Pest Management & Crop Development Bulletin No. 10 / May 30, Hot Topics! Sporadic Black Cutworm Injury Reported

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1 Hot Topics! Southern Corn Leaf Beetles: A New Annual Insect Pest of Corn? In 1996 and 1997, southern corn leaf beetles severely damaged many cornfields in southwestern and western counties of Illinois. The small beetles (3/16 inch) chew notches in the edges of corn leaves and occasionally in the stems. We have received several reports that suggest no-till cornfields have been hit the hardest. In some cases, no-till cornfields have required replanting. It s probably premature to suggest that this insect is a pest that growers will have to watch for carefully from now on; however, the fact that southern corn leaf beetles have made their presence known for two consecutive years has left us surprised. If southern corn leaf beetles strike again in 1998, we may have to begin showing this insect pest more respect. FOR IMMEDIATE RELEASE No. 10 / May 30, 1997 INSECTS Executive editor: Kevin Steffey, Extension Entomologist Web subscriptions available: For subscription information, phone , or acesnews@uiuc.edu In This Issue Sporadic Black Cutworm Injury Reported, this page Southern Corn Leaf Beetle Injury Confirmed, 88 Billbug Injury Reported in Southwestern Illinois, 88 More Information on 4-Inch Soil Heat-Unit Accumulations and Corn Rootworm Egg Hatch, 89 European Corn Borer Moths Are Emerging, 89 Update on Heat Units for Stalk Borer Development, 90 What Insects Are in Alfalfa? 90 Note on Cereal Leaf Beetles, 90 Corn Nematodes Thriving, 91 Sporadic Black Cutworm Injury Reported This spring has been characterized by very few reports of black cutworm injury to seedling corn plants. Although intense flights of moths have occurred in certain areas of the state, black cutworm larvae have not made a big splash yet. Let s hope they don t. Until fields move beyond the 4-leaf stage of development, continued vigilance in your scouting efforts is well worth the effort. Dave Mowers, of Mowers Soil Testing Plus, Inc., indicated recently that several fields in Peoria County had black cutworm injury with 4 to 5 percent of the plants affected. Ellen Phillips, Crop Systems Educator, DeKalb Extension Center, reported that some cornfields in southern DeKalb and Kane counties had black cutworm injury. Ellen described the injury as noneconomic; however, many late-planted fields will remain at risk for several weeks. Because of the very cool spring, plants will continue to be susceptible to cutting well into the month of June. Bottom line don t forget about this insect pest as we move beyond May. Cooperators in our black cutworm monitoring program reported moth captures in 22 counties for the monitoring period of May 17 to 23. Moths were caught in pheromone traps as far south as Alexander County northward to Boone, McHenry, and Stephenson counties. Volunteers also reported captures in western counties, such as Brown, Greene, and Hancock. Not to be left out, the eastern edge of the state also reported moth captures in counties like Clark, Douglas, Iroquois, and Vermilion. This wide distribution of moth captures has been a typical pattern this spring. An intense capture of moths was reported in Ford County on May 22 the only intense capture for the entire state for the most recent monitoring period. Table 1 provides updated information regarding potential cutting dates. Next week will be the last monitoring period for the black cutworm migratory flight of However, black cutworm larval injury could linger well into the month of June. Mike Gray, Extension Entomology, 87

2 Table 1. Potential dates when 300 heat units above 50 F have accumulated from an intense moth capture, indicating when black cutworm larvae are large enough (fourth instar) to cut corn seedlings. Date of intense moth capture Projected date when 300 heat units (9 or more moths caught over a (base 50 F) have accumulated from an 1- to 2-day period) County of intense moth capture intense capture April 28 Ford May 31 April 29 Adams May 28 May 3 Clark May 30, June 1 May 6 Pike June 1 May 6 Wayne May 31 May 7 LaSalle June 3, June 7 May 10 Ogle June 9 May 11 Monroe June 1 May 14 Macon June 4 May 14 Hancock June 6 May 15 Logan June 4 May 22 Ford June 9 Note: Two dates may be listed for the same county if the heat-unit accumulations were generated from different Illinois Climate Network sites. Heat-unit projections were provided by Bob Scott, Illinois State Water Survey. Hot Topic Southern Corn Leaf Beetle Injury Confirmed In last week