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JenREES 8-9-20

Fair: As fairs wrapped up in the area, in my opinion, it was a great way to cap off the summer for the youth. So much has been taken away from them and I really appreciate Ag Societies working hard with Extension staff to give the youth an opportunity to showcase their projects! There were several moments throughout fair where I thought “this is why we do this”…to watch youth and adults so excited to see the ribbons on projects, watching siblings and club members supporting each other, families helping other families, and friends catching up. Fair did look different this year. But it forced us to think about things differently with the blessing of some changes may be kept as a result! Thank you to all the Ag Society, 4-H Council members, Extension staff, newspaper staff, and volunteers who gave youth and adults alike the opportunity to showcase projects and safely gather at fairs! Thank you also to health departments for advising on directed health measures and providing PPE and nurses who helped with screenings!

Crop Updates: I didn’t get into the field much this past week but the primary questions I received were regarding tip back on corn, spidermites flaring, and if it was too late to spray fungicides in corn. The answer to the latter is no. If southern rust is showing up pretty good low-mid canopy of your field, it’s something to consider to help with stalk strength as that’s my concern. I’m hearing of some guys having to apply a second round of fungicide due to rust. Hard for me to see guys spending the money to do that thus prefer avoiding automatic tassel applications. While I’m not aware of research to prove it, I think coverage is another issue. Consider asking the aerial applicator to use 3 gallons/acre to increase coverage. I hear some are refusing to do more than 2 gallons/acre and I think that’s part of the problem. Some farmers are also chemigating fungicide and insecticide through the pivot in hopes of improving coverage.

Typically we’d say southern rust occurs on the top side of leaves unless severe, whereas common rust typically occurs on both sides of leaves. On leaves that were flipped over from the wind, I’m seeing southern rust spores (confirmed via microscope) on the undersides of leaves that are now technically facing upward, but not on the ‘normal’ top side of leaf (an interesting observation that a crop consultant asked me about and then I also saw this week to confirm it truly was southern).

Spidermites continue to flare 7-10 days later because most of the products used don’t kill eggs. Sometimes second applications are needed. Insecticides with activity against eggs and immature stages (not adults) include Zeal, Oberon, and Onager whereas the pyrethroid (Bifenthrin products like Brigade in corn and soybeans) and organophosphate products (like Lorsban used in soybean) can help with adults but not eggs. Product has to come in contact with the mites. Thus at least 3 gallons/acre are recommended with aerial applications. Entomologists share aerial applications early in the morning or late in the evening can be more effective to avoid hot rising air away from plants (be careful of inversions). With twospotted spider mite, perhaps all that can be accomplished is to slow the rate of population increase.

Tip back on corn occurs most often from some sort of stress. For this year having good pollination weather, some are surprised regarding how much tip back we’re seeing. It’s important to count kernels long as there may be more kernels than one realizes in spite of tip back occurring. You can tell approximate timing of stress events by the appearance of the kernels. If kernel formation isn’t evident, the stress occurred before or during pollination. If kernels are very small or appeared to have died, the stress was after pollination as the kernels were filling. Water stress is a major stress outside of temperature as to kernels not pollinating and/or aborting. Each ovule (and later, each kernel), competes for water and nutrients. Water and nutrients are necessary for pollen tube formation down silks to fertilize ovules. Water and nutrients are necessary to fill individual kernels with the tips being sacrificed for filling kernels at the base of the ear first.

CARES Act Tax Planning for Farmers: The CARES Act included the Payroll Protection Program (PPP) and Economic Injury Disaster Loans (EIDL), which many farmers utilized. However, several other provisions didn’t get as much attention. For tax planning this fall, check out this helpful info. from Tina Barrett: https://go.unl.edu/re6e.


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True topside of leaf that was flipped over with windstorm to be on underside. Can see indentations of lesions but not pustules.

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True bottomside of leaf that after being flipped over with windstorm was showing as the top side. Notice the pustules on this side of the leaf.

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Under the microscope, the spores were truly southern rust (oval-shaped). Common rust pustules are circular in shape.

JenREES 8-2-20

York and Seward County Fairs: Here’s wishing the best to all the youth competing in the York and Seward County Fairs this week!

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One group of youth competing at the York Co. 4-H Trap Shooting competition today.

