the BulletinPest Management and Crop Development Information for Illinois

17

No. 2 / April 8, 2010

Executive editorVince M. Davis,

Extension Soybean Specialist

www.ipm.illinois.edu/bulletin

Copyright © 2010, Board of Trustees, University of Illinois

Also in This Issue

• Key Corn and Soybean Insect Outlook for 2010: What Should Producers Anticipate? 2

• Corn Herbicide and Insecticide Precautions 3

• Identifying Early-Season Weeds 4

• Managing Glyphosate-Resistant Weeds in Illinois 6

• Fungicide Seed Treatment Considerations for Soybean 6

• Soybean Planting, Variety Selection, White Mold, and Seed Treatments 6

• Looking at the Wheat Crop 8

• Regional Reports 9

COLLEGE OF AGRICULTURAL, CONSUMER AND ENVIRONMENTAL SCIENCES

UNIVERSITY OF ILLINOIS

EXTENSION

Insects

Establishment of Refuges Critical in Maintaining Long-Term Durability of Bt Hybrids

It won’t be long before planters begin to roll across the landscape of the Corn Belt. With the increasing use of Bt hybrids as the foundation of many corn insect man-agement programs, it’s important to remember the requirement to establish refuges to delay or prevent the development of resistant populations of key insect pests, such as the European corn borer and western corn rootworm. To date, we have been fortunate that field-level resistance has not developed for either of these species despite the widespread adoption of this impressive technology (Figures 1 and 2).

Since 2005, producers in Illinois have significantly increased their use of “stacked” gene corn hybrids. These stacks include corn hybrids that express Bt proteins target-ed against the lepidopteran complex (e.g., European corn borers, black cutworms, western bean cutworms) and corn rootworms as well as offer herbicide tolerance. In 2009, stacked hybrids comprised nearly 60% of all corn planted in Illinois. Although escalating seed costs remain a viable concern among producers, I suspect we will continue to witness a steady increase in the use of these versatile corn hybrids.

In addition to the stacked hybrids, pyramided corn hybrids (SmartStax) will be introduced to the market in 2010. These pyramided hybrids express several Cry proteins for corn rootworm (Cry3Bb1, Cry34/35Ab1) and lepidopterans (Cry1A.105+Cry2Ab2, Cry1F) and were developed through a cross-licensing agree-ment between DowAgroSciences and Monsanto. Of particular interest to producers who plant SmartStax hybrids is the refuge reduction from 20% to 5% in the Corn Belt. For 2010, the 5% refuge must still be a structured one (seed mixtures cannot serve as the refuge). For producers who elect to plant other Bt hybrids this spring, the 20% requirement remains in place.

In surveys (using Turning Point Technology) of producers who participated in the 2010 Corn and Soybean Classics, slightly fewer than 80% said they planted a refuge in 2009 according to suggested guidelines (Figure 3). Over time, as more pyra-mided hybrids become commercialized, I suspect that seed mixtures (transgenic and nontransgenic seed) will form the foundation of resistance management plans. This will ensure grower compliance, and with the pyramided technology in place should help prolong the long-term durability of Bt hybrids.

A large majority (approximately 80%) of producers at the Classics indicated being receptive to using a seed blend as a refuge. Key concerns regarding a seed mixture approach were the potential for significant insect injury to non-Bt seed and the in-ability to rescue injured plants. However, the convenience offered by a seed mixture refuge strategy seems to trump this concern for most producers, up to a point. Ap-proximately 90% indicated their willingness to use a seed blend that contained non-Bt seed in the 2% to 5% range (Figure 4). However, if the non-Bt seed falls in the

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6% to 10% range, interest falls below 60% (Figure 5).

During the 2010 growing season, I would be interested to learn if produc-ers experience corn rootworm control problems despite their use of Bt hybrids. In 2009 there were many reports of severe corn rootworm damage to some Bt hybrids in areas of southeastern Min-nesota, northeastern Iowa, and western Wisconsin. Often corn rootworm larval damage goes unnoticed unless severe lodging occurs. In many instances, this lodging is not detected until harvest. It may be worthwhile to check the value of your investment in Bt corn this year. Grab a shovel and remove some corn roots from Bt as well as refuge areas of your fields. Mid-July is the best time to check for corn rootworm pruning, de-spite the heat and pollen. If you find that nodes of roots have been removed from Bt plants, give me a call or send me an email. I look forward to your observa-tions and comments.—Mike Gray

Key Corn and Soybean Insect Outlook for 2010: What Should Producers Anticipate?