s Bulletin, we indicated that several fields in southwestern Illinois were being injured by what appeared to be southern corn leaf beetles. Our guess was correct! For the second year in a row, southern corn leaf beetles have been positively identified as the culprits. John Bouseman, an entomologist with the Illinois Natural History Survey, confirmed our identification of beetles that were collected from cornfields in Jersey County. Matt Montgomery, Extension Unit Assistant for Crops in Fulton County, observed a cornfield on May 21 with 55 to 60 percent of the plants with leaf feeding. Clipping of plants (1- to 2-leaf stage) also was noted. We also have received some reports of southern corn leaf beetle injury to cornfields in Schuyler County. It s a little early to assume that this insect will be a regular problem from now on. However, with the number of cornfields affected in southwestern and western counties the last two seasons, we should be alert for the possible presence of this insect in For more details about the southern corn leaf beetle, please refer to last week s Bulletin (No. 9, May 23, 1997). Mike Gray, Extension Entomology, Billbug Injury Reported in Southwestern Illinois We have had a few reports that some cornfields in southwestern Illinois are infested with billbugs. The presence of billbugs in some cornfields may create confusion with suspected black cutworm problems. Fields most at risk are ones in which yellow nutsedge has become an established weed. Bluegrass and other species of grass also may serve as hosts. There are several species of billbugs, but the maize billbug is the most common. Adults are gray, brown, or nearly black snout beetles from 2/5- to 3/5- inch long. Billbugs have chewing mouthparts at the end of a prominent snout. Adult billbugs are rarely seen because they blend with the soil and are active only at night (Figure 1). The grubs are off-white with a brown or yellow-brown head. They are legless and humpbacked, shaped much like a kidney bean. Figure 1. Billbug adult. Billbugs overwinter as adults in the soil, grass, or litter and become active as corn begins to emerge in the spring. The beetles crawl into nearby fields and begin feeding at the base of the stalk, gouging small holes in the stem. Small plants may be killed, whereas older plants may have only transverse rows of holes in emerging leaves. However, if their feeding affects the growing point, distorted growth and excessive suckering may occur. The adults lay their eggs in the gouged-out holes in the stems. Developing larvae that feed inside corn stems may also cause some injury. Later in the season, the larvae may drop from the stem and resume feeding on the roots. Pupation takes place either in the stem or in the soil. The life cycle requires several months for completion, and there is only one generation per year. 88

3 Billbugs usually cause no economic damage to corn. Control is warranted only if a significant number of plants are killed or if their growth is affected. Leaf feeding is not economic. Lorsban 4E at 2 to 3 pints per acre will control billbug adults. For best results, use only ground equipment and apply 20 to 40 gallons of finished spray per acre. Mike Gray and Kevin Steffey, Extension Entomology, (217) More Information on 4-Inch Soil Heat-Unit Accumulations and Corn Rootworm Egg Hatch In last week s Bulletin, we indicated that the corn rootworm egg hatch this season might be very late, as it was in Recall that last year corn rootworm eggs didn t start to hatch until mid-june, some two weeks later than normally expected. By comparing Figures 2 and 3 (actual 4-inch heatunit accumulations, base 52 F) for 1996 (through May 26) and 1997 (through May 19), respectively, it appears that we can expect another delayed corn rootworm egg hatch for the 1997 season. Although heat-unit accumulation data for 1997 include one less week, soil heat-unit accumulations this season are low, especially for western areas of the state. In addition to delaying corn rootworm egg hatch, many other subterranean insect pests are likely to remain in the upper profiles of the soil for longer periods of time this spring. This lingering increases the chances for seedling injury to those below-ground portions of the stem. As mentioned last week, soil insecticides will likely be under increased pressure to protect roots against corn rootworm injury this year. This is especially true for early planted fields. Although a very warm June may help us close the gap with regard to heatunit accumulations, we have some distance to go. Mike Gray, Extension