INSECTS. Field Crop In-Depth Workshops on Insects and Diseases

INSECTS Field Crop In-Depth Workshops on Insects and Diseases Producers and agribusiness professionals who want to know more than the basics about pest management will want to attend the Field Crop In-Depth Workshops on Insects and Diseases. The workshops will be held at the Crops Training Center, Northern Illinois Agronomy Research Center, near Shabbona, Illinois. The In-Depth Insects Workshop will be held on July 14, 1999. Emphasis will be on new technology, management strategies, and outlook for corn rootworms, European corn borer, potato leafhopper, bean leaf beetle, and grasshoppers. Beneficial insects also will be identified and discussed. Certified Crop Advisor credits (5.5 in IPM) have been approved for this workshop. FOR IMMEDIATE RELEASE No. 14 / June 25, 1999 Executive editor: Kevin Steffey, Extension Entomologist Available on the Web at http://www.ag.uiuc.edu/cespubs/pest/ For subscription information, phone 217.244.5166, or e-mail acesnews@uiuc.edu In This Issue Development of Corn Rootworms Is Progressing, 133 Not Much Noise from First- Generation European Corn Borers, 134 Southwestern Corn Borers Are at It Again in Southern Illinois, 134 Japanese Beetles Observed Near the East Coast of Illinois, 135 Heads-Up for Spider Mites in Soybeans, 135 Watch for Potato Leafhoppers in Soybeans, 136 Early Summer Root Rots, 136 The In-Depth Disease Workshop will be held on August 19, 1999. The workshop will focus on field crop disease management; basics of disease identification; and recent research findings and strategies for short- and long-term management of sudden death syndrome (SDS), Sclerotinia white mold, and nematodes (both in corn and soybeans). Individuals attending are encouraged to bring one soil sample for screening for soybean cyst nematodes (SCN). Certified Crop Advisor credits (6.0 in IPM) have been approved for this workshop. The format for both workshops will consist of informal, interactive, classroom and in-field sessions. The programs are scheduled to start at 9:00 AM and adjourn by 3:30 PM. The preregistration fee for either of the workshops is $55 and is due one week before the program date. The late registration fee is $75. The fee includes course materials and lunch. Additional information and registration forms for either of these workshops are available from the Rockford Extension Center at (815)397-7714 or Ellen Phillips at (630)833-2171, phillipse@mail.aces.uiuc.edu. Ellen Phillips Development of Corn Rootworms Is Progressing Some corn rootworm larvae in corn planted after soybeans Corn rootworm pupae observed near West Lafayette, Indiana Emergence of adult corn rootworms is imminent In last week s issue of the Bulletin (No. 13, June 18, 1999), Mike Gray discussed how to sample for corn rootworm larvae and summarized the questions people ask about assessing performance soil insecticides for control of corn rootworms. This is just a brief reminder to encourage you to make plans for assessing corn rootworm damage in July and to prepare you for the emergence of corn rootworm adults. 133

On June 16, Jeff Bunting, American Cyanamid Company, found some corn rootworm larvae in a cornfield in northern Ford County. The field had been planted to soybeans in 1998. Obviously, the problem with western corn rootworms in corn planted after soybeans has not gone away. (No, we really didn t think it would.) We are very interested in documenting where the problem exists to determine if this new biotype of western corn rootworm has extended its range north, west, or south in Illinois. The spread of this new biotype to the east occurred relatively rapidly; we are fortunate that the affected area in our state is still reasonably confined. However, we want to hear from you if you encounter the problem beyond the known affected counties: Champaign, DeWitt, Douglas, Edgar, Ford, Grundy, Iroquois, Kankakee, LaSalle, Livingston, Macon, McLean, Piatt, Vermilion, and Will. We suspect or have heard rumors that the problem has been verified in Christian, Coles, Logan, Moultrie, Sangamon, and Woodford counties. Please help us keep accurate records by reporting the problem. The only positive verification is the presence of rootworm larvae in the field or corn rootworm larval damage to the roots. Try to ignore all of the claims of rootworm problems that actually are problems associated with other causes (such as wind-lodged corn). We will assess many fields of corn planted after soybeans for rootworm larval damage this summer. In fact, we have an ambitious on-farm research effort under way, an effort that involves many extension personnel, farm managers, company representatives, consultants, and growers. We are attempting to refine our current economic injury index and determine the extent of the problem in Illinois. As the data accumulate, we will inform you of our findings. The entomologists at Purdue University have found at least one corn rootworm pupa in one of their plots near West Lafayette, Indiana. This means that emergence of corn rootworm adults is imminent. In