Field Crop News, Vol. 06:19, September 6, 2006
September 6, 2006 Vol. 06:19
IN THIS ISSUE:
- Weather Outlook
- Weed Alert
- Silo Fires — A Review for Preparedness
- Fall Forage Fertility Management
- Tillage Effects On Corn and Soybean Yields In The U.S. and Canada
- Stem Diseases of Soybean: update on late season disease
- Late Season Corn Crop Issues
Weather Outlook — Paul Knight
Much of the period between Wednesday and Sunday will be dry, though any day could see a few showers pop-up. A gradual warming trend is expected as temperatures rise a bit above seasonal levels, mostly due to milder nights. Partial sunshine will return allowing for better drying conditions, though winds will remain light and mostly from the southwest. By the weekend, it may become ‘almost’ warm and a bit humid. A cold front should pass through the region either later Sunday or Monday with a broken line of showers or thunderstorms. Somewhat cooler and drier air is likely to be entering the state by this time next week. Florence should develop into a major hurricane by the weekend, but odds favor it staying over the open Atlantic
Editor’s Comment: Rainfall this past week from Ernesto related weather deposited from under one inch in the extreme west and northwest to 3 inches plus in central and south east Pennsylvania. In some areas, total rainfall for the past 10–12 days exceeded 7 inches.
Weed Alert — Melissa Bravo, Botanist/Weed Scientist and William Curran, Extension Weed Specialist
Apple of Peru (Nicandra physalodes) also known as shoofly was identified in late summer in a soybean field on a certified organic grain farm in Lancaster County, PA. All plants were removed and destroyed and continued monitoring of this field and others nearby will occur to ensure its eradication on the farm. This weed is an invasive member of the nightshade family and although the plant was first identified over 100 years ago in Pennsylvania, it has not had a common presence. Most if not all of the previous sightings occurred along railroad tracks, roadsides, or in coal yards, not in agricultural fields. This weed has caused problems in other states and countries, so pay note to any unusual weed species that you encounter this harvest season. Here’s a little more information about Apple of Peru.
“Apple of Peru” is an annual weed in the nightshade family, reproducing only by seed. Seeds have a relatively thick seed coat consisting of an outer and inner layer, and are dormant at maturity. Germination occurs in mid- to late spring and continues through the summer if moisture is available. Leaves are arrowhead shaped and pointed at the tip (much like eastern black nightshade), with irregularly toothed margins. It has trumpet-shaped lavender flowers that may occasionally be white. Fruits (berries) are borne singly in a bladder casing structure resembling that of smooth and clammy ground cherry. Plants have been known to emerge in late summer and still flower and produce viable seed.
This weed is more common in Ohio, where OSU Scientists estimate that it is found on about 2500 acres with at least 100 of those acres being severely infested. It is most severe in vegetables and cannot be controlled with many commonly used herbicides. Ohio State research showed unsatisfactory control with preemergence applications of Dual (metolachlor) and Command (clomazone) as well as several other products. Glyphosate was moderately effective, but later emerging seedlings may escape an application in soybean or other Roundup Ready crops. Ohio State has produced a nice fact sheet with more details of the problem in Ohio, their research results, and some photographs to help with identification (http://ohioline.osu.edu/hyg-fact/1000/1649.html). Some additional information can be found at www.oardc.ohio-state.edu/weedworkshop/appleofperu.asp.
Silo Fires — A Review for Preparedness — Paul Craig, Dauphin County
During the later weeks of August many corn silage fields were discovered to be rapidly drying down due to extremely low soil moisture conditions. Many fields were harvested at moistures below optimum moisture levels and quite a few were harvested at moisture levels below 50%. In addition to the challenges of feeding dry silage there is also a significant risk of the silage igniting in the silo resulting in a silo fire. A review of causes and approaches to fighting a silo fire may be timely.
During “normal” silage fermentation the fermentation bacteria and plant cell respiration consume all of the available oxygen within 24 hours and the dense forage mass becomes anaerobic. When silage is harvested at low moisture levels the forage mass does not compact as easily as wetter and heavier silage would. If this less dense forage mass, with abundant oxygen levels, provides an ideal environment that can lead to spontaneous combustion.
The start of a silo fire is not a rapid process. Frequently silo fires do not occur until weeks and possibly a month or two after filling. Rarely will there will any visible flames. The most common sign is smoke rising from the top layer of silage. Usually the fire will be confined to hot spots within the silo.
Silo fires burn slowly so there is ample time to analyze the fire and seek advice. Do not attempt to address the situation yourself due to many potential hazards. One immediate practice is to seal off the bottom of the silo chute to prevent updrafts from fanning the fire and then call the fire company.
