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How To Interpret Scn Soil Test Results, Gregory L. Tylka Dec 2006

How To Interpret Scn Soil Test Results, Gregory L. Tylka

Integrated Crop Management News

Soybean yield loss due to the soybean cyst nematode (SCN) occurred throughout much of Iowa in 2006. Damage from this pest was particularly noticeable in areas of the state that were very dry. There seems to be increased interest in testing for and managing SCN in Iowa this fall, and there likely has been more fields sampled for SCN this fall than in recent years. Following are some commonly asked questions and answers that illustrate things to consider when interpreting SCN soil sample results. This information is excerpted from Iowa State University Extension publication IPM 61, Interpreting SCN Soil Sample ...


Brown Stem Rot And Its Interaction With The Soybean Cyst Nematode, G. M. Tabor, G. L. Tylka, C. R. Bronson Nov 2006

Brown Stem Rot And Its Interaction With The Soybean Cyst Nematode, G. M. Tabor, G. L. Tylka, C. R. Bronson

Proceedings of the Integrated Crop Management Conference

Brown stem rot (BSR) of soybeans is caused by the fungal vascular pathogen Cadophora gregata (previously named Phialophora gregata). BSR is an economically important disease of soybeans in the north central United States, being prevalent in 68 to 73% of the soybean fields of Illinois, Iowa, and Minnesota (Workneh et al. 1999). There are two genetic types (called genotypes) of C. gregata that differ in their ability to cause foliar symptoms on susceptible soybeans (Chen et al. 2000). Infection by genotype A of the fungus can result in mild to severe brown discoloration of the pith and severe foliar symptoms ...


Strategies For Management Of Soybean Sudden Death Syndrome And White Mold, X. B. Yang, S. S. Navi Nov 2006

Strategies For Management Of Soybean Sudden Death Syndrome And White Mold, X. B. Yang, S. S. Navi

Proceedings of the Integrated Crop Management Conference

Soybean sudden death syndrome (SDS) caused by Fusarium solani f. sp. glycines and soybean white mold caused Sclerotinia sclerotiorum were two of the most prevalent diseases in 2006. The two diseases have become even year production problems for some producers. This workshop will review results of the latest studies from the past two years and discuss management strategies for the two diseases. The SDS has been recognized as a major disease of soybean (Glycine max (L.) Merrill) in the southern United States for nearly three decades. In 1995 Scherm and Yang using computer model predicted that the disease would become ...


Using Resistant Soybean Varieties To Manage Soybean Cyst Nematode, Gregory L. Tylka Nov 2006

Using Resistant Soybean Varieties To Manage Soybean Cyst Nematode, Gregory L. Tylka

Proceedings of the Integrated Crop Management Conference

The soybean cyst nematode (SCN) was a serious yield-limiting pest of soybeans throughout Iowa in 2006. It caused severe damage in areas of Iowa that received less-than-normal rainfall. This nematode is widely distributed throughout the state and does not increase its numbers extraordinarily (i.e. does not flare up) in dry years. The nematode has excellent long-term survival and its population densities build up each year that susceptible soybeans are grown, regardless of the precipitation that occurs. Research in Iowa has shown that up to 40% yield loss can occur without the appearance of any above-ground symptoms.


Strike Two For Soybean Rust - 2006 In Review, Alison Robertson, X. B. Yang Nov 2006

Strike Two For Soybean Rust - 2006 In Review, Alison Robertson, X. B. Yang

Proceedings of the Integrated Crop Management Conference

Asian soybean rust is caused by the fungus Phakopsora pachyrhizi. This disease was first reported in November 2004 and survived the past two winters on kudzu in the south. Soybean rust can seriously reduce soybean yields and/or significantly increase the cost of soybean production when the disease occurs with high incidence and severity


Foliar Fungicide Application Techniques On Soybeans, H. Mark Hanna, Alison Robertson, W. Mark Carlton, Robert E. Wolf Nov 2006

Foliar Fungicide Application Techniques On Soybeans, H. Mark Hanna, Alison Robertson, W. Mark Carlton, Robert E. Wolf

Proceedings of the Integrated Crop Management Conference

Soybeans (Glycine max L.) are a major commodity crop grown on over 29 million hectare (72 million acres) in the United States. A large part of the cropland base in Iowa, 5 million hectare (11 to 13 million acres) annually, is devoted to soybean production. Although long term crop yield trends are upward, soybean yield increases have been more stagnant than corn, the common companion rotational crop, causing growers to question factors such as disease that might be slowing yield growth. In late 2004 Asian Soybean Rust (Phahopsora pachyrhizi) was detected in the United States. Because of the potential for ...