Crop Update: It’s unfortunately not hard to find southern rust in fields anymore as I’m finding it in every field I walk into. Incidence is mostly confined to lower canopies with the highest I’ve seen so far on the ear leaf. What’s concerning to me is the amount of rust I’m seeing (ear leaf and below) in canopies of fields that have already been sprayed. Some fields sprayed in mid-July will be out of residual soon, which is also concerning to me. Physoderma brown spot, which moves with water and isn’t a significant pest, can be confused with southern rust. While it can look bad, a major difference with Physoderma is that there’s no raised pustules (bumps) on the leaves. I haven’t seen gray leaf spot at ear leaves or above yet. I’ve added pictures of what I’m seeing on my blog at jenreesources.com. There’s been some questions about ‘late season’ Nitrogen applications. I’ve had to ask how late is ‘late season’; brown silk has always been the latest I recommended. Most University research considered ‘late season’ as by tassel time. I haven’t found any University research that has said applications should be made later than brown silk or would be beneficial past this time.

In soybeans, there’s a disease called Phyllostichta leaf spot that I had never before seen.

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Phyllostichta leaf spot. Photo courtesy John Mick, Pioneer.

It’s one caused by a fungus that begins often as brown lesions on leaf margins and can move between leaf veins. In learning more about it, it can be residue born or seed transmitted. It doesn’t sound like anything to be too concerned about, just something different that’s been seen in some fields this year.

Painted lady butterflies are the orange and brown butterflies that are flying now that are often confused for monarchs. A painted lady female can lay up to 500 pale green eggs on plants individually instead of in egg masses. The larvae (called thistle caterpillars) hatch in around a week and can feed from 2-6 weeks depending on weather conditions. They feed on around 100 different host species including thistles, soybeans, asters, zinnias, etc. These butterflies are often used in schools to teach students about complete metamorphosis using the life cycle of a butterfly.

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Painted lady butterfly (underside) on soybean leaf.

Soybean Defoliators: In addition to thistle caterpillars, other defoliators including various worms, grasshoppers, Japanese beetles are also present. Thresholds for damage for all soybean defoliators is 20% defoliation of plants during the reproductive stages. If you’re unsure what 20% defoliation in soybean looks like, check out the graphic in CropWatch at: https://go.unl.edu/7qjg. It’s actually a good graphic to keep on one’s phone as it’s very easy to over-estimate 20% defoliation.

Unsolicited Seeds from China: I haven’t heard of anyone in this area officially receiving a packet yet. USDA is aware that people across the country have received suspicious, unsolicited packages of seed that appear to be coming from China. USDA’s Animal and Plant Health Inspection Service (APHIS) is working closely with the Department of Homeland Security’s Customs and Border Protection, other federal agencies, and State departments of agriculture to investigate the situation. Anyone in Nebraska who receives an unsolicited package of seeds should immediately contact Julie C. Van Meter at 402-471-6847) or Shayne Galford at 402-434-2346. Please hold onto the seeds and packaging, including the mailing label, until someone from your State department of agriculture or APHIS contacts you with further instructions. Do not plant seeds from unknown origins. At this time, there’s no evidence indicating this is something other than a “brushing scam” where people receive unsolicited items from a seller who then posts false customer reviews to boost sales.

Squash Vine Borers tend to be a problem at some point every year. If you’re seeing zuchinni, squash, or pumpkin plants looking wilted and suddenly dying, check the stems at the base of the plant. If you see insect frass (like sawdust), squash vine borers are most likely the culprit. You can remove the plants and discard if you’re done with them. Otherwise, you can also slit the stems and kill the larvae. Then cover the stem base with soil to encourage new root growth. There’s only one generation a year and it’s too late to apply insecticides (should be applied to plant base beginning in late June-mid-July). Some master gardeners also say wrapping the base of stems with aluminum foil discourages moths from laying eggs.


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Southern rust: Small, orange to tan clustered pustules primarily on the upper sides of leaves.

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Physoderma brown spot: the tiny clustered tan spots (below mid-rib) and purple blotches on mid-rib that also occur around leaf axils and on outer stalk tissue. Upper left-hand corner of this picture is bacterial leaf streak.

Physoderma brown spot on outer stalk tissue. It looks bad but not penetrating beyond the outer stalk tissue.

JenREES 7-19-20

Crop Update: The smell of pollen is in the air! Did you know each tassel contains around 6000 pollen-producing anthers? Two good articles from Dr. Bob Nielsen, Purdue University at https://go.unl.edu/x5tv.

How does heat impact pollination? Dr. Tom Hoegemeyer, former UNL Professor of Practice, shared that high humidity, without a drop in humidity during the day, can delay pollination or prevent pollen from leaving anther sacs. While heat over 95°F depresses pollen production, one day of 95-98°F has no or little yield impact when soil moisture is sufficient. After 4 consecutive days, there can be a 1% loss in yield for each day above that temperature. Greater yield loss occurs after the fifth or sixth day. Thankfully we’re not in a high heat pattern during this critical time of pollination!

