The following articles are excerpted from the Field Crop Advisory Team Alert newsletters. To read additional issues of the newsletter, please visit: http://www.ipm.msu.edu/fieldCAT.htm
To view information about another new soybean pest, soybean rust, visit:
http://www.ipm.msu.edu/soybean/rust.htm

Get current status reports on soybean aphids and soybean rust from regional trapping effort at:
http://www.sbrusa.net/

Large fall flight of soybean aphid leads to…
More eggs on buckthorn in the winter, which means…
Higher spring aphid populations on buckthorn in May, so there is…
A heavier flight to the soybeans in June, and finally…
An aphid outbreak in July and August.

At the end of 2006, dozens to hundreds of winged soybean aphids were captured in the suction trap network (Table 1), The numbers may not seem high, but remember the trap is a vertical PVC pipe drawing in air 25-30 feet above ground. It is sampling a small amount of air overall, so the trap catch is a tiny fraction of the aphids actually flying from soybean to buckthorn.

In the winter of 2006-07, entomologists sampled buckthorn for soybean eggs. Eggs were found at numerous locations, hundreds on branches at some locations. Again, this may not seem very impressive, but aphid eggs are very small and generally difficult to find. Finding eggs at all, much less multiple eggs on a bud or branch, is significant. Because of the fall suction trap counts and egg numbers, we predicted an outbreak.

A spring freeze in April damaged buckthorn buds across the Midwest. In central Michigan, buckthorn shrubs growing along the edge of wood lots or the road were severely hit, and the damaged branches did not leaf out quickly, and did not support soybean aphids. However, many buckthorn shrubs further back from the edge were not damaged, and leafed out normally. Thus the aphid population was probably “dinged” a bit, but not knocked out.

In Michigan, aphids colonized soybean fields as normal, beginning in early June. By mid-June, fields in the Frankenmuth area were over threshold, reminiscent of the early aphid infestation in southwest Michigan in 2005 – our last big outbreak year. Only fields planted early (in April) went over threshold; May-planted fields emerged later and missed the aphid flight that colonized the April fields. Early-planted fields in Ontario also went over threshold.  The over-threshold fields were treated, and predators and parasitic wasps attacked the survivors.

Aphid numbers increased slowly until early July. Then unseasonably hot weather and minimal canopy resulted in very hot temperatures at the soil surface. In research plots, the ground was too hot to sit on. That same week, the building aphid numbers took a dive. Soybean aphids can survive hot weather when they are under a cool plant canopy, but they likely cannot tolerate 90-degree days when plants are still small. The population growth rate appeared to slow, and perhaps predators had a chance to catch up. Fields were essentially aphid-free until August, until winged aphids blew in from surrounding states. Some fields went over threshold, but for most fields it was too late to build aphid populations.

Surrounding states, northern Indiana and the Toledo, Ohio area, had a similar experience to Michigan. An outbreak was predicted, but did not materialize. In contrast, many other states did have their predicted “aphid year.” From Quebec to the Dakotas, millions of acres were treated for soybean aphid.  Michigan didn’t have an outbreak, but many other states did.  We were the hole in the outbreak donut, so to speak.

What about 2008?  Table 1 shows that the suction trap catches in the fall of 2007 were considerably lower than at the same locations in 2006, with one exception, Michigan.  A couple of traps did catch aphid moving out of soybean to buckthorn.  That makes some sense, because 2007 was essentially a non-outbreak year for Michigan, and low years tend to be followed by outbreak years. However, I have not found any eggs this winter on buckthorn. Across the Midwest, a low aphid year is expected in 2008, but Michigan is more of a mixed bag. We may see some pockets of infestation if certain locations have high egg numbers. The key is to scout fields to catch these potential infestations before they go over threshold.

Table 1. Soybean aphid suction trap catch in 2006 and 2007

• Aphid numbers have increased in the eastern Great Lakes area, dramatically in some locations.
  