Update Of Soybean Rust Research: What We Have Learned In The Last Two Seasons And How To Position For The Future In Soybean Rust Risk Management, X. B. Yang, Ana Paula Dias, Xun Li Nov 2006

Update Of Soybean Rust Research: What We Have Learned In The Last Two Seasons And How To Position For The Future In Soybean Rust Risk Management, X. B. Yang, Ana Paula Dias, Xun Li

Proceedings of the Integrated Crop Management Conference

In the last two seasons, soybean rust has shown limited dispersal during a growing season in the southern US. In summer, it mainly spread in the Gulf Coast states. Dry weather conditions in past two summers have been considered as a possible reason for the slow development of this disease in the US. The disease did not take off to the further northern states until September. This year it was found in three new states, Illinois, Indiana, and Virginia. So far, it was found 15 states in total242 counties (See the map on right). In Iowa, the disease was not ...


Virus In Your Beans - What To Do?, John H. Hill, Jeff Bradshaw, Marlin Rice Nov 2006

Virus In Your Beans - What To Do?, John H. Hill, Jeff Bradshaw, Marlin Rice

Proceedings of the Integrated Crop Management Conference

Soybean viruses have become an increasing problem in Iowa soybeans since the late 1990's. Losses due to virus disease include both decreased yield and seed quality conferred by mottling of seed coats or hilum bleeding. The principle viruses involved are Bean pod mottle (BPMV) and Soybean mosaic viruses (SMV). Of the two, BPMV has been by far the greater problem in Iowa. Unfortunately, the two viruses cannot be differentiated based upon symptoms. Both viruses cause similar foliar symptoms and seed coat mottling. However, the viruses belong to different virus families and have different insect vectors. The BPMV is primarily ...


Late Movement Of Soybean Rust, Daren S. Mueller Nov 2006

Late Movement Of Soybean Rust, Daren S. Mueller

Integrated Crop Management News

After a hot, dry summer with very little movement, soybean rust made a late push both up the East Coast and into the Ohio River Valley. After the dust settled from the excitement in October, rust was reported in 159 new counties, including seven new states (Arkansas, Illinois, Indiana, Kentucky, Missouri, Tennessee, and Virginia). Soybean rust season totals to date are 230 counties in 15 states on soybean and 262 counties total (including kudzu). Last year at this time, there were only 130 counties in seven states positive for soybean rust. No rust was found in Iowa despite extensive scouting ...


Scn-Resistant Soybean Varieties For 2007: Many Choices, Few Sources Of Resistance, Gregory L. Tylka Nov 2006

Scn-Resistant Soybean Varieties For 2007: Many Choices, Few Sources Of Resistance, Gregory L. Tylka

Integrated Crop Management News

The soybean cyst nematode (SCN) is a major yield-limiting pest of soybeans throughout the Midwest that can be managed very effectively through use of SCN-resistant soybean varieties. Resistant varieties reduce the amount of SCN reproduction (and population density buildup) that occurs while producing significantly greater soybean yields than non-resistant (susceptible) varieties in fields infested with the nematode. The Iowa State University Extension publication titled Soybean cyst nematode-resistant soybean varieties for Iowa has recently been updated, is now available, and lists SCN-resistant soybean varieties available to Iowa growers in late maturity group 0 and maturity groups 1, 2, and 3.


What's Your Type?: An Hg Type Test For Scn Populations, Gregory L. Tylka Nov 2006

What's Your Type?: An Hg Type Test For Scn Populations, Gregory L. Tylka

Integrated Crop Management News

SCN-resistant soybean varieties reduce the amount of SCN reproduction that occurs when soybeans are grown. But if resistant soybean varieties are grown repeatedly, an SCN population capable of reproducing readily on the resistant varieties can develop. This is because resistant varieties are not immune; they allow some low level of SCN reproduction. The possibility of SCN populations building up on resistant varieties is especially a concern because almost all resistant soybean varieties have SCN resistance genes from the soybean breeding line PI88788 (see article on newly published list of SCN-resistant soybean varieties for 2007 in this issue).


