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Corn Disease Update

corn disease meeting

Wheat Updates-May 2016

2016-05-20 16.01.45

May 27: Wheat is in the milk to soft dough stages of filling with later heads still pollinating in Clay/Nuckolls county fields.  Stripe rust greatly increased in severity, particularly on susceptible varieties. This photo is showing progression on Overland.  I haven’t seen stripe rust yet in fields planted to Wolf.  Barley yellow dwarf is appearing in small amounts in more fields, but is limited to field corners/borders thus far.

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May 23: (Photo: barley yellow dwarf in wheat-characterized by yellow-purple flag leaves.  It is vectored by aphids). Wheat is in the late flowering to beginning milk stage in many Clay/Nuckolls county fields.  Stripe rust increased in severity this past week in more susceptible varieties and barley yellow dwarf is also appearing more often in patchy areas of fields.

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May 15: Rain is falling this morning in parts of our area and wheat is in a variety of heading and flowering stages.  While the risk management tool at:  http://www.wheatscab.psu.edu/ still says “low risk” I’ve been concerned it had the potential to be higher with our growth stage and weather conditions.  Last week I received numerous wheat fungicide questions.  Caramba and Prosaro are the two products you can apply legally once your wheat is flowering.  Twinline is off-label once flowering begins.  Yes, it has metconazole in it (also active ingredient in Caramba) in addition to a strobilurin, but it only legally can be applied to Feekes 10.5 which is full heading and is off-label once flowering occurs.  Caramba and Prosaro will help prevent scab in addition to kill the rust already occurring in your plants.  Unfortunately, I was also starting to see barley yellow dwarf appearing in Nuckolls County fields.  This virus is vectored by a number of aphid species.  We’d been seeing aphids and stripe rust for a month at this point but both remained below threshold levels/low incidence.  Barley yellow dwarf can be identified by the flag leaf turning a bright yellow-purple color.  With 80% of wheat yield coming from the flag leaf and there being nothing you can do about barley yellow dwarf, this also needs to be part of your decision making process if you were planning on applying a fungicide for preventing scab/controlling stripe rust.

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May 9: We’ve been seeing stripe rust in wheat for over a month now, but the amount of rust has remained low.  Some have chosen to spray wheat at this point; however I’m also concerned about the potential for Fusarium Head Blight (scab) in wheat.  Fusarium head blight is caused primarily by Fusarium graminearum, the same fungus causing Fusarium stalk, root, and ear rot in corn.  The fungus survives the winter in corn and other small grain residue and then releases spores in the spring.  However, wheat planted into soybean ground can still be affected by scab because the fungal spores can be wind-blown in addition to being water-splashed to wheat that is in the flowering stage.

According to research, wheat is susceptible from flowering through soft dough development stage.    “Typical” fungicides used for control of fungal leaf diseases are off-label thus illegal to apply once the wheat has flowered and they do not have activity on the Fusarium fungus causing scab of wheat.  Management for scab includes the use of the preventive fungicides Caramba or Prosaro.  Both are labeled for headed and flowering wheat.  There’s a 30 day pre-harvest restriction for both.  Rainfast varies from ¼ hour to 2 hours or when dry depending on environmental conditions.  Both fungicides can help prevent scab and control rust on the plant.

Research from the US Wheat and Barley Scab Initiative (which is a combined effort of several Universities in the U.S. and Canada) has found that the best prevention using these products occurs when wheat is headed and 30% of the plants are in the beginning flower stage.  Application within five days of these criteria still showed positive results.  This research also showed that application before or after this time period greatly reduced effectiveness of preventing scab.  Understandably, the economics of fungicide application are difficult in wheat, yet, if you are aiming to make one application, this could be your best option for both scab prevention and controlling rust in your plants.  The risk map for scab can be found at:  http://www.wheatscab.psu.edu/.  With wheat at heading to beginning flower and rain/humidity this risk in reality could be higher for us.

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May 1: Wheat progressed quickly in one week!  Wheat in Clay and Nuckolls counties have flag leaves emerged even though wheat is really short.  The color is getting better thanks to moisture, root establishment, and nitrogen uptake.  I also didn’t see an increase in rust incidence this past week and aphid numbers were holding steady.  For those asking about fungicides, I’m still hoping we can hold off a little longer with current wheat economics, especially since in those counties rust wasn’t increasing due to the colder temps.  With warmer temperatures this coming week, please be checking your wheat.  If possible, one option that could be more economical in non-irrigated situations would be to consider treating your wheat once during flowering with either Caramba or Prosaro (as these products both prevent scab at the proper application timing and also kill fungal diseases including rust already present on the leaves).  We’ll have to see what happens with rust development and with how long it takes for heads to emerge.  There’s also been consistency with some varieties rated high for rust resistance where I have yet to find rust in them-so that’s a good thing!

