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Fda Releases Guidelines For Fumonisins In Corn, Gary P. Munkvold Dec 2001

Fda Releases Guidelines For Fumonisins In Corn, Gary P. Munkvold

Integrated Crop Management News

Last month, the U.S. Food and Drug Administration (FDA) released its official guidelines for safe levels of fumonisins in corn used for foods and animal feeds. Fumonisins are mycotoxins produced by species of Fusarium fungi that cause Fusarium ear rot. Fumonisins are the most common mycotoxins found in corn; because they are acutely toxic to animals (especially pigs and horses), and have been linked to increased cancer rates and other human health problems, the FDA feels that "human health risks associated with fumonisins are possible."


Varietal Differences In Frogeye Leaf Spot Susceptibility, Michael D. Uphoff, X. B. Yang Dec 2001

Varietal Differences In Frogeye Leaf Spot Susceptibility, Michael D. Uphoff, X. B. Yang

Integrated Crop Management News

Frogeye leaf spot of soybean, caused by the fungus Cercospora sojina, causes damage in warm, humid soybean-growing regions and has been more important in southern states than in Iowa. Recently, however, the incidence of frogeye leaf spot has increased in north central states, including Iowa, with reports of severe damage in several areas. Symptoms of the disease include small, gray spots with reddish brown borders forming on the upper leaves in mid- to late August.


Changes In Disease Occurrence In Iowa, X. B. Yang Dec 2001

Changes In Disease Occurrence In Iowa, X. B. Yang

Integrated Crop Management News

A warm winter this year has generated discussion on the effects of climate on disease occurrence. At the 1998 Iowa State University ICM Conference, we discussed how diseases favored by cool temperatures may became less important, whereas warm-temperature diseases may increase in future years. At this year's ICM Conference, there were numerous comments and questions about new soybean diseases becoming increasingly important to production. Changes in disease occurrence have provided new challenges in disease management practices.


Nearly 400 Scn-Resistant Soybean Varieties Available To Iowa Growers, Gregory L. Tylka Nov 2001

Nearly 400 Scn-Resistant Soybean Varieties Available To Iowa Growers, Gregory L. Tylka

Integrated Crop Management News

The soybean cyst nematode (SCN) is a widespread and very serious pest of soybean throughout Iowa and most of the Midwest. A primary strategy for managing the nematode is through the use of SCN-resistant soybean varieties. Iowa State University Extension recently compiled and published a list of public and private SCN-resistant soybean varieties in maturity groups I, II, and III. There are nearly 400 SCN-resistant varieties from 48 seed companies and five universities listed in the publication, titled Soybean cyst nematode-resistant soybean varieties for Iowa.


Common Smut More Common Than Usual, Gary P. Munkvold Nov 2001

Common Smut More Common Than Usual, Gary P. Munkvold

Integrated Crop Management News

Dark, dusty clouds are lingering behind many combines this fall as smut-infected ears are harvested. During the latter half of the season I received more calls than usual about this disease, and reports of smut have accelerated as some of the previously unnoticed fields were harvested. Common corn smut, caused by the fungus Ustilago zeae or Ustilago maydis, is a well-known disease that usually does not cause economic damage.


Ear Rot And Mold Problems, Gary P. Munkvold Oct 2001

Ear Rot And Mold Problems, Gary P. Munkvold

Integrated Crop Management News

Corn ear rot problems are often related to how long the corn stands in the field in the fall, the amount of second-generation European corn borer damage, and the late-season weather. This year, corn dry-down is progressing more slowly than anticipated and there was a healthy second generation, so there are more ear rots being reported than usual. The dry weather that was widespread earlier in the summer resulted in someAspergillus infection (the fungus that produces aflatoxins).


Phomopsis-Infected Seed, X. B. Yang Oct 2001

Phomopsis-Infected Seed, X. B. Yang

Integrated Crop Management News

In recent years, there has been an increase in diseases caused by Phomopsis fungi, and these diseases have contributed to premature yellowing or death of many soybean fields in the 2001 growing season. This fall, the Iowa State University Plant Disease Clinic received samples of soybean with the stems covered with black lesions, diagnostic of Phomopsis pod and stem blight.