Models And Applications For Risk Assessment And Prediction Of Asian Soybean Rust Epidemics, Emerson M. Del Ponte, Cláudia V. Godoy, Marcelo G. Canteri, Erlei M. Reis, X. B. Yang Nov 2006

Models And Applications For Risk Assessment And Prediction Of Asian Soybean Rust Epidemics, Emerson M. Del Ponte, Cláudia V. Godoy, Marcelo G. Canteri, Erlei M. Reis, X. B. Yang

Plant Pathology and Microbiology Publications

Asian rust of soybean [Glycine max (L.) Merril] is one of the most important fungal diseases of this crop worldwide. The recent introduction of Phakopsora pachyrhiziSyd. & P. Syd in the Americas represents a major threat to soybean production in the main growing regions, and significant losses have already been reported. P. pachyrhizi is extremely aggressive under favorable weather conditions, causing rapid plant defoliation. Epidemiological studies, under both controlled and natural environmental conditions, have been done for several decades with the aim of elucidating factors that affect the disease cycle as a basis for disease modeling. The recent spread of ...


Check Fields For Scn To Prepare For 2007, Gregory L. Tylka Oct 2006

Check Fields For Scn To Prepare For 2007, Gregory L. Tylka

Integrated Crop Management News

The soybean cyst nematode (SCN) continues to be an extremely damaging and widespread pest of soybean in Iowa and many other Midwestern states. The nematode infests more than 70 percent of the fields in Iowa and more than 80 percent of the fields in Illinois. Often there is no obvious stunting or yellowing of soybean plants in infested fields. Consequently, many SCN-infested fields in Iowa have not been diagnosed.


Trans Regulation Of Cap-Independent Translation By A Viral Subgenomic Rna, Ruizhong Shen, Aurélie Mamisoa Rakotondrafara, W. Allen Miller Oct 2006

Trans Regulation Of Cap-Independent Translation By A Viral Subgenomic Rna, Ruizhong Shen, Aurélie Mamisoa Rakotondrafara, W. Allen Miller

Plant Pathology and Microbiology Publications

Many positive-strand RNA viruses generate 3′-coterminal subgenomic mRNAs to allow translation of 5′-distal open reading frames. It is unclear how viral genomic and subgenomic mRNAs compete with each other for the cellular translation machinery. Translation of the uncapped Barley yellow dwarf virus genomic RNA (gRNA) and subgenomic RNAI (sgRNAI) is driven by the powerful cap-independent translation element (BTE) in their 3′ untranslated regions (UTRs). The BTE forms a kissing stem-loop interaction with the 5′ UTR to mediate translation initiation at the 5′ end. Here, using reporter mRNAs that mimic gRNA and SgRNA1, we show that the abundant sgRNA2 ...


Soybean Stem Colonization By Genotypes A And B Of Cadophora Gregata Increases With Increasing Population Densities Of Heterodera Glycines, G. M. Tabor, G. L. Tylka, C. R. Bronson Oct 2006

Soybean Stem Colonization By Genotypes A And B Of Cadophora Gregata Increases With Increasing Population Densities Of Heterodera Glycines, G. M. Tabor, G. L. Tylka, C. R. Bronson

Plant Pathology and Microbiology Publications

Growth chamber experiments were conducted to investigate whether parasitism by increasing population densities of Heterodera glycines, the soybean cyst nematode, increases the incidence and severity of stem colonization by the aggressive genotype A and the mild genotype B of Cadophora gregata (Phialophora gregata), causal agents of brown stem rot of soybeans. Soybean genotypes with three combinations of resistance and susceptibility to H. glycines and genotype A of C. gregata were inoculated with each genotype of C. gregata alone or each genotype with two population densities of H. glycineseggs, 1,500 or 10,000 per 100 cm3 of soil ...


Two Nematode Soil Sample Analysis Options, Gregory L. Tylka Sep 2006

Two Nematode Soil Sample Analysis Options, Gregory L. Tylka

Integrated Crop Management News

The Iowa State University Plant Disease Clinic offers two different nematode analyses for soil samples--the complete nematode count and the soybean cyst nematode (SCN) egg count. Following is a description of how the two analyses differ and when each analysis should be requested. A complete nematode count gives a count of the worm stages of plant-parasitic nematodes in a soil sample. This analysis does not give a count of the SCN eggs that may be contained in the sample.