Accurately predicting what insects may do before corn and soybeans have been planted is always tough, but I’ll offer some thoughts for a few key insect pests of those crops. Of most entomological interest in soybean is the soybean aphid. Many of us remember the swarms of soybean aphids across central and southern Illinois late in the growing season last year. They were abandoning soybean fields and seeking out their overwintering host—buck-thorn plants. Based on observations by David Voegtlin, a retired entomologist with the Illinois Natural History Survey, buckthorn leaves were “dripping” with aphids following the growing season (late summer to early fall). Perhaps not surprisingly, a fungal epizootic swept through this impressive aphid buildup on buckthorn and decimated the popula-tion. Consequently, I anticipate a very small spring flight from buckthorn to soybean fields.

 Figure 1. USDA—Economic Research Service estimates of stacked gene varieties, Il-linois and USA.

 

Figure 2. Responses to the question “Did you plant a Bt hybrid in 2009?” from at-tenders at the 2010 Corn and Soybean Classics in five Illinois cities.

 

Figure 3. Responses to the question “If you planted a Bt hybrid in 2009, did you plant a 20% refuge according to the suggested guidelines?” from attenders at the 2010 Corn and Soybean Classics in five Illinois cities.

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Figure 4. Responses to the question “If you answered ‘yes,’ would you be willing to use a seed blend that contains non-BT seed in the 2% to 5% range?” from attenders at the 2010 Corn and Soybean Classics in five Illinois cities.

 

Figure 5. Responses to the question “If you answered ‘yes,’ would you be willing to use a seed blend that contains non-BT seed in the 6% to 10% range?” from attenders at the 2010 Corn and Soybean Classics in five Illinois cities.

Once again last year, we reached all-time population lows for the European corn borer across Illinois. Densities were slightly larger in some areas of western Illinois. With such low over-wintering numbers, the spring flight of European corn borers should be hardly noticeable in 2010 throughout Illinois. It seems that western corn rootworms create management challenges almost every year, through either root prun-ing or silk clipping. However, in 2009, their densities were very low. Consider-able speculation has arisen regarding whether the large-scale increase in Bt usage may be suppressing corn root-worm populations, similar to what has

been witnessed for European corn borer densities. Because Bt hybrids targeted at corn rootworms are considered low-to-moderate dose in their effects on corn rootworms, I suspect that environmental conditions last season contributed to the collapse of the corn rootworm popula-tion. Specifically, the very wet soil con-ditions throughout the spring resulted in high mortality of larvae soon after hatch occurred. Consequently, I believe many Illinois producers in 2010 should ex-perience very light to moderate infesta-tions of western corn rootworms.

Japanese beetle infestations will con-tinue to vex producers in 2010. In spite

of the very cold winter, the snow cover across many areas of Illinois should serve as a buffer and enhance the sur-vival of overwintering grubs. Last year Andy Morehouse, a graduate student in the Department of Crop Sciences, conducted the first year of his thesis re-search in many producers’ fields across Illinois. After the first year, his results clearly indicate that sampling only mar-gins of a soybean field should not form the basis of a treatment decision for the entire field. It was common for densi-ties of Japanese beetles to be impres-sive in field margins and quickly fall below economic levels in field interiors. Andy intends to conduct his second year of field research this season.

For many insects that migrate into Illinois (e.g., black cutworms, corn leaf aphids, potato leafhoppers, fall armyworms, corn earworms), it’s too early to assess the potential impact on production this season. I look forward to sharing observations from around the state and region this summer with re-spect to insect infestations.—Mike Gray

Weeds

Corn Herbicide and Insecticide Precautions

The commercialization of corn hybrids with “built-in” resistance to certain insect pests has greatly contributed to the decline in use of soil insecticides. Some farmers, however, are considering applying a soil insecticide at planting for control of “other” insect pests or for control/suppression of certain corn nematodes. Many insecticide choices are available to farmers, but several could restrict the use of certain corn her-bicides. Specifically, using an organo-phosphate (OP) insecticide at planting or after corn emergence could restrict the use of herbicides that inhibit either the ALS or HPPD enzymes. The precau-tions and restrictions most often appear on the herbicide label and are due to the increased potential for corn injury fol-lowing use of OP insecticides and ALS- or HPPD-inhibiting herbicides.

