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Plant Pathology

Integrated Crop Management News

1999

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1999 Season Review Of Soybean Diseases, X. B. Yang Dec 1999

1999 Season Review Of Soybean Diseases, X. B. Yang

Integrated Crop Management News

The soybean diseases encountered in the 1999 growing season were different from those of the last couple of years. Brown stem rot and white mold were not concerns in 1999, but diseases that favored warmer weather gradually emerged as production problems. In this article, I review the prevalence of soybean diseases that occurred in the 1999 growing season.


Corn Diseases In 1999, Gary P. Munkvold Dec 1999

Corn Diseases In 1999, Gary P. Munkvold

Integrated Crop Management News

This year brought some notable disease problems to the corn crop, and it is surprising that the average yield for the state turned out as well as it did. Of course, I spend most of my time in the worst-looking fields so I usually have a pessimistic outlook. Significant disease problems in 1999 included seedling blights, Stewart's disease (Stewart's wilt), rusts, gray leaf spot, and stalk rots.


Tolerance Results To White Mold And Sds, Michael D. Uphoff, X. B. Yang Nov 1999

Tolerance Results To White Mold And Sds, Michael D. Uphoff, X. B. Yang

Integrated Crop Management News

The Department of Plant Pathology at Iowa State University conducts an annual white mold tolerance test with funding from the Iowa Soybean Promotion Board. This year, for the first time, we also have tested varieties from commercial companies for tolerance to sudden death syndrome (SDS). The data for 1999 are presented below.


Check For Ear Rot Diseases, Gary P. Munkvold Oct 1999

Check For Ear Rot Diseases, Gary P. Munkvold

Integrated Crop Management News

This year does not appear to be a particularly bad year for ear rots, but there are a few unusual occurrences. First, there seems to be more corn earworm damage than usual this year. This can lead to increased Fusarium ear rot. Second, I have noticed that Diplodia ear rot is more prevalent than usual. Neither of these observations constitutes a major outbreak, but it might be worthwhile to look for these problems. Also, if cold, wet weather persists, be on the lookout for Gibberella ear rot. Corn that has been frosted can be very susceptible to Gibberella ear rot ...


Check For Ear Rot Diseases, Gary P. Munkvold Oct 1999

Check For Ear Rot Diseases, Gary P. Munkvold

Integrated Crop Management News

This year does not appear to be a particularly bad year for ear rots, but there are a few unusual occurrences. First, there seems to be more corn earworm damage than usual this year. This can lead to increased Fusarium ear rot. Second, I have noticed that Diplodia ear rot is more prevalent than usual. Neither of these observations constitutes a major outbreak, but it might be worthwhile to look for these problems. Also, if cold, wet weather persists, be on the lookout for Gibberella ear rot. Corn that has been frosted can be very susceptible to Gibberella ear rot ...


Improved Scn Egg Extraction Technique, Gregory L. Tylka, Paula Flynn Oct 1999

Improved Scn Egg Extraction Technique, Gregory L. Tylka, Paula Flynn

Integrated Crop Management News

This fall, the Iowa State University Plant Disease Clinic began using a new technique that increases the efficiency of extracting eggs from soil samples infested with the soybean cyst nematode (SCN). SCN egg counts from soil samples processed with this technique will be 100 to 200 percent greater than in the past. For example, a soil sample with a reported density of 1,585 eggs per 100 cm3 of soil with the previous technique now will have an egg density of 4,225 eggs per 100 cm3 of soil.


New Soybean Disease Slide Sets, X. B. Yang Oct 1999

New Soybean Disease Slide Sets, X. B. Yang

Integrated Crop Management News

A few years ago, the Iowa State University "Plant Disease Clinic" started to receive reports on diseases relatively new to soybean growers, such as soybean sudden death syndrome (SDS) and diseases that cause seed discoloration. The prevalence of these diseases is increasing, especially in the last 2 years. As of this summer, SDS has been reported in more than 40 Iowa counties. The Clinic also received seed samples with as many as 40 percent of the beans showing black seed coats.


Rust And Other Diseases Are Accelerating Corn Maturity, Gary P. Munkvold, Dale E. Farnham Sep 1999

Rust And Other Diseases Are Accelerating Corn Maturity, Gary P. Munkvold, Dale E. Farnham

Integrated Crop Management News

During the last 2 weeks, the appearance of many cornfields has begun to deteriorate; plants in some fields are dead. Although we expect plants to be maturing about this time of year, clearly some plants are dying early. Statewide, we reached 50 percent silking about July 22, which means theoretically, the "average" corn plant should reach physiological maturity about September 17. In some areas, the crop will be mature prior to its expected maturity date. When corn plants don't live for the full season, they do not achieve maximum potential yields. Even though the kernels on prematurely dead plants ...


