C.O.R.N. Newsletter 2013-19

Dates Covered: 
June 25, 2013 - July 2, 2013
Editor: 
Amanda Douridas
Double Crop Soybean Considerations

Double Crop Soybean Considerations

With wheat harvest beginning south of I-70, here are some double crop soybean considerations:

1.)    Soil moisture and rainfall-  Soil moisture and subsequent rainfall are essential to double crop soybean after wheat.  When seeds are planted into dry soil, it may take weeks for soybeans to germinate/emerge and only occurs after rainfall (which we saw during the drought of 2012).  If possible, adjust planter to place seed in moist soil, but do not plant deeper than 1.5 inches as soil crusting may become problematic.  

2.) Relative maturity-  As planting is delayed, there is concern about whether late maturing varieties will mature before frost.  When planting late, we recommend planting the latest-maturing variety that will reach physiological maturity before the first killing frost.  Soybean flowering is triggered by day length.  As days get shorter (and nights get longer) after June 21, soybeans are triggered to flower which generally occurs around the first week of July.  Later maturing soybeans will put on more vegetative growth before flowering.  The table (adapted from the Ohio Agronomy guide) gives relative maturity guidelines for late planted soybeans.

3.)  Row spacing and seeding rate-  Plant double crop soybean in 7.5-inch row spacing.  Canopy closure is necessary to maximize yield of late planted soybeans.  If planting during the second half of June, 225,000 to 250,000 seeds per acre is recommended.  In early July, 250,000 to 275,000 seeds per acre is recommended.

Controlling marestail in double-crop soybeans

This is essentially a repeat of an article that ran last year at this time.  Little has changed since then with the exception that Liberty has been even harder to procure this year, so using a glyphosate+Sharpen burndown may be more realistic.

A weed free start is the most critical aspect of a weed management program for double-crop soybeans.  This can be challenging to achieve where glyphosate-resistant marestail are present after wheat harvest.  Problems with marestail include the following:  1) most populations are now glyphosate-resistant and many of these are also ALS-resistant; 2) it’s usually not possible to use 2,4-D ester and wait 7 days until double-crop soybean planting; and 3) marestail that were tall enough to be cut off by harvesting equipment will be even more difficult to control.  Our research indicates that there are no herbicide treatments that consistently control glyphosate-resistant marestail populations that have regrown following mechanical disturbance or prior herbicide treatment.  Certainly one of the best options is to plant LibertyLink soybeans, which allows for a POST application of Liberty to help control plants that survive a preplant burndown.  The following are the most effective burndown options for control of marestail prior to double-crop soybean emergence:

Liberty (32 to 36 oz) + Sharpen (1 oz) + MSO + AMS (can also add metribuzin)

Liberty (32 to 36 oz) + metribuzin (4 to 8 oz of 75DF) + AMS

Glyphosate (1.5 lb ae/A) + Sharpen (1 oz) + MSO + AMS

We suggest using a spray volume of 20 gpa for any of these treatments, and avoiding nozzles that produce large droplets.  Results with a combination of glyphosate and 2,4-D may be more variable then the treatments listed. 

With regard to the control of weeds that can emerge after double-crop soybean planting, and the entire weed control system, the following approaches can be considered.

1.  Plant any type of soybean, and include a residual herbicide with the burndown treatment so that POST herbicides are not needed.  A good strategy in Roundup Ready or nonGMO soybeans even where POST treatment is needed, since POST marestail control might be impossible in these systems.  Residual herbicides used at this time of the year should be restricted to those that have little or no carryover risk – such as metribuzin, Valor, or low rates of chlorimuron or cloransulam products.

2.  Plant a LibertyLink soybean, and apply Liberty POST as needed.  Probably the best option for control of later-emerging marestail or plants that regrow after the burndown, assuming that there is any Liberty available.

3.  Plant a Roundup Ready soybean and apply glyphosate POST.  Should work for most weeds, but not a good choice if the POST application needs to control marestail.

4.  Plant a nonGMO soybean and apply conventional POST herbicides (Flexstar, Fusion, Select, etc) as needed.  This system has the most potential for soybean injury, but seed may be cheaper than the other systems.  Not a good choice if the POST application needs to control marestail.

 

First Western Bean Cutworm of the season caught

First Western Bean Cutworm of the season caught

In Northwest Ohio last week, we caught our first western bean cutworm (WBC) adult for the 2013 season.  The timing of the catch is on par with what we have seen over the past few years, usually the 2nd or 3rd week of June.  All of our traps have now been deployed, and, as the summer progresses, we expect to see additional catches coming in.  It is still too early to predict what we will see with WBC this year in Ohio, but we need to be on the lookout with the fair amount of late planted corn we have.  Check back next week to see our updated map.

Early Fungicide Application in Corn: Is it Worth It?

Ohio corn producers are still interested in early foliar fungicide applications in field corn and have been asking a lot of questions about the effects of applications made between V4 and V10 on grain yield. Over the last three years we have tested several foliar fungicide treatments under low disease pressure in field trials at South Charleston and Wooster and here is what we have found in terms of yield response compared to the untreated check.