• If you haven't already, check fields for aphids, especially late-planted and potassium deficient fields. Even a quick walk into the field will alert you to a problem.
  
• Think coverage, coverage and COVERAGE.
  

Recipe for spider mite surprise (Acarides voila!)

• Start with a pinch of spider mites.
  
• Add very little water.
  
• Stir in a reduced rate of an insecticide, poorly applied, to kill mobile predators, but avoiding most of the mites.
  
• Fold in a fungicide, thoroughly, to cover all surfaces.
  
• Repeat.
  

Check April-planted beans for soybean aphid now
Christina DiFonzo, Entomology

As in 2005 Monroe County, this summer we have at least one area, in eastern Saginaw County, where soybean aphids are over threshold (view photos). The fields I saw were specifically near Frankenmuth. I did not see buckthorn in the immediate area, but this part of Saginaw County is downwind from the Shiawassee and Titibawassee Rivers, and a national game area south of Saginaw City, all with a lot of buckthorn. This situation appears to be unique – a combination of early planted beans plus a likely large flight of winged aphids from buckthorn in early May that settled in this area. On June 8, one particular V3 field was 100 percent infested, averaging 70 plus soybean aphid per plant. This field was planted in late April. By June 11, the field was over threshold, averaging 255 per plant. I recommended that this field be treated.

When should small beans be sprayed? Heavy early-season infestations are rare, so research is lacking in this area. The 250 threshold was developed and tested in larger beans, so there is no good data to set a threshold for small beans. The infested fields I saw had adequate moisture to replace the aphid feeding (but in the last few days, they need rain), and the plants aren't putting on flowers or other critical structures. They appear to be able to tolerate 100 soybean aphid per plant, and maybe even 250. My lab, as well as researchers in Ontario, which has a similar situation, put out spray trials this week to try to answer this question.

Be aware there are risks to spraying so early. Aphid populations are likely to rebound or “flare.” Predators will be killed, and any surviving aphids will reproduce fast in the absence of the predators. In early-sprays, insecticides can be mixed with Roundup from the crop-injury standpoint. However, it is critical to get excellent coverage to achieve excellent kill. Otherwise, you are leaving aphids alive to reproduce in the absence of predators. Some suggest using half-rates of insecticide because the plants are small. I do not have data to show that reduced rates are effective on small beans. Using half-rates makes me a bit nervous, because again, the goal is the excellent aphid kill to reset the field to “0” to avoid flaring. Because of the problem with flaring, early-sprayed fields may end up needing to be sprayed three times instead of once or twice to achieve the same yield.

Spraying in Saginaw does not mean other fields in Michigan need to be treated. There is no cause for concern unless fields are 50-80 percent infested (in other words, the majority of plants have aphids). Once aphids spread out across plants, then numbers per plant begin to climb. If you are finding just a few infested plants in a field or a hot spot here and there, that is NOT a sprayable population. Aphids are present in most fields, but still at low levels, as in typical outbreak years. Aphids will spread out across plants and then numbers will climb as we head into July. The main point is to get out and look at the earliest planted fields to determine the percentage of infestation.

Links to get insect trapping information:

www.sbrusa.net - Aphid numbers in soybean. Currently Mchigan, Ohio, Indiana and Ontario have entered count data.

http://www.ncpmc.org/traps/index.cfm: Northcentral Aphid Suction Trap Network. The web site now has 2007 trap catches. Simply click on the state or trap to see suction trap catches of soybean aphid.

And to follow up on the previous article about suction traps, here is the latest update on soybean aphid in soybean.  Dave Ragsdale from the University of Minnesota reports that soybean aphid was found in multiple locations throughout Minnesota on V1 soybeans. The earliest find was in mid-May on volunteer beans along the Minnesota River in south-central Minnesota. Soybean aphid was later found at the end of May in commercial soybean in northwest Minnesota (Dave says this is a good two to three weeks earlier than ever recorded in that part of the state.) and in a research plot south of the Twin Cities.