Fall Soybean Disease Scouting, X. B. Yang, Peter Lundeen Sep 1999

Fall Soybean Disease Scouting, X. B. Yang, Peter Lundeen

Integrated Crop Management News

Every September, the Iowa State University Plant Disease Clinic receives more soybean disease samples than at any other time during the year. This year is no exception. This article describes the diseases that we have seen in the clinic, observed in the field, or received from ISU Extension staff and agronomists this year.


Soybean Top Dieback Shows Up, Soum Sanogo, X. B. Yang Sep 1999

Soybean Top Dieback Shows Up, Soum Sanogo, X. B. Yang

Integrated Crop Management News

In the 1997 and 1998 growing seasons, some soybean fields had plants with bright yellow leaves and plants that were dying from the top down, a condition called top dieback (growers may call this condition tip blight). Top dieback was pronounced in 1997 and 1998 from late July to mid-August when most soybean plants were in the reproductive phase. Top dieback showed up again this year.


Scout Now For Sudden Death Syndrome, X. B. Yang Aug 1999

Scout Now For Sudden Death Syndrome, X. B. Yang

Integrated Crop Management News

Over the last 2 years, Iowa growers have seen a rapid spread of sudden death syndrome (SDS) in some Iowa counties. SDS was first reported in 1994 in four Iowa counties. Since then the disease has been found in 31 counties. Among other measures, preventing the spread of this disease is still an effective means of controlling the disease for the majority of Iowa soybean growers. Early detection of SDS is critical to control disease spread.


Corn Disease Slide Set Available, Gary P. Munkvold Aug 1999

Corn Disease Slide Set Available, Gary P. Munkvold

Integrated Crop Management News

A new slide set, Corn Disease Identification, IPM 57, is now available from the ISU "Extension Distribution Center" (515-294-5247) or through county extension offices. Ideal for training scouts, the slides show different stages of disease development for 27 corn diseases found in Iowa and elsewhere in the Corn Belt. There are 125 slides in the set and the cost is $125.00.


Scn Field Day At Bruner Farm, Gregory L. Tylka Aug 1999

Scn Field Day At Bruner Farm, Gregory L. Tylka

Integrated Crop Management News

A field day is scheduled for Friday August 27 to showcase ongoing applied and basic research on the soybean cyst nematode (SCN) at Iowa State University. The event, sponsored by soybean checkoff funds administered through the Iowa Soybean Promotion Board and the Iowa SCN Coalition, will be held at the ISU Bruner Research Farm, located west of Ames. The program will consist of five in-field oral presentations by ISU faculty and staff. Topics to be discussed include SCN biology and scouting; screening of SCN-resistant soybean breeding lines; the effects of SCN on soybean growth and development; the effects of herbicide-resistant ...


Soybean Foliar Diseases In July, X. B. Yang Jul 1999

Soybean Foliar Diseases In July, X. B. Yang

Integrated Crop Management News

As we head into the mid-season of crop growth, some foliar soybean diseases are visible. Based on my observations and reports from growers and agronomists, the following foliar diseases are relatively common in Iowa soybean fields. Bacterial blight has been observed in some soybean fields. The disease is caused by the bacterium Pseudomonas syringae. Lesions associated with this disease are normally first observed on younger, top leaves of soybean plants. The lesions are small, angular, water-soaked, yellow-to-brown spots. The angular lesions enlarge in rainy weather and merge to produce large, irregular dead areas. The bacteria also can infect pods and ...


Mid-Season Corn Leaf Diseases, Gary P. Munkvold Jul 1999

Mid-Season Corn Leaf Diseases, Gary P. Munkvold

Integrated Crop Management News

Leaf diseases are appearing on corn in many areas of the state. This is not too surprising, considering the amount of rain we have had. Fortunately, in most fields so far the symptoms are due to holcus spot or anthracnose, which do not tend to spread rapidly among the plants during mid-season. Anthracnose has become severe in some fields following the heavy rains, but the new leaves should escape infection. No in-season control measures are recommended for anthracnose. Other diseases are appearing and some of these are a bigger concern, especially in seed corn. Paul Klemme of Novartis Crop Protection ...


