Greetings from out in the middle of my soybean fields.When I graduated from high school back in 19 . . . (well, never mind when I graduated from high school!), I was voted most likely to be outstanding in my field.That is exactly what I seem to be doing a lot of these days, watching the crops grow.I guess I better get in for dinner pretty soon though!
Iron Deficiency Chlorosis.
We are once again in the middle of the period of time when iron deficiency chlorosis (IDC) is visible in soybean fields.Fields, or small patches of fields, will appear various shades of yellow depending upon the severity of iron deficiency.Symptoms often occur from about growth stage V2 – V6, and will be more visible on the youngest leaves.Depending upon environmental condi-tions, chlorosis will be visible for about 1 – 3 weeks.Except under the most extreme cases, soybean will eventually “green up” again, although measureable yield losses may still occur.
Usually there is ample iron present in the soil.Furthermore soybean does not require much iron for optimum growth.However, soybean does not absorb iron well from the soil.The traditional underlying cause of IDC in soybean is the presence of high levels of carbonates (lime) found in soils, as a result of calcareous hard-shelled organisms that lived, died, and accumulated in ponds and wetlands following the retreat of the last glacier covering North America.These calcareous soils bind iron in a chemical form which becomes even more difficult for the soybean to absorb.
However, other factors seem to also have a pronounced (or perhaps confoun-ding) effect on the severity of IDC, such as high pH, above-average soil moisture, poor soil drainage, salt accumulation in the soil, high nitrate levels, and presence of soybean cyst nematode (SCN).High pH may be due to high levels of carbo-nates in the soil.Wet or poorly drained soil allows accumulation of water-soluble salts at the soil surface.High nitrate levels may be causing iron to be tied up in a non-available form.SCN may simply like living in the high pH soil environment, and therefore are often found in the same fields as IDC.
What can be done to overcome IDC?The best option seems to be the use of IDC resistant or tolerant varieties.Relatively few high-yielding IDC resistant varieties are available in the seed market today, but there are some.And breeding work continues to make progress.Galena Genetics has several newly developed non-GMO experimen-tal lines with excellent IDC resistance and yield.One of these, a 2.0 maturity clear-hilum soybean, may be available for commercial release for the 2011 planting season.Several others may be available for 2012.
Another option that some growers are considering is the use of a soil-applied, or seed-applied, or foliar-applied iron fertilizer treatment.At best, the research conducted on iron fertilizers, to date, shows inconsistent results.Some pre-liminary research from Kansas State University suggests a yield increase on IDC soils from the use of a chelated-iron seed treatment.However results from other research have been less promising.Soil-applied and foliar-applied iron treatments have not shown significant promise.
Some thoughts on soybean foliar fungicides.
Considerable interest has surfaced in the last few years in the use of foliar fun-gicides to control or reduce disease pressure in corn and especially soybean.In soybean, interest in foliar fungicides has risen with the incidence of soybean rust (Phakopsora pachyrhizi) in the southern USA since 2004.Other soybean fungal diseases of potentially significant economic importance are frogeye leaf spot (Cercopsora sojina), Cercospora blight (Cercospora kikuchii), and Septoria brown spot (Septoria glycines).These fungal diseases generally may begin to appear after about growth stage R2 in soybean.The $64,000 question is whether fungicide treatment will help control these diseases, and whether this treatment is economically beneficial.
Research across the Midwest over the last few years shows that about 60 – 70% of the fungicide trials conducted have shown at least a modest yield gain from a fungicide application made somewhere between stage R1 – R3.However, when the cost of fungicide, ground application, and yield loss from wheel damage were taken into account, less than half of these trials demon-strated a positive return on investment from the fungicide application.Put another way, over half these trials lost money by applying foliar fungicide.
Research efforts continue in order to determine factors, such as application rate, pressure, and timing, geographic region, disease severity, soil and environmental conditions, and fertility, which may play a role in the effectiveness of fungicide application.
For soybean rust, fungicide application is the only viable means of control when the disease is present.Currently there are no commercially available varieties with rust resistance.However, since soybean rust cannot survive the winter in cold Midwest soils, new spores must blow in from Mexico and South America every spring.Thus far in 2010, the northward spread of rust lags far behind the spread of rust at the same date of the last couple years.Therefore soybean rust appears to not be a serious threat in 2010.
Frogeye leaf spot, Cercospora blight, and Septoria brown spot can all be found throughout the Midwest to varying degrees.However the incidence and severity have usually been relatively low.Conditions which tend to favor development of these diseases are warm, humid, and moist conditions.Since these organisms can over-winter on crop residue in cold soils, crop rotation and deep tillage can help reduce inoculum load and disease spread.