Northcentral Regional Aphid Suction Trap Network was turned on last week in at least eight states. As in 2005, Michigan has three trapping locations that cover a north-south transect:  MSU’s Saginaw Valley Bean and Beet Research Farm in Saginaw County; the MSU Entomology Farm in Ingham County; and the Kellogg Biological Station in Kalamazoo County.  By the end of June, we will set up two new locations: one at the MSU Extension office in Monroe County to cover southeast Michigan and another in western Michigan in Oceana County.  Monroe County has a high population of buckthorn, the overwintering host for soybean aphid; it experienced heavy, early aphid infestation in 2005, and thus may benefit from trapping information.  The location in Oceana County is specifically targeted to provide information to vegetable growers in Western Michigan, where soybean aphid is implicated in virus spread.

The traps suck in migrating insects, including winged aphids, flying over 20 feet above the ground.  The insects end up in a jar of antifreeze just above the fan in the base of the trap.  Sample bottles are changed weekly and mailed to the University of Illinois where aphids are removed, identified and counted.  The soybean aphid counts are posted on a web site, http://www.ncipmc.org/traps/, where you can view individual traps from each of the eight states. There are currently 33 traps on the network, plus 5 to 6 more that will come on line in June.

How can you use the suction trap data?
In early to mid-July, increasing flight tells you that winged soybean aphids are being produced in early infested fields and are now dispersing across the landscape. These infested fields could be local, in another part of the state or even in a neighboring state.  This means that previously uninfested, low-infested fields or seed-treated fields may get an influx of landing aphids that leave babies behind. This is how fields in areas that lack buckthorn (for example, many locations in southwest Michigan) get infested in July.

Later in the season, in late July and early August, increases in flight often time with peak infestations in soybean fields.  For example, last season (see the 2005 data at http://www.ncipmc.org/traps), tremendous numbers of soybean aphids were trapped in early to mid-August, when aphid populations peaked in nearby fields.  Such heavy aphid flights increase the risk of reinfestation in previously-sprayed fields we certainly experienced that frustrating situation in 2005.

In the last four years, heavy aphid flights in late July/early August coincided with virus infection in vegetable crops in Michigan. The suction traps can alert growers to a potential virus threat and may eventually help vegetable growers make decisions about late-plantings, for example, variety selection.

At the end of the season, the suction traps play their most important role, potentially predicting next year’s soybean aphid population.  Suction traps catch the winged males and females that leave soybean and go back to buckthorn, where soybean aphid overwinters.  In Illinois, the number of fall migrants caught in suction traps correctly predicted the next year’s aphid population (outbreak versus no outbreak) in four out of four seasons, including 2005. The 2005 season was the first year for the Regional network, across eight states. At the end of 2005, some areas (such as Michigan) had low fall trap catches; others (for example Minnesota) had high fall flights.  June 2006 is a critical test for the predictability of the traps in theory, Michigan should have low colonization this spring and Minnesota should have early, heavier colonization.  Stayed tuned!

Soybean rust website expands to include soybean aphids
Christina DiFonzo, Entomology

The following article is from the May 25th, 2006 Field Crop CAT Alert.

Many of you are aware of the soybean rust web site (http://www.sbrusa.net/) sponsored by USDA last year. That site provides a map that shows soybean rust detections in sentinel plots and on kudzu, an alternate rust host. There is also commentary provided by state specialists. Knowing the progression of the disease north will help producers target scouting and apply preventative fungicide applications.