Entomology, European Corn Borer Moths Are Emerging Rick Weinzierl, Extension entomologist in the Department of Crop Sciences, confirmed the emergence of European corn borer moths in central Illinois. A trickle of moths were captured in a light trap near Urbana during the Memorial Day weekend. Although the numbers captured in traps in both southern and central Illinois are not significant right now, the captures indicate that the flight of moths that will lay eggs for the first generation has begun. We have some indication that a large percentage of some populations of overwintering corn borer larvae were infected with Nosema pyrausta (see issue No. 3 of this Bulletin, April 11, 1997). In addition, the weather right now is not conducive for moth flights and egg laying. If the weather remains cool and rainy, the first generation of corn borers may get off to a puny start this spring. As the season progresses and we receive scouting reports and moth-capture data from around the state, we will keep you informed. Figure 2. Actual heat-unit accumulation (4-inch, base 52 F) from January 1 to May 26, Figure 3. Actual heat-unit accumulation (4-inch, base 52 F) from January 1 to May 19, Figure 4. Actual heat-unit accumulation (base 41 F) from January 1 to May 26, 1997, for estimating the development of stalk borers.

4 Update on Heat Units for Stalk Borer Development For those of you tracking stalk borer development and planning to manage these pests in areas where they are problematic almost every year, Figure 4 (previous page) shows actual heatunit accumulations (base 41 F) from January 1 to May 26, Remember the following: Overwintering eggs hatch when approximately 575 to 750 heat units have accumulated since January 1. Larvae first begin to move into corn when about 1,100 heat units have accumulated since January 1. 50% movement occurs when about 1,400 to 1,700 degree days have accumulated. Begin scouting when about 1,300 to 1,400 degree days have accumulated. Also remember that very small stalk borer larvae could be causing damage to small corn seedlings now in fields that were infested with weedy host plants last fall. The presence of these larvae cannot be predicted based on the accumulated heat units associated with larval movement. You can find details about biology, identification, and management in issue No. 8 (May 16, 1997) of this Bulletin. What Insects Are in Alfalfa? The alfalfa weevil seems to be leaving us with a whimper this year. We have received very few reports of alfalfa weevil activity that requires much attention this spring. Also, enough heat units have accumulated throughout the state that maps predicting their development no longer seem necessary. However, because surviving larvae and adults can feed on regrowing buds after the alfalfa has been cut, growers should watch the fields closely after cutting to make certain the alfalfa greens up nicely. The other key insect in alfalfa is the potato leafhopper. We reported its presence as early as mid-april this year, and folks scouting alfalfa fields are beginning to find leafhoppers with relative ease. At least one person reported numbers of leafhoppers above the economic threshold in western Illinois. Remember that the static economic thresholds for potato leafhoppers vary with the height of alfalfa. An insecticide application might be warranted if the following combinations of leafhopper numbers and alfalfa height are reached or exceeded: 0.2 per sweep in alfalfa 0 to 3 inches tall; 0.5 per sweep in alfalfa 3 to 6 inches tall; 1 per sweep in alfalfa 6 to 12 inches tall; and 2 per sweep in alfalfa 12 inches or taller. The next few weeks will be a critical time to monitor the development of potato leafhopper populations in alfalfa fields. Numbers of leafhoppers tend to increase around the time the first cutting of alfalfa is made. Tender alfalfa that is regrowing after a cutting is particularly susceptible to leafhopper injury. Although current weather conditions are not ideal for rapid buildup of leafhopper populations, the arrival of warmer weather will accelerate their development. Scout for leafhoppers by using a 15- inch-diameter sweep net. As indicated previously, economic thresholds are based on numbers of leafhoppers per sweep of a sweep net, not on the appearance of injury. In fact, when you see symptoms of leafhopper injury, initially a V-shaped yellowing at the tips of the leaflets, some yield loss and reduction in hay quality already has occurred. Don t let potato leafhoppers get ahead of you this year, as they did in some fields of alfalfa in Some