University of Illinois Off-Campus Courses, Fall 1999

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1 University of Illinois Off-Campus Courses, Fall 1999 As a follow-up to an article in last week s Bulletin (issue no. 16, July 9, 1999), we are providing more information about off-campus courses that will be offered this fall. The University of Illinois at Urbana-Champaign Office of Continuing Education and Public Service, in cooperation with other UIUC academic departments, is offering several agriculture-related courses at various locations throughout Illinois during the 1999 fall semester. Following are the specifics. CPSC 300, Crop Sciences for Educators (Urbana). 3 undergraduate hours ($411) or 3/4 graduate unit ($456). 5:00 to 8:00 PM, Tuesdays, August 31 December 10, Lecturer Patricia Brandau and Associate Professor Fred E. Below. FOR IMMEDIATE RELEASE No. 17 / July 16, 1999 Executive editor: Kevin Steffey, Extension Entomologist Available on the Web at For subscription information, phone , or acesnews@uiuc.edu In This Issue University of Illinois Off- Campus Courses, Fall 1999, 161 Root Ratings and Evaluations of Rootworm Control Efforts Are Under Way, 162 Western Corn Rootworms and First-Year Corn Injury: Questions and Answers, 163 Leaf Blights of Corn, 164 CPSC 318, Crop Growth and Production (Quincy). 3 undergraduate hours ($411) or 3/4 graduate unit ($456). 6:30 to 9:45 PM, Mondays, September 13 December 13, Associate Professor Gary Pepper. CPSC 329, Fundamentals of Insect Pest Management (Springfield). 4 undergraduate hours ($548) or 1 graduate unit ($608). 6:30 to 9:45 PM, Tuesdays, September 7 December 7, Professor Kevin L. Steffey, Professor Michael E. Gray, and Instructor Susan Ratcliffe. CPSC 330, Plant Physiology (Kewanee). 3 undergraduate hours ($411) or 3/4 graduate unit ($456). 6:30 to 9:45 PM, Wednesdays, September 8 December 15, Professor Donald Briskin. CPSC 418, Crop Growth and Development (Joliet). 1 graduate unit ($608). 6:30 to 9:45 PM, Tuesdays, September 7 December 14, Associate Professor Fred E. Below. CPSC 426, Herbicide Behavior in Plants (Vandalia). 1 graduate unit ($608). 6:45 to 9:45 PM, Mondays, September 13 December 13, Adjunct Assistant Professor David Pike. NRES 342, Plant Nutrition (Malta). 4 undergraduate hours ($548) or 1 graduate unit ($608). 6:30 to 9:45 PM, Wednesdays, September 8 December 15, Associate Professor John M. Swiader. NRES 387, Soil Chemistry (Rock Island). 3 undergraduate hours ($411) or 3/4 graduate unit ($456). 6:30 to 9:45 PM, Mondays, September 13 December 13, Professor John Hassett. For further information, please contact any of the following people: Robbin Nelson, University Outreach and Public Service 1601 Parkview Ave., Rockford, IL 61107, (815) Richard Kalus, University Outreach and Public Service 1010 Jorie Blvd., Ste. 200, Oak Brook, IL 60523, (630)

2 William Sutton, University Outreach and Public Service Lincoln Trail, Fairview Heights, IL 62208, (618) Kathleen Johnson, University Outreach and Public Service Lake County Multi-University Center, 1120 S. Milwaukee Ave., Vernon Hills, IL 60061, (847) Faye Lesht, Academic Outreach 302 E. John St., Ste. 1405, Champaign, IL 61820, (800) , ext Faye Lesht, Kevin Steffey INSECTS Root Ratings and Evaluations of Rootworm Control Efforts Are Under Way During July, many people spend time in corn trying to assess the amount of rootworm injury, either in growers fields or in research or demonstration plots. Therefore, we thought it might be worthwhile to refresh your memory about root ratings. Most entomologists in the Corn Belt still use the Iowa State University 1 6 root-rating scale that was developed in the 1960s. Although other scales have been used, the 1 6 scale is still the most universally recognized. Follow these steps to assess the amount of rootworm larval injury to corn roots. After you extract roots from the field, wash off the dirt so you can see the roots and rootworm injury clearly. Examine the root systems for the overall amount of injury and assign a rating to each root. An explanation of the rating scale follows, and schematic illustrations of root ratings 2, 3, 4, and 5 are shown in Figure No visible damage, or only a few minor feeding scars. 2. Some roots with feeding scars, but no roots eaten off to within 1 1/2 inches of the plant. Figure 1. Schematic illustrations of root ratings 2, 3, 4, and 5 from the Iowa State University 1 6 rating scale for rootworm larval injury. 