Now's The Time To Sample Fields For Soybean Cyst Nematode, Gregory L. Tylka Oct 2001

Now's The Time To Sample Fields For Soybean Cyst Nematode, Gregory L. Tylka

Integrated Crop Management News

The soybean cyst nematode (SCN) is an extremely damaging and widespread pest of soybean in Iowa. The nematode infests approximately 70 percent of the fields statewide. However, SCN usually causes no obvious aboveground symptoms for many years after being introduced into a field. Consequently, many SCN-infested fields in Iowa have not been diagnosed. The lack of symptoms and subsequent missed diagnosis are unfortunate because the key to effective management of SCN is early detection, before large nematode population densities develop.


Why Is Soybean Yellowing Prematurely?, X. B. Yang Sep 2001

Why Is Soybean Yellowing Prematurely?, X. B. Yang

Integrated Crop Management News

After mid-August, many soybean fields had patches of yellow plants. These plants exhibited yellowing of the top leaves, often followed by brown margins on the leaves. My colleagues and I received many questions on why soybean turns yellow prematurely and whether top dieback, a disease caused by the fungi Phomopsisand Diaporthe, is the cause. Visits to problematic fields and examination of samples submitted to Iowa State University Plant Disease Clinic revealed three factors that can stress soybean, consequently causing leaf yellowing.


Nematodes Can Cause Poor Corn Growth, Gregory L. Tylka, Gary P. Munkvold Aug 2001

Nematodes Can Cause Poor Corn Growth, Gregory L. Tylka, Gary P. Munkvold

Integrated Crop Management News

The wet spring and variable growing conditions this year have resulted in many uneven corn stands. These problems often can be attributed to poor root development, fungal root infection, or occasionally, moisture stress. But every summer there are instances of unthrifty corn growth throughout Iowa with no apparent cause. A possible explanation for the poor corn growth that probably is not considered very often is damage due to plant-parasitic nematodes. There are many species of nematodes that can damage corn.


Soybean Phytophthora In August, X. B. Yang Aug 2001

Soybean Phytophthora In August, X. B. Yang

Integrated Crop Management News

The prevalence of Phytophthora rot this year has been higher than in past years, perhaps due to more races that can infect soybean cultivars with the Rps-1k gene. Reports indicate that occurrence of this disease was still high in late July. So, how much damage will this disease cause for the rest of the growing season? In Iowa, major documented damage by this disease occurs in seedlings as stand reduction caused by damping-off. Stand reduction by root rot and stem rot in advanced growth stages is minor, thus damage by this disease in the rest of the season should be ...


Start Scouting For Corn Stalk Rot Now, Gary P. Munkvold Aug 2001

Start Scouting For Corn Stalk Rot Now, Gary P. Munkvold

Integrated Crop Management News

Stressful growing conditions this year are an indicator that stalk rots could be very common. It is a good idea to go out to the field now and identify problem fields so that they can be harvested early enough to avoid lodging. Driving through Missouri on August 10, I saw numerous fields with 50-75 percent of the plants dead, apparently from a combination of drought stress, poor roots, and stalk rot. I have not seen any fields that look as bad in Iowa, but there are some that look very stressed, and they will die prematurely.


Scn Responsible For Yellow Soybean Fields, Gregory L. Tylka Aug 2001

Scn Responsible For Yellow Soybean Fields, Gregory L. Tylka

Integrated Crop Management News

During the past few weeks, areas of many soybean fields throughout Iowa have turned yellow. In several of these fields, the yellowing is due to feeding by the soybean cyst nematode (SCN). SCN usually is present in fields for many years before population densities increase to a level that causes visible stunting or yellowing. When yellowing occurs, it generally appears in late July or early August. The yellowing often fades after rainfall.


Corn Disease Outlook For 2001, Gary P. Munkvold Jul 2001

Corn Disease Outlook For 2001, Gary P. Munkvold

Integrated Crop Management News

As we enter into the post-pollination phase of the season, many corn diseases will accelerate their development. So far, leaf diseases have not been very severe, largely because of the dry weather. Common rust is evident in many fields but only at very low levels, and traces of gray leaf spot and eyespot can be found. Gray leaf spot has the potential to increase rapidly during the post-pollination period, even when rainfall is not plentiful.


Soybean Disease Scouting In July, X. B. Yang Jul 2001

Soybean Disease Scouting In July, X. B. Yang

Integrated Crop Management News

July is an interesting month for disease scouting. This article discusses some soybean diseases you may see during scouting this month. Rhizoctonia root rot and Phytophthora root rot continue to be problems in some soybean fields.Rhizoctonia damping-off was more prevalent this year than in other years based on samples submitted to the ISU Plant Disease Clinic and reports from field staff. Following application of herbicides for weed control, many samples examined showed root rot resulting from fungi-herbicide interactions. Check ICM articles from spring 2001 issues for management information on these diseases.


