Ron Blackwell’s survey of overwintering European corn borer (ECB) is complete and statewide corn borer numbers are somewhat higher than those observed over the last five years (see accompanying graphs and table). However, compared to 41 years of survey data, 2001’s overwintering population is about average. Breaking the numbers down by state regions show that higher numbers of stalk cavities and borers are present in northwestern and west central counties. What does this mean for 2002?
ECB larvae now either nestled in crop residue or in the stalks of yet to be harvested corn form the bulk of next year’s threat to Indiana corn. However, environmental factors during the growing season, more than anything else, will determine whether this insect becomes an economic threat in 2002. Entomologists are cautious when making predictions since it is very difficult to accurately predict if an insect such as ECB will reach its biotic potential. Under optimal conditions, each female moth can produce over 400 eggs spread in masses among many plants and fields!
What about using Bt corn for 2002? A major drawback with using this excellent pest management technology is that producers must anticipate economic corn borer damage before the corn crop is even planted. As stated above, the previous year’s infestations and overwintering survey information won’t accurately predict next year’s population and damage. Therefore, in order to benefit from using Bt corn, it is best to assess the potential field risk to ECB moth attraction, egg laying, and subsequent larval damage.
First brood females are generally attracted to the tallest, greenest corn for egg laying – normally early-planted corn. This, coupled with conventionally tilled, and rotated fields and adequate soil fertility levels increases the risk of first generation attack. Many producers traditionally plant certain fields first, e.g., fields close to the farmstead, well drained fields, etc. If these fields are expected to be ahead in their growth and development compared to neighboring corn the first week in June, then there is a greater likelihood of return on investment in Bt corn.
Predicting second, or even third generation populations and damage is impossible due to an extensive list of variables. Our advantage when dealing with second generation ECB is that we understand the pest’s behavior enough to know that these later flights are attracted to actively pollinating corn – thus late-planted or late-maturing corn. For late-planted fields, the investment in Bt corn could pay good returns.
Producers who grow Bt corn must implement a resistance management program that includes the planting of a corn borer refuge(s) of non-Bt corn. Refuges should be planted within a half-mile (0.5) of Bt corn at approximately the same time and with a similar maturity corn. Academic, industry, and producer organizations support the EPA requirement of a 20% refuge for the 2002 growing season. Neighbors planting non-Bt corn cannot be considered as providing the refuge for another producer. Without these refuges, which preserve genetic diversity of the corn borer population, this technology will likely be short lived. More specific information on resistance management is available from seed company agronomists.As many of you know, Bt corn is presently under review by EPA. A similar review for Bt cotton has just been completed and the technology has received reregistration. Apparently the monarch caterpillar situation is being thoroughly investigated before a final decision on reregistration of Bt corn is made. Because many recent scientific studies have been favorable toward the positive co-habitation of monarch caterpillars and Bt corn, reregistration of Bt corn is expected any time. It is anticipated that the refuge management plan will also stay the same. However, it would be a good idea to obtain confirmation of this before making 2002 planting decisions.
The Purdue cultivar ‘INW9811’ which carries H13 resistance to biotype ‘L’, was tested against Hessian fly populations collected in fall-winter of 1999-2000 from central and eastern Maryland, eastern North Carolina and Virginia, central and west central South Carolina, and southwestern Arkansas. The frequency of biotype ‘L’ in fly populations from Maryland, North Carolina and Virginia ranged from 60 to 96%. There was 16% biotype ‘L’ in the Arkansas population and none in the South Carolina population. INW9811 was highly resistant to populations from eastern and central Maryland, eastern Virginia, west central South Carolina, and southwestern Arkansas. Molly was highly resistant to all fly populations except that from central South Carolina, to which it demonstrated 70% resistance. These results, and those reported in 1999 for tests with INW9811 against fly populations from Alabama and Georgia, demonstrate the broad range of effectiveness of H13 resistance against the Hessian fly in the eastern U. S soft winter wheat region.