My concerns regarding pollination: bent ear leaves covering silks in wind-damaged fields. Seeing a great deal of this. Also seeing silks continuing to elongate and grow through broken mid-ribs to increase exposure to pollen. Will continue to observe impacts.

Preliminary storm prediction center weather data showed a total of 93 wind, 11 hail, and 13 tornado damage reports on July 8th in Nebraska. Univ. of Wisconsin found lodged plants had yield reductions of 2-6% (V10-12 stage), 5-15% (V13-15 stage), and 12-31% (V17 and after stages). For greensnapped plants (below ear), Iowa State found in the worst case situation, yield reduction may range up to a 1:1 percent broken:yield loss. It’s possible these losses will be as low as 1:0.73 or even 1:0.50. We have an article in this week’s CropWatch (https://go.unl.edu/cwy2) with more detailed information. Recovery pics also at https://jenreesources.com.

Southern Rust was confirmed at low incidence and severity in Fillmore, Nuckolls, and Jefferson county fields this past week (probable for Thayer). Received questions on fungicide applications. In conversations, it seems like there’s fear of making the wrong decision and ultimately pressure to apply them. I realize economically it’s easier to justify adding a fungicide with insecticide when insect thresholds are met to save application costs. Most fungicide studies focus on VT applications; however, yield increases with automatic VT applications aren’t consistently proven in Nebraska.

In fact, in 2008-2009, a UNL fungicide timing trial was conducted near Clay Center on 2 hybrids (GLS ratings ‘fair’ and ‘(very) good’) with a high clearance applicator. Timing over the two years included: Tassel, Milk, Dough, 25%, 33%, 50%, and 100% Dent comparing the fungicides Headline, Headline AMP, Quilt and Stratego YLD.

  • 2008: No yield difference on GLS hybrids rated ‘good’ at any of the timings (Tassel, Milk, 33% and 100% Dent) nor the check when Headline or Stratego YLD were applied. For the ‘fair’ hybrid, no yield difference for any application timing nor the check for the April 30th planting except for Headline applied at milk stage (increased yield). Low gray leaf spot pressure.
  • 2009: No yield difference on GLS hybrids rated ‘very good’ or ‘fair’ nor the check on any timings (Tassel, Milk, and Dough) using Headline, Headline AMP, or Quilt. Moderate gray leaf spot disease pressure.

Thus I’ve recommended waiting till disease pressure warrants the application (have personally recommended apps as late as hard dough in previous years). Hybrids vary in disease susceptibility (thus response to fungicide application). The main ‘plant health’ benefit observed in Nebraska when disease pressure was low (ex. 2012) was stalk strength and that may be something to consider again in this lower disease year. Regarding any improved water use efficiency for drought-stressed plants, the peer-reviewed research published on this was in 2007. The researchers found slightly increased efficiency in well-watered plants, but it was reduced in water-stressed plants. They suggested fungicide use in water-stressed plants could potentially negatively influence water use efficiency and photosynthesis.


 

Same area of a York County Field taken morning of July 9th (left photo) and morning of July 13th (right photo). Grateful to see how plants are re-orienting themselves in many impacted lodged fields!

Leaned plants trying to upright themselves

Plants re-orienting themselves by ‘pushing’ and establishing more brace roots on the leeward (leaned side) helping roots reconnect with soil on the windward side. Notice the additional brace root development within the circled area of this photo.

Plants reorienting themselves at each node at various angles and bends

Plants reorienting themselves at each node at various angles and bends. Nodes become thicker to aid in reorientation.

Splitting open of thickened node

Splitting open of thickened node. Additional cell division and/or elongation occurring at these nodes appears to help ‘push’ the stalk upward (geotrophic response).

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Consistently seeing bent ear leaves covering silks in wind-damaged fields. Will have to watch any impacts to pollination.

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Also seeing how either the ear or silks are working their way through tears in leaves or silks elongating to the side of the plant to try to pollinate.

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Severely greensnapped field of later-planted corn.

Seeing some new growth on some greensnapped plants. Dissecting the growth revealed baby corn ears (they won’t amount to anything). Just shows the resiliency in plants regarding how they’re created to survive and reproduce. I never cease to be amazed by their Creator!

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Seeing this very minor. Ear trapped within thickened husk/stalk tissue so forcing itself through side of plant. Silks visible first.

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Opened this one to see curving of ear and some potential pinching occurring where ear was trapped above where it was forcing out of husk. Will be interesting to see any pollination and ear development impacts on plants like this.