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Why do certain combinations of OP in-secticides and ALS- or HPPD-inhibiting herbicides cause injury to corn? Most of these herbicides are systemic, mean-ing they move extensively (translocate) from their site of uptake. Translocated compounds often accumulate in areas of the plant undergoing active cell divi-sion (meristems). Both insecticides and herbicides are compounds foreign to the corn plant. The plant tries to defend it-self against any potential injury a foreign compound could cause by rendering it inert, or nonphytotoxic. This process is commonly referred to as metabolism, or breakdown, of foreign compounds. A corn plant uses several different path-ways to detoxify foreign compounds, but the OP insecticides and many ALS- and HPPD-inhibiting herbicides share a common metabolic pathway. When an insecticide or herbicide is present within the plant, the plant can usually metabo-lize the compound before it may cause any deleterious effects. However, if both insecticide and herbicide are present, the pathway cannot effectively metabolize both compounds. When this happens, corn injury can result.

Table 1 summarizes herbicide label information with respect to the potential for corn injury caused by various OP–her-bicide interactions. As always, be sure to consult the most current product labels for additional information.—Aaron Hager

Identifying Early-Season Weeds

Ample soil moisture and warming tem-peratures are promoting rapid growth and development of many early-season weed species. Most weeds currently growing in fields emerged last fall and successfully overwintered (winter annuals, bienni-als, and perennials), but several early-season summer annual species recently have emerged. Existing weed vegetation should be controlled before planting by using tillage, herbicides, or a combina-tion of tactics so the crop can become established under weed-free conditions.

Field scouting to identify the weeds present and their relative densities will provide the information needed to tailor

a burndown herbicide program for any particular field. Many species can be present in any particular field, and ac-curate identification is sometimes chal-lenging. Following are brief descrip-tions and photographs of weed species common to Illinois fields at this time of year. [Editor’s note: The photographs are grouped at the end of the newsletter in order of their mention.]

Annual bluegrass is a shallow-rooted grass species that often roots at the lower nodes. Plants grow to about 12 inches tall and often have begun to flower by the time of crop planting. Leaves lack au-ricles and possess a membranous ligule. Leaf blades are glabrous on both surfaces and keeled with sharp-pointed tips.

Over a dozen species of buttercup exist in Illinois, which can make accurate iden-tification a bit challenging. Smallflower buttercup is one species that can be found across much of the state. Its lower leaves are rounded and broad with toothed mar-gins, generally bright green in color and borne on long petioles. Upper leaves are deeply lobed, with much shorter petioles. Flowers have yellow petioles, and seeds are contained within a cone-shaped struc-ture known as an achene.

Butterweed (aka cressleaf groundsel) is a winter annual species that produces bright yellow flowers in later spring. The plant overwinters in a rosette stage and “bolts” in the spring to produce a hollow stem that is green or red and smooth to the touch. From a distance the yellow flowers of butterweed resemble those of yellow-flowered mustard species, but butterweed is not a mustard species.

Common chickweed often forms very dense mats of vegetation that can make planting difficult. It has a shal-low, fibrous root system and a stem that branches extensively and often roots at the nodes. Leaves are small, opposite, and pointed at the tip. A perennial chick-weed species, mouseear chickweed, can be differentiated from common chickweed by the dense hairs covering its stem and leaf surfaces.

Dandelion is a simple perennial species that forms a large, often deeply rooted

taproot. The leaves have irregular mar-gins, are often deeply lobed, and form a basal rosette. The flower is large and yellow.

Field pennycress begins as a basal rosette of leaves, then produces an erect flowering stem that is smooth and tends to smell unpleasant when bruised. Leaves on the upper stem are alternate and sessile about the stem, with earlike projections and either entire or slightly toothed margins. Field pennycress is one of several mustard species in Illinois that produces white flowers consisting of four petals. Other mustard species that produce white flowers include shepherd’s-purse and Virginia pep-perweed. The most common yellow-flowered mustard species in Illinois fields is yellow rocket.

Henbit and purple deadnettle are close botanical relatives; both exist as winter annuals, and both have square stems. Henbit is more common throughout Illinois, while purple deadnettle appears more often in about the southern half of the state. The lower leaves of henbit are attached to the stem with petioles, while the upper leaves grasp the stem (i.e., lack petioles). The upper leaves of purple deadnettle, however, are attached to the stem with petioles, are more trian-gular than those of henbit, and are less deeply lobed.

Fall-emerging horseweed plants (aka marestail) form a basal rosette that represents the plant’s overwintering stage. In the spring, plants bolt by rap-idly elongating the main stem. Leaves, very numerous and hairy with toothed margins, alternate around the stem and become progressively smaller toward the top of the plant. The leaves on ma-ture plants lack petioles and have entire or slightly toothed margins. As the plant matures, leaves toward the base of the plant deteriorate and fall off the stem.