For 2006, there is a new feature on the web site – maps for soybean aphid. When you enter the site, simply go to the drop down menu in the top right corner, under the date and select soybean aphid. Two maps appear on the right side of the screen. The top map shows “SB Aphid Observations.” As of this writing (May 25) this map is blank (it isn’t active yet), but once reports of soybean aphid come in, dots will appear. While USDA is funding the sampling some sentinel plots for aphids, additional research plots and production fields may be sampled in certain states by Extension educators, state government, university entomologists and others. Unlike the rust map, which only has two colors (green for no detection, red for detection), the color of the dots on the aphid map will reflect the number of SBA per plant with purple dots indicating fields or plots over the 250 per plant threshold. The second map has the “SB Aphid State Update,” commentary by state specialists. Note that the color of the state reflects when the commentary was last updated.

By clicking on Michigan, you can read commentary by me on aphids. I will also include my detailed management recommendations, if aphid populations increase. Some of this information may be redundant of the Field Crop CAT Alert, but I since can update the rust web site daily if needed, the information will be more up-to-date.

A note of caution about the soybean aphid web site – entomologists in the region agree it should not be used to make spray decisions in your individual fields. This is different from how the rust maps are used. Detections of rust near your location will help to time preventative fungicide applications across a region. However, detecting soybean aphid in your area and even having fields go over threshold do not necessarily indicate your individual fields should be treated. We definitely know from 2005 that soybean aphid populations during an outbreak differ dramatically from field to field and that some fields need to be treated while other do not. We also know from 2005 that optimal timing of insecticide applications protects yield, which argues for scouting as needed and making field-by-field decisions. Use the soybean aphid maps to get information about aphid populations in general, but do not use the maps to make a decision about whether or not to treat your own fields.

Soybean aphid control with seed-applied insecticides
Kurt Thelen and Terry Schulz
Crop & Soil Sciences

The following article is from the May 4th, 2006 Field Crop CAT Alert.

Seed treatment insecticides such as Cruiser and Gaucho have been marketed for early season soybean aphid and bean leaf beetle control. Results from two years of performance trials conducted in Michigan indicate that soybean yield response to these seed-applied insecticides depends primarily upon the aphid pressure experienced during the early growing season.

In 2004, when aphid pressure was light, the soybean yield response to Cruiser and Gaucho averaged just under 1 bushel per acre over six locations across the state. Conversely, in 2005, with heavy early season aphid pressure, yield response to these seed applied insecticides averaged 6 bushel per acre across four Michigan locations. Results of the 2005 trials showed there was early season suppression of aphid populations through the R1 (flowering) growth stage. However, as aphid pressure increased over the growing season, the level of population suppression seen by the seed-applied insecticide treatments decreased significantly (see accompanying graph). Based on this data, it appears unlikely that an insecticide seed treatment would keep aphids from reaching economic threshold and prevent the need for a foliar-applied insecticide application during a heavy aphid pressure year. However, some yield benefit may be gained if early season aphid pressure is high.

Late summer scouting in 2005 and early season scouting this spring suggests that aphid levels may be down in 2006 throughout most of the state. However, some areas, especially those with nearby Buckthorn infestations, which serve as the overwintering host for the aphid, may experience high localized soybean aphid populations. In deciding whether to invest in these insecticidal soybean seed treatments, it is important to assess expected early season aphid pressure and weigh that against the cost of the product.

Soybean aphid chemical control: foliar sprays
Christina DiFonzo
Entomology

The following article is from the April 6, 2006 Field Crop CAT Alert

General lessons from many trials in 2005

• Scouting pays: Soybean aphid (SBA) problems were detected early by scouting and variability in infestation (and need for treatment) was also noted.
• Residuals differ: OPs tend to have better initial kill but shorter residual. Pyrethroids tend to have longer residual.
• Yields often don’t differ: In the end, however, yield generally depends more on spraying itself, then on choice of insecticide.
• Coverage counts: Coverage probably explains many of the performance problems with various insecticides.
• Tank mixing: Tank mixes of pyrethroids with Lorsban did not improve yield.
• Reduced rates: Reduced rates of insecticides did not provide adequate control or improve yield.

