C.O.R.N. Newsletter 2009-28

Late Season Insect Concerns in Soybean

Authors: Bruce Eisley, Andy Michel, Ron Hammond

As we are getting into the later growth stages of soybeans, we are being asked about two situations, soybean aphids on late R5-R6 growth-stage soybeans and bean leaf beetle pod feeding. Aphid populations nearing or reaching the threshold level of an average of 250 aphids per plant during growth stages late R5-R6 is a unique concern because as of yet, researchers have not been able to establish an economic injury level (EIL). We believe that it is higher than the EIL during the R2-early R5 stages (700-800 aphids per plant). Thus, the action or economic threshold should probably be higher than the 250 aphids per plant that is for the R2-early R5 stages. Additionally, we assume that plants in the late R5-R6 stages are probably not as good of host plants compared with earlier growth stage plants. Thus, we are not sure of the potential for the aphid population to go much higher. Related to that is the time from those stages until the plants begin to mature. We would suggest that prior to making any decision to spray, that growers sample multiple times over a number of days to make sure that the level is indeed rising well above the current threshold of an average of 250 aphids per plant. As discussed, how much higher the population should get to in order to spray is not currently known. Leaving unsprayed check strips and reporting any results to your county Extension Educator would help us determine whether economic damage is actually occurring at the late R5-R6 growth stages.

On the other hand, bean leaf beetles are an annual concern in soybeans in late pod development stages, especially in late maturing soybeans, which will remain green well into September. These fields can often have higher levels of pod feeding because the fields act as trap crops for second-generation bean leaf beetles, providing a food source prior to overwintering. Fields could include those that were late planted, double-cropped soybeans, and relay-intercropped soybeans. Although bean leaf beetles have not been extremely high this year, we still felt it important to caution growers of potential pod feeding. Growers are advised to continue monitoring these fields until they begin to mature in mid to late September. Although leaf defoliation will not be a major concern, injury to the pod is a problem because of yield loss potential and seed quality issues. Of note, this concern is especially important with food grade soybeans and soybeans being grown for seed. If bean leaf beetle populations are high, insects are still active, and pod injury has reached 10% and is relatively new, an insecticide treatment is perhaps warranted to prevent further pod injury.

For any insect pest, growers should be careful with any insecticide used during the later growth stages because of the shorter time period from application to harvest, the PHI or pre-harvest interval. See the Agronomic Crops Insects website on insecticide information provided in Bulletin 545 (http://ohioline.osu.edu/b545/pdf/b545.pdf) that lists the PHI for all labeled insecticides.

Assessing the Risk of Frost Injury to Late Maturing Corn

Authors: Allen Geyer, Peter Thomison

Visual inspection of kernel development stages in research plots at the Western Agricultural Research Station near S.Charleston this past Friday (8-21-09), revealed that corn planted in late April and early May was in the dent stage, corn planted about May 20 early dough, whereas corn planted in early June was in the milk stage; at the Northwest Agricultural Research Station near Custar, corn planted the second week of May was in the dough stage whereas corn planted the first week June was in the late blister stage. These observations are fairly consistent with what OSU Extension Ag Educators are reporting across the state. This year’s delay in corn development is not surprising given the record low temperatures experienced in July and reduced accumulation of heat units. What’s the likelihood that this slower than normal crop development will result in frost damage?

Physiological maturity (when kernels have achieved maximum dry weight and black layer has formed) occurs about 7 to 8 weeks after silking. At physiological maturity (kernel moisture approximately 30-35%), frosts have little or no effect on the yield potential of the corn crop. Results from Indiana and Ohio research on corn development with delayed planting suggest that corn planted in mid- to late-June in Indiana and Ohio will typically mature from 68 to 71 days after silking The number of days from silking to maturity increases with later-planted corn primarily because growing degree day (GDD) accumulation per day decreases dramatically toward late summer and early fall and so it simply requires more calendar days for a late-silking crop to accumulate a minimum number of GDDs to reach physiological maturity (Nielsen, 2008).

Table 1 shows the average number of calendar days and growing degree days (GDD) required to reach physiological maturity after silking. With average daily high and low temperatures of 80 and 60 degrees F, 20 GDD accumulate each day. At these temperatures, 65 days from silking to maturity are required (1300 divided by 20). With "cooler" high and low temperatures of 75 and 55 degrees, only 15 GDD accumulate daily, requiring more than 87 days from early August silking to maturity.

Table 1. Relationship between kernel growth stage and development.
 

Stage	Calendar Days To Maturity*	Growing Degree Days To Maturity
	(days)	(GDD)
Silk	65	1300
Blister	52	1040
Late Milk/Early Dough	39	775
Early Dent	25	510
Fully Dented	12	250

* Based on average daily high and low temperatures of 80 and 60 degrees F, respectively, during grain fill

Source: National Corn Handbook. Chapter 40. Growing Season Characteristics and Requirements in the Corn Belt. R.E. Nield and J.E. Newman, 1986.

