Welcome to Crop Update for April 25, 2007, published by Sangamon-Menard Extension.

In This Issue:

• IN BRIEF – Weevils, Credits, Rust, and …Nitrogen on Beans?
• PLANTING UPDATE – 10 days of planting made a lot of difference.
• SANGAMON-MENARD EXTENSION AUTHORS NEW FUNGICIDE RESOURCE – FYI.
• WHITE GRUBS – Three different types and a couple impressive reports.
• REMEMBER GLYPHOSATE BMP’s – Jodie Tate, ICBMP.

IN BRIEF

• NITROGEN ON BEANS – What is the impact of nitrogen fertilizer on beans? Minimal yield reductions appear more probably than yield increases, and “status quo” yields (at best) when combined with nitrogen input prices, cause agronomists to discourage the practice. Some specialists note an approximate one pound reduction in nitrogen fixed by nodules for each pound of nitrogen applied.
• RUST UPDATE – Two troublesome rust spots caught the attention of plant pathologists in Illinois as we entered 2007. The first was in central Alabama (placing rust within approximately 500 miles of central Illinois). The second was in southern Texas (placing rust spores in a location that has traditionally provided the inoculum for other rust species to appear in Illinois). Late February/early March cold weather eliminated both these troublesome spots and current distribution patterns in Florida/extreme southern Georgia now pale in comparison to rust distribution patterns observed last year. Asian soybean rust is now at least 750 miles from central Illinois. Stay vigilant as the bean season gets underway and monitor rust movement at http://sbrusa.net.
• CEUS AT PASTURE WALK – University of Illinois Extension will offer 3 CCA Credits at the Healthy Horses in Healthy Habitats pasture walk on May 8th. This is the 3rd in a series of equine workshops. Certified Crop Advisors can obtain 2.0 credits (CEU’s) for crop management and 1.0 credit for integrated pest management. For more information and to register, please call Sangamon Extension at (217) 782-4617.
• ALFALFA WEEVIL – As noted last week, Kelli Bassett (Montgomery County Extension) noted alfalfa weevils that “faired well” despite April’s cold spell. Weevils also seem “fine and dandy” in the Sangamon Menard area, with our first observation of weevils occurring on April 20th. We remind readers that the economic threshold for alfalfa weevil is 25-40% leaf tip skeletonization with 3 or more larvae present.

PLANTING UPDATE

A windshield survey showed the following progress in planted corn acres for the mentioned regions:

• Oakford to Petersburg – 20-25% of the corn was planted as of April 20th with 60% planted as of the 25th (65% is the 5-year average)
• Petersburg to Springfield – 15-20% of the corn was planted as of April 20th with 50% planted as of the 25th (70% is 5-year average)
• Springfield to Auburn – 35-40% of the corn was planted as of April 20th with 55% planted as of the 25th (80% is the 5-year average)
• Corn acres appear to have increased by 15-18% this year.

While we are behind in corn planting, from a historic perspective, we still have time left on the calendar before potential yield begins to drop away.

SANGAMON-MENARD EXTENSION AUTHORS NEW FUNGICIDE RESOURCE

Sangamon-Menard Extension has authored a new publication entitled Utilizing Fungicide Mode of Action to Combat Resistance. The resource was co-authored by Matt Montgomery of the Sangamon-Menard Extension Unit, Dr. Suzanne Bissonnette of the Champaign Extension Center, and Dawn Nordby and Dr. Carl Bradley of U of Is Crop Sciences Department.

Patterned after the popular publication Utilizing Herbicide Site of Action to Combat Weed Resistance to Herbicides and another Sangamon-Menard co-authored resource Utilizing Insecticide Mode of Action to Combat Insect Resistance to Insecticides, the publication’s goal is to assist producers as they attempt to ward off fungicide resistance.

Those interested in obtaining a copy may contact Sangamon-Menard Extension for details. Those interested in purchasing the entire packaged set of resistance management resources, at a cost of $5, should call 217-333-4424 to place an order.

WHITE GRUBS

Those that have bothered to scout fields over the last couple weeks report some impressive white grub numbers – especially in eastern Sangamon County (recently noted by Jerry Harbour, LLFS and Dave Love, Stone Seed). What species are we likely encountering and which species should producers take most seriously?

Three categories of white grub typically appear in area fields. The first is termed the annual white grub, the second is termed the true white grub, and the third is termed the Japanese beetle grub.

