CMEG Crop Management Extension Group

Field Crop News

Website Address: http://fcn.agronomy.psu.edu/

July 19, 2006    Vol. 06:12

IN THIS ISSUE:

Weather Outlook — Paul Knight, Pennsylvania State Climatologist

After a rather warm, though a bit humid day on Wednesday, a surge of sultry air will return on Thursday accompanied by scattered thunderstorms mainly in western and northern sections. Readings will rise above 90°F in the eastern counties. The heat will be short-lived as a cold front with some potent thunderstorms pushes southeast across Pennsylvania on Friday. It will still be rather hot and sticky east of the mountains until the front passes. A period of dry, tranquil and pleasant weather is likely during the weekend. However, a developing disturbance in the upper atmosphere will entreat clouds back into the state early next week with showers possible later Monday or Tuesday as winds blow in from the southeast.

Soybean Fungicides for “Plant Health” and Soybean Rust — Erick De Wolf, Plant Pathology

As soybeans move through flowering and the early reproductive stages of growth in Pennsylvania, some producers may begin to ask interesting questions about the use of fungicides on soybeans.  The following article is intended to provide some information about a number of factors related to fungicide application to soybeans including the risk of soybean rust in Pennsylvania and using fungicides for “plant health”.

Soybean rust: The risk of soybean rust for Pennsylvania is very low.  At this time, rust remains limited to the deep south.  To date most of the reports of rust have been on in FL, GA, and AL.  This past week Louisiana reported rust on kudzu in three locations (parishes) in that state.  Our colleagues there report that the fungus is reproducing at these sites; however, they have not fund rust in soybean.  The weather there has been hot and dry in these areas so it will likely take a significant amount of time for the rust to reach high levels.  Soybean producers should continue with their normal management plans, but should carefully watch rust in the deep south. If the rust gets out of control in the South we may need to be ready for action.  I would suggest you check the USDA website frequently for updates. I post comments about the rust situation in the U.S. and its implications to Pennsylvania each week.  Interested parities can find the site at: http://www.sbrusa.net/

Soybean Plant Health: Don Hershman, University of Kentucky, has a very nice article addressing the numerous issues related to plant health applications of fungicides. I have summarized some of the main points here for your consideration.

In the absence of soybean rust and significant risk of infection by the rust pathogen, the decision to apply a “plant health” fungicide application is not as straight forward as some might believe. There is not general agreement among university and industry scientists regarding the potential for plant health applications to result in economical benefits to producers. By economical, I mean that the $ return per acre exceeds the $ invested in fungicide/application costs.

Replicated plots: The results of replicated tests by University scientists and crop consultants are mixed, but generally, applications of fungicides to soybean, in the absence of specific foliar fungal diseases, frequently did not produce a statistically significant (i.e., economical) yield response. Specifically, over the three years of study in KY, significant yield results were encountered in six (6) of twenty-four (24) experiments (25.0% response rate). A similar rate of statistically significant treatment responses (26.9%) was seen in 62 replicated experiments conducted throughout the Midwest and Northeast during 2005. These experiments involved both large and small plot tests.

On farm testing: In contrast to the above, results of “plant health” fungicide applications based on a large number of strip plot, side by side comparisons, in grower fields have been much more favorable to potential yield benefits. For example, 162 side by side comparisons, summarized by BASF from Indiana and Ohio in 2005, showed an average yield response to “plant health” fungicide applications of 5.6 bu/ac (3 – 4 bu/ac is considered to be break even, depending on the fungicide and application cost, and the price received per bushel of soybean). Comparisons summarized from 192 fields across the Midsouth in 2005, including Kentucky, were even more favorable with an average yield response of 8.5bu/ac. It is my understanding is that Syngenta can produce similar results from their on-farm trials over the last few years.

The bottom line: What is one to make of the apparent discrepancy between the results of 84 replicated experiments, conducted by numerous scientists, and the results of non-replicated, but numerous, on-farm treatment comparisons conducted by industry? To be honest, I am not sure. Certainly, the great disparity in results should be a “red flag” to anyone considering making applications of foliar fungicides to soybean in the absence of specific foliar fungal target diseases. On the other hand, very high treatment yields in many strip plot comparisons (and some replicated experiments) over the last few years make it clear that something significant is going on. I have seen enough positive results to conclude that “plant health” applications of fungicides to soybean cannot not be discarded, offhand. Yet, I have also seen enough negative results to know that there are many, many scenarios where “plant health” fungicide applications simply will not pay for themselves.