Kochia is one of the summer annual weed species that emerges earliest. Its leaves are opposite, simple, and very hairy. Stems are erect and often become grooved as the plant ages. Mature plants can vary in color from green to red.

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Poison hemlock is a biennial species becoming increasingly common in reduced-tillage environments. Leaves are arranged alternately on the stem, triangular in outline, four to five times pinnately compound (fernlike), with-out hairs, and borne on petioles. Basal leaves have a long petiole, while upper leaves have a much shorter one. Stems (produced during the second year) are erect, much branched, smooth (without hairs), and hollow except at the nodes. Stem color is light green; lower portions of the stem are spotted or streaked with red or purple blotches. The inflorescence of poison hemlock is a compound umbel

consisting of multiple white flowers, each flower bearing 5 petals.

Prickly lettuce, a winter or early sum-mer annual with a large taproot and stem, grows up to 6 feet tall. Leaves are large and coarse, with prickles along the margins. Older leaves also have a row of prickles along the underside midvein. The stem, roots, and leaves exude a milky sap when injured.

Speedwell species are generally consid-ered winter annuals, although some pe-rennial species exist. Some species grow close to the ground and form dense mats of vegetation, whereas others grow

more upright. Leaf shape varies by spe-cies, but most speedwell species have lower leaves that are opposite and upper leaves that are alternate.

Wild carrot is a biennial species that most often occurs along the edges of reduced-tillage fields. Typical of bien-nial species, its first year of growth occurs as a rosette of leaves followed by rapid stem elongation and maturation during the second year. Some confusion may arise in trying to differentiate poi-son hemlock from wild carrot. Both are biennial species that produce an umbel inflorescence, but poison hemlock is more toxic. Differences include plant

Table 1. Corn herbicide label statements: Interactions with organophosphate (OP) insecticides. Soil-applied OP insecticides

Counter 15G Aztec or Fortress Foliar OP insecticide

applied Corn herbicide Furrow T-band Thimet Lorsban Furrow T-band Days before Days after Nicosulfuron and rimsulfuron

Accent Q No No UCI UCI Yes Yes 7 3 Basis No No UCI UCI Yes Yes 7 3 Prequel Noa Yes Noa Noa Yes Yes – 60 Require Q No No UCI UCI Yes Yes 7 3 Resolve Q No No UCI UCI Yes Yes 7 3 Steadfast Q No No UCI UCI Yes Yes 7 3 Stout No No UCI UCI Yes Yes 7 3

Primisulfuron and prosulfuron Beacon No No TCI TCI TCI TCI 10 7 Northstar No No TCI TCI TCI TCI 10 7 Spirit No No TCI TCI TCI TCI 10 7

Flumetsulam Hornet WDG (PRE) No No No TCIb Nob TCI – – Hornet WDG (POST) No No No TCI TCI TCI 10 10 Python No No No TCIb Nob TCI – – SureStart (PRE) No No No TCIb Nob TCI – – SureStart (POST) No No No TCI TCI TCI 10 10

Thifensulfuron Harmony GT XP No No UCI UCI Yes Yes – –

Mesotrione Callisto SCI SCI Yes SCI Yes Yes 7 7 Callisto Xtra SCI SCI Yes SCI Yes Yes 7 7 Camix No No TCI TCI TCI TCI 7 7 Halex GT SCI SCI SCI SCI SCI SCI 7 7 Lexar SCI SCI TCI TCI TCI TCI 7 7 Lumax SCI SCI TCI TCI TCI TCI 7 7

Foramsulfuron Option No No No TCI Yes Yes 7 7

Thiencarbazone Corvus No No No No Yes No 7 7 Capreno No No No No Yes Yes 7 7

Saflufenacil Integrity No No No No No No - - Sharpen No No No No No No - -

No: Do not use this herbicide on corn if this insecticide was previously applied. Yes: This herbicide may be applied to corn previously treated with this insecticide. UCI: unacceptable crop injury; TCI: temporary crop injury; SCI: severe crop injury; –: no information on label. aDo not apply Prequel within 60 days of crop emergence where an OP insecticide was applied in-furrow. bSoil-applied OP insecticides should not placed in furrow, but rather applied in a band or T-band.

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height (poison hemlock may reach 6 to 10 feet at maturity; wild carrot rarely exceeds 4 to 5 feet at maturity); stem coloration (poison hemlock stems have red to purple blotches; wild carrot stems lack such coloration); stem hairs (poison hemlock has stems with no hairs; wild carrot has stems with bristly hairs); flowering time (poison hemlock flowers in mid- to late spring; wild carrot flow-ers later in summer); the pungent odor of poison hemlock foliage; and the hairy leaves of wild carrot.