MSU Recommendation

• Do scout fields more than once, beginning in mid-June;
• Do use a threshold of 250 SBA per plant with increasing aphid populations, through the R5 plant stage [in practice: nearly every plant has aphids, aphids cover the top leaves of the plant, and may be moving to the stems]
• Do use a full rate of an insecticide;
• Do optimize coverage = 40 psi, at least 20 GPA, nozzles recommended for insecticides;
• Do not tank-mix reduced rates of several products.

The 2005 field season was a great year to test foliar sprays for soybean aphid control. Below I summarize the results of several trials comparing insecticide sprays to untreated plots. Please note that some of the products in the trials are not currently registered for soybean. Table 1 shows a complete list of products tested in our trials, plus information on chemistry, manufacturer and registration on soybean.

Efficacy trials were done at the Saginaw Valley Bean and Beet Farm in a field planted on May 5 and at the MSU Campus Farms in fields planted on May 17 (Entomology) and in mid-June (Botany). At all locations, treatments were made when SBA populations crossed the threshold of at least 250 SBA per plant, using 23 GPA, 40 PSI and Twinjet nozzles. The field at the bean and beet farm was sprayed on July 14 in the R2 plant stage at an average aphid population of 830 SBA per plant. Aphid counts were taken 4, 7, 14, and 21 days after treatment. The field at the MSU Entomology Farm was sprayed on July 27 in the R4 plant stage at an average aphid population of 356 SBA per plant. Aphid counts were taken two and seven days after treatment. The field at the MSU Botany Farm was sprayed on July 20 in the V4 plant stage at an average aphid population of 372 SBA per plant. Aphid counts were taken 5 and 14 days after treatment.

Table 2 summarizes insecticide rankings at various days after treatment (DATs). Treatments were included in the table only if they were done in at least two of the three trials. Counts from the MSU Entomology Farm (2 and 7 DAT) and Botany farm (5 and 14 DAT) are reported together, since the fields were adjacent.

At the MSU Farms, treatments including Lorsban knocked aphids back quickly (white cells, 2 DAT). But within five to seven days, several of the pyrethroid and nicotinoid treatments (Assail, Proaxis, Warrior) had the lowest aphid counts, an effect of residual kill. By 7 DAT, some treatments were back over threshold and by 14 DAT many plots were near or over 1,000 SBA per plant. The effect of residual is clear by 14 DAT; plots sprayed with shorter-residual products (Lorsban, Orthene) had over 1,000 SBA per plant (black shaded cells), while plots sprayed with longer-residual insecticides (some pyrethroids and nicotinoid) had fewer aphids (dark gray-shaded cells). In late July through early August, a large number of winged aphids landed in soybean at MSU, and fields were re-infested quickly. This made it very challenging to maintain aphid control.

In contrast to the challenges at the MSU Farms, insecticides worked well at the bean and beet farm. Even by 14 DAT, SBA numbers were still under 100 SBA per plant in most treatments (light-gray shaded cells), compared to nearly 2,000 SBA per plant in the untreated check. By 21 DAT there was over 2,800 SBA per plant in the untreated check. However, most treated plots were still below 250 SBA per plant (Table 2 medium-gray shaded cells). The treatments over threshold have known shorter residual. Table 2 clearly shows this difference in residual. This table shows the aphid populations in treatments sprayed with insecticides currently registered on soybean. At 4, 7 and 14 DAT, all treatments still had less than 250 SBA per plant. By 21 DAT, treatments were separating out by residual: the OPs Orthene, Lorsban, or a tank mix of Lorsban with Baythroid all had over 250 SBA per plant, while the longer lasting pyrethroids remained under 250.

Rank: For each date, treatments are ranked from fewest SBA per plant (1) to the highest. If counts were close, within a few aphids of each other, the treatments were tied.

A star* indicates that the aphid population is significantly less than the population in the untreated check.