Crown Rot Affecting Corn Development, Gary P. Munkvold Jul 2001

Crown Rot Affecting Corn Development, Gary P. Munkvold

Integrated Crop Management News

The spring weather obviously was very challenging for corn seedlings, resulting in a record number of replanted acres in the state. The effects of the wet spring are not over yet, even though we have experienced a dry period. In many fields, plants that survived the wet conditions are suffering from lingering fungal infections of the root and crown tissue.


Soybean Root Rot Management, X. B. Yang Jul 2001

Soybean Root Rot Management, X. B. Yang

Integrated Crop Management News

Soybean fungal root rot is commonly seen in summer. Soybean plants with root rot are noticeable in fields because of uneven growth. Affected plants may appear yellow, stunted, and wilted. The plants may be scattered or found in large patches; they often occur in fields or areas with poor drainage. Cool weather promotes these root rot problems because cooler than normal temperatures slow soybean root development and are ideal for some soilborne fungi.


Soybean Iron Chlorosis, X. B. Yang Jul 2001

Soybean Iron Chlorosis, X. B. Yang

Integrated Crop Management News

The Iowa State University Plant Disease Clinic usually receives soybean samples with iron chlorosis in mid- to late June, depending on planting date and weather. This year some iron chlorosis in soybean is anticipated because this problem is more pronounced with cool temperature and excessive moisture.


Controlling Leaf Diseases In Seed Corn In 2001, Gary P. Munkvold, Charlie A. Martinson Jun 2001

Controlling Leaf Diseases In Seed Corn In 2001, Gary P. Munkvold, Charlie A. Martinson

Integrated Crop Management News

The wet spring has been very favorable for pathogens and we can already see leaf diseases developing on corn. Fortunately, the most common leaf disease at this point seems to be holcus spot, which rarely, if ever, causes economic damage. Fungal leaf diseases are also beginning to appear, with anthracnose and eyespot especially evident.


Leaf Diseases On Small Corn, Gary P. Munkvold Jun 2001

Leaf Diseases On Small Corn, Gary P. Munkvold

Integrated Crop Management News

Now that the corn has started to grow again, producers and crop scouts are starting to notice disease problems other than poor emergence, seed rot, and seedling diseases. We have had a couple of reports of leaf diseases and one sample was received at the ISU Plant Disease Clinic with symptoms of holcus spot, caused by the bacterium Pseudomonas syringae. Symptoms of holcus spot are light tan (sometimes almost white) round or oval spots on the lower leaves, initially about 1/4 inch in diameter, but sometimes growing larger and coalescing into irregular spots and streaks of dead tissue.


Disease Problems After Soybean Damping-Off, X. B. Yang Jun 2001

Disease Problems After Soybean Damping-Off, X. B. Yang

Integrated Crop Management News

With this wet planting season, soybean damping-off and poor emergence are prevalent in Iowa. Several fungi are contributing to the problems, especially Phytophthora, Pythium, and Rhizoctonia. After the seedling stage, soybean may or may not grow out of these disease problems, depending on the pathogens involved. This article discusses what may happen after damping-off.


Soybean Damping-Off This Season, X. B. Yang Jun 2001

Soybean Damping-Off This Season, X. B. Yang

Integrated Crop Management News

Excessive moisture this planting season has promoted damping-off problems. ISU Extension has received numerous reports on damping-off across Iowa, especially in southern Iowa. Both preemergence damping-off and postemergence damping-off have been found. This year seedling diseases are more complicated than in past years because of the alternating warm and cool weather. If the soil temperature is warm (70-80°F), damping-off by Phytophthora or Rhizoctonia is more likely to occur. If the soil temperature is cool (60°F or below), Pythium or Fusarium are more problematic.


Phythophthora-Infected Plants Needed, X. B. Yang, Michael D. Uphoff May 2001

Phythophthora-Infected Plants Needed, X. B. Yang, Michael D. Uphoff

Integrated Crop Management News

Field reports indicate that the Rps-1k gene of Phytophthora resistance is no longer as effective as it was few years ago. We plan to conduct a survey to determine what Phytophthora races defeat the Rps-1k gene in Iowa. The first step of this survey is to collect Phytophthora-infected plants. If you have damping-off or plants suspected to be infected by Phytophthora and would like to know whether disease symptoms are caused by Phytophthora damping-off, we can identify samples for you. Please submit diseased plants to the ISU Plant Disease Clinic, c/o XB Yang, Department of Plant Pathology, Iowa ...