Sudden Death Syndrome and Corn Residue

SDS

Symptoms of Sudden Death Syndrome (SDS) on leaves show green veins with discoloration between the veins (left photo). Signs of the blue/gray/white Fusarium fungus causing SDS on a rotted soybean root (right photo).

Grazing corn residue provides many benefits to both livestock and grain farmers, yet many corn stalks in our area are not grazed for various reasons.  With as much hail as we’ve had this fall, grazing is also an option to remove ears and kernels that were lost, preventing volunteer corn next season.  Normally there is less than a bushel of ear drop per acre, but we most likely have more than that in some of our fields this year.  Two kernels per square foot or one ¾ pound ear in 1/100 of an acre is the equivalent of 1 bu/ac yield loss.  In 30” rows, 1/100 of an acre is 174’ long if you count in one row or 87’ if you count in two rows.

Soil

Soil samples (0-8″) for soybean cyst nematode (SCN) can be taken at any time but always good to sample areas that were affected with SDS to determine if SCN is also present.

What may also be of interest to you is a recent finding between corn grain loss pre-and during harvest and sudden death syndrome (SDS) of soybean.  Many asked me this this year, “Why did I see SDS this year when we’ve never had it in this field before?”  It’s a great question and I often responded by saying we need to sample the areas affected with SDS for soybean cyst nematode (SCN) as the two diseases are synergistic.  Sampling for SCN still remains free through your Nebraska Soybean Board Checkoff dollars and you can stop by the Extension Office for free sampling bags.  Crop consultants should contact the UNL Plant and Pest Diagnostic lab directly at (402) 472-2559 if you are requesting 10 or more sampling bags.

Anything that moves soil can transport the fungal soil-borne pathogens causing these diseases.  But recent research from Iowa State University also suggests that the fungal pathogen causing SDS (Fusarium virguliforme) survives on grain lost during the harvest process in fields and that SDS management in soybean actually needs to begin at corn harvest.

Studies were conducted for two years in greenhouse and in field plots with nine treatments to determine the survivability of Fusarium virguliforme (Fv) on corn and soybean residue.  The treatments were:  1-Corn kernels + Fv; 2-Corn roots + Fv; 3-Corn stem/leaves/husk + Fv; 4-No residue + Fv; 5-Soybean seeds + Fv; 6-Soybean stem/leaves/pods + Fv; 7-Soybean roots +Fv; 8-Corn stalk on soil surface + Fv; 9-Corn kernels and stalk on soil surface + Fv.  The researchers consistently found in both the greenhouse and field experiments that Treatment 1 of corn kernels at average harvest loss resulted in the most SDS.  Treatment 2 consistently resulted in the second most SDS.

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From Iowa State University, September 2010, “Good Harvest in Corn Should Help Manage SDS“.

This helps to explain why some farmers are finding SDS in fields that have been continuous corn for a period of years, are finding SDS in corn and soybean rotation when little or no SDS was previously observed, and why SDS has increased in seed corn fields that may have higher harvest losses.  They did not experiment with tillage systems and their recommendation is to reduce harvest losses to reduce the risk of SDS.

Grazing residues can reduce your risk from these harvest losses and for those losses which were incurred with the hail/wind storms we’ve experienced since Labor Day.  When grazing corn residue, cattle are selective.  They will eat the grain first followed by the husk and leaf followed by the cob and stalk.

It’s also important to be aware of grazing restrictions from herbicides applied to row crops; you can read more about that in this post.

Corn Disease July 2015

Radio advertisements, email blasts, and other media are warning of corn diseases and the need for fungicides.  Two months of humid, wet weather has allowed for disease development.  It’s important to know what diseases truly are in your field before spraying a fungicide, particularly with today’s economics.  Here’s what we’re seeing in fields right now in the Clay, Nuckolls, Thayer, Adams county area.  Based on the diseases we’re seeing, we would recommend you scout your fields to know whether you have mostly bacterial or fungal diseases present.  Consider disease pressure, where on the plant the disease is occurring, growth stage, and economics.  We have had southern rust show up in 10 of the last 11 years I’ve been serving in this area.  If you spray a fungicide at tassel, you may not have enough residual to ward off southern rust when it appears later, potentially resulting in the need for a second application.  In our area thus far, I’m not seeing enough disease pressure in many fields to warrant a fungicide at tassel; consider delaying an application till later for economic and resistance-management reasons.  Ultimately this decision needs to be done on a field by field basis.  Please also see this UNL CropWatch article regarding fungicide application and corn growth stage.  Although I don’t have a photo of it, I’ve also seen common rust in the mid and lower portions of corn canopies thus far.