How many GDD can be expected from now until an average date of a killing frost? To answer this question (approximately), estimate the expected GDD accumulation from August 26 until the average frost date (50% probability) for different regions of the state (Table 2). These GDD expectations are based on 30-year historical normals reported by the OASS. The growing degree day accumulation was calculated using the 86/50 cutoff, base 50 method.

If you want to determine the "youngest stage of corn development" that can safely reach black layer before the average frost date at a given weather station, use the information in Table 2 on remaining GDDs in conjunction with Table 1 which indicates GDD requirement to reach black layer at various stages of grain fill. Compare "GDD remaining" for the site with the GDDs required to achieve black layer depending on the corn's developmental stage.

Table 2. Estimated GDDs remaining from August 26 to the first fall frost for Ohio.

Region	Average Frost Dates (50% Probability)	Estimated GDD Remaining From August 26 to Fall Frost
Northwest	Oct 10 – Oct 20	538 – 622
North Central	Oct 10 – Oct 25	523 – 608
Northeast	Sept 30 – Oct 25	472 – 618
West Central	Oct 10 – Oct 15	577 – 634
Central	Oct 5 – Oct 15	527 – 653
East Central	Sept 30 – Oct 15	507 – 625
Southwest	Oct 10 – Oct 15	673 – 719
South Central	Oct 15 – Oct 20	693 – 745
Southeast	Oct 5 – Oct 15	511 - 634

If your corn is in the early dent stage as of Aug.26 will it be safe from frost? Table 1 indicates that it needs about 510 GDDs to reach black layer from the early dent stage and Table 2 indicates that except for northern areas, most regions of the state will accumulate sufficient GDDs to escape frost injury.

If your corn is in early dough stage as of Aug. 26 will it be safe from frost? Maybe, it needs about 775 GDD to reach black layer based on the kernel development - GDD accumulation relationships indicated in Table 1. While Table 2 indicates no region of the state with that number of GDDs remaining until the 50% frost date, late planted corn has shown the ability to adjust its maturity requirements. Corn planted in early June compared to early May requires 200 to 300 fewer GDDs to achieve physiological maturity. Therefore, this physiological “adjustment” may allow corn presently in the early dough stage to reach physiological maturity before frost. However the grain moisture of the corn will be much higher than is typical.

Although written with 2008 Indiana growing conditions in mind, the following article by Dr. Bob Nielsen, corn extension agronomist at Purdue University, provides a good perspective on assessing the likelihood of frost damage to late corn plantings.

Nielsen, R.L. (Bob). 2008. Late Planted Corn: Enough Time to Mature? Corny News Network, Purdue Univ. [On-line]. Available at http://www.kingcorn.org/news/articles.08/DaysAfterSilk-0729.html
[URL verified 8/26/09].

 

Planting Soybeans in the Same Field Again Next Year? Scout Those Fields Now

Authors: Anne Dorrance

Approximately 1/3 or more of Ohio’s soybean production acres are fields of soybeans following soybeans. These tend to be the fields which we have had frogeye leafspot, Sclerotinia white mold and Soybean cyst nematode issues. We’ve also seen SDS, Brown stem rot and Diaporthe stem canker more often in these fields compared to those with more crops in the rotation. The late growth stages are a perfect time to scout fields and identify problems – so you know if you need to move this field out of soybeans or make sure you’ve got a “defensive” soybean going into that field the following year. Soybeans are tall throughout the south and eastern portions of the state so pick the area of the field that lies in the lowest portion, where moisture and fog settle in and look in that area. Walk in several feet and look at the upper portion of the canopy for frogeye leaf spot lesions. Look for those dead plants scattered around – is it Sclerotinia, charcoal rot, SDS, brown stem rot, or Phytophthora? If you find only one plant, that is a signal that for next year there will be more inoculum and it is time to pay attention to variety selection. “Offensive” soybeans are great as long as the weather is perfect and the pathogens are absent. But Ohio has many pathogens, just waiting for that susceptible soybean variety and that perfect environment to substantially lower your soybean yields. So get out there while the weather is cool, and look around— see how that variety did under this years' conditions and what can be improved for next year.

Mealybugs Found on Soybean Roots in Ohio

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Recent news out of some Midwest states, and a report in Kevin Black’s GROWMARK Agronomy Production Solutions Newsletter, made reference to a possible new pest of soybeans, a root mealybug. From a literature search, this insect appears to have been first reported from soybeans last year in Kentucky. Researchers in that state got it identified as the trochanter mealybug, Pseudococcus sorghiellus, which is a root feeder on numerous plants, including soybeans. Ants are usually found attending this mealybug in a symbiotic relationship. We believe that the trochanter mealybug is a different species of mealybug that is often found on soybean leaves, although this remains to be seen.

