kill the adults that emerge after application. The University of Illinois does a statewide sample of corn rootworm adults, but found low numbers this year even though root damage by larval was increased form 2010.

Growers should be evaluating corn roots for damage, even if lodging isn't obvious. You should be able to see adults feeding and mating at this time as well. Knowing more about the current population will help you make seed selection decisions for next year.

Drought favors spider mites and grasshoppers

Although some parts of Iowa have had adequate moisture (or even flooding!), other areas could use some rain. Drought stress combined with high temperatures is good news for field crop pests like grasshoppers and spider mites. If your area is hot and dry, consider scouting fields now and throughout August. 

The two-spotted spider mite thrives in hot, dry weather. Spider mite injury to soybean can resemble herbicide injury or a foliar disease; however, characteristic signs are tiny yellow spots, or stipples, on leaves. As the injury becomes more severe, leaves turn yellow, then brown, and finally die and drop off. Spider mite injury can reduce soybean yields by 40 to 60 percent, and cause pod shattering, wrinkled seed, and early maturity.

Heavy spider mite damage to corn and soybean will cause leaves to look stippled. Photo by Whitney Cranshaw.

In corn, prolonged spider mite feeding will turn leaves yellow with stippling on the upper surface. Heavy infestations can cause premature drying, which results in the loss of leaf tissue, stalk breakage, and kernel shrinkage. 

Under dry conditions, foliar treatments are recommended when corn or soybean have substantial stippling or leaf-yellowing and spider mites are active. Although spider mites are not insects, they are often treated with insecticides. Pyrethroid chemicals are not very effective at reducing outbreaks, so consider using organophosphates. Using pyrethroids to control other pests (e.g., soybean aphid) may actually flare spider mites in the field. 

Warm and dry weather also favors grasshoppers growth and development. When late summer grasshopper damage does occur, it usually is related to drought conditions and is frequently, but not always, restricted to field edges. There are two common grasshoppers in soybean in Iowa, the differential grasshopper and the redlegged grasshopper. 

Young grasshopper nymphs eat irregular-shaped holes in tender leaf tissue and may consume the entire seedling. Older nymphs and adults can consume all of the leaf except the tougher veins. Grasshoppers chew through green soybean pods (which bean leaf beetles will not do) and destroy the seeds within. They can also feed on developing corn ears and destroy kernels. 

Grasshoppers chew through soybean pods and can damage corn kernels. 

Photo by Marlin E. Rice.

Reducing grasses and other weeds within and around fields will discourage adults from feeding and mating in that area. The economic thresholds are based on leaf area consumed or percent defoliation. In soybean, a foliar treatment may be justified if defoliation exceeds 40 percent before R1 (full bloom) or 20 percent after R1. Consider an insecticide application in corn if grasshoppers are clipping silks or ear tips, or are removing foliage above the ear leaf. Border treatments are recommended if infestations are restricted to field edges.

Japanese beetle damage is detected

For the last few weeks, I have been seeing Japanese beetle activity throughout Iowa. Ornamentals, trees and shrubs have large numbers of adults feeding and mating, and defoliation is becoming obvious in our small plot research. In addition, ISU field agronomists have been reporting defoliation in commercial soybean. Although Japanese beetles have been reported here since 1994, plant damage has been erratic. I strongly encourage growers and crop consultants to scout corn and soybean fields for this pest this year. 

Adults prefer to feed between soybean leaf veins, but can ultimately consume most of the leaf. The treatment threshold for Japanese beetles in soybean is 30 percent defoliation before bloom and 20 percent defoliation after bloom. Most people tend to overestimate plant defoliation, but this reference can help with estimations. 

 Japanese beetles are skeletonizers that cause leaves to look lacy. 

Photo by Mark Licht.

In corn, Japanese beetles can feed on leaves, but the most significant damage comes from clipping silks during pollination. Consider a foliar insecticide during tasseling and silking if: there are 3 or more beetles per ear, silks have been clipped to less than ½ inch, AND pollination is less than 50% complete.

 Adults aggregate during tasseling and can clip corn silks. 

Photo by Mark Licht.

There are many insecticides labeled for Japanese beetle control; however, do not expect season-long control from a foliar application. Adults are highly mobile and move frequently in the summer. Japanese beetles release a strong aggregation pheromone, and are commonly seen feeding and mating in clusters. Beetles present during the application will be killed, but beetles migrating into sprayed fields may not be controlled. If soybean defoliation continues, additional applications may be necessary to protect the seed-filling stage. If corn pollination is complete, Japanese beetles may not be economically important anymore. Also consider a border treatment if Japanese beetles are aggregated in the edge rows.