Anthracnose has been observed in fields for a good month now.  It is mostly seen on lower leaves of plants, particularly in fields where we've had high amounts of rainfall, standing water, and/or hail.  I haven't seen it moving up the plant very far yet.  There are fungicides labeled for this, but we rarely recommend fungicide treatment for anthracnose.

Anthracnose has been observed in fields for a good month now. It is mostly seen on lower leaves of plants, particularly in fields where we’ve had high amounts of rainfall, standing water, and/or hail. Lesions are tan in the center and have a wavy yellow colored margin.  I haven’t seen it moving up the plant very far yet. There are fungicides labeled for this, but we don’t often recommend fungicide treatment for anthracnose.

We saw this disease in the Saronville/Sutton area last year.  This year, we are seeing it throughout Nuckolls, Thayer, Clay, and Adams counties...and most likely others too.  Some hybrids (and have seen this across companies) are highly affected by this bacterial disease.  We have informally called it

We saw this disease in the Saronville/Sutton area last year. This year, we are seeing it throughout Nuckolls, Thayer, Clay, and Adams counties…and most likely others too. Some hybrids (and have seen this across companies) are highly affected by this bacterial disease. Neither last year, nor this year, has the pathogen causing this disease been confirmed. Plants will have vein-limited lesions in streaks on the leaves. It is often confused with gray leaf spot early on.  Take a hand-lens and looking closely, you will see wavy margins on the lesions which doesn’t usually occur with gray leaf spot.  Over time, these lesions become elongated and can coalesce with other lesions. Also looking closely with a handlens or microscope, one finds the leaf tissue eventually becomes transparent. While other diseases can look similar to it, under the microscope, no fungal spores are found other than secondary ones. Putting an infected leaf in water reveals cytoplasmic streaming in which the bacteria is escaping the leaf tissue. (The pathogen causing Goss’ wilt also does this, but this disease is not the same as Goss’ wilt). Fungicides will not cure bacterial diseases and the products advertised for targeting bacterial diseases haven’t been researched for this disease.  This is the primary disease we are seeing in our area right now-and it looks nasty in some fields!  Unfortunately there’s nothing we can do about it.  If you are considering testing one of the products for bacterial diseases, please let me know as I’d appreciate testing it with you via on-farm research.

Goss' wilt (bacterial disease) has been observed in fields as well.  I typically notice it along field edges, pivot tracks, pivot/well roads or hail-damaged fields as plant wounds in general allow an entry for bacterial pathogens.  However, research has shown that the bacterial pathogen causing Goss' wilt can enter through the leaf stomates as well.  Leaf miner damage can be observed at the top of this photo, and often, but not always, I notice this occurring together in fields.  There is nothing we can do for Goss's wilt if you have this disease in your fields right now.  There are products targeting bacterial diseases on the market.  If you're interested in trying these, please consider an on-farm research experiment to prove the efficacy to yourself and help us obtain data.

Goss’ wilt (bacterial disease) has been observed in fields as well. I typically notice it along field edges, pivot tracks, pivot/well roads or hail-damaged fields as plant wounds in general allow an entry for bacterial pathogens. However, research has shown that the bacterial pathogen causing Goss’ wilt can enter through the leaf stomates as well. Leaf miner damage can be observed at the top of this photo, and often, but not always, I notice this occurring together in fields. There is nothing we can do for Goss’s wilt if you have this disease in your fields right now. There are products targeting bacterial diseases on the market. If you’re interested in trying these, please consider an on-farm research experiment to prove the efficacy to yourself and help us obtain data.

Physoderma brown spot typically doesn't occur in our area until tasseling (which is where we are at now in some fields).  However, I was seeing this as early as two weeks ago on some hybrids.  The pathogen causing this disease is a fungal-like pathogen that moves with water.  You will notice a purple/brown color on midribs of leaves, leaf sheaths, stalks, and tiny yellow/brown/purple spots on leaves.  This disease isn't considered yield-limiting or of significance to us in Nebraska.  Some confuse this disease with southern rust, but there are no pustules produced with Physoderma brown spot.

Physoderma brown spot typically doesn’t occur in our area until tasseling (which is where we are at now in some fields). However, I was seeing this as early as two weeks ago on some hybrids. The pathogen causing this disease is a fungal-like pathogen that moves with water. You will notice a purple/brown color on midribs of leaves, leaf sheaths, stalks, and tiny yellow/brown/purple spots on leaves. This disease isn’t considered yield-limiting or of significance to us in Nebraska. Some confuse this disease with southern rust, but there are no pustules produced with Physoderma brown spot.

