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Around the County

Frequent information updates for agricultural audiences

Weekly Update - from Matt Montgomery in Sangamon/Menard Unit

Posted by John Fulton -

- SOUTHERN CORN LEAF BEETLE - While not really a 2007 area problem, the Southern Corn Leaf Beetle is at least "detectable" in the Sangamon-Menard Unit. Southern Corn Leaf Beetles are a more recent addition to our pest spectrum, only noted in our unit during the 1998 growing season. They became somewhat infamous during that brief period of time riddling the leaves and stems of seedling corn with small holes. One generation occurs in Illinois each year. The larvae, which resemble grape colaspis larvae, are typically deemed less significant than the adults, which overwinter in our area. As adults feed during the early spring, they also deposit eggs near the base of the corn plant. Adult injury to the plant, typically wraps up by mid to late June in our area. Cutworm thresholds of 3 percent stand reduction are used to gauge the severity of SCLB infestations and to gauge any need for management. (Picture type "southern corn leaf beetle" at http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).
- CLOVER ROOT CURCULIO - These small 1/4 inch long, gray-brown mottled beetles are somewhat teardrop shaped and are very difficult to find in alfalfa (usually noted on the ground where they blend nicely with their surroundings). The leaf damage that they cause is more easily noted. The margins of alfalfa leaves are removed in crescent shape notches and stems are sometimes gnawed upon as well. Regrowth in our area has recently been damaged by the feeding of both clover root curculio in and alfalfa weevil adults. We recommend that producers use weevil thresholds to guide management "50 percent of the crowns damaged and regrowth prevented by 3 to 6 days." The larvae scar and pit legume roots and are usually deemed the more damaging stage. (Picture type "clover root curculio" at http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).
- COMMON STALK BORER - Stalk borers are in "migration mode" and can occasionally be spotted as they move from small girth stem plant materials to larger girth stem plant materials. These insects overwinter as eggs on leaf material in border or "waste" areas, hatch in May, and begin to feed on plant material. Larvae injure corn when they borer into the stalk and begin to feed. The moths of the species will emerge in August. Larvae are typically of minor importance and usually appear only in that corn nestled against border areas and waterways. However, no-till and strip till areas (especially those plagued by weed management issues) may prove ideal for economically significant distribution. The critical period for management is that period when larvae migrate from small girth to large girth plant material. (Picture type "common stalk borer" at http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).
- LEAF HOPPERS AND APHIDS - We remind producers to keep a wary eye on potato leafhopper populations in alfalfa, which seem to reached impressive levels. Remember that 0 to 3 inch alfalfa requires approximately 0.2 leafhoppers per sweep with a 15 inch sweep net. 3-6 inch alfalfa requires 0.5 leafhoppers per sweep, 6-12 inch alfalfa requires 1.0 per sweep, and 12 plus inch alfalfa requires 2.0 per sweep. In addition, producers are reporting impressive populations of cowpea aphid. While populations must be exceptional for this pest to warrant management, we still recommend that producers keep their eyes open for these small black shiny insects.

RUST UPDATE

Asian Soybean Rust has been detected in Louisiana in an area that "might" yield spores capable of reaching Illinois via prevailing winds in 2007. As happened last year, January and February appeared a little disturbing from an Asian Soybean Rust (ASR) standpoint but cold weather has once again largely driven ASR back into the state of Florida (which "might" be good news). Readers will remember that ASR did reach the state of Illinois in 2006 (a total of 8 Illinois counties). Additionally, it was detected in West Lafayette, Indiana. The ASR "remnants" detected in an Iowa grain bin just a couple months ago are now suspected to have been "planted" there by "less scrupulous" individuals. Regardless of this Iowa peculiarity, 2006 did indicate exceptional northward progress for this disease and thus accents the need for vigilance. Remember that U of I Extension offices serve as sites for initial rust diagnosis and that sentinel plots are scattered throughout the state to monitor for this disease as well. One should keep a vigilant eye on the lower quarter of the soybean plant. Should rust appear, this region of the plant will be more prone to display the roughly polygon-shaped lesions centered about a pustule. Also remember that a 40X lens should allow one to easily observe the spores nestled within the pustule (a quick means of identifying rust). (References include "Look Low As You Go" at: http://ipm.uiuc.edu/bulletin/pdf/protocol.pdf and "National Pest Alert Soybean Rust" at http://www.ncpmc.org/alerts/soybeanrust/soybeanrust_alert.pdf).

