Welcome to Crop Update for March 27, 2006, published by Sangamon-Menard Extension. This publication is updated weekly. Call us with comments at (217) 782-4617 or or e-mail us.

In This Issue:

• ANNOUNCEMENT – Supervisor of Assessments meeting on March 27th.
• BLACK CUTWORM TRAPPING – Help us keep track of the moths.
• WINTER ANNUALS AND GROWTH REGULATORS – A very brief review.
• DON’T DISCOUNT SOYBEAN RUST – Think its old news, think again.
• TWO “YOUNG” SEED TREATMENT FAMILIES – A little FYI on two families.

ANNOUNCEMENT

Jason LeMar, Menard County Supervisor of Assessments, will hold an informational meeting on farmland assessment changes in Menard County on Monday, March 27 at 7 pm at the New Salem Visitors Center. For more information, call Jason LeMar at 217-632-4461.

BLACK CUTWORM TRAPPING

Sangamon-Menard Extension will once again evaluate black cutworm problems in our area by resuming black cutworm moth trapping on a local level. We have ordered six traps (three for each county) that will be distributed to best represent the Sangamon-Menard area. For U of I Extension, these traps help us evaluate the intensity of cutworm problems in the region. For the participating producer, these traps can indicate an approaching problem in the field that might require an insecticide application. Those interested in placing such traps on their farm should contact Matt Montgomery at the Sangamon-Menard Unit, (217)-782-4617 or (217) 632-7491.

WINTER ANNUALS AND GROWTH REGULATORS

Marestail, mustards, chickweeds, and especially henbit are commonly found winter annuals in cornfields, and one of the most prevalent preplant, and/or preemergent mode of action options used in corn to manage those weeds are the growth regulators. These materials act like synthetic “plant hormones” that stimulate rapid, haphazard growth. They typically result in “pinched off or clogged” vascular systems that choke the plant to death.

DON’T DISCOUNT SOYBEAN RUST

The 2005 winter meeting season was dominated by discussions pertaining to Asian Soybean Rust. The fungus entered the continental U.S. for the first time in 2004, and winter meetings were feverishly scratched together to place important rust information in the hands of producers/agri-business. Those speaking at such meetings noted the causal organism was termed Phakopsora pachyrhizi and also noted that potential yield losses could be 10-80%. None of our commercial soybean varieties were currently (nor are they now) “ASR resistant.” Scouting information was provided, fungicide recommendations were submitted, and sample submission procedures were refined as the industry worked together in an unprecedented fashion. Everyone wanted to know about, and prepare for, soybean rust. The 2005 season dawned, producers nervously waited for this pustule-forming, wind-blown fungal disease, and then…it didn’t show up. A crude survey of those participating in the 2006 Illinois Crop Protection Technology Conference highlighted the change in “soybean rust attitude” that occurred over the last year. When asked if they believed Asian soybean rust would be a ’06 problem, only 15% of attendees said, “yes.” In other words, most people involved in agriculture discount ASR as a likely threat in 2006. Sangamon-Menard Extension would council continued vigilance and preparedness because the 2006 rust season already looks very different than it did in 2005.

The first positive 2005 soybean rust find in the continental United States occurred in late February in west-central Florida. By June, rust had only spread to a few additional counties, all of which were still confined within the boundaries of Florida. Six months after that initial, Floridian detection of soybean rust, the disease had only moved a few hundred miles. Nine months later, in November, rust was found within one county of Illinois and was also found in the eastern gulf area of Texas. The latter location was a positive find on kudzu that apparently died out in early January. The “near Illini” ASR find occurred too late to impact Illinois soybean production.

What does the 2006 “rust positive” map look like? A mid-January 2006 rust map of the United States already showed several rust-positive locations in our country. January marked a much earlier detection for rust than was the case in 2005. A quick look at the state of Florida is also disconcerting. The rust positive map of Florida currently looks more similar to the map of Florida for June 2005. That map has appeared “June similar” since January. In other words, Florida, at this time, appears “ahead of where it was last year.” Finally, soybean rust has been found in east-central Alabama. The Alabama location marks exceptional (all-be-it outlying) northern progress for rust. Combine that information with soybean rust detection in Mexico, and one might say rust seems to be doing very well in 2006.

At the very least, rust has been much easier to find in the southern U.S. which does not bode well for Illini bean producers. Scouting, timely diagnosis, timely management, and preparedness are as critical this growing season as they were last growing season. Producers need to be ready lest the disease sneak up on them in 2006.