observers are finding aphids and spittlebugs in alfalfa fields. The aphids are probably pea aphids, and unless their numbers become extremely large, they cause no economic damage to alfalfa. Dave Feltes, IPM Educator at the Quad Cities Extension Center, and Jim Morrison, Crop Systems Educator at the Freeport Extension Center, scouted some alfalfa fields in northwestern Illinois during the week of May 19. They found very few alfalfa weevils and noted the presence of aphids and spittlebugs. Ellen Phillips, Crop Systems Educator at the DeKalb Extension Center, also observed spittlebugs in some alfalfa fields in DeKalb County. These spottings make it worthwhile to discuss spittlebugs. The spittle masses found in alfalfa fields were created by the nymphs, which require a moist environment to survive. If you tease apart a spittle mass, you should be able to locate one or more orange-yellow to yellowgreen or green nymph (color varies with size) inside the spittle. These insects have piercing-sucking mouthparts with which they extract fluids from the plants. Nymphs typically are present for 5 to 8 weeks, depending on the temperature. Although spittle masses may seem prevalent in some fields, don t overreact to their presence. Spittlebugs infrequently cause economic damage in alfalfa. However, if their numbers exceed one per plant, which is an exceptionally large population, they can cause yield losses. Note on Cereal Leaf Beetles Robert Bellm, Crop Systems Educator at the Edwardsville Extension Center, observed a significant number of cereal leaf beetles in a wheat field in the Jersey/Greene counties area during the 90

5 latter part of the week of May 19. He found as many as three to four larvae per flag leaf near the edge of the field, but the density decreased dramatically to less than 0.5 per flag leaf toward the interior of the field. The economic threshold is three or more eggs and/or larvae per stem. Because cereal leaf beetle larvae are not very mobile, a spot treatment could be effective in this field. This situation emphasizes the importance of scouting the entire field and recognizing that thresholds usually are based on average numbers of insects for the entire field. Consequently, single samples, especially samples taken near the edges of fields, often do not represent the average population density of a pest within a field. More information about cereal leaf beetles was printed in issue No. 5 (April 25, 1997) of this Bulletin. PLANT DISEASES Corn Nematodes Thriving The cool and wet weather passing through Illinois is ideal for the development of corn nematode populations. These nematodes are most common in sandy soils, although they can also be a problem in some of the areas where the heavier prairie soils predominate. Irrigation also aids in population development and survival by maintaining a better soil environment (cooler and wetter). Corn nematodes feed by inserting a hollow feeding tube (called a stylet) into the plant roots and using a muscular pumping bulb to withdraw plant cell contents. This feeding apparatus works like a hypodermic needle attached to a bulb. The common corn nematodes remain outside of the roots and can move from one feeding site to another. Once an area of roots is severely damaged, the corn nematodes simply migrate to another area and continue to feed. Soybean cyst nematodes, on the other hand, cannot move once a feeding relationship is established. Three genera of nematodes are often associated with corn, depending on the soil type and location in the state. In sandy soils, the dagger nematode and the needle nematode are common. In some areas, even in heavier soils, the stunt nematode is found. All three may have been established in Illinois feeding on native grasses long before corn was introduced. They need moderately wet soils and cool temperatures to thrive and reproduce. In a study conducted with Dave Feltes, IPM Educator for the Quad Cities area, soil samples collected in May of this year prior to planting corn were found to already have above-threshold numbers for the needle nematode. This nematode can cause severe damage at population levels as low as 10 per 100 cc s of soil (about 2/3 of a styrofoam coffee cup). We have detected 11 to 25 in some plots and expect that there are many more at this time. All of the nematodes seen were juveniles and not adults, meaning that they hatched from the eggs very early in the season and should begin laying eggs very soon. The data from these plots have also shown that corn nematodes tend to have a population peak within 6 to 8 weeks after corn