Of importance for Ohio’s growers is that we also found this insect on soybeans in Ohio in Wayne County. So far, all the known soybean fields in the Midwest where the mealybug has been found have shown potassium deficiency-like symptoms, a fertility problem that was discussed in last week’s C.O.R.N. newsletter. At this time, it is not known if there is a cause and effect relationship (i.e., does the mealybug feeding on the roots cause the symptoms), or even if there is a relationship between those symptoms, potassium deficiency, and the mealybugs. We would point out that we often see similar symptoms on soybeans with the presence of heavy soybean aphid feeding.

We would ask growers who have fields showing potassium deficiency-like symptoms dig up a few plants with a shovel to examine the roots to see if any of these mealybugs are present. As mentioned, there might be ants in that sample which might give an indication that mealybugs are present. See the soybean images at the Agronomic Crops Insects website (http://entomology.osu.edu/ag/pageview3.asp?id=1152) to see what mealybugs look like. They are quite small, so a hand lens might be necessary. However, they should at least be noticeable to the naked eye because of the waxy coating, which gives them a whitish appearance. We would appreciate hearing of any additional finds where these mealybugs are present and potassium deficiency-like symptoms occur. Please contact your county Extension Educator or contact us directly with any information.

Weather Update and Forecast

Authors: Jim Noel

The outlook for the next two weeks is for a 20-40% chance for 2 inches of rain and about a 50-80% chance of 1 inch of rain over Ohio. The overall tendency is we have resumed our below normal rainfall pattern after getting some timely rains.

Temperatures should return toward normal or even slightly above this week and then resume the below normal tendency by this weekend into next week followed by normal the week of Sept. 6-12.

Also, note that after a very cool weekend, indications are this coming weekend into early next week will be quite cool too with some lows in the 40s by early next week!

Soybean Cyst Nematode Field Day September 2, 2009

Authors: Joy Aufderhaar, Roger Bender

Wanted: Criminals invading and stunting soybean roots, stealing food from the soybean plants, vandalizing the root vascular tissue function and allowing other criminals (pathogens) to invade, and the final blow, robbing soybean producers of profitable yields. The thief is known as SCN aka Soybean Cyst Nematode.

Learn more about stopping these SCN criminals at the Soybean Cyst Nematode Field Day on September 2, 2009 from 1:00-3:00 p.m. in Shelby County, Ohio.

Ohio Agriculture Research and Development Center’s (OARDC) Dr. Anne Dorrance, in conjunction with the Soybean Checkoff, worked with us in Shelby County to plant a replicated plot of SCN resistant varieties on a field south of Sidney. Farmed by Jason Frantom, the acreage has shown symptoms of Sudden Death Syndrome in past years, one of those pathogens that invades soybean plants after SCN damages the roots. Dr. Dorrance plans to detail management strategies of all soybean diseases and respond to farmer questions.

Another well known criminal of soybean fields is the soybean aphid. OARDC Entomologist, Dr. Mary Gardiner will also be on tap to speak at the September 2 field day. Gardiner has tracked lady bug populations locally and several other Ohio locations this year in 15-inch row soybeans, long term CRP fields and alfalfa fields. Come to learn more about these beneficial insects “policing” aphid criminals and Dr. Gardiner’s “Buckeye Lady Beetle Blitz” volunteer based lady bug monitoring program.

Want to learn how to keep your number one customer of soybean meal in Ohio? Jeff Wuebker, Darke County crop and livestock farmer and volunteer board member of the Ohio Soybean Association is also on list of field day speakers. Wuebker will discuss why Ohio Voters should approve the Ohio Livestock Care Board, a 13-member bi-partisan board composed of Ohio experts in food safety and animal care that will set care and well being standards for Ohio's livestock farms. Wuebker explains, “As most farmers know in western Ohio, most soybeans are processed for their oil and the by-product, soybean meal, which is fed to the livestock and poultry in this region. This synergy has added millions of dollars to our regional and state economies. If radical, out-of-state organizations impose their ideas of animal rights on Ohioans, the states livestock industry could be lost forever”.

Throughout the afternoon Roger Bender, OSU Extension, Shelby County Agriculture, will explain importance of hosting and conducting these research projects. This was at least the fifth consecutive year we have monitored a soybean sentinel plot on a weekly basis during the growing season. Originally established as part of a nationwide Soybean Rust monitoring system, the program has morphed into an overall regular pest check, with reports forwarded on to Ohio State researchers. The 2009 Sentinel Plot is located at the field day site and we will discuss our observations on that day.

Directions to the Soybean Cyst Nematode Field Day on Wednesday September 2, 2009 from 1-3pm are as follows: Travel south from Sidney on Co. Rd. 25A (Sidney-Piqua Road) approximately 3.5 miles to Kirkwood Road. Turn Right on Kirkwood Road and travel 2.5 miles to Miami River Road. Turn left on Miami River Road and travel about 1 mile to E. Lockington Road and the Field Day is located on the northeast corner of the intersection. No registration is necessary.