Two members of the smartweed fam-ily that emerge during early spring are Pennsylvania smartweed and prostrate knotweed. Both species (as well as most members of the Polygonaceae fam-ily) have swollen nodes covered with a membranous sheath called an ocrea.

—Aaron Hager

Managing Glyphosate-Resistant Weeds in Illinois

The occurrence of glyphosate-resistant weed populations in Illinois has un-questionably increased since the initial discovery of glyphosate-resistant horseweed (aka marestail) several years ago. Populations of glyphosate-resistant waterhemp, the other weed species in Illinois with confirmed resistance to glyphosate, will likely spread across much of the state during the next few years, further complicating postemer-gence weed control. No novel herbicide active ingredients for postemergence control of broadleaf weeds in soybean are likely to be commercialized in the next few years, so managing herbicide-resistant weed populations will become increasingly challenging into the fore-seeable future.

For the past three seasons, the Illinois Soybean Association has provided generous funding to support applied research focused on defining viable op-tions for managing glyphosate-resistant weeds in soybean. Weed scientists from the University of Illinois, Southern Il-linois University, and Western Illinois University have collaborated on a vari-ety of (mostly) on-farm field research

projects, culminating in the publication Help Stop Glyphosate Resistance. This new brochure provides recommenda-tions for managing glyphosate-resistant waterhemp and horseweed in soybean and is available in PDF format to download at www.vipsoybeans.org. We encourage soybean farmers to peruse the information and contact Dr. Roskamp (WIU), Dr. Young (SIU), or me with any questions.—Aaron Hager

Plant Diseases

Fungicide Seed Treatment Considerations for Soybean

Fungicide seed treatments for soybeans can be used to help ensure good emer-gence and uniform stands, but they may not always result in a yield advantage. In general, there are two potential reasons to treat soybean seeds with a fungicide: when poor-quality seed is being planted, and to protect against seedling diseases.

Poor-quality seed. It is always recom-mended that the highest-quality seed be planted, but this is not always possible. Fungicide seed treatments may help improve stand establishment of a variety with poor-quality seed (Figure 6). This is especially true if the poor quality is due to infection by a fungal seedborne patho-gen. If it is due to mechanical damage, a fungicide seed treatment will not increase the germination rate of the seeds, but it may help in providing a more uniform stand, which could (but does not always) translate into greater yields.

Protection against seedling diseases. Seedling diseases of soybean can be caused by pathogens such as Pythium, Phytophthora, Rhizoctonia, and Fusar-ium. In some cases, a complex of these pathogens may affect soybean seedlings. Fungicide seed treatments can be ef-fective in protecting seeds and seed-lings from these pathogens for a short period, which may allow the seedlings to become established and be produc-tive plants. The risk of being affected by seedling diseases may increase when planting early (April to early May),

when planting into a field with a history of seedling disease problems, and when weather conducive for seedling diseases (generally cool and wet) appears just after planting. A summary of Univer-sity of Illinois soybean seed treatment trials conducted from 2001 to 2008 shows that the average increase in yield obtained with a fungicide seed treatment was 0.8 bu/acre; however, the yield advantage increased when fields were planted earlier (late April to first week of May; Figure 7).

Which product(s) should I use? If you decide to use a seed treatment on soy-bean, it is important to use products that provide broad-spectrum control of many pathogens. The treatment should include either mefenoxam or metalaxyl as the active ingredient, which provides some protection against oomycete patho-gens (Pythium and Phytophthora). The treatment should also contain at least one other fungicide (i.e., fludioxonil, tri-floxystrobin, pyraclostrobin, ipconazole) that will provide broad-spectrum control against Fusarium and Rhizoctonia.—Carl A. Bradley

Crop Development

Soybean Planting, Variety Selection, White Mold, and Seed Treatments

Selecting appropriate genetics is always the first and best way to increase your yield and profits. I suspect many of you decided during the winter months what soybean varieties to plant for all or most of your acres. However, you might need to purchase a final few bags, or you may develop additional needs as the spring progresses. If so, don’t rush your final selection. Continue to take the necessary time to select varieties with the appropriate maturity, soybean cyst nematode resistance, disease resistance, and overall agronomic characteristics to match the needs of your fields and farm-ing operation. Use the yield and lodging information generated by the University of Illinois Variety Testing program (vt.cropsci.illinois.edu/soybean.html). If

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73

9085

90

75

83

0

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40

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60

70

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Untreated Maxim 4 FS 0.08 fl oz

Dynasty 0.15 fl oz

Rancona 3.8 FS 4 fl oz

Stamina 0.4 fl oz

Trilex FL 0.32 fl oz

Ger

min

atio

n (%

)LSD 0.05 = 14

Figure 6. Effect of fungicide seed treatments on germination of a soybean seed lot infected with both Sclerotinia sclerotiorum and Phomopsis longicolla. Data courtesy of Carl Bradley, University of Illinois.