Soybean aphid chemical control: seed treatments
Christina DiFonzo
Entomology

The following article is from the April 6, 2006 Field Crop CAT Alert.

There are now two new seed treatments registered for soybean. Cruiser (thiamethoxam) was available in 2005; Gaucho (imidacloprid) can be used in 2006. Soybean seed can be ordered already treated, or treated by a commercial outfit after purchase. In most cases, insecticide-treated seed will also be fungicide-treated. The prices we were recently quoted for Cruiser and Gaucho treated seed were between $9 and $12 per unit (50 lb bag) = $10 to $14 per acre.

Cruiser and Gaucho protect seeds in the ground from early season insect pests, such as seedcorn maggot and wireworm. Both products may have an impact on grubs, although grub control is not listed on either label. Both products are also systemic. The active ingredient moves up into the plant as it grows, protecting foliage from insect feeding for approximately 30 to 40 days. Bean leaf beetle is one target for the systemic action. Bean leaf beetles overwinter as adults, and the adults emerge in the spring to feed on small soybean plants. First generation bean leaf beetle feeding is usually not a concern in Michigan, but there may be areas in southern Michigan with isolated problems. Another obvious target for seed treatments is the soybean aphid. Early season aphid colonizers from buckthorn probably deposit nymphs on treated bean leaves (they likely cannot detect treated beans), but the nymphs themselves do not survive. This delays colonization of the field by several weeks.

Eventually, as the plant gets larger and the insecticide breaks down, the dose of insecticide in the plant is no longer lethal. At that point, aphids feeding on treated beans get a sub-lethal dose of insecticide; research from the University of Minnesota shows that aphids have fewer nymphs on seed-treated beans. But these aphids may not die. Populations on treated beans can still go over threshold when populations are heavy, although the number of aphids per plant may remain less than untreated beans.

From an economic standpoint, Cruiser and Gaucho treatment is an insurance policy, not an IPM-based strategy. When soybean aphid isn’t present or numbers are low (as in 2004), seed treatments generally do not yield any more than untreated beans (see Table 1). As insect pressure increases, Cruiser and Gaucho will protect yield from early season aphid feeding, but if the outbreak continues, seed treatments wear out. You may need to spray seed-treated fields later in the season. Cruiser and Gaucho might be more useful on early-planted beans in areas with heavy overwintering populations of soybean aphid (for example, southeast Michigan). In outbreak years, these fields are colonized early by aphids, when a lethal dose of insecticide is still in the plant. Over the long-term, you probably are better off with a well-timed, scouting-based foliar spray made only if fields are over threshold. In years with low aphid numbers, you essentially preserve $10-$12 per acre in profit by not spending money on aphid control.

Targeting the use of seed treatments may be possible if researchers can predict aphid outbreaks using, for example, the regional suction trap network set up in 2005. But for now, we do not have a reliable way to predict the need for seed treatments next year. The bottom line is to understand what seed treatments will do for you, what insects they control and how long they last. Also remember to scout seed-treated fields as well, because they may need to be treated in outbreak years.

Table 1 summarizes three years of fieldwork with seed treatments at MSU, under varying aphid pressure.

In 2003, cages were used over small plots to generate high aphid pressure. SBA first survived on treated plants 37 days after planting. Seed treated plants went over threshold two weeks later (July 28) than untreated plants (July 14), but aphid numbers on both untreated and treated plants increased rapidly into the thousands. No yield was taken from the small cages.

In 2004, small plot studies were done under natural aphid pressure. Aphid numbers were extremely low throughout the field season. Neither treated nor untreated plots approached threshold, and yields did not differ significantly. Using a seed treatment as “insurance” would not have paid economically in 2004.