At this point, I would simply caution producers who are considering making fungicide applications for plant health benefits, to make those applications with the awareness that a significant economic response is not assured. At this point, we (university and industry scientists) do not have enough information to be able to recommend which fields/situations have a high probability of an economic response and which fields have a low probability of response. In addition, applications of any pesticide in the absence of a specific target pest(s) is contrary to integrated pest management principles. Thus, there may be unintended, long term implications (environmental, regulatory, and/or sociological) associated with applying fungicides to soybean in the absence of specific target pests. One consequence could be the suppression of native fungi that keep insect populations in check, naturally. There is already some evidence that indiscriminate use of fungicides in soybean has resulted in increased insect/mite activity in some states. Another consequence could be stricter future pesticide laws and regulations. The point is we must be very cautious when we get into the realm of applying fungicides (or any pesticide) to large acreages of soybean (or any crop), even if there is a good rationale for doing so. In this article, I am making it known that the rationale for making “plant health” fungicide applications to soybean is not firmly in favor of making the applications. Thus, caution is advised at multiple levels.

Corn Crop Pollination and Development — Greg Roth, Grain Crop Management

The corn crop is doing well in many areas with the good soil moisture and heat we are getting this week. Some fields with thin stands due to cutworms or other issues may show more than usual symptoms of tillering and tassel ears that are often associated with good growing conditions and thin stands. Some fields silked as early as July 4, but many have recently reached silk emergence or will soon. Silking is an important indicator of maturity and can be used as a guide in planning silage harvests.

A recent Cornell study tracked days and growing degree days between silking and harvest and found that depending on hybrid maturity, hybrids can take from 35 to 45 days to reach silage maturity from silking. This will vary a bit on the year and is dependent on some other factors besides degree days. Pay particular attention to early planted, early maturity hybrids, which will mature rapidly in southeast and southcentral parts of the state. Often these fields that silk in early July may be ready for silage harvest in mid-August, which is consistent with the Cornell study.

Some hybrids will develop silks before the tassels emerge. This is usually not a problem as the silks remain receptive for 10 days or so.  Once pollination is complete, you can assess the success of the process using the shake test. Carefully unwrap the husk leaves and then gently shake the ear. The silks from fertilized ovules will drop off.

Late N on Corn — Doug Beegle

There were some questions this week about adding N corn well beyond normal sidedress time.  Because corn takes up most of it’s N during the major growth stage from knee high to tassling, it will respond to N up to around tasseling time. Thus if the crop is short on N and showing N deficiency symptoms between normal sidedressing (V6–7)  time and tassling there can be a significant benefit to applying some N.

Nitrogen deficiency symptoms will be on the lower leaves of the corn plant and will start at the tip of the leaf and then go back the midrib forming a “V” shaped pattern on the leaf.  The higher up on the plant that leaves are show this symptom the more severe the deficiency.

The sooner that you recognize that you have a problem and get the N on the better. At this stage you will probably not get a profitable response to more than about 50 to 75 lb N/A. As it gets later and the deficiency gets worse the yield potential will be reduced.  Thus, applying N late will not likely give you the same yield as if the crop had never run short on N, but it should certainly help.

The challenge is how to apply this N. The best method would be to dribble UAN between the rows with a high boy. Try to avoid burning the upper leaves. I have heard of some N going on wet, tall fields with an airplane. There will be some burning if urea is broadcast over the top but if the field is N deficient, the benefit from the N will over shadow any injury that might occur.

Winter Grain Crop Updates — Greg Roth, Grain Crop Management

In contrast to last week, there is some good news this week on our wheat crop. Last week wheat harvest started here in central Pennsylvania and the reports on the yield of the wheat crop have been impressive. Several growers reported yields to me this week in the 85-95 bu/acre range, with excellent test weights and straw yields as well. Our variety trial yields appear to be in this range as well.  There appears to be no evidence of sprouting, probably due to the lower rainfall levels and later crop maturity compared to other parts of the state.  These wheat yields are likely due to the mild winter temperatures and cool conditions this spring that promoted good tillering and tiller development.  Generally wheat has been standing well also.  The combination of good grain and straw prices combined with the high yields are contributing to some good returns from this small grain crop in this area this year.

Some of our sprouted wheat crop has been stored and there may be an opportunity to market it later in the season for feed or milling quality wheat. Sprouts are often difficult to see and evaluation is a bit subjective.  The falling number test can provide a better estimate of the marketability of the crop. This test can be performed at some local mills. Also, the Illinois Crop Improvement Association can perform this analysis.  Visit their website for details:  http://www.ilcrop.com/ipglab/othrtest/othrtest.htm.