planting. Unfortunately, this peak may be before the stunting and poor growth symptoms begin to show and growers recognize a problem. The last two years, populations of dagger nematode were greatest in June or early July, depending on weather. They fell rapidly after this time and were at low levels during the rest of the season. So, if you suspect corn nematode problems or want to see if they are present, sample early in the season. Both dagger and needle nematode populations seem to produce one or, at most, two generations per year. Some juveniles of the needle and both juveniles and adults of dagger nematode were detected in August and September of 1996, but at very low populations. Very few were found this late in These late populations seem to depend on the weather and lateness of the crop. How do you manage corn nematodes? Unfortunately, there are few options compared to soybean cyst nematode (SCN) management. Crop rotation is important because corn nematodes are grass feeders. Needle nematode populations will drop rapidly with a single year of soybeans, but dagger populations may remain somewhat higher. However, two years of corn generally result in very high populations that cause extensive damage. Corn nematodes are most damaging in second- or third-year corn, not in rotations. There are two nematicides currently labeled: Mocap and Counter. Neither has the needle nematode listed on the label. I believe that this absence is due in part to the extremely low threshold (5 nematodes per 100 cc s of soil) for the needle nematode. No company will guarantee to control pest populations down to fewer than five individuals per sampling unit. If a nematicide is used, it can still provide protection against other nematodes for which it is labeled and help reduce stress from these pests. Because these compounds are highly hazardous, read and follow all label and handling directions. Sample soil now in fields where you suspect corn nematode problems. How do you tell nematode damage in the field? That s also difficult to do because nematode damage can resemble many other problems. Typically, plants are stunted, may be yellowish, and can wilt more rapidly than healthy corn if dry conditions occur. Nematode infestations tend to be circular to oblong areas in fields. Roots may have a bottlebrush appearance (similar to DNA herbicide carryover) or small necrotic (dead) areas along the roots, or the root volume may simply be smaller than expected. 91

6 Dig the plants, wash the roots, and examine them carefully for these symptoms. Collect soil samples around the root zone to a depth of about eight inches. Place soils in a plastic bag, seal the bag, and keep it in a cool place until mailing to a lab. Because corn nematodes are not in a resistant stage like SCN cysts, they will die very quickly if exposed to heat. If possible, mail on a Monday or Tuesday to a lab to ensure that the sample won t remain in a post office over the weekend. Because population thresholds vary for corn nematodes, it is important that they be correctly identified. Typically, at least three to five different genera are found in soils. These genera must be correctly identified in order to determine the most appropriate and environmentally sound management approach. If the corn nematodes are not correctly identified, unnecessary pesticide applications or rotation systems may be suggested. Consult with local agricultural dealers or Extension workers to find labs with people who can identify corn nematodes. H. Walker Kirby, Department of Crop Sciences, (217) The information provided in this publication is for educational purposes only. References to commercial products or trade names do not constitute an endorsement by the University of Illinois and do not imply discrimination against other similar products. 92

7 CES Newsletter Service University of Illinois at Urbana-Champaign 69 Mumford Hall 1301 West Gregory Drive Urbana, IL Presorted First Class Mail U.S. Postage Paid Permit No. 75 Champaign, IL The Pest Management & Crop Development Bulletin is brought to you by the Cooperative Extension Service and Information Services, College of Agricultural, Consumer and Environmental Sciences, University of Illinois at Urbana-Champaign; and the Natural History Survery, Urbana, IL. This newsletter is edited by Mary Overmier and formatted by Oneda VanDyke, ACES Information Services. Helping You Put Knowledge to Work State County Local Groups U.S. Department of Agriculture Cooperating The Cooperative Extension Service provides equal opportunities in programs and employment. 93