OTHER SOYBEAN LEAF DISEASES

The following represent some common soybean diseases, noted from May through August. We encourage readers to review these diseases as they attempt to "spruce up" their identification skills in preparation for rust scouting.

- SEPTORIA - Caused by the fungus Septoria glycines, Septoria leaf blight is sometimes the earliest disease spotted in the field. The disease can be noted on unifoliate leaves and is commonly noted on the lower part of the plant as the season progresses. Leaves may turn yellow and are covered (upper and lower surfaces) with small chocolate brown spots. The disease overwinters in debris, infects the lower part of the plant first (similar to the infection pattern of rust), and progresses up the plant via wind, rain, and contact with infected tissue. Septoria can appear over a much wider range of temperatures than some other noteworthy soybean leaf diseases (ideal temperatures range from the low 70s to the mid 90s). Minimum tillage and wet weather increase the chances that one might observe this disease as well. This disease is not deemed to cause noteworthy yield losses. (Picture type "septoria brown spot" at: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).

-FROGEYE - Caused by the fungus Cercospora sojina, frogeye leaf spot has been known to occasionally appear in our area over the past few years. However, leaf symptoms have typically been restricted to a few haphazard markings as opposed to the more prolific "speckling" of trifoliates sometimes noted in other parts of our state. The fungus responsible for this disease overwinters in crop debris and can also be transported by infected seed. Spores are primarily transported via wind and tend to infect young tissue more easily than old tissue. For this reason, lesions associated with this disease are often noted on upper plant trifolates as opposed to lower trifolaites (a pattern of infection less similar to rust). Favored by temperatures in mid 70s to mid 90s, frogeye leaf spot also tends to appear when the weather has been wet. Crop scouts typically note 1/8 inch, light brown, slightly round lesions bordered by a thin dark brown band (thus the frogeye appearance). This disease is not deemed to cause noteworthy yield losses in our area in most cases. (Picture type "frogeye" at: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).

- DOWNY MILDEW - The canopy of the bean crop generally is well established by the time this disease appears. Caused by the fungus Peronospora manshurica, Downy mildew typically does not cause significant yield losses when it shows itself in the field. The upper surface of infected leaflets is spotted with light yellow areas. Corresponding with each of these spots is a mass of fuzzy gray or slightly purple fungal hair that juts from the leaf underside directly below each area of discoloration. The fungus overwinters on infected leaf debris and can be transported via infected seed. It is primarily transported via wind and often is noted on the upper portion of the plant. Favored by cool temperatures (upper 60s to low 70s), the disease tends to show itself during wet, dewy, or humid conditions. (Picture type "downy mildew" at: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).

- SUDDEN DEATH SYNDROME - Leaf symptoms of this disease are well known in the Sangamon-Menard area. The veins of infected plants remain green while the region between the veins turns brown during. Initially, small, irregular yellow blotches appear between the main veins of the plant. Symptoms typically appear throughout an impressive region of the upper 3/4 of the soybean canopy. Caused by the fungus Fusarium solani f. sp. glycines, Sudden Death Syndrome (SDS) tends to appear when spring temperatures are cool and wet and late season conditions are slightly "stressful." A soil-borne fungus that actually infects the root in the spring, F. solani eventually produces toxins that are translocated to leaf tissue resulting in the leaf symptoms typically noted by producers. The fungus overwinters in debris (some studies also indicate that the fungus may be housed inside soybean cyst nematodes as well). Its look-a-like is "Brown Stem Rot," which also colonizes the root resulting is similar leaf symptoms. Brown Stem Rot is differentiated from SDS via a brown discoloration of the pith. (Picture type "sudden death syndrome" at: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).

- BACTERIAL BLIGHT - Unlike the other, previously mentioned, leaf diseases; this leaf disease is caused by a bacterium termed Pseudomonas syringae pv. glycinea. The bacteria responsible for this disease overwinter in debris and can be transmitted via seed. Wind, rain, and infected leaf contact serve as the mode by which these bacteria are transported to otherwise healthy portions of the plant and a little bit of injury (such as the scouring of leaf tissue caused via blowing sand) increases the chances that one will encounter bacterial blight. Small, angular water-soaked spots eventually turn yellow then turn brown and then coalesce. These areas then drop from the plant and/or wind causes these areas to rip from the plant. The end product is a ragged, brown margined trifoliate that gives the infected field an unsettling appearance. Favored by temperatures in the mid 70s to mid 80s, this disease tends to be more prevalent on the upper portion of the plant (symptoms polar opposite to Asian soybean rust). Leaves also tend to remain on the plant. (Picture type "bacterial blight" at: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).

