Rain makes grain...certainly not rootworms. A combination of cool and saturated soils this spring did not bode well for rootworm larvae. Therefore, the egg “load” from the high beetle numbers the previous season didn’t equate to the amount of root damage expected in this year’s corn.
Though initial rootworm egg hatch occurred on schedule, late May, the continual cool soils extended this activity through much of June. Newly hatched larvae are vulnerable to harsh soil conditions, such as high moisture levels and/or low temperatures. When the sky let loose in early July, not only were some fields flooded, but many early instar larvae were drowned.
Correlating early-season root reduction, whether from agronomic or biological factors, to corn yield is next to impossible. Too many variables interact to determine the plant’s ability to regenerate roots without sacrificing ear size. This was the case with rootworm damage in 2003 and the resulting corn yields. Though there were some fields with significant rootworm feeding, especially before the early-July rains, most damaged plants were able to regenerate a substantial root mass and still produce good to excellent yields. “Rain makes grain.”
It only goes to reason that high rootworm larvae mortality will result in fewer emerging beetles. Indeed, 2003 western corn rootworm beetle numbers are the lowest we’ve had for over five years. The good news is that the potential risk of rootworm damage is reduced for next season, the bad news...risk is still present. Refer to the following article on perceived risks for 2004.
For several years, we’ve assigned risk categories to first-year corn rootworm guided by previous year’s soybean sweeps taken while western corn rootworm (WCR) beetles were actively laying eggs and any other factor we considered important. There was an inherent problem with providing an annual risk map delineated by county, that is, producers took it too literately. The intent was to provide estimates of risk, not absolutes. Because we draw these conclusions from at best a few fields sampled per county, there is a large margin of error. Should you desire to see the state map with specific soybean sweep numbers from 2003, refer to the October issue of the Pest&Crop or click HERE (download the state map).
The following “new and improved” perceived risk to first-year corn rootworm map is a compilation of many years of research, surveys, and discussions with Indiana agribusiness personnel. Unless western corn rootworm infestations and subsequent damage to first-year corn are deemed to be shifting, this map will remain as drawn. Other changes are that county boundaries have been removed and a new category, “Very High,” has been added. We continue to encourage pest managers to monitor soybean fields in their specific area so that more precise risks can be assigned and appropriate management strategies implemented.
Perceived First-Year Corn Rootworm Risk Areas
“Very High” indicates that consistently high numbers of WCR beetles have been found in soybean fields. First-year WCR damage is likely and may be severe in parts of or whole fields.
“High” risk indicates that most soybean fields sampled or observed in that area contained high numbers of WCR beetles coupled with the fact that first-year corn rootworm damage frequently occurs.
“Moderate” risk means that WCR beetle numbers vary from field to field and that significant first-year rootworm damage is expected to be spotty.
“Low” risk areas have consistently low WCR beetle numbers in soybean with few, if any, damaged first-year corn fields expected.
When one uses a soil insecticide it is important to remember that protection of the primary portion of the root system from economic rootworm attack is the goal. Also, one needs to understand that products do not provide 100% control (60-80% control more likely) and occasionally some economic damage may occur depending on the larval population, weather, planting date, plant development, and time of larval hatch. All of these factors can ultimately impact product performance and must be considered when using a soil insecticide. The important thing for producers to understand is the positive and negative aspects of each product, and determine which one(s) fits best within their farming system. Also, one needs to understand what the warranty for each product really means. Additionally, it makes sense to have untreated check strips in fields to gauge the performance and economics of the products used.
Listed below, by application method, are the current registered soil products and their efficacy in protecting roots in 2003 Indiana and Illinois university rootworm trials. All data, except the transgenic trial, are from the same tests. Separation by application technology was made so that like-products could more easily be compared. There is no consideration of other insect pests, e.g., wireworms, white grubs, cutworms, in these evaluations.
Insecticide-coated seed: There have been many questions about the newer pre-applied insecticide seed treatments available for corn. The attractiveness of having a soil insecticide “wrapped” directly on the seed is understandable. Cruiser (1.4 rate) and Poncho 1250 are both from the newer insecticide class, nicotinoids. ProShield contains the same active ingredient as Force granular soil insecticide, the pyrethroid tefluthrin. All of these products must be custom applied to seed with specialized equipment, therefore producers must order them at the time of seed purchase. Using seed applied insecticides for corn rootworm control in high-risk areas (see previous article) may be a gamble. This is because of the inconsistencies that have been seen in university trials throughout the Midwest (Poncho 1250 may be the exception, see following discussion under Bt Corn Rootworm). The labels literally state “protect” or “protection” from rootworm...not control. For producers in areas with low to moderate rootworm pressure, these seed treatments may be beneficial and may also offer protection from other soil insect pests, e.g., wireworms, seedcorn maggots, etc.
Liquid soil insecticides: Producers have had the option of the liquid insecticides Capture and Regent for several years. At first, the niche market for these products and their unique application equipment were for producers without granular soil insecticide applicators on their planters, and who were beginning to notice rootworm damage in first-year corn. We became concerned when companies aggressively targeted the rootworm market in high-risk areas of the state. Producers soon found that the performance of these products under high rootworm pressure was inconsistent, some with disastrous results. The recent release of the new John Deere 1790 planter with the FMC “LiquidReady” system as the only insecticide application equipment option certainly has gotten our attention. We would encourage producers in the very high-risk, first-year rootworm areas contemplating using the currently available liquid insecticides to evaluate their recent experiences with rootworm. The new transgenic corn for rootworm (see discussion below) might be a better fit in high-risk areas.