Figure 7. Summary of University of Illinois fungicide seed treatment trials on soybean from 2001 to 2008. (Trials in 2001 to 2006 were conducted by Dr. Wayne Pedersen; in 2007 and 2008 trials were conducted by Dr. Carl Bradley.)

you don’t find the varieties you use on your farm, nominate a variety to be tested in the future, sponsored by the Illinois Soybean Association. Testing results from 2009 are summarized in Figure 8. Average yields ranged from 48.6 bu/acre for Region 4, Maturity Group 3 to 67.2 bu/acre for Region 5, Maturity Group 4. Within each region-by-maturity group category, yields ranged 12% to 27%.

Additional variety information, includ-ing SCN resistance data and disease ratings, are provided by the Varietal Information Program, funded by the Illinois Soybean Association; they can be found at www.vipsoybeans.org. I want to point out that there were a lot of problems with white mold (Sclero-tinia stem rot) in the northern regions of Illinois last year. There are greenhouse white mold tolerance ratings available

on VIPS for varieties that were grown in Region 1 testing locations last year (www.vipsoybeans.org/v4/vpcompare/cvSSRgreen2009.cfm?b=y). The Re-gion 1 yields are also available in the same table. The tolerance ratings were generated by a greenhouse screening technique, so the yield column does not reflect the yield in an environment with that disease rating. Furthermore, the greenhouse technique may not perfectly reflect a variety’s white mold toler-ance under field conditions, but it likely provides some indication. These ratings might help guide final planting deci-sions or provide or confirm suspicions of causes of poor performance from par-ticular varieties you planted last year if white mold was an issue in your fields.

Once you have decided on your seed, you may be left with another decision—should you treat it? More specifically, should it be treated with a fungicide seed treatment, insecticide seed treat-ment, inoculants, or other potential micronutrients or products? These are not easy issues, and Carl Bradley will be providing results from his 2009 soybean seed treatment studies. The overlying agronomic principle to keep in mind is that you want to establish at least 100,000 healthy and uniformly spaced soybean plants to maximize yield.

The necessity of seed treatments to accomplish that establishment goal depends on a couple of things. First is the likelihood of needing to ward off seedling disease and early-season insect feeding where a field has a history of these problems or conditions that favor them. Second, how many seeds you plant and into what field conditions are important factors. The fewer seeds you plant, the more important it becomes to have every one become a productive plant. In this regard, seed treatment is a form of insurance, and that is certainly how it is marketed. Historically, it was much easier to plant many more seeds (up to twice as many) than the number of plants needed. However, seed prices have escalated to a point that brings that strategy into question, so it is hard to de-velop a hard-and-fast rule. A grower who still finds comfort in planting at high

-15.0

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Yie

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iffe

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Average = 0.8 bu/A; N = 447

Early plantings

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Figure 8. 2009 soybean yield data from the University of Illinois Variety Testing Pro-gram. Bars represent yield for 90% of the varieties tested in each testing region by ma-turity group category. Region 1 is in northern Illinois; Region 5 is in southern Illinois.

seeding rates (say 170,000 seeds/acre or greater) is probably not likely to find much value in soybean seed treatments. However, for a grower who is reducing seeding rates to the newer economic optimum ranges (say 130,000 to 150,000 seeds/acre), seed treatment has greater potential to be a good investment.

The use of soybean inoculant, Brady-rhizobium japonicum, is yet another issue. On one hand, inoculants are fairly inexpensive; on the other hand, they rarely provide large yield increases in most Illinois soils. I think it’s fair to say that in general you should only expect at most an extra couple of bushels, and more likely an extra bushel or less. In 2009 I tested several inoculants at three locations in Illinois and found no statis-tically significant differences. In a few cases the inoculants might have paid for themselves by increasing yield by a par-tial bushel of extra yield, but that could not be separated from random chance alone. Since I only have one year of re-sults, I will not present more detail here, but I will be testing more inoculants, in more locations, this year.