3. Several roots eaten off to within 1 1/2 inches of the plant, but never the equivalent of an entire node of roots gone. 4. The equivalent of one node of roots pruned off to within l 1/2 inches of the plant. 5. The equivalent of two nodes of roots pruned off to within 1 1/2 inches of the plant. 6. The equivalent of three or more nodes of roots pruned off to within 1 1/2 inches of the plant. By adding all of the ratings of roots from an individual field and dividing by the number of root systems examined, you can obtain an average root rating for the field. If you are comparing the efficacy of different treatments or comparing roots from a soil insecticide treated area of the field with roots from an untreated check strip, follow the same procedure to obtain averages for the different treatments. Such comparative root ratings may provide insight for future reference. We began our month-long assessment of rootworm damage and effectiveness of different control tactics on July

3 We started with our trials in Urbana; we will evaluate our trials at the outlying research farms near Monmouth and DeKalb during the week of July 19. The objective of most of the trials at Urbana, Monmouth, and DeKalb is to assess the effectiveness of different formulations of registered and experimental insecticides. During the last week of July, we will join forces with a team from Purdue University to evaluate rootworm damage in the fields in our areawide management study in Iroquois County, Illinois, and Benton and Newton counties in Indiana. To wrap it all up this summer, we will evaluate roots from as many as 75 cornfields in east-central Illinois. Several extension educators, farm managers, consultants, and growers placed yellow sticky traps in their soybean fields last year to sample for western corn rootworm adults. In an effort to help us refine our thresholds for western corn rootworm adults in soybeans, cooperators will extract roots from untreated check strips in the cornfields and bring them to us for rating. The more information we have, the more confident we can be with our thresholds of two to seven beetles per trap per day. On July 12 and 13, we observed some serious rootworm feeding damage to some untreated plots in our trials at Urbana, suggesting that rootworm densities are higher this year than they were last year. Although some variability in root ratings always occurs, average root ratings in some of our untreated check plots were close to 5 or greater. As soon as we have some data compiled, we will share some preliminary results. In the meantime, let us know what you are finding in fields in your area. Kevin Steffey, Mike Gray Western Corn Rootworms and First-Year Corn Injury: Questions and Answers We continue to receive many questions regarding western corn rootworm injury in first-year corn (rotated corn). Along with these questions are continuing concerns regarding the performance of soil insecticides. The following questions and answers hopefully will shed some light on corn rootworms, soil insecticides, and firstyear corn rootworm injury. Is the rootworm injury worse this season than last year? So far, reports from throughout the state and our own observations verify greater densities of corn rootworms this year. We have speculated about reasons for this occurrence in the previous issue of the Bulletin (no. 16, July 9, 1999). Now is a good time to check for larval injury in continuous corn as well as first-year corn in eastcentral Illinois. The only way to evaluate soil insecticide performance is to compare root injury (rate roots on the Iowa State 1 6 injury scale; see previous article) in untreated strips (no soil insecticide used) with treated portions of a given field. The bottom line: Grab a shovel, and be prepared to dig, wash, and rate roots in order to begin adequately assessing the return on your soil insecticide investment. Are root ratings of 4.0 (one node of roots pruned) required before yield losses begin to accrue? No. During a 4-year period, we evaluated the responses of 12 hybrids grown in DeKalb and Urbana to rootworm injury. In stressful growing seasons, characterized by soil moisture shortages during pollination, root rating averages as low as 2.0 (minor to moderate root scarring) reduced yields of certain hybrids. For some hybrids grown in a less stressful year, a root rating of 4.0 (one node of roots destroyed) may be required to elicit a negative yield response. Are hybrids with large root systems and good root regeneration characteristics always the best yielders? 