Controlling Leaf Diseases In Seed Corn In 1999, Gary P. Munkvold, Charlie Martinson Jul 1999

Controlling Leaf Diseases In Seed Corn In 1999, Gary P. Munkvold, Charlie Martinson

Integrated Crop Management News

Gray leaf spot is now appearing in southern Iowa seed cornfields. This disease and others can be very serious in seed corn production, and fungicidal control will be necessary in some fields. Seed corn presents different challenges (and opportunities) when it comes to disease management. Some unique features of seed production compared with grain production include the following:

  • high value per acre,
  • a broader range of leaf diseases cause economic damage,
  • a need to grow specific genotypes regardless of susceptibility,
  • leaf loss due to detasseling, and
  • more fungicide options.


Soybean Root Rot, X. B. Yang, Michael D. Uphoff Jun 1999

Soybean Root Rot, X. B. Yang, Michael D. Uphoff

Integrated Crop Management News

Soybean root rot problems are showing up due to the excessive rainfall in early summer. ISU field crop specialists in different regions are reporting the occurrence of Rhizoctonia root rot and Phytophthora root rot. Unfavorable soil conditions can slow soybean root development and are ideal for some soilborne fungi. In last week's ICM issue, we addressed Phythophthora and in this article we discuss other root rot diseases.


Label Change For Tilt Fungicide, Gary P. Munkvold Jun 1999

Label Change For Tilt Fungicide, Gary P. Munkvold

Integrated Crop Management News

Special Local Need label under FIFRA Section 24(c) for use on corn after silking in Iowa. Tilt is used to control gray leaf spot and other foliar diseases on corn. Until now, the label did not allow applications to field corn, popcorn, and seed corn after silking. The new label supplement allows applications on these crops until 30 days prior to harvest. Applications may be made to sweet corn until 14 days prior to harvest (the same as the previous label). An important restriction on the Special Local Need label is that forage or fodder may not be fed ...


Phytophthora Damping-Off Of Soybeans, Michael D. Uphoff, X. B. Yang Jun 1999

Phytophthora Damping-Off Of Soybeans, Michael D. Uphoff, X. B. Yang

Integrated Crop Management News

Phytophthora root rot of soybean is a persistent and widespread problem affecting much of Iowa. We have received many reports of damping-off caused by Phytophthora sojae in the last few years, and with the warm soil conditions and wet weather in early June, we anticipate that it will be a problem again this year.


Corn Seedling Diseases Causing Problems, Gary P. Munkvold Jun 1999

Corn Seedling Diseases Causing Problems, Gary P. Munkvold

Integrated Crop Management News

As producers squeezed in their corn planting between storms this spring, corn seeds experienced very wet conditions in many cases, and emergence problems are being reported widely by extension field specialists and seed company agronomists. The Plant Disease Clinic also has received several samples of corn seedlings with disease problems. The stand problems are generally worse in the southern part of the state, except in local areas where heavy rain washed out fields or caused flooding. Iowa Agricultural Statistics reported on June 1 that 6 percent of the corn acreage will be replanted due to disease, flooding, or crusting and ...


Seedling Damping-Off By Phomopsis/Diaporthe, X. B. Yang, Soum Sanogo Jun 1999

Seedling Damping-Off By Phomopsis/Diaporthe, X. B. Yang, Soum Sanogo

Integrated Crop Management News

In the past 2 years, soybean top dieback, also called tip blight by growers, has emerged as a disease concern to some growers. The disease was initially reported in Ohio 20 years ago and was first noticed in Iowa in 1997. Foliar symptoms of this disease occur during the reproductive stage of soybean plants in August, but the fungi associated with the disease can cause damage during the seedling stage. In the 1998 growing season, we received reports and questions from producers on the occurrence of black lesions on cotyledons. In this article we provide information on seedling disease caused ...


Viral Diseases In Small Grains, Gary P. Munkvold May 1999

Viral Diseases In Small Grains, Gary P. Munkvold

Integrated Crop Management News

Last week the Plant Disease Clinic received the first sample of the year with symptoms typical of barley yellow dwarf virus. This disease can be seen on oats and wheat every year, and it is one of the major disease problems on oats in the state. This year yellow dwarf symptoms will probably be less severe than normal on oats because of the early planting that occurred.


Soybean Damping-Off And Replanting, X. B. Yang May 1999

Soybean Damping-Off And Replanting, X. B. Yang

Integrated Crop Management News

In spring 1998, damping-off caused by Phytophthora was a production problem in parts of Iowa, especially southern and some central areas. Many disease questions that I received last spring were related to damping-off. Because most areas in Iowa have had plenty of rain so far this spring, damping off may become a problem. In this article I address two important aspects related to damping-off: identification and replanting.