The larger, rectangular lesion is typical of gray leaf spot found in some lower leaf canopies right now.  It is easy to confuse with anthracnose as both diseases appear a little different on various hybrids.  Gray leaf spot will be vein-limited while anthracnose is more blotchy in appearance.

The larger, rectangular lesion is typical of gray leaf spot found in some lower leaf canopies right now. It is easy to confuse with anthracnose as both diseases appear a little different on various hybrids.  Gray leaf spot will be vein-limited while anthracnose is more blotchy in appearance.  Comparing gray leaf spot with the unknown bacterial disease, the lesion edge will be straight for gray leaf spot and wavy for the bacterial disease.

Northern corn leaf blight is a disease we're hearing a lot about but I have yet to see it in our area.  Most have been mistakingly calling the unknown bacterial disease shown above northern corn leaf blight, but there's truly a difference as you see these photos.  Compared to gray leaf spot, northern corn leaf blight will be more cigar-shaped instead of forming a rectangle.  As this photo taken from the Mead, NE area shows, lesions are often forming in close proximity to each other on the leaves in Nebraska right now.  This disease is one to watch as it has been expanding on certain hybrids in some fields, particularly in eastern, Nebraska.  However, I still haven't seen it in our area and haven't received any confirmations of it being found in our area.

Northern corn leaf blight is a disease we’re hearing a lot about but I have yet to see it in our area. Most have been mistakingly calling the unknown bacterial disease shown above and even Goss’ wilt, northern corn leaf blight, but there’s truly a difference as you see these photos. Compared to gray leaf spot, northern corn leaf blight will be more cigar-shaped instead of forming a rectangle. As this photo taken from the Mead, NE area shows, lesions are often forming in close proximity to each other on the leaves in Nebraska right now. This disease is one to watch as it has been expanding on certain hybrids in some fields, particularly in eastern, Nebraska. However, I still haven’t seen it in our area and haven’t received any confirmations of it being found in our area at this time. (Photo courtesy of Aaron Nelson, Nelson Precision Agronomics).

Options for Stripe Rust in Wheat

Stripe rust has exploded in wheat in the past 3-7 days in South-Central Nebraska due to theIMAG5065-1 rain and cooler weather.  Nebraska Extension is receiving numerous questions regarding options to consider.  Rain has also increased our risk for Fusarium Head Blight (head scab).

Wheat is at such a variety of stages in the area; many fields are just heading and/or flowering right now while others are in soft-dough.

Stripe rust on the flag leaf, as shown in this photo, will continue to progress with cool, wet conditions, reducing yield.  If your fields are currently yellow with stripe rust, here are a few options:

1-Do nothing and see what happens regarding what yield is obtained.  If your wheat is past flowering, fungicide application is not an option as all fungicides would be off-label.

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Susceptible wheat varieties to stripe rust that have not been treated with a fungicide to date have a yellow cast to them in South-Central Nebraska.

2-If your wheat is headed and beginning to flower, you could still consider a fungicide application of Caramba or Prosaro.  Both are labeled for headed and flowering wheat.  There’s a 30 day pre-harvest restriction for both.  Rainfast varies from ¼ hour to 2 hours or when dry depending on environmental conditions.  Both fungicides can help prevent scab and control rust on the plant. However, research has shown that best scab prevention occurs when wheat is headed and 30% of the plants are in the beginning flower stage.  Application within 5 days of these criteria still showed positive results.  Research showed that application before or after this time period greatly reduced effectiveness of preventing scab.  Understandably, the economics of a fungicide application are tight with current wheat prices.  The following article includes economic considerations.

3-Consider haying it.  Dr. Bruce Anderson, Nebraska Extension Forage Specialist shared the following:

“Baling hay or chopping silage are two potential options.  Rust pustules are not toxic to cattle although sometimes the spores can irritate respiration.  It can be difficult to make good silage, though.  Rusty leaves dry out rapidly so it can be hard to get the best moisture content for silage packing and fermentation.

Usually it is best to harvest rusty wheat hay just before heading to retain reasonable forage quality.  As plants mature further, quality can decline rapidly.  Digestibility of rust affected cells is much lower than that of normal cells.  Fortunately, protein doesn’t seem to be affected greatly.  Properly made hay should not deteriorate in the bale due to the rust any more than normal.

Be sure to have the forage tested before feeding.  It is likely that nutrient concentration will differ from typical wheat hay so testing will help in developing rations.  Also consider the impact of removing the wheat residue.  Adequate residue helps retain soil moisture, boosting yield of your next crop.

There never are good choices when problems like this develop.  All you can do is weigh your options and choose what is best for you.”

Also, please continue to check out UNL CropWatch for wheat disease and all our crop updates.

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