If you are growing corn or soybean, herbicides may not be top on your list of things to think about at the moment. Nor are winter annuals such as chickweeds (Stellaria sp., Cerastium sp.), Purple deadnettle (Lamium purpureum), or henbit (Lamium amplexicaule) on your mind. However, using herbicides during the fall months have been on the rise.
Why worry about it?
One reason is that winter annuals are doing well in the state of Indiana. Reasons for this may be mild winters, reduced use of soil-residual herbicides, reductions of fall tillage, or a combination of these factors. Although not generally a problem during the production season, but they can slow the warming of the soils in the spring and compete for resources early in the growing season. In some case they may harbor certain pests as nematodes, seedcorn maggots, and cutworms. A burndown application is often used in the spring, but sometimes this can be inconvenient and can not be applied in a timely manner. The use of a fall application of a residual herbicide could be considered.
What would some of the advantages be to applying in the fall?
Weed control is generally more effective when the plant is actively growing. Winter annuals start their life cycle in the fall, after harvest, and by the time a burndown may be applied in the spring growth may have already stopped, decreasing efficacy. An application of a residual may aid in planting in a timely manner, spreading the workload out.
What would some of the disadvantages be to applying in the fall?
With a fall applied program, you may lock yourself into one particular crop. Rotation restrictions can range from none up to 48 months depending on the crop and herbicide used. For example, only soybean can be applied when following applications of Canopy XL, Classic, FirstRate, or Squadron. Applying herbicides in the fall may increase potential of off site movement through the soil of some products. Also, if your soil is prone to erosion, a bare soil surface from the control of winter annuals may not be a direction you wish to go.
A study was conducted in the state of Indiana looking at fall applied herbicides in the control of common chickweed and purple deadnettle. Applications were put out late October and early November. This table was taken from an upcoming Extension Publication. Please keep in mind that the table below is based on a single year’s research and may give different results depending on the environmental conditions of any given year.
Saturday football games in Ross-Ade Stadium, tailgate parties and beer cans; ah, yes, the familiar signs that classes are in session at Purdue again. Interestingly enough, a few corn fields out in the state seem to be supporting the cause by their exhibition of a peculiar oddity known as ‘beer can’ ears. Also called ‘pop can’ ears or simply stunted ears, this phenomenon was identified in several fields and hybrids in Wells and Grant counties this past week.
Although the plants and ear shoots (husk leaves) appear normal, the cobs of ‘beer can’ ears are remarkably short and the tip inch or so is barren. Interestingly, kernel row numbers at the butt end of these ears appear to be normal or at least acceptable. Part way up the ear, however, kernel row number goes from normal to nothing. Compared to an acceptable 35 to 40 kernels per row, these ears only contain about half that in terms of ovules per row and often only 12 to 16 actual kernels per row due to silk balling that occurred when the final silks could not elongate successfully through the remainder of the normal length husk leaves. More severe ear stunting also occurs, leaving one with what looks like a corny hand grenade.
A tassel branch-like appendage sometimes exists at the tip of the cob, while other ears exhibit an apparent remnant ear initial similar to that visible by dissection of ear shoots at about leaf stage V9 (nine visible leaf collars). The latter symptom suggests that development of the ear initial was interrupted or arrested between the time ear initiation occurred (about V5) and kernel row number was finalized (about V12). The half-length size of the cobs suggests that ear development was stopped in the neighborhood of leaf stages V8 to V9.
Because ear development was apparently arrested or stopped so completely and suddenly (normal row numbers, then nothing), the cause of the problem would appear to be a single triggering event, not a lingering stress like nutrient deficiency. One possible cause could be the application of certain post-emergence herbicides (growth regulators or ALS-type), but none were applied to the fields I visited last week.
Another possible cause of such a dramatic cessation of ear development could be chilling injury. Indeed, research reported from France (Bechoux et al., 2000; Lejeune and Bernier, 1996) documents the potential for chilling injury at the time of ear and tassel initiation (about V5) to prevent ear initiation altogether and reduce tassel branch and spikelet formation. Perhaps chilling injury to the developing ear a few leaf stages down the road could similarly abort continued ear development.