The rule of thumb for inoculating soy-bean seed is to do so if a field has not had soybean grown in the last five years. The questions continually arise for our growers who are planting more corn in

their rotations and may have many fields that are on rotations of 3 or 4 years of corn between soybean. We do not have good data to evaluate the benefit of inoculants versus number of previous years in corn as a curve. All I can say is that is makes sense that the more years the field has previously grown corn, the greater the likelihood that inoculants will pay for themselves and may boost your fields’ average yields. So inocula-tion is a cheap investment and provides some level of insurance for proper nodulation, but don’t expect too much on most Illinois soils.—Vince M. Davis

Looking at the Wheat Crop

The spring so far has been reasonably good for bringing the wheat crop along, but many questions remain about the potential for many fields to produce high yields. After what was the worst fall for planting wheat in at least three decades, and a reduction of about 60% in acres planted from the previous year, wheat prices remain low enough that we need to assess the crop carefully to see if it’s worth keeping. Crop insurance consider-ations also are in play for many producers.

The wheat crop in Illinois is currently rated at 9% very poor, 21% poor, 23% fair, 28% good, and 1% excellent. In contrast, the early April rating for the

crop in 2009, which was perhaps a little above average, was 3% poor, 23% fair, 64% good, and 10% excellent. Hav-ing less than a third of the crop rated as good or better is very likely to mean that some of the current crop will not (and should not) be kept to harvest.

The first things to evaluate in a strug-gling wheat field are the stand and stand uniformity. This evaluation requires that stand counts be made in enough areas of the field to provide a good picture of both numbers of plants and variability. Low, drowned-out areas will be a factor in many fields, and decisions will have to be made about whether to keep the field based on the extent and distribu-tion of such areas. If drowned-out areas are large but the rest of the crop is good, it may work well to plant another crop in the low areas. The fill-in crop would likely be soybean, but it could be oats in northern Illinois, though it’s already time to plant oats and these areas are probably still wet. Keeping weeds down will be helpful, even if these areas remain without a crop until the field is double-cropped in June.

Complicating the stand count this year are the delayed planting and small size of wheat plants coming into the spring. I suggested back in the winter that a crop that had barely emerged before dormancy or would emerge in the spring may need 30 to 35 plants per square foot to compensate for the likely reduction in tillering. This drops to 25 to 30 plants per square foot if plants covered about a third of the ground area at green-up, or 20 to 25 plants if half the ground area was covered at green-up. We have normally suggested keeping stands with counts as low as 15 to 20 plants per square foot, but that works only if plants make normal fall growth and cover two-thirds or more of the ground area by the time they green up in the spring.

It’s the tiller count that is really needed to assess yield potential. At this point in the season it should be possible, at least in the southern half of the state, to get an idea of how many tillers might form and to use that information to make decisions about keeping a stand. Our normal rule

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of thumb is that one head per square foot means about one bushel per acre. So if we set 50 bushels per acre as the thresh-old to keep a stand, you will need about 50 heads to form per square foot. It takes a tiller to make a head, of course, but not all tillers form heads. It’s difficult to pre-dict which tillers will form heads until into jointing (Feekes 7), or when plants are about 8 inches tall. By then you can start to see which tillers are growing vigorously enough to win the race and form heads. Before then, you can only guess at likely head numbers. Assume that the small tillers hidden beneath the rest of the plant are not likely to form heads. More tillers form on plants in low stands, but not always enough to com-pensate for low plant numbers.

The length of the tillering period, which lasts up to the start of jointing, varies with temperatures; above-normal tem-peratures like we’ve had the past week improve crop color and growth, but they can also hasten the end of tiller forma-tion and result in lower head numbers. The expected return to more normal temperatures this week may give a small boost to tiller and head formation, but we can expect jointing to begin within the next week or 10 days in southern Illinois, and we should be able to assess yield potential more fully after that.

