CMEG Crop Management Extension Group

Field Crop News

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

September 8, 2009    Vol. 09:26

IN THIS ISSUE:

Weather Outlook — Paul Knight, Pennsylvania State Climatologist

The vast majority of the time between now and Labor Day will be dry with a slow warming trend. A disturbance near the Carolina coast should spill some clouds across the eastern and southern sections of Pennsylvania either Thursday or Friday. There is a 25% chance of a light shower in the southeast corner of the state during that time. A fresh push of dry and slightly cooler air will arrive on Saturday with a return of warmth by early next week. The next widespread risk of rain is not until the middle or later part of next week. One wild card that is not in this scenario is the possible development of tropical storm Erika near the Leeward Islands during the next day or two. There is a small chance (10%) that its movement could impact Pennsylvania’s weather in an unfavorable way early next week.

Another very cool spell is likely during mid-September, with perhaps an unusually early end to the growing season in the northern counties. However, the latest indications point to a warmer than average September and early October and then much colder second half of October. There are increasing signs that November will be rather mild in this region. The development of a moderate El Nino in the Pacific portends a wetter winter (and probably snowier) in the state.

Controlling weeds prior to cover crop establishment — Bill Curran, Weed Science

September and October are the time to sow winter cover crops. Consider your weed management needs before you plant the seed. Two things to consider: 1.) Are there sufficient weeds in the field that will compete with a young struggling cover crop that could reduce the stand going into the winter? If the field is green with summer annual weeds that are or have already gone to seed, you may still want to burndown the residue (Gramoxone) to quickly stop weed competition. If summer annual weeds are scattered throughout the field and are at the end of their lifecycle, then an herbicide is generally not necessary. 2.) If winter annual weeds have emerged (henbit, chickweed, etc.) or more importantly, perennials (pokeweed, Canada thistle, etc.) are still active, then a timely herbicide application prior to seeding the cover crop can pay off. Not only can you potentially better control the perennials with the fall application, but you will also help the cover crop succeed. Of course glyphosate can be safely used prior to the emergence of any crop, while the PGR herbicides such as 2,4-D will persist for a week or two and dicamba up to several weeks depending on the rate and both can cause injury to cereal grains, ryegrass, etc. (and certainly legumes) as the seedlings attempt to emerge and establish.

tillage

Fig. 1. Vertical coulter/rotary harrow (left) vs. nothing (right) shortly after using the shallow tillage tool.

As an alternative, some farmers are using shallow tillage tools (i.e. vertical coulter/rotary harrow such as the Great Plains Turbo-Till) to manage residue prior to planting. These types of tools can provide some limited weed control for small annual weeds. We have been testing a similar type of tool in the spring prior to corn and soybean planting. Last spring, we had a fair amount of common chickweed in our soybean trial. The accompanying photo shows a no-till plot compared to one that received the vertical coulter/rotary harrow treatment shortly after the operation in mid May. Some of the chickweed had recovered (∼70% control 10 days later), but we would expect better control in the fall when winter annuals are smaller and more susceptible.

Poisonous Plants and the Fall Harvest — Bill Curran and Dwight Lingenfelter, Weed Science

With corn silage harvest coming into full swing, we have had some questions about harvesting poisonous plants with the forage or perhaps even with grain. A number of plants contain potentially poisonous substances that may be toxic to livestock if consumed. If you suspect livestock poisoning, call your local extension educator or veterinarian immediately. Once the poisoning has occurred, it can be very difficult to pinpoint the exact cause. Scouting fields and identifying potential poisonous plants prior to or during harvest can help avoid livestock losses. Some of the more common poisonous plants that we should pay attention to this time of year are:

Mexican bean beetle — John Tooker, Penn State Entomology Specialist

We have heard reports from York County of soybean fields that have been treated for Mexican bean beetles (MBB). It is not often that we encounter damaging populations of this insect species in Pennsylvania, so we thought would address the topic. Soybeans are most vulnerable to loss from MBB feeding from flowering to pod fill and defoliation levels of 15% over an entire field could warrant treatment. This late in the season, when pod fill in many parts of Pennsylvania is winding down, treatment would likely not be fruitful; however, late-planted, late-maturing, or double-crop soybeans that are still in early reproductive stages may still be vulnerable to MBB defoliation. If pods are present and tissue loss exceeds 35%, it would probably be wise to take action.

Mexican bean beetles have two generations in Pennsylvania. Adults overwinter in plant debris and other similarly protected locations in and around soybean fields. Upon emergence they feed upon various legumes, including non-crop species, and move to the earliest planted soybean fields where they feed and lay eggs. Individual females have been known to lay more than 1000 eggs, so populations can build quickly. Both larvae and adults can feed on soybean foliage, tending to feed between leaf veins. Larvae skeletonize leaves by removing a single layer of leaf tissue whereas adults feed through the leaf, leaving heavily damaged leaves with a lacey appearance. Adults look like orange lady beetles (they are classified in the same family as lady beetles) and have three rows of spots on their wing cover.

Bt Corn Stover…Does it Persist Longer? — Greg Roth, Penn State Grain Crop Management Specialist

During the past week I have had several inquires about the persistence of corn stover and in particular whether Bt hybrids produced stover that breaks down more slowly. It seems we have more problems with stover when planting in high yielding corn on corn fields than before. If Bt corn stover did break down more slowly, it might be a good thing from a carbon sequestration standpoint. Theoretically this could be due to a change in the corn stover composition in Bt lines, increased stalk strength or some impact on the soils microbial community that inhibited the breakdown.