We are in the final stages of processing our winter barley data as well and our report should be posted soon on our small grains website ( http://smallgrains.psu.edu/.) Yields of this crop were also very good with many reaching over 100 and some to 115 bushels per acre.  Winter injury was minimal and some of the less winterhardy lines performed well this year.  Our winter was more like a “Virginia winter” this year with minimal winterkill and good spring vigor for all varieties.

Weed Control in Small Grain Stubble — Kevin Fry & Bill Curran

Now is a good time for controlling problematic weeds in your small grain stubble, especially prior to forage seeding.  Once the grain is harvested and the straw is baled, a systemic herbicide can be applied at this time to control actively growing weeds.  Application should be made within 1 to 3 weeks after harvest. Glyphosate control is reduced as weed size increases above 6 inches.

Your goals will be to control summer annual seed production (lambsquarter, ragweed, foxtail, etc.).  Mowing alone will not control seed production, they can regrow — this is especially true for annual grasses like foxtail which will require two to three mowings to prevent seed production.  An application of Glyphosate and 2,4-D will be very effective on most weeds.  If weeds are tall and beginning to flower, spraying the regrowth following mowing may provide better control, but wait two to three weeks before you make the herbicide application.  This can be particularly effective on perennial weeds.

Speaking of perennials, this can be also an excellent time to control troublesome perennials. At this time of year, perennial’s root reserves are at their lowest which coincides with the bud to bloom stage of growth. Frequent rainfall and good soil moisture ensure healthy perennial weeds that are susceptible to systemic herbicides. Weeds in drought stress or flooded fields may not respond as favorably and you should probably mow to prevent seed production and make a later summer application. An application of Glyphosate and 2,4-D or dicamba (Banvel/Clarity) will be  effective in controlling most of those troublesome perennial weeds.

Cover Crops — Joel Hunter

As our small grains come off, producers are afforded an excellent opportunity for cover crop establishment. This is also an excellent time to plan and prepare for cover crops following corn silage harvest or anywhere “open ground” and timing/conditions permit. With current fertilizer prices, cover crop nitrogen values alone from manure and/or legumes may offset cover crop costs. However, some of the many other cover crop benefits include: erosion control, nutrient scavenging and recycling, improved soil tilth (the physical condition of the soil in relation to plant growth) and organic matter (OM), and improved yields. The conditions thus far this season seemed to reveal and even amplify any soil “issues” present in the form of poor crop development. There were also excellent examples where cover crops demonstrated the potential to ameliorate and improve such areas. Seeing is believing. These cover crop attributes are real and tangible.

A little insight into the processes may be helpful. Cover crops provide an excellent source of fresh (and rich) organic material for feeding the critically important and diverse soil ecosystem. Ample fresh organic matter additions, such as killing a cover crop, generally result in an explosion of soil microbial activity that may result in an increase in biomass of as much as 1/6 of the total soil OM. Then, the decomposition of dead microbial cells is associated with the mineralization or “release ” of simple organic products (plant nutrients) such as nitrates and sulfates. It is in this “active ” portion of the soil organic matter where the greatest amount of biological nutrient cycling actually takes place. The other two soil OM fractions (the “passive ” fraction and “slow ” fraction) are relatively inert biologically, but have other important attributes, such as CEC and water holding capacities. Furthermore, over time, keeping soils covered will also add to the passive and slow fractions increasing total soil OM and soil health/quality long term.

There are many options for species, function, purposes, methods, etc. Today, herbicide resistant crops (Roundup Ready, Liberty Link, etc.) give us some added flexibility and insurance for control. Give cover crops a try. Experiment. We can make it work and pay! (As my wife’s hero, Oprah, says, “This I believe!”) Many good sources of additional information are available and a few are listed below.

Contributors: State Specialists: Erick DeWolf, Greg Roth, Bill Curran.  Extension Educators:  Andrew Frankenfield (Montgomery), Mena Hautau (Berks), Joel Hunter (Crawford), Kevin Fry (Armstrong), Mark Madden (Sullivan), John Rowell (York), Don Fretts (Fayette) and Dave Messersmith (Wayne).

Editor: Joel Hunter (Crawford)

Real time pest and heat unit activity: http://psu.zedxinc.com/cgi-bin/site.cgi?location=2&user=psu#

Calendar of Events: http://www.events.psu.edu/cgi-bin/cal/webevent.cgi?cmd=opencal&cal=cal209&

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