163 No. In wet growing seasons, particularly from mid-july to mid-august, certain hybrids with small root systems that lacked good root regeneration characteristics have been shown to be very competitive with respect to yield. In dry years, these smallerrooted hybrids also have been shown to suffer significantly greater yield losses compared with larger-rooted hybrids. Having a large root system and possessing good root regeneration potential appears to be an asset in a dry year; this is not always the case in a wet season. The interaction among root injury, hybrid, and soil moisture with respect to yield can be quite complex. Should I consider treating my soybean field in east-central Illinois to suppress the egg-laying activities of adult western corn rootworms? No. We are continuing to learn more about the phenology of egg laying by western corn rootworms in cornfields and soybean fields of east-central Illinois. Unfortunately, we have much research to conduct before we can make responsible recommendations regarding the optimum time to trigger applications to prevent economic loads of eggs from being laid in soybean fields. If producers treat soybean fields for western corn rootworm adults, they will still be left with uncertainty about the effectiveness of the application. Because of this uncertainty, many producers also will be asked to consider the use of a soil insecticide at planting next spring. Two insecticide applications that are targeted at the prevention of root injury make neither environmental nor economic sense. This is especially true at the current extremely low commodity prices. Should I consider the use of another type of sticky trap to monitor adult western corn rootworms in soybean fields? I ve been told some other traps capture more adults. Capturing more adults with another type of trap may not be an advantage. Counting more beetles requires more time and may not provide any additional information. Our economic threshold of two to seven beetles per trap per day was based on the use of

4 Pherocon AM traps. If you use another type of sticky trap, be aware that comparing your trap counts with our threshold may be similar to comparing apples with oranges. Can I use Pherocon AM traps in continuous corn systems? Yes. In fact, most of the early research with Pherocon AM traps and corn rootworms was conducted during the 1980s in continuous cornfields in Iowa. In continuous corn, researchers suggested that 12 traps be evenly deployed throughout a field. If beetle densities reached six beetles per trap per day, producers were encouraged to rotate to another crop or consider the use of a soil insecticide the following spring. Researchers in this study also suggested that Pherocon AM traps should be used during the last 3 weeks of August. Why hasn t the use of Pherocon AM traps been accepted in corn as a pest management approach? During the mid-1990s, we conducted many on-farm trials (continuous corn) with producers in northern Illinois using Pherocon AM traps. The bottom line of the study: All of the 17 producers in our experiments indicated that traps were too difficult to locate in corn and consequently too inefficient to use. In addition, finding Pherocon AM traps within a pollinating cornfield during the heat of the summer was no picnic. The use of Pherocon AM traps within soybean fields has received a more positive reception. We believe that this is largely due to the much greater visibility of these traps across a soybean field. We continue to be impressed with the number of producers who express interest in Pherocon AM traps for monitoring western corn rootworm adults in soybean fields! The next few weeks will undoubtedly bring more reports of rootworm problems across Illinois. Please let us know how your rootworm season progresses. Mike Gray PLANT DISEASES Leaf Blights of Corn Management of corn leaf diseases relies on several factors. First is a working knowledge of what are the common as well as unusual diseases in your area. Then the disease must be properly identified based on signs, symptoms, and field distribution patterns, and observation of the severity of the disease must be done. And finally, familiarity with the damage threshold for a given disease is necessary so that management decisions can be made before the economic injury level is reached. The critical period