Annual white grubs, the larvae of the southern masked chafer (Cyclocephala lurida) pass through one generation each year. The adult beetles tend to flit about at dusk during the early summer. Adult southern masked chafers do not feed, and seemingly have one purpose – to generate progeny (Masked Chafers HYG 2505-91, Ohio State University). The eggs, resulting from this “progeny fervor,” are deposited in the soil and hatch within the span of a couple weeks. The larvae or grubs feed on roots and organic matter until fall when they migrate down in the soil profile. Spring temperatures draw the grubs back up into more shallow regions of the soil profile where they feed until about mid-late May. They pupate, at that time, resulting in another batch of southern masked chafer adults. Since planting in our area historically did not begin until May and annual white grubs pupated soon after, specialists typically termed annual white grubs “insignificant” to corn. However, as “Crop Update” has noted in the past, our shift toward late March/early April planting has seemingly created a niche for this pest that once synchronized poorly with our growing season.

The term “true white grub” actually refers to a genus of grub-producing beetles rather than a distinct species. True white grubs are the immature stage of what many term May/June Beetles (genus Phyllophaga). Species belonging to this genus have a three year lifecycle. Adult beetles also appear in the spring, depositing eggs 1-8 inches deep in the soil. Those eggs hatch in a few weeks – later resulting in the small, cream colored, C-shaped larvae that we commonly refer to as “grubs.” The individual grub molts once during that first growing season and then migrates deep into the soil profile (much like the annual grub). The following year, spring temperatures draw the grub back into more shallow regions of the soil profile initiating a second season of root feeding that tends to be the most destructive of the three feeding years. Fall again drives those grubs down, spring again draws them up, and the grubs feed into the late summer of the third growing season. They then pupate and later emerge as adults that begin the process anew the following spring. The extended nature of the Phyllophaga grub stage has typically cause entomologists to deem Phyllophaga species the more significant stand threat in central Illinois. However, we again mention that times have changed and that May/June Beetle grubs likely face stiff competition for the title of “most significant grub species.”

The Japanese beetle, Popillia japonica, produces the third category of grubs. While described as a separate category in this article, Japanese beetle white grubs also abide by a one year lifecylce in central Illinois. Adult beetles deposit their eggs in the soil from mid-June into August (unlike annual white grubs which originate from eggs deposited in the spring and early summer). The resulting larvae overwinter several inches deep in the soil profile. Again drawn to the root zone by spring temperatures, they feed on roots and/or decaying organic matter until late May when they pupate, emerging as adults in June. 2001/2002 marked the first exceptional movement of this pest into Sangamon County fields. Over the past five years the pest has steadily moved westward with producers in Tallula now noting the pest as well. The volume of beetles observed last year likely means that many grubs observed this year (especially those in central/eastern Sangamon County) are of the Japanese beetle persuasion.

While opinions vary as to the potential injury associated with each of these “grub categories” (many university specialists still deem the “annual” grub a non-issue – Pest Management and Crop Development Bulleting – April 5, 2002), Sangamon-Menard Extension has traditionally counseled producers to take all grub species seriously.

REMEMBER GLYPHOSATE BMP’s

By Jodie Tate, Illinois Council on Best Management Practices.

Glyphosate herbicides (Roundup, Mirage, Glyphomax, Touchdown, Rattler and Rodeo*) have changed production agriculture with many producers planting only glyphosate resistant bean and corn varieties this spring. This shift in management style raises herbicide resistance concerns. The Illinois Council on Best Management Practices (C-BMP) encourages all producers using glyphosate resistant crops to follow glyphosate best management practices to ensure these products will continue to be available for years to come. Glyphosate best management practices include:

1. Scout your fields. Know the economic threshold for treatment of common weeds, or consult with your Certified Crop Advisor to determine if an herbicide application is warranted economically. Do not apply herbicides for aesthetic purposes.
2. Use mechanical weed removal. Fuel is expensive, so teaming this with a scheduled herbicide treatment will reduce costs.
3. Use different modes of action. This can be accomplished by rotating herbicides annually, or using tank mixes that contain herbicides with multiple modes of action.
4. Rotate crops. Rotating crops allows the producer to switch cultivation practices, use a variety of herbicides (with different modes of action) and change the environment, making it more difficult for weeds to become established.
5. Rotate herbicides. Do not use the same herbicide (or a herbicide with the same mode of action) more than two years in a row.

Trademark names are used for reference only. Mention of said names does not indicate an endorsement. University of Illinois Extension provides equal opportunities in programs and employment.

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