The nearest weather reporting station to the field I visited in Wells County was at Bluffton. Using the reported daily maximum and minimum temperatures (<http://shadow.agry.purdue.edu/sc.index.html>), I calculated the daily growing degree days (GDDs) and their accumulation from the reported day of planting (May 8) of this field. Based on earlier research of one of my graduate students that documented the relationship between corn leaf stage development and GDD accumulation (Wuethrich, 1997), I then estimated the leaf stage progression of the corn for that field.
Interestingly, there was a single night of cold temperatures down into the high 40’s at about the time the crop should have been at the V8 to V9 stages of development. That leaf stage range is similar to what the length of the cobs suggests was the time of arrested development. Coincidence? Perhaps.
The ‘beer can’ ear phenomenon has been reported in other years in Indiana. The first rash of reports in dent corn occurred in 1992, that year often lovingly referred to as our ‘ice age’ summer because of the season-long unusually cool temperatures. The problem was last reported in 1996 in parts of northern Indiana and Ohio, most frequently in fields planted during the last two weeks of May. Several nights of temperatures in the mid- to high 40’s were reported that summer during the time when these late-planted fields were also estimated to be at leaf stages V8 to V9.
The fact that this phenomenon does not occur frequently in Indiana probably relegates it to the curiosity shelf along with dumbbell ears, pinched ears, two-headed ears and other corny oddities. However, the possibility that chilling injury may be a contributing factor to its occurrence is interesting from the viewpoint that far less research has been conducted on the injurious effects of cold temperatures on corn reproduction than on those effects due to heat stress or drought.
Bechoux, N., G. Bernier, and P. Lejeune. 2000. Environmental effects on the early stages of tassel morphogenesis in maize (Zea mays L.). Plant, Cell & Environment. 23(1):91-98.
Don’t forget, this and other timely information about corn can be viewed at the Chat ‘n Chew Café on the World Wide Web at <http://www.kingcorn.org/cafe>. For other information about corn, take a look at the Corn Growers’ Guidebook on the World Wide Web at <http://www.kingcorn.org/>.
(Bob Nielsen’s note: This article comes from Missouri Extension Corn Specialist Bill Wiebold, but Indiana farmers should also take heed of this reminder about the harvest of certain transgenic corn hybrids this fall.)
Corn harvest in Missouri has begun and it is important to remind producers that grain from hybrids selected to tolerate glyphosate must be segregated from other corn grain. These hybrids, usually called Roundup Ready, produce grain that has not been approved for import into most European countries. This grain should be marketed only to merchandisers that have agreed to accept such grain.
When release of varieties without full import/use approval happens grain that results from these varieties must not enter specific market channels. It is illegal for grain to be sold to unapproved markets, even if the marketing is unintentional. Small amounts of unapproved grain can contaminate whole grain lots and these grain lots may be destroyed or turned back at the market. Seed companies that release varieties not approved for all markets attempt to control the flow of grain into specific approved channels, thus the word channeling.
Growers that purchase hybrids that are not fully approved take on much of the responsibility of making sure that the resulting grain is sold only to approved markets. Often, producers are asked to sign an agreement in which they promise to follow marketing recommendations made by the seed company. Producers should review these forms and coordinate harvest and delivery plans with their grain merchant.
Tracking and identifying grain resulting from unapproved varieties can be difficult for cross-pollinated crops such as corn. Pollen from biotech varieties carries genes that can produce unapproved grain and that pollen can move great distances. Regardless of the difficulty, it is important that producers do what it takes to ensure the integrity of the U.S. corn supply and our relationships with foreign buyers. Failure to do so will put this specific technology in jeopardy and may impact the development of other, much-needed hybrids.
(Note: This article was taken from the Integrated Pest & Crop Management Newsletter , University of Missouri-Columbia, Vol. 11, No. 22, Article 1 of 7, September 14, 2001.)