TWO “YOUNG” SEED TREATMENT FAMILIES

“You gonna use strictly an OP or you gonna add an OC?” Not that long ago, the choice between a diazinon seed treatment (an OP – organophosphate), a lindane seed treatment, or a diazinon plus lindane seed treatment (the latter an OC – organochlorine) was about the only “in the bag insecticide” choice available to the producer. Then, not long ago, a few “young gun seed treatments” were added to the spectrum. While some of those new additions lasted little more than a couple seasons, today’s seed treatment list is larger than what it was ten years ago. Two major insecticide families sit alongside the traditional OP and OC options. They are the neonicotinoids and the pyrethroids. This article will note the active ingredients in those families and will briefly note how those materials work.

Neonicotinoid seed treatments include such active ingredients as thiamethoxam (marketed as Cruiser), imidacloprid (marketed as Gaucho or Prescribe), and clothianidin (marketed as Poncho). Various sources state that these products are “nicotinic acetylcholine receptor agonists or antagonists,” but what exactly does that mean?

Readers will remember that neurons convert a nerve impulse into a chemical signal as they “send” an impulse from one neuron to the next. The chemical signal is that “something” which is physically passed from one neuron to the next and is thus critical for an impulse to progress along length of a nerve. One of those chemical signals (neurotransmitters), often mentioned in entomology, is termed acetylcholine. Acetylcholine is released from a stimulated neuron. It then passes across a small space between the two neurons (termed a synaptic cleft). Along the other side of this “cleft” is the swollen, branch-like top of the next/neighboring neuron. Acetylcholine binds to a spot (receptor site) on that neighboring neuron which results in the neuron “firing” an impulse along its length. If acetylcholine attaches, the neuron “fires” and important information is sent. If acetylcholine does not attach, the neuron does not “fire” and important information is not sent.

Neonicotinoids attach to the previously mentioned spots (acetylcholine receptor sites) on the neighboring neuron. At first, they “falsely tell” the neuron to fire as if acetylcholine had actually attached. With time, this “false impulse” tapers but the neonicotinoid remains attached and thus effectively blocks that spot for any “legitimately sent” acetylcholine. In other words, neonicotinoids kill the target pest by first sending “a batch of false information” and then block the transfer of information from one neuron to the next.

Pyrethroid seed treatments include such active ingredient as permethrin. Various sources state these products are believed to function as “sodium channel modulators.” While interesting terminology, one again questions, “What exactly does that mean?”

Neurotransmitters, such as acetylcholine, were said, in the previous discussion, to physically transfer a nerve impulse from one neuron to the next. Such chemical signals were said to initiate an impulse as they attach to receptor sites on that neighboring neuron. The exact process at work in the neuron is a little bit more complex than what was just stated, and the subtleties of this complex process are “messed up” by pyrethroids.

Small molecules are embedded in the cell membrane along the “top” of a neuron. These small molecules are termed “gated channels,” and they are called that because they actually function as a gate for material moving into the nerve cell. As with any gate, a key is needed to open it. In the case of a neuron, the “key” that opens the gate is the neurotransmitter. Should a neurotransmitter be added, the gate will open. Once the neurotransmitter is removed, the gate is closed. When gated channels are open, sodium cations (positively charged) rush into the nerve cell. The influx of positively charged particles causes a sudden significant change in the neuron’s electrical charge. This is the means by which the chemical signal (neurotransmitter) is changed into an electrical signal that “causes the nerve cell to fire.” In other words, sodium rushes in via a small gate once a neurotransmitter binds to the neuron, the charge of the neuron changes, an impulse is initiated, and important information is transferred.

Pyrethroids wreck the previously mentioned process. These insecticides wedge open the gates and keep them open. Gates, once shut fast, start to “leak in” sodium without a neurotransmitter telling them to do so. A lot of sodium (i.e. a lot of positive charge) is already present inside the neuron when a legitimately released neurotransmitter “tells” the gates to open. In other words, sodium still flows into the neuron, but the change in charge is less pronounced. The neuron has already suffered a gradual change in electrical charge via the leaking gates and the neuron has already been “firing falsely” for a while. Clear concise information is either note sent or lost in a mass of static.

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

U of I Extension Sangamon-Menard Unit Crops
Matt Montgomery, Crop Systems
P.O. Box 8467
Springfield IL 62791
(217) 782-4617

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