Granular soil insecticides: Granular insecticides have long been considered the standard from which other soil products are compared. They’ve been criticized for being bulky, dusty, and time consuming albeit considered the most consistent in performance. Though formulations and product names have changed over the last several years, chemical class has remained the same...organophosphates and synthetic pyrethroids. EPA has hinted several times in the past that granular soil insecticides, especially the organophosphates, will be phased out. Recent formula registrations and product re-registrations doesn’t reflect that. Insect resistance or enhanced biodegration has not been an issue with the current registered products.
Bt Corn Rootworm: EPA approved YieldGard-RW late last winter and the “stacked” event for both rootworm and corn borer (YieldGard Plus) has just been labeled. This combination should remove the confusion many producers have in separating the two different genetic events targeting specific pests. It will be imperative that producers follow refuge guidelines (20% within or adjoining field). Trials the last several years with this technology have shown that a new “benchmark” in rootworm control has been reached. Though there is some rootworm feeding, root ratings have always been as good if not better than the best performing granular insecticide. All YieldGard seed will be “wrapped” with either Cruiser (low rate) or Gaucho for protection from other soil insect pests, e.g., wireworms, seedcorn maggots, etc. YieldGard-RW and YieldGard Plus will be very attractive to producers in high-risk areas to first-year corn rootworm damage and those with the new John Deere 1790 planter. The 20% non-Bt refuge will need chemical protection from rootworm, and discussions with producers vary on how they intend to treat this acreage. Poncho 1250 seems to be the popular choice. Purdue’s rootworm trials over the last several years support this as the most efficacious product over the other seed treatments and liquids.
Few industry or university replicated trials correlate secondary soil insects to stand and yield losses. Many experiments have been tried but often fail because the insects don’t show up or damage to yield correlation was poor. However, we know these losses occur, we just can’t predict when and where. Producer testimonials tout promising results with Cruiser, Gaucho, and Poncho 250 so much that some seed companies are pre-treating a majority of their hybrids. Will producers recoup this additional $4-6/acre (depending on seed drop) expense?
These pre-applied seed treatments are from the new insecticide chemistry, nicotinoids that have systemic activity during the early life of the corn seedling. Data exist that show some seed/seedling protection from seedcorn maggot, wireworms, and cutworms. Certainly the biggest question for producers and researchers is how effective these products are against white grubs, considered a primary pest by some. Scant data have shown a mixed bag of results, as is true with many granular soil insecticides. Most likely there will be some suppression of grubs, but not control. The labels of these products literally read “protect” or “protection” from grubs.
Should one use the pre-applied insecticide seed treatments for soil insects other than rootworm? Return on investment of seed applied treatments may improve for some pests if:
Thanks to those who have sent plot and yield information concerning soybean aphid. If you haven’t done so already, please send ASAP (email@example.com). The variability in soybean yields where treatments were applied has been fascinating. We’re still analyzing data from our research trials, certainly this information will be shared with you at upcoming winter meetings.
University researchers throughout the north central states will soon be meeting and sharing data and observations from the 2003 season. There is hope that a preliminary treatment threshold can be refined from this effort. Please be patient as we develop future management strategies for this pest.
We have started putting out our fall applied herbicide treatments this week and just wanted to provide a few application tips to those who are also in the process of making fall herbicide applications.
Almost everything you would want to know about weeds will be available at the annual North Central Weed Science Society meeting December 2, 3, and 4 in Louisville. If you don’t care to attend the entire conference, 1 day registrations are available for $40. Additional registration and program information can be found at the NCWSS website listed below. I took the liberty of reproducing the Program Chair’s (Dr. Jerry Doll, University of Wisconsin) comments from the fall edition of the NCWSS Newsletter to give you a feel for the information available at this years conference.
Purdue University is offering a “Hands-on Post Harvest Training and Recertification Workshop” to be held December 5, 2003 from 8 AM to 5 PM at the Marion County Extension Office in Indianapolis, IN. This workshop is Co-organized by the Indiana Grain and Feed Association and Purdue Cooperative Extension Service. CCH and CCA credits are available. A pre-registration fee of $70.00 is due by Nov. 28 and on-site registrations are $80.00. Registration is limited and checks should be made payable to Agribusiness Council of Indiana and mailed to:
For more information please contact Dr. Linda Mason, Dept. of Entomology, Purdue University, (765) 494-4586 or email to firstname.lastname@example.org
You can find program information and the registration form at: <http://www.entm.purdue.edu/entomology/ext/index.htm>.
Asian Lady Beetle
Bean Leaf Beetle
Black Light Catch Report
Corn Blotch Leafminer
Corn Flea Beetle
European Corn Borer
Southwestern Corn Borer
Wheat Stem Maggot
Heat Unit Accumulations, Indiana Weather Summary and Heat Unit Forecasts appear in most issues.