A Step Toward Control Of Bean Pod Mottle Virus: Identifying Field Tolerance, John H. Hill, Craig Grau Sep 2006

A Step Toward Control Of Bean Pod Mottle Virus: Identifying Field Tolerance, John H. Hill, Craig Grau

Integrated Crop Management News

So, have you been wondering what to do about all those soybean plants that have mottled leaves? Populations of bean leaf beetles, the insect that efficiently transmits bean pod mottle virus, have been very high. The last issue of the ICM newsletter told you to expect potential yield reductions this fall and reduced seed quality evidenced by seeds that are stained (hilum bleeding). But there may be some soybean cultivars/accessions that are not so bad. We have known for some time that soybean cultivars can vary significantly in response to disease caused by the virus.


Sudden Death Syndrome Prevalent This Summer, X. B. Yang Sep 2006

Sudden Death Syndrome Prevalent This Summer, X. B. Yang

Integrated Crop Management News

As the summer ended, sudden death syndrome (SDS) of soybean has been found in many fields in Iowa. Widespread infestation has been reported by producers and agronomists in eastern and central Iowa, and the disease also has been found in western Iowa. This year, the disease showed up in early July with many reports before the first week of July. Cooler temperatures this summer may have contributed to its occurrence. In central Iowa, the incidence of infested fields is high, but the severity is not. In most fields where SDS is spotted, the disease occurs in small areas with limited ...


Sentinel Plots At End Of The 2006 Season, Ralph Von Qualen, X. B. Yang Sep 2006

Sentinel Plots At End Of The 2006 Season, Ralph Von Qualen, X. B. Yang

Integrated Crop Management News

We are completing our second crop season since Asian soybean rust (ASR) was found in the United States. We can breathe a sigh of relief and give thanks that ASR did not make its way to Iowa. Indeed, this potentially devastating disease has not plagued the entire north-central United States. Had conditions been favorable for this disease, we were ready to give producers fair warning.


A New Greenhouse Method To Assay Soybean Resistance To Brown Stem Rot, G. A. Tabor, S. R. Cianzio, G. L. Tylka, R. Roorda, C. R. Bronson Sep 2006

A New Greenhouse Method To Assay Soybean Resistance To Brown Stem Rot, G. A. Tabor, S. R. Cianzio, G. L. Tylka, R. Roorda, C. R. Bronson

Plant Pathology and Microbiology Publications

Greenhouse, growth chamber, and field experiments were conducted to develop a method to assess resistance of soybeans to Cadophora gregata (Phialophora gregata), causal agent of brown stem rot (BSR). In the new method, C. gregata is introduced at the base of the stems of 2-week-old soybeans, and the presence of the fungus is assessed in the tips of the stems 5 weeks later. To test the effectiveness of the method, two populations of soybeans and 10 checks were inoculated at the stem base and then assayed for fungal colonization of the stem tips, percentage of symptomatic leaflets, and percent internal ...


Update: Soybean Rust And Other Foliar Diseases, Daren S. Mueller Aug 2006

Update: Soybean Rust And Other Foliar Diseases, Daren S. Mueller

Integrated Crop Management News

Another growing season is passing and soybean rust remains confined to the southeastern United States. With drier-than-normal conditions throughout much of the southeastern United States early in the spring and well into summer, soybean rust has not been able to spread too far from the overwintering sites. To date for 2006, there are 28 counties in six states with soybean rust. In comparison to 2005, there were 21 counties with soybean rust in early August (see maps).


Bean Pod Mottle Virus: Back With A Vengeance, John H. Hill, Palle Pedersen, Jeffrey D. Bradshaw Aug 2006

Bean Pod Mottle Virus: Back With A Vengeance, John H. Hill, Palle Pedersen, Jeffrey D. Bradshaw

Integrated Crop Management News

As stated in an earlier article in the ICM Newsletter (May 15, 2006), bean leaf beetles are back with a vengeance this year. Based on observations from agronomists across the state, this year seems to have the highest level of bean leaf beetles since 2002. This also has resulted in an apparent high incidence of bean pod mottle virus disease in Iowa fields. Infected plants can be characterized by the leaves, which show a yellow to green blotchy appearance called leaf mottle. Sometimes leaves have a raised or blistered appearance.