Alfalfa Leaf Diseases Appearing, Gary P. Munkvold, X. B. Yang May 1999

Alfalfa Leaf Diseases Appearing, Gary P. Munkvold, X. B. Yang

Integrated Crop Management News

Alfalfa is reportedly in good condition throughout the state with little winter injury and surprisingly few reports of leaf disease problems. But frequent April rains provided good conditions for leaf disease development, and significant levels of spring black stem and leaf spot were reported last week by extension field specialist Brian Lang in northeastern Iowa. The ISU Plant Disease Clinic also has received several samples with either spring black stem, common leaf spot, bacterial leaf spot, or stem blight.


Plan Your Disease Scouting - Updated, X. B. Yang May 1999

Plan Your Disease Scouting - Updated, X. B. Yang

Integrated Crop Management News

Detecting a disease in its early stages of development is important to managing disease risk. Last spring, I wrote an article on making a scouting plan for soybean diseases. I received some comments and decided to redo the article by adding new disease problems and specifying regions where certain diseases have been prevalent in the past few years. There are several reasons for making a scouting plan. First, early detection of a disease can help you to make management decisions to prevent disease problems before they take place. Second, the occurrence of different diseases varies in a growing season and ...


Controlling Wheat Leaf Diseases In 1999, Gary P. Munkvold May 1999

Controlling Wheat Leaf Diseases In 1999, Gary P. Munkvold

Integrated Crop Management News

Now is the time to start thinking about controlling leaf diseases in wheat, if necessary. Conditions have been wet enough in the southern Iowa wheat-producing areas to promote significant leaf disease development. Wheat can be affected by several foliar diseases that are caused by fungi, including Septoria leaf blotch, powdery mildew, and tan spot. There are also three different rust fungi that can infect wheat. Leaf rust, Puccinia recondita, is the most common rust disease and has the most destructive potential of the foliar diseases.


Planting Date Affects Crop Diseases, Gary P. Munkvold, X. B. Yang May 1999

Planting Date Affects Crop Diseases, Gary P. Munkvold, X. B. Yang

Integrated Crop Management News

Planting date can affect many crop diseases; early planting increases the risk of seedling disease and some other soilborne pathogens, but for some diseases there is a risk of greater yield loss with late planting. Increased risks associated with late planting occur because plants are at an earlier growth stage at the onset of disease. Plants infected earlier in their development suffer greater yield reductions. It can pay to be aware of how specific diseases are affected by planting date.


Alfalfa Seedling Diseases In 1999, Gary P. Munkvold Apr 1999

Alfalfa Seedling Diseases In 1999, Gary P. Munkvold

Integrated Crop Management News

New alfalfa seedings are reported to be in good shape throughout the state, but the recent wet weather may result in some seedling disease problems. The most important fungi attacking alfalfa seedlings areAphanomyces euteiches, Phytophthora medicaginis, and several species of Pythium. Other seedling pathogens include Fusarium and Rhizoctonia. According to a survey we did in 1994, Aphanomyces is more common than Phytophthora in Iowa soils, and these two fungi should be considered equal threats to seedlings. Seedling diseases should be suspected when emergence is poor or when there are obviously stunted, discolored, or dead seedlings.


Soil Texture And Disease Risk, X. B. Yang, Gregory L. Tylka Apr 1999

Soil Texture And Disease Risk, X. B. Yang, Gregory L. Tylka

Integrated Crop Management News

In the last 10 years, conservation tillage has been a popular farming practice to reduce soil erosion and production costs. There are reports of increases in some soybean diseases following the use of conservation tillage, and there is a view that use of no-till would be associated with the increase in disease risks. However, this view should be readdressed in light of site-specific production. Plant pathologists have long understood that tillage effects on diseases may be site specific. We also know that soil texture interacts with tillage practice to affect plant diseases.


Soybean Seed Treatments In 1999, X. B. Yang Apr 1999

Soybean Seed Treatments In 1999, X. B. Yang

Integrated Crop Management News

In the last 2 years, the incidence of soybean seedling diseases has been relatively high in some areas of Iowa. There are growers who are considering seed treatments to prevent stand reduction from soybean seedling diseases. Growers who replant due to damping-off are more likely to use seed treatments. The problematic fungi causing the seedling diseases vary, and they are often dependent on the planting date. In some fields, early planting is associated with damping-off by cool-temperature fungi. Disease risk may increase because soybeans are planted in soils that are cold and wet.