Identification Of Soybean Seedling Diseases, X. B. Yang May 2001

Identification Of Soybean Seedling Diseases, X. B. Yang

Integrated Crop Management News

Stand establishment problems may be increased this spring because of the higher than normal precipitation and low seed quality. I have received more disease samples or questions on damping-off up to mid-May compared with this same period the past three springs. Determining which fungi are the cause of a problem in a particular field is key to managing seedling diseases because these fungi require different management treatments. This article describes how to identify fungal diseases in soybean.


Wet Fields Prone To Seedling Diseases, Gary P. Munkvold May 2001

Wet Fields Prone To Seedling Diseases, Gary P. Munkvold

Integrated Crop Management News

The frequent rains this spring are having an impact on corn seedlings, as many fields contain standing water for days at a time. The ability of corn seeds and seedlings to withstand periods under water is influenced by the activity of pathogenic fungi. The standing water aids dispersal of fungi, especially Pythium, which produces swimming spores. Damage due to Pythium typically is worse when soils are cooler, but it can still function in warmer soils. Also, other fungi are capable of attacking seedlings under current soil condition.


Questions Related To Soybean Replanting, X. B. Yang May 2001

Questions Related To Soybean Replanting, X. B. Yang

Integrated Crop Management News

With low soybean seed germination and high soil moisture, some growers may have stand establishment problems this spring. There is also concern about seedling diseases in regions that have had excessive rain. This article addresses some common soybean replanting questions at planting and emergence.


Stewart's Disease Publication Revised, Gary P. Munkvold May 2001

Stewart's Disease Publication Revised, Gary P. Munkvold

Integrated Crop Management News

The latest revision of Corn Stewart's Disease, ISU Extension publication PM 1627, is now available. This disease has become a serious issue in Iowa over the past decade, especially for seed producers. A series of warm winters enabled the insect vectors, corn flea beetles, to reach high populations and cause widespread transmission of the disease in Iowa. This publication discusses identification, impact, and management of the Stewart's disease. You may order a single copy of this publication free of charge from the ISU Extension Distribution Center, by calling 515-294-5247. Additional copies are 25 cents each.


Delayed Planting May Increase Rust And Yellow Dwarf In Oats, Gary P. Munkvold Apr 2001

Delayed Planting May Increase Rust And Yellow Dwarf In Oats, Gary P. Munkvold

Integrated Crop Management News

Oats in Iowa suffer from two major diseases, crown rust and barley yellow dwarf virus. Crown rust appears as orange leaf pustules and also causes yellowing and death of the leaves. Severely affected plants are stunted and produce little grain. The disease usually first appears in late May and can remain active throughout the rest of the season. Spores can be windblown long distances, but in Iowa some initial infections are the result of spread from local buckthorn shrubs. Buckthorn is the alternate host of the crown rust fungus Puccinia coronata.


Phytophthora Race 25 And Soybean 1k Gene Strategy, Mark W. Carlton, X. B. Yang Apr 2001

Phytophthora Race 25 And Soybean 1k Gene Strategy, Mark W. Carlton, X. B. Yang

Integrated Crop Management News

Soil moisture in many regions of Iowa is at field capacity or more so planting will occur in wet soils this spring. Wet soils increase the risk of damping-off in soybean by the fungi Phytophthora and Pythium. Seedling disease concerns are further compounded this year by low-to-poor seed quality. If damping-off occurs this year, growers may have difficulty finding soybean seed for replanting and may want to consider the following strategies for controlling Phytophthora and Pythium damping-off.


Late Planting Date And Soybean Diseases, X. B. Yang Apr 2001

Late Planting Date And Soybean Diseases, X. B. Yang

Integrated Crop Management News

Last spring, Iowa had a warm and early planting season; some growers were done planting corn and had started to plant soybean by early April. This year is different. So far, corn has not been planted. This article focuses on how planting date can affect soybean disease occurrence. A late planting may increase, reduce, or not affect a soybean disease, depending on the nature of the disease. Last years' early planting was associated with outbreaks of bean pod mottle virus (BPMV) in most of Iowa and sudden death syndrome (SDS) in some Iowa regions. A late planting this year may ...