Field Crop News
Website Address: http://fcn.agronomy.psu.edu/
October 10, 2006 Vol. 06:24
IN THIS ISSUE:
- Weather Outlook
- Fall Herbicide Applications Revisited
- Viruses and Green Stem Disorder in Soybeans
- Tillage Comparisons Show No-till Competitive
Weather Outlook — Paul Knight
A cold snap is expected late in the week and during the weekend with parts of northern and central Pennsylvania noting their first snowflakes and also the first frosts and freezes. On Wednesday, clouds will congregate with patches of drizzle in eastern sections (particularly the Poconos) and developing showers and even a thunderstorm in western parts. It will not be as warm as recent days. Showers are expected to push across the state Wednesday night and Thursday morning as the first surge of colder air arrives. Most sections will receive 0.20–0.40 inches with more in the west. Chillier winds will usher in a slot of dry air for part of Thursday allowing for a large temperature contrast between eastern sections (60’s) and western portions (40’s). The second surge of cold air will arrive Thursday night and Friday morning with several hours of cold rain in the valleys of central and northeast Pennsylvania and some wet snow in the mountains from the Laurel Highlands to the Poconos. Expect several inches above 1,700 feet — enough to bring some trees down. Bitter cold air will follow for Friday with blustery winds, flurries in the mountains and readings struggling above 50 southeast and staying in the lower 30’s northwest mountains. Winds and clouds will keep the gelid air from collecting on Friday night, but Saturday night and perhaps Sunday night too will bring widespread freezes in the mountain—valley section of the state. Monday will see moderation, but clouds, wind and rain will return on Tuesday.
Fall Herbicide Applications Revisited — Bill Curran, Extension Weed Science, Crop and Soil Sciences
We have been evaluating fall herbicide applications for winter annual, biennial and some perennial weed control in front of soybean and corn for several years now. This tactic can work well for those growers that often have trouble controlling these weeds in the spring. Fall herbicide treatments are by far the most effective method for controlling dandelions, poison hemlock, and wild carrot, which are difficult to control in the spring. Fall treatments in front of soybeans have had the greatest interest where effective spring herbicides are fewer in number. Also, with the increasing presence of glyphosate—resistant horseweed/marestail, interest in fall application has grown.
On the negative side, applying a residual herbicide in the fall can 1.) limit your crop rotation options in the spring; 2.) will likely preclude the use of cover crops (which are also an excellent way to suppress winter annual weeds) and; 3.) can pose a risk to the environment and especially water quality should the herbicide leave the field in water or sediment. Also, excess money spent on fall treatments results in less money available for weed control in the crop, where it is usually needed. For these reasons, carefully consider whether fall application is right for you.
According to Mark Loux and Jeff Stachler at Ohio State, for control of winter annual weeds, apply herbicides anytime after early October. For the most effective dandelion control, delay application until after a frost. Mark and Jeff have applied as late as early December for control of winter annual weeds, but generally recommend application when dandelions are still mostly green, or by mid—November if possible. Apply glyphosate—containing treatments with ammonium sulfate (AMS), and additional nonionic surfactant if specified by the product label. Treatments that do not contain glyphosate should generally be applied with crop oil concentrate (COC) for best results.
In our 2005⁄2006 trials at Landisville, one or two treatments really proved superior in providing residual control into June. Herbicides were applied on November 8, 2005 and the last rating was taken on June 7, 2006 prior to a post glyphosate application. Most treatments looked fairly clean on April 1, but by June 7, obvious differences were observed. The control ratings are an overall rating considering all weed species present. Weeds included common chickweed, dandelion, corn speedwell, purple deadnettle, some downy brome, and the beginning of summer annuals including lambsquarters and giant foxtail. Other soybean herbicides (Valor, Scepter, Python, Aim, etc) can also be applied in the fall, but most of these will not effectively control winter weeds without the addition of glyphosate and⁄or 2,4–D to help control emerged weeds at application time.
| Soybean Trial | |
|---|---|
| Treatments | % Control |
| Glyphosate (0.75 lb ae) + 2,4-D (1 pt) + AMS | 40 a |
| Canopy EX (2.2 oz) + 2,4-D + COC | 88 b |
| Valor (2 oz)+ 2,4-D + COC | 50 a |
| Sencor (8 oz) + 2,4-D + COC | 50 a |
| Corn Trial | |
| Treatments | % Control |
| Glyphosate + 2,4-D + AMS | 50 a |
| Autumn (0.3 oz) + 2,4-D + COC | 68 b |
| Basis (0.5 oz) + 2,4-D + COC | 75 b |
| Princep (1.1 lb) + 2,4-D + COC | 87 c |
The bottom line according to Loux and Stachler on fall herbicide treatments — The utility of most residual herbicides is maximized when applied in the spring prior to planting, not in the fall. A better alternative is use of a non–residual herbicide program in the fall, such as glyphosate plus 2,4–D, followed by spring application of residual herbicides. This tactic would even allow for establishment of a winter cover crop if desired. This approach provides for the greatest flexibility in the postemergence application window and the most effective control of weeds such as lambsquarters, marestail, and ragweed.