Most fire companies have thermal imaging equipment that is useful to pinpoint the exact location of the fire. Frequently silo fires will be in the upper 5 to 10 feet of a silo. Gaining access to the interior of the silo presents a challenge to firefighters in full turnout gear. An aerial ladder truck can provide significant advantage to access the silo. The recommended practice for silo fires is to use a small, straight-tip nozzle to penetrate the silage pile and reach deep seated hot spots. Applying too much water can result in the water moving away from the intended target.
After the surface fire is extinguished the forage mass will still need to be examined for subsurface hot spots. Digital imaging equipment or thermometer probes are required. Do not walk or stand directly onto the silage. Lay wooden planks on the silage to distribute weight if personnel must enter the silo. Temperatures of 140 to 170 degrees indicate potential problems and need monitoring. Temperatures approaching 180 degrees will soon result in burning. Temperatures below 140 degrees indicate no serious heating problems.
Recommend fire firefighters not use any type of chemical water additives to fight the fire. All damaged silage will need to be removed but may be too wet for removal with an unloader. Be alert for additional hot spots at other locations in the silo. Fire fighting conditions vary by silo type, size of fire and location. Monitor your silos closely at this time. Additional information on fighting silo fires is available at: http://www.cdc.gov/nasd/docs/d000701-d000800/d000759/d000759.html
Fall Forage Fertility Management — Douglas Beegle, Soil Fertility Specialist
As always, begin with a soil test. Even though it maybe getting late, the Ag Analytical Services Lab at Penn State normally has about 2 day turn-around with soil samples. So if you overnight your samples to the lab and have signed up for free web access to your results you would still have your results in plenty of time to make fertility management decisions for this fall. Other labs have similar service.
When you get your soil test reports back, look for fields that are low in P and especially K and, as always, look for low pH fields. These are the ones that you want to focus on for fall fertility management. Low fertility going into the winter can weaken the stand and often result in poor stands the following year. Make sure you get the recommended nutrients on these fields as soon as possible. Certainly get them on before the crop goes dormant because if the nutrients are not taken up by the plants they won’t do much good for helping the plant get through the winter. Potassium is especially critical for winter survival.
If the soil tests are in the optimum range and the recommendations are for maintenance fertilization, timing is less critical. It certainly will not hurt to get them on early and it may give the stand a little extra protection over the winter. However, you could put maintenance P and K on after dormancy as long as there is not a serious threat of physically losing the nutrients in runoff. This would be a concern if you spread on frozen or snow covered sloping ground.
The other priority is to lime fields with low pH. Ideally for legumes the pH should be maintained between 6.5 and 7.0. If you have fields below this and especially if they are down around 6 or lower, these should be a priority for liming this fall. Fall liming will give the lime time to react before the next growing season. Also, freezing and thawing over the winter will help to incorporate the limestone. Watch the soil conditions before you have heavy lime trucks run over the field. If the soils are wet wait until they dry out or freeze. There is not problem with winter applications of limestone again as long as it is not susceptible to physically being washed off the field.
Fall fertility management in forages is critical if soil nutrient levels or pH are low. However, if you do a good job of maintaining soil nutrient levels and pH then fall may still be a good time to take care of this important task, but it is less critical thus giving you more management flexibility.
Tillage Effects on Corn and Soybean Yields in the U.S. and Canada — Sjoerd Duiker, Soil Management Specialist
Three Pioneer agronomists reviewed 61 corn and 43 full-season soybean tillage trials in the U.S. Their findings were reported in the online journal Crop Management in June. The comparison was between no-till and fall tillage (moldboard or chisel) followed by spring secondary tillage. On average for North America, corn and soybean yields with no-till and conventional tillage were the same. There were, however, important regional and soil differences. No-till corn and soybean yields were commonly higher than those achieved with conventional tillage (12.2 and 5.0% for corn and soybeans, respectively) in the southeastern, southern, and western parts of the U.S. In a transitional zone no-till yields were 1.8% (corn) and 0.6% (soybeans) lower than those obtained with conventional tillage. In the northern zone no-till corn yields were 5.5% lower and soybean yields 3.9% lower than conventional till yields. On average, no-till yields were higher than conventional till yields on well-drained soils, while they were lower than conventional till yields on poorly drained soils. The benefit of crop rotation was approximately the same with no-till and conventional tillage. According to maps included in the article, Pennsylvania straddled the transitional and southern zones, suggesting no yield penalty or a yield advantage if producers switch to no-till.