Bear in mind that some fungal diseases are NOT effectively treated or controlled with foliar fungicide.White mold (Sclerotinia sclerotiorum) and powdery mildew (Microsphaera diffusa), in particular, are not easily controlled by foliar fungicide due to timing of disease development.In addition, NO bacterial diseases, such as bacterial blight, or viral diseases are controlled by fungicide.So before making application decisions, KNOW YOUR DISEASE.
Two of the more common foliar fungicides currently used on soybean are Headline and Quadris.Both are in the strobilurin family of fungicides.Both fungicides should be applied before significant disease symptoms have developed, around stage R2, in order to control spread of inoculum.It has been suggested that these fungicides may cause a yield increase even when disease pressure is low, simply by improving general plant health of the soybean.However this may only be anecdotal, with little research to substantiate it.
My advice regarding foliar fungicide treatment would be to scout your fields and determine whether these diseases are present.If a particular farm or field has a history of frogeye, Cercospora blight, brown spot, or soybean rust, and if the fields have previously responded favorably to fungicide application, then apply fungicide.Leave a couple untreated check strips in the middle of your fields with which to compare the fungicide treatment.
Mixing micronutrients with glyphosate herbicide.
I have had a few questions lately about foliar application of micronutrients to either corn or soybean for mid-season correction of micronutrient deficiencies and imbalances of nutrients such as zinc, manganese, iron, and boron.Although I have never been a huge fan of foliar fertilization (if leaves were suppose to take up nutrients, they would have roots on them), some growers around the country are routinely using a foliar micronutrient application system.I am not going on record here about whether you should or should not foliar fertilize your crops.Some research indicates positive results.Some does not.However caution must be taken to avoid excessive fertilizer rates which can burn the leaves and actually cause yield reduction.
My main point here is with regard to tank mixing micronutrients with glypho-sate herbicide.Since micronutrient deficiencies can be treated around the same time that glyphosate herbicide is applied, it would seem a good idea to tank-mix and apply them together in order to save time and expense.Unfortunately, tank mixing micro-nutrients with glyphosate can render the gyphosate inactive, thereby reducing weed control of the glyphosate.The glyphosate binds to the micronutrient, thereby inactivating the glyphosate and at the same time converting the micro-nutrient to a less useable form.Univer-sity research shows that even using AMS or other adjuvants will not completely correct this negative interaction between gyphosate and micronutrients.In fact, “very hard water”, i.e. – water contain-ing trace amounts of various minerals like iron, calcium, and manganese, from country wells can also partially inacti-vate glyphosate.My recommendation is that if you must apply foliar micro-nutrients, do NOT tank mix them with glyphosate herbicide.
There are some new products from several companies coming onto the market now that claim to overcome the negative interaction between glyphosate and micronutrient solutions.However I have no independent verification of the claims made by these products, and thus can not endorse them.
Rapid elongation and “green snap” in corn.
Once again, it is the time of year when corn is undergoing rapid stem elongation (from approximately V6 to V16 growth stage).Corn is especially vulnerable to green snap or brittle snap near the end of rapid stalk elongation, since the nodes on the corn stalk have not yet “hardened” following rapid elongation.As luck and “mother nature” would have it, June through July is the time of year most likely to encounter severe thunderstorms and wind storms, which can provide the lateral force needed to snap the stalk at or below the node where the ear would normally develop.
Not all corn hybrids or fields of the same hybrid are vulnerable at the same time due to differences in maturity, planting date, fertility, and growing conditions.Ironically, fields with the best fertility and growing conditions are often the ones most vulnerable to green snap, since they have elongated most rapidly.
All corn hybrids are at least somewhat vulnerable to green snap, but genetic differences do exist.The best solution to at least partially control green snap is selection of resistant hybrids.If green snap has already occurred in a field, nothing can be done to alleviate the damage.Sometimes if green snap occurs at the dominant ear node, a secondary ear at the next lower node may partially compensate by developing an ear.However the secondary ear will produce significantly less grain because of the structural damage to the corn plant.
Independence Day.
It seems we are hearing a lot of bad new lately about oil in the Gulf of Mexico, an economy that is slow to recover, and unemployment rates that are declining at a rate that would make snails giggle.However, people from all over the world still want to come to the USA to live.I wonder why that is?Maybe it is because we have a nation in which we have the freedom to travel, to assemble, to speak our minds, and to make our own personal decisions about what we want to do and how we want to live.Please take a moment this Independence Day to reflect on the commitment and sacrifice made by that handful of patriots 234 years ago.Read a copy of the Declaration of Independence (you can easily find it on the web).These patriots were making a life or death commitment to an idealistic goal of self-government, which change the entire course of world history.
Enjoy the parades, the picnics, the baseball games, the fireworks, and the time with friends and family this holiday.But please remember those patriots, gathered in Philadelphia in the summer of 1776, did so because they wanted you to enjoy those activities.
Grant Metz, PhD
Research Director
Galena Genetics, LLC
501 Main Street
PO Box 548
Ormsby, MN 56162
(grant_metz@rabbeusa.com)