Viruses and Green Stem Disorder in Soybeans — Erick De Wolf, Assistant Professor, Plant Pathology
The soybean crop has matured in most fields in Pennsylvania and will be drying down over the next few weeks. As the soybean mature it is becoming very common to see plants that do not mature normally. In some cases these plants may have mature pods, but the stems remain green until they are killed by frost. These green stems may cause harvest delays and troublesome weathering of the grain. Many explanations have been offered for this green stem disorder in soybeans including viral diseases such as bean pod mottle virus (BPMV), insect injury, and variety by environment interactions. This past year some areas of PA experienced significant levels of bean leaf beetles, and some of these fields are now showing signs of the green stem disorder. On the surface these observations seem to have a clear link... Of course it is never that easy.
The possible causes of the green stem disorder were evaluated as part of a multi—year conducted in Illinois, and Wisconsin and the result recently published in the journal Plant Disease. Since this journal is not likely on your nightly reading list, I hope you will allow me to summarize the conclusions.
Multi—year surveys of BPMV indicate that the percentage of plants infected with the virus at the R6 growth stage was higher than the incidence of green stem disorder at harvest maturity. Many plants infected with BPMV did not develop the green stem disorder. This data indicates that the incidence of green stem disorder is independent of BPMV infection at the R6 growth stage. The researchers also compared an identical set of soybean varieties and breeding lines at two locations with different levels of natural virus infection. Despite different levels of viral infection nearly all entries had similar levels of green stem disorder at the two locations. This suggests that variety does not play major role in the incidence of the disorder. In order to test whether insect injury was triggering the disorder, the researchers also grew soybean plants in cages that eliminate the potential for insect feeding. Yep, you guessed it... Feeding by bean leaf beetle, leaf hopper or stinkbug did not have an effect on the incidence of green stem disorder. The bottom line is we still don't know what is causing the green stem disorder.
Here is my take on these issues and some useful tips: (1) Many things can cause plants to stay green long after the majority of the field has matured. I suspect that just about anything that can cause a soybean plant to abort pods or delay pod fill can result in delayed maturity. One way to test this idea is to count the pods and number of seeds per pod in the affected plants compared to plants that matured normally. In my experience, many of the plants that are still green have very low numbers of poorly filled pods. Give it a try and let me know what you find. (2) Given the level of bean leaf beetle we have seen in the past two years it seems wise to do some testing for BPMV. I suspect the virus is out here and it may be causing some yield loss that we are currently attributing to other problems. If you are interested in testing for the BPMV and other viruses, I suggest you consider sending a sample of any remaining green tissue to a private company called Agdia. The testing will cost at least $60 (more if you screen for multiple viruses), but it is the only way to know if the virus is present. You can find more information about the testing service at http://www.agdia.com/testing/
Tillage Comparisons Show No-till Competitive — Sjoerd Duiker, Soil Management Specialist and David H. Johnson, Station Manager
Since 2002 we have been comparing different tillage systems at the Penn State Southeast Research and Extension Center in Landisville, Lancaster County. The research was done with continuous corn and included no—till, zone—till, strip—till, and chisel⁄disking. Zone—till was done with the Unverferth three coulter zone—till system and strip—till with an CASE—IH Ecolotill unit mounted in 2003 and 2004 with no—till shanks run to 16–17” and berm—tuck’rs. In both cases, the corn was planted right in the prepared zones with the tillage machines. We tested these systems to determine whether there was a yield penalty with straight no—till and, if so, whether the use of in—row tillage could alleviate this yield reduction. After 3 years of no yield reduction in no—till compared with chisel⁄disking, and no yield benefit of the in—row tillage systems, we deserted the in—row tillage systems. However, we continued the comparison of no—till with chisel/disking. The other treatments were converted to no—till in 2005. Results of this trial are shown below.
| 2002 | 2003 | 2004 | 2005 | 2006 | |
|---|---|---|---|---|---|
| Yields (bu/A) | |||||
| Note: Yields were not significantly different between treatments in any year. | |||||
| CD-CD-CD-CD-CD | 70 | 149 | 154 | 124 | 127 |
| ST-ST-ST-NT-NT | 73 | 144 | 153 | 138 | 133 |
| ZT-ZT-ZT-NT-NT | 75 | 149 | 157 | 140 | 145 |
| NT-NT-NT-NT-NT | 75 | 148 | 155 | 149 | 148 |
No yield reductions were observed with no—till. We can say nothing more than this, because statistical analysis showed no significant differences in yields in any of the years due to the high variability. The “low” yields in 2006 were probably the result of poor corn rootworm control with the Poncho 1250 applied with the seed. We observed a lot of ‘goose—neck’ and lodged corn in our trial in 2006. To avoid further problems with corn rootworm we are planning to rotate to another crop next year.
Contributors: State Specialists: Marvin Hall, Eric DeWolf, Sjoerd Duiker, Bill Curran, and Doug Beegle. Extension Educators: Gary Micsky ( Mercer ), Del Voight (Lebanon), Kevin Fry (Armstrong), Andrew Frankenfield (Montgomery), Mena Hautau (Berks), Susan Alexander (Jefferson), Jeff Graybill ( Lancaster), and Craig Williams (Tioga)
Editor: Susan Alexander — Extension Educator, Jefferson Co.
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