A recently published tillage article in the Agronomy Journal showed that no-till corn yields were no different from those with conventional tillage on a well-drained soil in southeastern PA. This research was done in short-term no-till. Over time, no-till yields are expected to improve due to organic matter increases, soil enzyme activity, microbial biomass, and changes in porosity and aggregation. No-till yields tend to exceed those with conventional tillage in regions where there are short-term droughts and hot temperatures. On poorly drained soils and cooler climates no-till poses more of a challenge.
The Pioneer researchers suggested comparisons of no-till with conventional tillage corn and soybean production are no longer needed in the U.S. and Canada. Management costs, farm size, labor and time constraints, soil conservation, and government programs all influence producers’ decisions to practice high residue systems like no-till or strip-till. The review showed that producers are unlikely to suffer a yield disadvantage by switching to no-tillage. Even in northern areas, no-till is gaining increasing favor due to these factors. These Pioneer researchers therefore suggested that future tillage research would most profitably focus on optimizing successful high residue no-tillage and strip-tillage production systems.
- M.S. DeFelice, P.R. Carter, and S.B. Mitchell. 2006. Influence of tillage and corn and soybean yield in the United States and Canada. Crop Management 2006-0626-01-RS.
- S.W. Duiker, J.F. Haldeman Jr. and D.H. Johnson. 2006. Tillage x maize hybrid interactions. Agronomy Journal 98:436-442.
Stem Diseases of Soybean: update on late season disease — Dr. Eric De Wolf, Extension Plant Pathologist
Reports from around the state indicate that some soybean fields are showing signs of late season disease. One common symptom this year includes patches of plants that appear shorter and paler than the surrounding canopy. Upon closer examination plants within the affected areas appear to be wilting and plants in the center of the patch may already be dead. The stems of the affected plants often have a lesions on the main stem that range in color from tan to almost black.
These symptoms are consistent with a number of diseases that can affect the stems of soybean plants late in the growing season including anthracnose, phomopsis, and stem canker. These diseases often get started early in the reproductive stages of growth, but show no symptoms until later in the growing season when the plants begin to invest more energy in filling pods. This late symptom development can be accelerated by drought or other stress factors that weaken the plant. I believe this is exactly the type of situation we had in Pennsylvania this season; rain in early - mid July followed by prolonged dry periods in late July and August. Fields with soil types prone to drought seem to have more disease relative to soils with greater moisture holding capacity.
Little can be done at this time to manage the diseases. Interestingly, at least some of these fields received a fungicide application during the early reproductive stages of growth. I would not expect fungicides to very effective at controlling these diseases because the application timing is a little too late for good control, the stems are not easy application targets, and the fungicides are only locally systemic (unlikely to move into the stem). We will continue to work on the samples and give an update soon.
Late Summer Corn Crop Issues — Dr. Greg Roth, Grain Crop Specialist
This year’s corn crop is moving toward maturity and there are a number of important issues to be considering as the crop winds down towards maturity.
First, for those completing the harvest of the silage crop, it may pay to carefully monitor crop moistures. We found last week that some of our silage experienced significant rehydration due to the recent rainfall. We noted that some of our corn silage increased in moisture content by around 8 percentage units from the previous week. This was likely because the crop was still immature but under drought stress, and then we received a drought ending rain. As the crop matures, there will be less potential for this extent of rehydration to occur.
The next issue would be to monitor corn grain for high moisture corn harvests. Some of our early varieties in the southeast and southcentral counties should be approaching the point where grain harvest can begin. Generally, ideal high moisture shelled corn is harvested in the 25–30% range, but there are many specifics that should be considered in conjunction with the customer and their nutritionists in identifying the ideal moisture target. For example, some prefer high moisture corn on the drier side of this range, but it may not ferment as well in some storage structures or store as well into the spring and summer.
As the crop matures, you will likely be able to observe some differences in disease, insect and stalk rot issues. Fields with the tops dying prematurely could be an indication of anthracnose or corn borer injury. Scouting fields now can give you an indication of corn borer pressure and whether Bt corn was justified in these environments this year. Also, I have seen more stalk rot problems developing in areas with significant late season stress. I would scout fields for potential stalk rot and lodging problems now and plan to harvest those fields early if possible. Note the hybrid and plant populations for future reference on these fields.
Contributors: State Specialists: Dr. Greg Roth, Dr. Doug Beegle, Dr. Marvin Hall, Ron Hoover, Dr. Eric DeWolf, Dr. William Curran. Extension Educators: Paul Craig (Dauphin), Dave Messersmith (Wayne), Kevin Fry (Armstrong), Mena Hautau, (Berks), Andrew Frankenfield (Montgomery), Susan Alexander (Jefferson).
Editor: Don Fretts, Senior Extension Educator, Fayette County
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