Late planting and cool March weather mean that most of the crop is well be-hind normal in development now. This means that heading is likely to be late and harvest is likely to be later than nor-mal. The only way this may not happen is if temperatures average well above normal from now into June. Because wheat is a cool-season crop, above-nor-mal temperatures may well reduce yield, especially if rainfall is normal or above normal. But if temperatures stay normal, the delay in harvest will result in a delay in double-crop planting. This may be a factor in the decision to keep a mar-ginal stand, especially if double-crop is necessary to make the system profitable. Most double-crop in 2009 was planted as early as full-season soybeans, but we hope that will not be the case in 2010.—Emerson Nafziger

Regional Reports

Extension center educators, unit edu-cators, and unit assistants in northern, west-central, east-central, and south-ern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season. The regions have been defined broadly to include the agricultural statis-tics districts as designated by the Illinois Agricultural Statistics Service, with slight modifications:

• North (Northwest and Northeast dis-tricts, plus Stark and Marshall counties)

• West-central (West and West South-west districts, and Peoria, Woodford, Tazewell, Mason, Menard, and Logan counties from the Central district)

• East-central (East and East Southeast districts [except Marion, Clay, Rich-land, and Lawrence counties], McLean, DeWitt, and Macon counties from the Central district)

• South (Southwest and Southeast districts, and Marion, Clay, Richland, and Lawrence counties from the East Southeast district)

We hope these reports will provide ad-ditional benefits for staying current as the season progresses.

East-Central Illinois

More consistent warmer and slightly drier weather has enabled a limited amount of fieldwork to occur. But as soon as activity really starts to pick up, another shower comes through, and waiting starts again. Most activity has been anhydrous ammonia application, with some general tillage and spraying also being accomplished. A few scattered acres have been planted. Winter annual weeds are really starting to take off.

Northern Illinois

Field activity was widespread through-out the region the week of March 29 until nearly daily precipitation April

2 through April 7. Total accumulation ranged from 0.8 inches to 1.8 inches, with heavier amounts in the northeast portion of the region. Activities focused on tillage and anhydrous ammonia application. There was also some corn harvested and planted the week of March 29. Other activities included oat seeding, alfalfa seeding, dry fertilizer application, and some preplant herbicide application.

Generally winter wheat looks surpris-ingly good except in low, poorly drained areas where water and ice accumulated.

Extension educators are monitoring black cutworm traps, and a few captures have been reported in Lee County.

Southern Illinois

Producers took advantage of several warm, sunny, windy days in the past week to get into the fields. While fertil-izer application, anhydrous ammonia application, and first-pass tillage were the primary practices being implement-ed, some corn planting was also accom-plished. Winter annual weeds are also taking advantage of the warmer condi-tions, and the lovely purple color of henbit and purple deadnettle is becom-ing more obvious. Storms late Sunday night dropped variable amounts of rain and hail across the region, putting a stop to fieldwork in some areas.

Wheat condition continues to be vari-able. Fields planted in November continue to tiller and fill in, but bare ground between the rows is still visible. Early-planted, well-drained fields look good, while fields with poor drainage are patchy and show damage from ex-cessive water. Winter annual weeds are becoming competitive in many fields.

A Cover Crop Field Day will be held Wednesday, April 14, at 2:00 at the Terry Taylor farm on IL Route 45 south of Geff. The program will review the different cover crop varieties, includ-ing hairy vetch, annual ryegrass, and crimson clover. Plots that contained oil-seed radish, planted alone or with hairy vetch, will also be reviewed. Several fields of aerial seedings will be looked at and evaluated. For more information,

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contact Mike Plumer (618-453-5563). No preregistration is needed to attend.

West-Central Illinois

Wet conditions the past week have prevented any fieldwork. Since April 2, the south and west portions of the region had rainfall up to and exceeding 3 inch-es, while the north and east sections had less than an inch. Prior to that, fieldwork (tillage and NH3 applications) began in scattered locations around April 1. A handful of fields were planted April 2.

Soils in the west and south are com-pletely saturated (again).

Wheat fields range from still (hopefully) tillering (on the late-seeded fields) to stem elongation (on those planted at the fly-free date). Stand counts are good.

Alfalfa fields saw good growth last week, with some fields at 6 inches in height. No noticeable weevil damage yet, but vole damage is apparent in many fields.

Contributing AuthorsCarl A. Bradley, carlbrad@illinois.edu, 217-244-7415

Vince M. Davis, davisv@illinois.edu, 217-244-7497

Mike Gray, megray@illinois.edu, 217-333-6652

Aaron Hager, hager@illinois.edu, 217-333-4424

Emerson Nafziger, ednaf@illinois.edu, 217-333-4424

Early-Season Weeds

Annual bluegrass

Buttercup

Butterweed

Common chickweed

Mouseear chickweed

Common chickweedDandelion

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Field pennycress

Shepherd’s-purse

Virginia pepperweed

Yellow rocket

Henbit

Purple deadnettle

Virginia pepperweed

Horseweed

Kochia

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Poison hemlock

Prickly lettuce

Prickly lettuce

Speedwell

Wild carrot

Prostrate knotweed

Smartweed