Soybean Aphids Down In July, Marlin E. Rice Jul 2006

Soybean Aphids Down In July, Marlin E. Rice

Integrated Crop Management News

Reports from extension field crops specialists across Iowa on July 24 indicate that soybean aphids have not reached the economic threshold of 250 aphids per plant in most fields. Soybean aphids can be found, but it appears that overall the populations range from just a few aphids per plant up to 30-50 per plant. There was a report of several fields being sprayed in northwest Iowa near Emmetsburg, but no aphid counts were given for these fields so the population size relative to the economic threshold is unknown.


Recent Soybean Yellowing May Be Symptom Of Scn, Gregory L. Tylka Jul 2006

Recent Soybean Yellowing May Be Symptom Of Scn, Gregory L. Tylka

Integrated Crop Management News

There have been many yellow spots in soybean fields throughout Iowa so far this season. In most cases, the yellowing is iron deficiency chlorosis. But since mid-July, additional yellowing of soybean fields has appeared, and it is likely that at least some of the newly appearing chlorosis is being caused by feeding of the soybean cyst nematode (SCN). SCN usually is present in fields for many years before population densities increase to a level that causes obvious stunting or yellowing.


Consider Nematode Feeding As Cause For Poor Corn Growth, Gregory L. Tylka Jul 2006

Consider Nematode Feeding As Cause For Poor Corn Growth, Gregory L. Tylka

Integrated Crop Management News

Plant-parasitic nematodes can cause serious damage to corn. There are numerous species that occur in Iowa, including those with common names like the dagger, lance, lesion, needle, spiral, stubby-root, and stunt nematodes. Symptoms of nematode damage on corn include stunting and/or yellowing of foliage, uneven tasseling, and stunting, swelling, and/or browning of roots.


Fungicides: Safety And Restrictions, Daren S. Mueller, Joyce Hornstein Jul 2006

Fungicides: Safety And Restrictions, Daren S. Mueller, Joyce Hornstein

Integrated Crop Management News

Reading through a pesticide label will give you most of the needed information concerning safety for both yourself and others while spraying field crops. Below is a synopsis of some of the dangers and restrictions for some common fungicides. For details on a specific fungicide, please follow the label's directions for mixing and application along with the instructions for safe use.


Assessing The Risk Of Soybean White Mold In 2006, X. B. Yang Jul 2006

Assessing The Risk Of Soybean White Mold In 2006, X. B. Yang

Integrated Crop Management News

Soybean white mold was prevalent during the 2004 season in eastern Iowa. Many of the infested fields were replanted with soybean this year. Some farmers, especially those in eastern Iowa, have questioned the risk of soybean white mold this year. White mold management measures are preventative and include the application of chemicals. This means that correctly assessing the risk of this disease helps guide our decisions on chemical controls. This article discusses the risk factors to help you assess the risk for this season.


Fungicides: Plant Health Fungicide Applications, Daren S. Mueller Jun 2006

Fungicides: Plant Health Fungicide Applications, Daren S. Mueller

Integrated Crop Management News

If you take a look at the current distribution of soybean rust in the United States and listen carefully to the experts on the chances of rust making it to Iowa, you have to be encouraged. Despite the good news about soybean rust not spreading quickly (or hardly at all), there have been several reports of chemical reps from major fungicide manufacturers trying to convince growers to purchase fungicides and apply them to soybean to enhance plant health, leading to higher crop yields; suggested treatments involve QoI-containing fungicides, such as Headline® or Quadris®.


Fungicides: Why Fungicides Fail, Daren S. Mueller Jun 2006

Fungicides: Why Fungicides Fail, Daren S. Mueller

Integrated Crop Management News

Sometimes management of plant diseases is accomplished through the application of fungicides. Many factors prior to, during, and after application will determine the success of the fungicide. On certain occasions, fungicide applications fail to manage the targeted disease. It is important to identify the reasons for these failures to prevent them from occurring in the future.


Soybean Cyst Nematode Females Now Apparent On Roots, Gregory L. Tylka Jun 2006

Soybean Cyst Nematode Females Now Apparent On Roots, Gregory L. Tylka

Integrated Crop Management News

The soybean cyst nematode (SCN), Heterodera glycines, is a widespread, destructive pest of soybeans in Iowa and much of the Midwest. Fortunately, SCN can be managed successfully by growing nonhost crops, such as corn, and resistant soybean varieties. But plants in many infested fields may not be stunted and yellow, at least not until SCN population densities (numbers) develop to high levels. It may take several years before noticeable symptoms of SCN damage become apparent.