In 2005, aphid numbers were higher than in 2004. At two locations on the MSU campus, Gaucho was included as a treatment. In both studies, Gaucho protected beans from aphids for two additional weeks compared to the untreated beans, but it started to run out by 35 days after planting. Untreated and Gaucho-treated plots went over threshold the same week, or shortly thereafter, and aphid numbers increased to moderate levels. By the end of the season, yields did not differ significantly between untreated (56) and Gaucho (61) treated plots. However, when the Gaucho treated plots were sprayed with Trimax (= imidacloprid, not yet registered on soybean), yield improved significantly over the untreated check to 68 bu/ acre, equaling the best foliar treatment in the same field (Asana, also 68 bu/acre)

In a study that included Cruiser at the MSU Bean & Beet Research Farm, aphid populations were tremendous, reaching nearly 17,000 soybean aphid per plant in early August. Treated and untreated plots went over threshold the same week. Cruiser suppressed aphid numbers by about 30% compared to the untreated, and increased yield significantly. However, a single well-timed spray of Warrior (37 bu/acre) outyielded the Cruiser treatment (30 bu/acre). At this location, SBA pressure was so high that it also paid to apply Warrior to Cruiser treated beans (50 bu/acre).

In summary, in years with low aphid populations, we do not see a yield gain (in the absence of other pests) from using a seed treatment. Under heavy aphid pressure, seed treatments do protect yield, but usually will not outperform a single foliar spray timed at 250 SBA per plant. Seed treatments begin to run out after 30-40 days, just as aphid pressure typically increases in most locations in Michigan. However, applying a foliar spray to seed-treated beans over threshold can result in additional yield. In the end, it’s a matter of pushing the pencil, figuring the cost of seed treatment vs. spraying vs. doing nothing over a time frame of several seasons. Eventually, researchers hope that aphid numbers in fall suction trap catches may be a great help in making a decision to use a seed treatment the following year.

Soybean aphids still a problem
Christina DiFonzo, Entomology

The following article is from the August 11, 2005 Field Crop CAT Alert.

1. The cause of downed corn
2. The efficacy of insecticides and transgenic corn
3. The presence of variant feeding on first-year, rotated corn.

Beetles are also heavy in soybean in southern Michigan and surprisingly in central Michigan as well. This is a sign of variant behavior, and these beetles may be laying eggs in soybean, so that larvae will feed on and damage corn rotated into the field next year. Variant may be sampled by using yellow sticky traps in soybean fields. Place four to six yellow traps on T-posts across the field, adjusting the height of the traps so they are just above the canopy. Change the traps on a routine basis, counting the number of rootworm beetles stuck on the trap. If possible, count the traps in the field to avoid getting sticky goop all over the place. Also, once traps are folded back together, then unfolded, insects have a tendency to break apart and identification is more difficult. Once you get the total number of rootworms on a trap, divide that number by the number of days that the trap was exposed. This gives you the number of beetles per trap per day. Finding less than one to two per trap per day is not of concern. Finding three to four beetles per trap per day suggests variant is in your area. Five to seven beetles per trap per day predicts that you will have root pruning on corn next year, and the damage may be economic. Finding 10 or more beetles per trap suggests that damage next year will be severe with entire nodes of roots gone.

Defoliation is present in many fields, caused by a complex of insects: Japanese beetles skeletonize leaves, creating a lacy appearance. Bean leaf beetle and corn rootworm beetle chew round holes in leaves. Grasshoppers often chew from the leaf margin. The threshold for defoliation during pod fill is 25 percent. The human eye often overestimates defoliation. It is common to find pockets of worse defoliation on upper leaves, particularly where Japanese beetles cluster to mate in a small area and feed heavily. When assessing defoliation, examine more than the top leaves. Plants can compensate for feeding, and light can also filter down to leaves in the mid-canopy. One thing to watch for is pod feeding by bean leaf beetle, rather than simply defoliation. Pod feeding can directly impact yield and quality, and the threshold is only 10 percent of pods damaged. This type of feeding usually occurs later into August.

How do the counts from Michigan compare with other states in the regional trapping network? In the accompanying map is a summary of the soybean aphid catch from traps in five states, all from the week of July 15.