Averaged across all fungicides (Headline, Headline AMP, Stratego, Stratego YLD, Domark, Prosaro, Quilt, Quilt Xcel, etc) locations, and years, the yield difference between fungicide treatments made at VT (tassel)/R1 (silk emergence) and the untreated checks ranged from -25 bushels/acre to 40 bu/acres, with an overall average yield increase of 2 bushels/acre. Similar trends were observed for applications made between V4 and V10, with yield differences ranging from -38 bushels/acre to 21 bushels/acre, at an overall average 0.80 bushels/acre. If we assume that it cost between $24 and $36/acre to put on a fungicide treatment (product plus application) and grain prices range from $7 to $9/bushel, you would need at least a 3 bushel increase in yield for the fungicide to pay for itself. Over the last three years, our data showed that when fungicides are applied in the absence of foliar diseases, the yield increase is greater than 3 bushels/acre 45% of the time. In other words, there is less than a 50% chance that the fungicide will pay for itself when applied in the absence of foliar diseases.

So what do we conclude? Both VT and early fungicide applications continue to show highly variable results in term of yield increase when applied in the absence of foliar diseases. With such high variability, there is great uncertainty as to whether and when the fungicide will pay for itself. Even at relatively high grain prices, there is less than a 50% chance that the yield increase will be high enough to cover the cost of the fungicide. We know that yield increases tend to be higher and more consistent when gray leaf spot, northern corn leaf blight or other foliar disease levels are high, however, further research is needed to better understand what drives such highly variable yield responses when disease levels are low or absent.       

Low Disease Levels and Cool Conditions May lead to Excellent Wheat Yields

We are quickly approaching the end of what will likely end up being a very good season for wheat production. So far only very low levels of diseases, pests and other problems have been reported, and post-pollination conditions have been excellent for grain development. Powdery mildew, and Septoria and Stagonospora leaf blotch all remained low and restricted to the leaves below the flag leaf in most fields. Recent reports coming in from across the state indicate that the levels of head scab are also low this season, with only a few fields reporting about 5 to 10% incidence (5-10 heads out of every 100 heads showing symptoms of scab). This is very consistent with the predictions made by the scab forecasting system and is likely due to the fact that in spite of relatively frequent rainfall this season, conditions remained cool throughout the critical flowering and early grain development growth stages in most areas. 

Wheat harvest is just getting started in southern Ohio and will likely continue across the state over the next three weeks. Contrary to the hot and dry conditions observed in 2012, which shorted the grain-fill period considerable, the 2013 wheat season has been relatively cool with good moisture during the weeks following anthesis. Typically grain-fill in Ohio lasts about 15 to 21 days, and poor growing conditions usually limit productivity to about three bushels per acre per day. However, when disease levels are low and conditions are cool during the month of June, the grain-fill period may be as long as 30 to 45 days and productivity could exceed three bushels per acre per day. Moreover, low scab incidence usually means low vomitoxin contamination of the grain. So, together, low disease levels, low grain contamination with vomitoxin, extended grain-fill, and high productivity may result in high yields and test weights and excellent grain quality in 2013.      

Hail damage to corn varies depending on growth stage

Hail damage to corn varies depending on growth stage

Some of the thunderstorms that rolled across Ohio recently were accompanied by hail that caused extensive damage to crops.  In corn, the impact of hail damage is largely dependent on the crop's stage of development.  Hail affects yield primarily by reducing stands and defoliating plants. Most of the hail damage results from defoliation. Generally, the corn plant is little affected by hail prior to the 6 to 7 leaf stage because the growing point is at or below the soil surface and in the leaf whorl. However, once the growing point is elevated above the soil surface due to internode elongation, the plant grows rapidly and becomes increasingly vulnerable to hail damage with the tassel stage/pollen shedding stage (VT) being the most critical period.

Severe hail damage prior to the 6 to 7-leaf stage can also result in “twisted” or “tied” leaf whorls as injured plants recover and new leaves try to unroll; however, most plants will grow out of this problem and tied whorls seldom cause major yield loss.

Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth. Shredded leaves and plants with broken midribs still have some capacity to contribute to plant growth. Plants not killed outright by hail usually show new growth within 3 to 5 days after injury occurs (i.e. if damage occurs prior to tasseling). For this reason, estimates of hail damage should be delayed several days to allow for this period of re-growth.

The hail insurance adjustor's growth staging system counts leaves beyond the last visible collar to the uppermost leaf that is 40-50% exposed whose tip points downward - usually this results in a leaf stage that is numerically 2 leaves greater than the "leaf collar method" (e.g. a V11 plant according to the leaf collar method would probably correspond to a 13-leaf plant according to the hail adjustor's method).

How do we estimate the potential yield loss from recent hail storms? Corn growth stages in Ohio vary considerably depending on location, planting date, etc. Within some corn fields, it’s not unusual to see corn differ by three or more growth stages because of differences in soil color and drainage. Most corn in Ohio has not progressed beyond the V10 stage (as of 6-24-2013). Based on estimates of the National Crop Insurance Association (see table below), at the 13-leaf  stage (or about V11) if 50% of the leaf tissue is destroyed by hail, a corn plant loses 10% of its grain yield potential; if 100% defoliation occurs, a corn plant loses 34% of its yield potential.

Percent yield loss in corn based on growth stage & defoliation

(Adapted from NCIA Corn Loss Instructions, rev. 1984)

 

Percent Leaf Defoliation

Growth Stage*

25%

50%

75%

100%

9-leaf (V7)**

1

4

7

13

11-leaf (V9)

1

7

12

22

13-leaf (V11)

2

10

19

34

15-leaf (V13)

3

15

30

51

*as determined using the hail adjustor’s leaf staging method; ** approximate V-stage within parentheses

For more detailed information on evaluating hail injury in corn, consult "Assessing Hail Damage to Corn" National Corn Handbook Chapter 1 (NCH-1)." Available on-line at http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-1.html.

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About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.