fact, I suspect that astute observers could find them in some fields in southern or south central Illinois right now. By the time you receive this issue of the Bulletin, corn rootworm adults may be emerging in central counties. Let us know when you find the first adult. And as the summer progresses, let us know about the densities of these pests you find. Kevin Steffey Not Much Noise from First-Generation European Corn Borers Highlight: Economic infestations of firstgeneration European corn borers have not been noted thus far. Apparently everyone is out scouting for first-generation European corn borers, but most people are finding low levels of injury and only a few larvae in cornfields. Dennis Epplin, Extension Educator, Crop Systems in the Mt. Vernon Extension Center, observed newly hatched corn borer larvae in Jefferson County late during the week of June 14. Mike Roegge, Extension Unit Educator, Crop Systems in Quincy, is still finding egg masses in cornfields in western Illinois. He reported that infested fields are not widespread in his area. Brian Oester, Pioneer Hi-Bred International, reported that numbers of European corn borers in Clark, Crawford, and Lawrence counties are still quite low. Many fields have no sign of infestation, and the most injury he observed in seed cornfields late in the week of June 14 was 3 percent. At that time, he was finding first through fourth instars. Kevin Nelson, Utica Elevator Co., observed a very small infestation (1 percent of the plants infested) in LaSalle County during the same week. And, believe it or not, I had an opportunity to spend time in one of our research plots on June 21! Although I could find shot holes in leaves and second and third instars in the whorls, the number of plants infested was quite low. I also observed a third instar in a midrib, so stalk tunneling should be occurring right now. We gave you the facts on corn borer development, scouting, management worksheet, and suggested insecticides in issue no. 11 (June 14, 1999) of this Bulletin. It s only a brief matter of time before we know, with hindsight, the full extent of our first go with European corn borers. After that, we can start guessing about what the second generation might have in store for us. Kevin Steffey Southwestern Corn Borers Are at It Again in Southern Illinois Injury by first-generation southwestern corn borers is evident in southern counties. Some stalk-boring activity has occurred. Economic damage caused by firstgeneration southwestern corn borers does not occur commonly. Apparently southwestern corn borers have decided to establish residence in southern Illinois. It s not that we haven t experienced problems caused by this important pest of corn in the past; it s just that southwestern corn borers have become much more obvious in recent years. Maybe our string of mild winters has enhanced their survival. Whatever the case may be, corn growers and other agriculturists in southern counties need to be on the lookout for this insect. Ron Hines, Senior Research Specialist at the Dixon Springs Agricultural Center, continues to be our sentinel for southwestern corn borers. According to cone-trap captures in Massac County, peak moth flight occurred during the first week of June. Both Ron and Dennis Epplin, Extension Educator, Crop Systems at the Mt. Vernon Extension Center, observed first-generation southwestern corn 134

borers feeding in 28-inch-tall corn at the Ewing field in Franklin County on June 21. Ron reported that about 10 to 15 percent of the non-bt corn plants were infested, some with as many as five to six larvae per plant. According to most experts on the subject, economic infestations of firstgeneration southwestern corn borer are uncommon and are restricted to corn planted near undisturbed corn stubble fields where adults emerge in the spring. Nevertheless, some entomologists have established 35 percent whorl-feeding injury as a static economic threshold, so the presence of first-generation borers bears watching. Larvae attacking whorl-stage plants feed on developing leaves in the whorl. Injury is evident as leaves unroll from the whorl. Leaf injury ranges from pinhead-sized holes and small circular lesions, or windows, on leaf surfaces to large, elongated holes. Third instars leave the whorl, crawl down the stalk, and tunnel into the plant, primarily between nodes. Ron Hines found some third and fourth instars bored into corn stalks at the Ewing field. Very large densities may cause economic yield loss. Female southwestern corn borers deposit eggs in masses of two to three on upper and lower surfaces of corn leaves. Eggs are yellow-green when first deposited, but within 36 hours they become white, with three broken orange-red lines across each egg. The eggs slightly overlap, much like fish scales. Southwestern corn borer larvae are white with a pattern of large, raised black tubercles on each body segment and are 1 to 1 1/4 inches long when fully grown. The head of first through third instars is black, whereas the head of older larvae is brown. Remember, unless densities are quite large, economic