Here is a quote from Dr. Dave Voegtlin, who is sorting the catches from the regional trapping network, “I am sure that you don't have to tell Chris that Michigan has lots of soybean aphids… The remnants of hurricane Dennis provided central Illinois with mild north west winds for two or three days in a row at the end of that week. A perfect situation for Michigan to export its aphid resource and I believe that is what we saw in the number of alates in the field. If this heat does not slow the aphids down, August is going to be lively.”

Soybean aphid update
Christina DiFonzo, Entomology

Insect update: Aphids and borers
Christina DiFonzo, Entomology

The following article is from the June 30 , 2005 Field Crop CAT Alert.

Soybean aphid numbers continue to climb across Michigan. In fact, we are more heavily infested than many of the states around the Great Lakes. We have numerous field plots in which 100 percent of the plants are infested with an average of 90 to 100 aphids per plant. However, none of our plots are truly over the 250 threshold, when aphids are directly counted and averaged. We expect that they will go over threshold within the next two weeks. Many fields are beginning to flower, so the timing for spray applications will be quite good. Remember to think timing and coverage for soybean aphid control.

This week, winged aphid production and flight began in infested fields. This is important for several reasons.

First, these winged individuals will move around the landscape and land on previously uninfested fields. For example, we counted two to seven winged aphids per plant on Gaucho treated beans on June 28 at MSU. If you live in an area that lacks buckthorn, you used a seed treatment that killed the initial flight of aphids from buckthorn, be ready to walk fields after July 4 because this new flight of aphids will colonize your clean fields. Also, if you sprayed early (within the last two weeks), be prepared to start scouting again, because your fields will be re-infested by winged migrants from neighboring fields.

Second, winged aphids spread viruses in vegetable crops, so watch for an increase in symptoms of CMV, WMV2, ZYMV, and other viruses in two to three weeks.

I am trying to get aphid information out to agribusiness and growers in numerous ways. This includes the CAT Alert newsletters, plus the MABA Ag Fax, the Michigan Soybean Promotion Committee, Farm Radio interviews and DTN. Also, I will be doing a call-in show for DTN on Tuesday, July 12, at 9:00 PM. The web site with more information, and a way to listen to the show after the fact is at: http://www.dtn.com/dtn_onair.cfm

Corn borer numbers are still high as well. There are a few reports of spraying in southern Michigan, especially areas with seed corn production. While I have not had a report of field corn over threshold, people do report shot-holing damage on up to 40 percent of the plants, close to the 50 percent threshold.

Pea aphid numbers are high in some alfalfa fields – presumably it is a good aphid year in general in Michigan. I looked at a field this week that had a heavy pea aphid infestation before, then after cutting as the aphid concentrated on the new growth. However, by the time I looked at the field within a day or two of the phone call, most of the aphids were dead. They were infected with naturally occurring fungi that attack and kill aphids under humid, warm environmental conditions. The good news is that once these fungal diseases start, they can move around the landscape to aphid species in other crops, for example, to soybean. While I haven’t seen any infected aphids on soybean yet, in previous years we observed infected soybean aphids in August, under the same conditions that lead to white mold.

• Reduce virus source by planting clean seed or transplants
• Plant resistant hybrids if available
• Reduce aphid landing rate using reflective mulches, cover and border crops, etc

• Increase gallons per acre and pressure (we use a minimum of 40 psi in research trials).
• Use nozzles specifically designed for coverage, for example, a Twin Jet.
• A ground rig will probably provide better coverage than aerial application in a heavy canopy.
• Drive at a reasonable speed across the field (avoid fantasies about NASCAR).
• To minimize crop damage and improve coverage, plant rowed beans or leave skip-rows in drilled beans.

Tank mixes
Given a similarity in spray timing and application method, tank mixes of fungicides and insecticides may be economical. This at least would save the cost of going over the field a second time.