During the past year or so several papers have been published addressing the issue. One study, conducted by a team of USDA scientists in South Dakota (Lehman et al., 2008) evaluated the breakdown of Bt and non Bt corn stover from two pairs of hybrids from different companies. They did not detect any differences in the decomposition rates over 384 days due to the Bt genes (both cry1Ab and cry3Bb1 genes) and also did not detect any difference in the stalk strength measurements they conducted. They also did not find any consistent compositional differences that would impact stover decomposition. Also, they compared stover sample decomposition in the root zone of both Bt and conventional hybrids and found they actually decomposed faster in the root zone of the Bt hybrid. Another study (Tarkalson et al. 2008) conducted in Nebraska monitored the decomposition of Bt and non Bt residues from two hybrid pairs for 23 months. They also concluded that there was no difference in decomposition rates due to the Bt genes and they should cause no difference in carbon sequestration in the soil where Bt hybrids are used. A third study (Kravechenko et al., 2009) conducted at Michigan State evaluated whether cropping with Bt corn for seven years led to an increase in soil carbon. They found no evidence that use of Bt corn resulted in higher soil carbon levels.

Although these are not the only studies on this topic, it seems like the data are mostly indicating that Bt genes are not the reason for the perceived slower breakdown of stover and will not likely lead to higher soil carbon levels compared to conventional hybrids.

Selling Considerations; Shell versus Silage, Don’t forget the nutrients! — Jonathan Rotz, Agronomy Franklin County

corn ear

As corn dries down many look to prices and markets to see what options they have. In many parts of the state we typically have the option of either selling silage or grain depending on what seems to have the most favorable economics. I am not an expert in the markets so I’m not going to tell you that this is black and white, however I do have a few considerations you should make prior to selling your crop.

The main difference on the agronomic side of silage versus grain is the nutrients removed from the field when we take the whole plant versus just the grain. For this example I’m going to look at only phosphorus (P) and potassium (K). Nitrogen can also play a role but the system is very complex so it is not clear exactly how much we will keep around until next year’s growing season either with or without cover crops (this is why we test prior to side dressing N).

If we look at removal of P and K from silage we can estimate (using Penn State’s Agronomy Guide) that we will remove approx. 5.0lbs/Ton of P and 11.0lbs/Ton of K. As a rough estimate we typically consider the conversion from bushels of corn to tons of silage as 6.5–7bu/ton of silage. If we use this conversion for our removal rates for grain end up at 2.8lbs of P and 2.1 lbs of K removed (7∗book values for grain removal). This means that roughly twice the amount of P is removed and over 5 times the amount of K is removed from silage harvest when compared to grain.

So let’s do a quick example to clarify. Imagine your initial estimates show a 150 bu/ac grain yield or 21.5 Ton/ac silage yield in a specific field. We are trying to decide if we should sell it to the neighbor or keep it for grain. December futures are showing a price of $3.09/bu or $464/ac for this yield. The difference between grain and silage in nutrients removed at this yield will be 47.5 lbs of P and 191.5 lbs of K. With today’s price of $0.25/lb. P and $0.50/lb. K this is a difference of $107.63/ac. just to buy back the nutrients you lost by selling silage. If we add that into our grain price ($464) we need $572/ac. or about $27/ton (on 21.5 Ton/ac) to break even with our grain price of $3.09. Obviously neither of these take into account the cost of harvest so keep in mind who is paying for that when pricing your corn. Lastly, consider the extra cost you may have when selling grain such as hauling, drying and shrink charges. All of these can take away from the $3.09/bu. you are accounting for.

One last note, this may be used in a positive fashion. In some fields this could be a way to remove excess nutrients from long term manure applications, however on fields where only commercial fertilizer is utilized make certain you take this cost into consideration.

Teff; injury, disease or cold weather? — Mena Hautau, Agronomy Berks County

Teff, a crop grown locally in livestock systems for additional forage, is adapted to warm and arid agriculture in Africa. Reports this past week describe the top of the crop canopy as deadened and resembling pest injury. However, this plant cannot tolerate very cold temperatures. Last Monday night, temperatures were down into the low 40’s in the south and upper 30’s degrees in the State College area. As the cool night temperatures advance, it might be best to consider when the final harvest is appropriate for your area.

Upcoming Events

Jefferson County Cover Crop Meeting October 9, 2009
http://www.jeffersonconservation.com/linked/brochure.pdf

Contributors: Extension Educators: Joel Hunter (Crawford), Susan Alexander (Jefferson), Paul Craig (Dauphin), Del Voight (Lebanon), John Rowehl (York), Jeff Graybill (Lancaster), Mena Hautau (Berks) State Specialists: Greg Roth, Marvin Hall, Bill Curran, Dwight Lingenfelter, Sjoerd Duiker, John Tooker

Editor: Jonathan Rotz, Penn State Extension Educator, Franklin County

Upcoming Events

Real time pest and heat unit activity: http://agsci.psu.edu/news/spotlight/pa-pipe

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

If you have any questions or would like to suggest a topic, please contact your local Extension Educator.

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