damage by first-generation southwestern corn borers is not common. Insecticides seldom are justified. However, we are interested in learning more about this pest in Illinois, so keep us informed if you encounter infestations. Kevin Steffey Japanese Beetles Observed Near the East Coast of Illinois Japanese beetles have been observed in corn in Lawrence County. Watch for Japanese beetles in both corn (especially during pollination) and soybeans. We ve discussed Japanese beetle grubs in previous issues of this Bulletin, but now it s time to talk about the showier and usually more noticeable adult, the insect that seems to scare some folks. Japanese beetles begin to emerge at about the same time as corn rootworm adults emerge, so it is not surprising that someone has observed them already. Rick Scranton with Monsanto Company found about three to four Japanese beetles per plant in a cornfield in Lawrence County on June 21. The corn was at growth stage V-10 through V-12. Although Rick did not see any apparent feeding injury to the corn leaves, the presence of so many beetles bears watching as the corn gets close to tasseling and silking. The adult Japanese beetle is shiny metallic green with hard, bronzecolored wing covers. Along each side of the abdomen, just below the wing covers, are six tufts of white hair. The adult is about 1/2 inch long. The beetles may feed on leaves if silks are not available; injured leaves appear skeletonized or lacy, similar to injury caused by corn rootworm beetles. However, leaf feeding seldom is economically important. More importantly, Japanese beetle adults may clip a sufficient number of silks to prevent proper pollination. If Japanese beetles are found in a cornfield, five randomly selected plants in each of five areas of the field should be examined and the number of beetles found on each plant should be recorded. The length of silks remaining on each plant and the maturity of the silks (i.e., no silks, green silks, some brown silks, or all brown silks) should be estimated. Control with an insecticide may be warranted if silks are clipped to less than 1/2 inch, fewer than 50 percent of the plants have been pollinated, and beetles are feeding. A rule-of-thumb economic threshold is three or more beetles per ear. Insecticides suggested for control of Japanese beetles are Penncap-M* at 2 to 4 pt per acre, Sevin XLR Plus at 2 to 4 pt per acre, and Warrior T* or 1E* at 2.56 to 3.84 oz per acre. (The use of products followed by an asterisk is restricted to certified applicators.) Japanese beetles have a wide host range and feed on many other plants, including soybeans, fruits, and flowers. As you begin to increase the frequency of scouting in soybeans, keep your eyes peeled for Japanese beetles. Don t overreact when you find them, but don t forget about them, either. Kevin Steffey Heads Up for Spider Mites in Soybeans Spider mite problems are showing up in soybeans in Ohio. Watch for spider mites building up at the edges of soybean fields. No, we haven t received any reports of twospotted spider mites showing up in soybeans, but I thought you might want to know what s happening in at least one nearby state. Ron Hammond, research entomologist at Ohio State University, contacted me on June 21 to find out if we were experiencing dry weather and spider mite problems associated with droughty conditions. I told him that we had had plenty of moisture in most areas of Illinois and had not heard anybody talking about spider mites. Ron informed me that much of Ohio is dry and that spider mites are showing up in isolated areas of soybean fields throughout the state. He indicated that this early incidence of spider mites in soybeans was reminiscent of occurrences in 1988. 135

Most of us will not soon forget the devastation caused by twospotted spider mites in 1988. Although I am not suggesting that anything like 1988 will happen again in Illinois in 1999, I do want to make you aware of developments to the east so that you can be vigilant. If rainfall ceases, spider mite populations can build rapidly, especially if the weather gets hot. As you scout soybeans for other pests and problems, always give a look to the plants near the edges of the fields. If spider mite densities begin to increase, you should notice them first at the field edges. Look for yellowing plants that appear sandblasted, and then look for the mites and webbing on the undersides of the leaves. If you think you have found some spider mites, let us know right away; we would want to get the word out quickly. Kevin Steffey Watch for Potato Leafhoppers in Soybeans Numbers of potato leafhoppers in alfalfa are still high. Watch for symptoms of potato leafhopper injury to soybean leaves. Much has been said already about the intensity of infestations of potato leafhoppers in alfalfa. Many people have reported finding large numbers of these pests causing noticeable and, in some instances, excessive damage. Spraying to control potato leafhoppers in alfalfa has been ongoing throughout much of June. However, don t forget that potato leafhoppers can cause injury