for scouting leaf diseases is from 2 weeks before pollination to 2 weeks after pollination. During this time, yield losses generally occur when whole plant infection reaches 15 percent severity. Leaf blights caused by fungi generally begin on the lower leaves. Some fungal leaf blight diseases that can be found on corn in Illinois include northern corn leaf blight (NCLB), southern corn leaf blight (SCLB), northern corn leaf spot (NCLS), and gray leaf spot (GLS). Symptoms of NCLB are long, elliptical, grayish or tan lesions. Race 1 is usually not a problem since most commercial hybrids have the Ht1 gene for resistance. Race 2 is in some areas and can infect hybrids that have only the Ht1 gene for resistance. Other genes for resistance to Race 2 have been incorporated into many commercial hybrids. Heavy dews, frequent light showers, high humidity, and moderate temperatures (64 to 84 F) favor NCLB. Symptoms of SCLB are not as distinct as those of NCLB. Generally, lesions are small, tan in color, and somewhat rounded, and have buff to brown borders. However, lesion appearance may vary greatly depending on the genetic background of the corn hybrid. SCLB is most common in the southern third of the state but can appear in the southern half of Illinois. High humidity and warm temperatures (69 to 90 F) favor SCLB. Long periods of sunny weather between rains are unfavorable for disease development. Lesions from NCLS on susceptible inbreds are tan and oval to circular but can vary depending on the race in the field. Race 2 produces oblong, brownish spots up to 1 inch in length. However, this type of infection is rare. Race 3 is the most common race in the Midwest and produces narrow, linear to oblong lesions on leaves, sheaths, husks, and ears. Lesion appearance varies with the genotype of the plant and the isolate of the fungus. Lesions are dark grayish tan and are commonly surrounded by a darker border. Moderate temperatures (68 to 80 F) and high humidity favor NCLS. Spore production occurs primarily in damp weather. GLS lesions are blocky to rectangular when compared to other leaf blights. They are pale brown or gray to tan in color and are characteristically restricted by leaf veins. Lesions may coalesce, resulting in large, dead areas of leaves or the killing of entire leaves. Continuous corn, no-till corn, warm to hot temperatures (71 to 85 F), high humidity, wet weather, and cloudy days favor GLS. GLS is usually found in low-lying fields, particularly in river bottoms, which tend to have more favorable environments for this pathogen. Control of leaf blights is best accomplished by selection of resistant hybrids. Choose hybrids with resistance to the most common leaf blights in your area. Tillage to bury infected residues may also be helpful where erosion is not a problem. Fungicides are useful when conditions favor diseases, especially if you are producing hybrid seed. Apply during 164

5 the 14-day period before and after tasseling. Multiple applications may be necessary when disease pressures are high. However, during periods of high temperatures or dry conditions, disease pressures will be low and additional applications may not be necessary. Crop rotation is also helpful because all leaf blights tend to increase in continuous culture. However, because spores of these fungi are windblown, rotation alone will not provide the necessary protection. Combine several pest-management techniques for the best results when managing corn leaf blights. Joe Toman Contributing Authors Mike Gray Extension Entomology, (217) Faye Lesht Academic Outreach, (800) , ext Kevin Steffey Extension Entomology, (217) Joe Toman Extension Educator/Integrated Pest Management, (815)

6 U of I Extension Newsletter Service University of Illinois at Urbana-Champaign 528 Bevier Hall, MC S. Goodwin Avenue Urbana, IL Presorted First Class Mail U.S. Postage Paid Permit No. 75 Champaign, IL Return Service Requested The Pest Management & Crop Development Bulletin is brought to you by University of Illinois Extension and Information Technology and Communication Services, College of Agricultural, Consumer and Environmental Sciences, University of Illinois at Urbana-Champaign. This newsletter is edited by Stacey Krejci and formatted by Oneda VanDyke, ACES/ITCS. Helping You Put Knowledge to Work State County Local Groups U.S. Department of Agriculture Cooperating University of Extension provides equal opportunities in programs and employment. 166