- BACTERIAL PUSTULE - This disease, of all the diseases mentioned, has the best chance to be misidentified as Asian Soybean Rust. Small yellow-green spots with brown centers, wrapped about a pustule contribute to easy misidentification. Unlike ASR, this disease is caused by a bacterium termed Xanthomonas axonopodis pv. glycines. The bacterium overwinters in unburied debris and wheat root tissues. Additionally, the bacterium can be transported via infected seed. Within the field, Xanthomonas is transported via the action of wind, rain, and leaf contact. Preferring warmer temperatures than those associated with Bacterial Blight (in this case mid 80s to mid 90s), bacterial pustule tends to appear on the upper portion of the plant (a distribution pattern atypical to soybean rust). Additionally, examination of the lesion via a 40X hand lens will show that pustules are devoid of spores.

GRAPE COLASPIS BACK FOR 2007

Grape Colaspis has made an "impressive" reappearance in our area with several area producers noticing evidence of injury from this pest in their fields. Sangamon-Menard Extension would rank area pressure as "the most intense observed in the last four years."
The adult Grape Colaspis resembles a brown Northern Corn Rootworm Beetle in size and shape and is typically noted on silks, corn leaves, or soybean trifoliates. Appearing around the middle part of June the adults mate, and females deposit egg clutches numbering approximately 30 per cluster. Egg deposition usually occurs in August, and the small white eggs hatch within a couple weeks. The resulting larvae, which resemble very small white grubs (roughly 1/8 3/16 inch long), spend the winter several inches deep in the soil profile. They migrate back into the root zone the following spring and cause the injury recently noted in several area fields. Following this period of feeding, which starts in May, they pupate in an earthen cell emerging as adults within a couple weeks. Then the process begins anew. A single generation of Grape Colaspis occurs each year in Illinois. (Picture type "grape colaspis" at: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1).
The larvae, as noted, are the more damaging stage of this insect pest and that damage consists of injury to the root tissue. Feeding reduced the ability of the root system to take up phosphorous (which results in purpling plus other nutrient deficiency symptoms). It also inhibits the plant's ability to take up moisture (which results in the browning and yellowing of leaf tips). Economically significant infestations may also occur where soybeans have been planted.
Management has typically focused on the use of such products as Aztec, Counter, or Poncho (registered trademarks - no promotion intended) at planting. Other products have proved ineffective on this pest, and there are no "after the fact" solutions to managing the larvae once damage appears. Rainfall should help plagued fields outpace root feeding injury.

AGRONOMY DAY

Thursday, August 16 has been set as the date for Agronomy Day 2007 at the Crop Sciences Research and Education Center on the Urbana campus of the University of Illinois. The theme for this year's Agronomy Day is "Growing Our Future"
This 51st consecutive Agronomy Day is a partnership among several academic units in the U of I's College of Agricultural, Consumer and Environmental Sciences (ACES). The event features four tours on the latest developments in agricultural research, as well as numerous tent displays.
A special program at noon will feature Hans Blaschek, Director of U of I's Center for Advanced BioEnergy Research (CABER). He will discuss the future of bioenergy and implications for Illinois agriculture.
"Agronomy Day provides faculty with the chance to discuss their latest research findings with clientele from Illinois and neighboring states," said Pat Tranel, associate professor of molecular weed science in the Department of Crops Sciences and chairperson for Agronomy Day. "The major focuses of this year's program will be bioenergy in Illinois and the expanding career opportunities for students in the field of crop sciences."
Tour topics will cover research on invasive insects and weeds, SCN management, soybean rust, biodiesel, and alternative energy sources.
Agronomy Day will begin at 7 a.m. Hour-long wagon tours around the research plots will repeat every half-hour as groups are available. Lunch will be available at a nominal charge.
The Crop Sciences Research and Education Center is located south of the U of I's main Urbana-Champaign campus off of St. Mary's Road on South Wright Street Extended.
Additional information about Agronomy Day 2007 is available at www.cropsci.uiuc.edu/agronomyday or by contacting Sharon Conatser, (217)333-4256.

University of Illinois Extension provides equal opportunities in programs and employment.


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