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.

Lots of Japanese beetle look-alikes out there

Based on a soil temperature prediction model, Japanese beetles should be emerging all over Iowa now. We've seen them at nearly all of our ISU Research Farms. Ok, it helps when we use pheromone traps because they are especially attractive. But we like to be able to catch the first adults of the season!

At the same time these beautiful beetles are moving around, many other close relatives are coming out, too. Japanese beetles and other "scarabs" belong in the beetle family called Scarabaeidae. There are about 30,000 scarabs around the world. Even though they are highly diverse and abundant, they have a couple things in common: stout bodies, clubbed antennae, and many have broad front legs for digging. Some scarabs can be metallic or brightly colored, while others blend into the landscape. Adults can be active during the day or night depending on the species. Because of their relative size and body weight, they are clumsy fliers that move short distances. Some scarabs are scavengers that feed on dung, carrion or decomposing organic materials; others are significant plant pests. The larvae are distinctive because they are ALWAYS in a c-shape and commonly called grubs.

Grubs are immature scarab beetles. Note they have three pairs of true legs but lack the fleshy abdominal legs commonly seen on caterpillars. Grubs can be white or transparent, and will always be in a c-shape. Photo by David Cappaert, www.ipmimages.org. 

With several scarabs emerging at the same time, proper identification can be difficult. Here is a quick review of the most common scarabs out in Iowa right now:

Japanese beetle: Adults are just over 1/2 inch in length. These scarabs have one generation per year. They are visually distinct because of the metallic green head and bronze forewings that do not fully cover the abdomen. They also have white tufts of hair along the sides of the abdomen. Adults have a wide host range (>300 plants), including roses, fruit and shade trees, grapes, corn and soybean. Japanese beetles skeletonize leaves by feeding between the veins.

Japanese beetles are metallic, with clubbed antennae and white tufts of hair. Photo by Dorothy E. Pugh. 

Japanese beetles aggregate to feed and mate, leaving skeletonized leaves. Photo by Mark Licht.  

False Japanese beetle. Sometimes called a sandhill chafer, this species is commonly mistaken for Japanese beetle. They are similar in body shape and size (1/2 inch in length), but is not metallic green and bronze. They can have white hair along the sides of the abdomen, but it is more evenly dispersed instead of in tufts. False Japanese beetles have one generation per year. Adults feed on flowers, fruits and leaves of many plants, but are not considered a field crop pest.

False Japanese beetles are hairy scarabs, but not metallic. Photo by Marlin E. Rice.

Masked chafers. There are several species of masked chafers in Iowa. These scarabs have one generation per year. Adults are 1/2 inch in length and oval in shape. Body color can range from dark yellow to tan with dark markings on the head. They can have hairy bodies, wings and legs. Masked chafers are not known to be field crop pests in Iowa. 

Northern masked chafers are hairy and tan scarabs. Photo by Mike Reding and Betsy Anderson, www.ipmimages.org. 

May/June beetles. There are several scarabs with the common names of May or June beetles. Most have a life cycle that takes 2-4 years. Adults are usually larger (1 inch in length) and oval in shape. Body color ranges from red to brown. Adults feed on a wide variety of plant foliage, but they are not considered field crop pests in Iowa. 

June beetles are attracted to street lights at night. Photo by Steven Katovich, www.ipmimages.org.

Just a few other scarabs that you could find out this summer. None would be considered field crop pests. 

Ten-lined June beetle. Photo by Eugene E. Nelson, www.ipmimages.org.

Little bear. Photo by Whitney Cranshaw. 

Bumble flower beetle. Photo by David Cappaert, 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. 

Seeing maggots in your beans?

Well, no two summers are the same. This wet spring has caused some fields to have slug problems. Then other fields are now experiencing some seedcorn maggot problems. Crop consultant in southeastern Iowa, Tom Hillyer provided some excellent photos of recent soybean seedling damage.

  

I don't have much experience with seedcorn maggot, so I extracted some biology and management recommendations from our former extension entomologist, Marlin Rice. Female seedcorn maggots (true flies) deposit eggs in the soil and larvae feed on organic residue. Decaying organic matter, like manure, is especially attractive to females. Larvae overwinter and will complete development in the spring. First generation larvae will feed on germinating seeds and seedlings, and can possibly kill the plant. Several generations are possible in Iowa, but generally are not an economic concern after stand establishment.  

If you suspect seedcorn maggot, carefully dig in the seed furrow and look for evidence. You may not find any maggots, but could see a few feeding scars, tunneling in the seed or stem, or the entire seed destroyed. But the same type of damage could be caused by wireworms, grubs or cutworms. 

Rescue treatments for seedcorn maggot do not exist. Areas with persistent populations should consider using an insecticidal seed treatment to protect corn and soybean fields the following year. Seed treatments are encouraged when planting into cool, wet soils with manure applications. 

It's alive!!

It's been a long time since my last post! But it's ALIVE again...

This cool and very wet spring had impacted planting progress and insect development. So the usual field crop suspects haven't started to show up and are especially behind the 2012 emergence schedule. Some of the questions popping up lately have been with soil-dwelling insects and saturated soils. My general thought on this is that eggs can survive in wet soil, but larvae can't for too long. So if they are small and not very mobile (like corn rootworm larvae), they will probably suffocate. Good news if you like to grow corn!

Cool wet growing conditions in May and June do favor slugs. I wrote up a recent ICM News article today about managing these early-season beasts. Unfortunately, no-till or minimal tillage practices are conducive to slug populations.

Slugs can destroy corn and soybean seedlings. Photo by Brian Lang, ISU.

I will try to post more regular updates about other emerging pest activity. Send some of your observations and pictures my way. Thanks for your continued interest in my blog!

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.