to soybeans, too. Although the extent of injury to soybeans caused by leafhoppers is still debatable, noticeable injury will catch your attention. The symptoms of leafhopper injury to soybean leaves are similar to symptoms of injury to alfalfa. The edges of injured leaves turn yellow and may eventually appear burned. Injured leaves may pucker or curl up, and severely damaged rows may be stunted. Soybean fields most at risk are those adjacent to or near alfalfa fields that have been cut. However, if densities of potato leafhoppers are high this year, some soybean fields not even within sight of an alfalfa field could be injured. So stay alert. Economic losses caused by potato leafhoppers feeding on vegetativestage soybeans probably are not common. However, the presence of leafhoppers in soybeans bears watching. For susceptible varieties, control in blooming soybeans may be warranted when you find six or more leafhoppers per plant. During early seed formation, control may be warranted if you find 13 or more leafhoppers per plant. Stay tuned to find out if economic infestations of potato leafhoppers develop in soybeans. Kevin Steffey PLANT DISEASES Early Summer Root Rots The most frequent disease concern this week has been about root rots in soybeans. Primarily, Rhizoctonia and Fusarium root rots have been the culprits. These two rots cause a dry-type canker at the soil line, usually extending down the entire root system. I say dry just to distinguish these types of root rots from wet rots such as Pythium or Phytopthora, in which the roots are typically slimy; roots infected by Fusarium or Rhizoctonia may still be a little mushy and not completely desiccated. Rhizoctonia root rot. The soilborne fungus Rhizoctonia solani causes Rhizoctonia root rot. Infection by Rhizoctonia alone typically will cause reddish or purple lesions at the soil line. A general rot of the taproot may also occur. Plants infected by Rhizoctonia usually make an attempt to reroot, so if soil moisture is adequate, the plant may recover. 136 Typically Rhizoctonia is favored by moist conditions at planting followed by some stressful condition that slows down the growth of the root system. Dry weather as the plants begin to emerge and grow is probably the most common environmental factor leading to infection by Rhizoctonia. Other stresses include compaction or herbicide injury. The picture becomes a little muddled at this point, especially if the stress is from a factor other than weather; yes, you may have root rot in the headlands where compaction is likely, but the disease probably wouldn t have gotten a good hold on the root system if the compaction wasn t there and the plants were actively growing. It is the same sort of situation if herbicide damage has slowed the growth of the plant. Fusarium root rot. Fusarium root rot caused by Fusarium solani doesn t cause the same diagnostic lesions as Rhizoctonia. It typically causes a more generalized dry rot of the root system. You would be hard pressed, though, to tell them apart in the field. This situation is usually compounded by the observation that Fusarium and Rhizoctonia often occur together. The same conditions that favor infection and disease development of Rhizoctonia also favor Fusarium. When infection by both pathogens occurs together, the condition is called Fusarium root rot complex. Stand reduction can occur from infection by these root rots, but significant losses typically occur only when stress to the crop is present. If you used a fungicide seed treatment active against these root rots, why might you still have infection? The explanation for this is that the fungicide does not remain active in the seed zone for a prolonged period of time. So if environmental conditions develop or are already present that slow growth approximately 10 days after planting, depending on the compound, the diseases may become active.

Management options are pretty limited at this point in the season. If the plants are showing some root regrowth, cultivation may put some soil up around the base of the stem and further encourage root growth; this is not a feasible option in drilled or no-till soybeans, though. Soybean cyst nematode. Start looking for symptoms and signs of soybean cyst nematode (SCN). Aboveground symptoms of leaf yellowing and some stunting are just starting to show up. At a scouting clinic in Piatt County, I was able to find white female cysts on soybean roots. If you see areas of the field that appear to have nutrient deficiency symptoms, don t forget to gently dig up the roots and have a look; SCN may be the problem. Suzanne Bissonnette Contributing Authors Suzanne Bissonnette (bissonnettes@mail.aces.uiuc.edu), Champaign Extension Center, (217)333-4901 Ellen Phillips (phillips@mail.aces.uiuc.edu), Rockford Extension Center, (815)397-7714 Kevin Steffey (ksteffey@uiuc.edu), Extension Entomology, (217)333-6652 137

U of I Extension Newsletter Service University of Illinois at Urbana-Champaign 528 Bevier Hall, MC-184 905 S. Goodwin Avenue Urbana, IL 61801 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. 138