JenREES 7-28-19

Southern Rust in Nebraska was confirmed in Nuckolls, Thayer, and Fillmore counties last week. The lesions were typically on one leaf in an isolated portion of fields at low incidence and severity. I was recommending to watch the fields instead of spraying right away. Greatly appreciate everyone who has gotten samples to me this month and to neighboring Extension offices serving as drop off points for samples. I’ve been looking at samples since early July and honestly, common rust at times has exhibited signs similar to southern rust. At my blog site (https://jenreesources.com), I’ve posted photos showing the differences of common vs. southern rust that we’re seeing this year. Southern rust typically is orange to tan colored with tiny, clustered pustules on the upper leaf surface. Common rust has had an orange appearance to it at times with smaller lesions than the ‘typical’ brick red larger ones. However, in every southern rust sample I’ve confirmed, the pustules have not gone through the back of the leaf…there’s been indentations but nothing has produced pustules on the backside. That doesn’t mean that the fungus can’t; it just rarely does. Also, these leaves have all occurred in the mid-canopy. I realize lowest leaves of plants often have a great deal of rust on them, but it’s been common rust in leaf samples I’ve pulled and received to date. I’ve also posted photos of another disease called Physoderma brown spot on my blog. Physoderma is the disease that has purple/brown on the midribs, around leaf axils and sheaths and it also can have tiny yellow-brown spots without pustules that look a lot like southern rust on leaves of plants. It’s one that we tend to see around pollination as the fungus-like pathogen swims in water on the leaf surface and feeds off of decaying pollen.

Confirming southern rust in a few Nebraska counties thus far doesn’t mean that every field has it and we don’t know how it will progress. So our recommendation is to continue scouting and if you have a suspect sample, you can get it to me (if you’re in the area) or to our Plant and Pest Diagnostic Lab in Lincoln. You can keep updated with counties that are confirmed by checking out the Southern Rust tracking site at: https://corn.ipmpipe.org/southerncornrust/. The wide range of planting dates across Nebraska this year has resulted in a wide range of corn growth and reproductive stages in fields, some of which are still in the vegetative growth stages. Keep in mind that late planted fields are at particular risk for southern rust if it increases in development. Right now corn disease pressure in general is low. I’m anticipating that to soon change for gray leaf spot susceptible hybrids. Some growers added a fungicide in with an insecticide treatment for western bean cutworm, which made sense to save an application cost. However, in general, automatic fungicide applications when one treats before disease develops may lead to loss of full product efficacy before critical disease levels. This can also result in the need for reapplication later if the disease worsens after the previous fungicide application and residual has worn off. And, always in my mind is eventual potential for pathogen resistance…so utilizing fungicides when we need them vs. automatically applying is wise for maintaining these fungicide chemistries.

York County Fair: This week is the York County Fair! All events and details can be found at: http://www.yorkcountyfair.com/. One special addition this year is “Brownies for Bergen” on Saturday, August 3 from 5:30-7:00 p.m. The late Gene Bergen was a 4-H icon and was planning on celebrating 50 years as a York County Ag Society Member at this year’s fair before retiring. While he won’t be with us in person, the York County Ag Society, 4-H Council, and Extension Office would like to honor him and his original plans to celebrate. So please join us for brownies and ice cream and share your favorite memories and stories of Gene!


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Lower corn leaf that is dying early and has a great deal of rust on it. So far, this has all been common rust as pictured here in spite of smaller, clustered pustules or even orange colored pustules.

 

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Common rust spores are circular in shape.

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Southern rust was confirmed on this leaf in 2019. Small, clustered, tan-orange colored pustules can be seen on this leaf.

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Southern rust spores are brown and oval in shape. Sharing this photo as the clear structures are spores (condia) and spore-holding structures (conidiophores) of Cercospora zeae-maydis which causes gray leaf spot (gls) in corn. Was seeing these spores/structures with only ‘specks’ of gls lesions on this leaf. With humid weather and longer leaf wetness from dews, we may see an increase in appearance of gls lesions in the next 7-10 days.

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Physoderma brown spot. Symptoms include both the purple/brown midrib in addition to the yellow-brown lesions on the leaf. These lesions are flat in comparison to southern rust which would have raised pustules.

Corn Disease Diagnostic Workshops

corndiseasediagnosticworkshop

Crop Update 8/1/14

Southern rust of corn confirmed in Clay County July 31.  This was found on one leaf in a field near Trumbull.  Just because southern rust has been found in the area, we don't recommend automatically spraying.  Scout your fields and consider disease pressure, growth stage, and economics.  Long season corn and late-planted fields have the potential for most damage.

Southern rust of corn confirmed in Clay County July 31. Very small, tan-brown lesions on upper surface of the leaf, usually in clusters.  Spores inside the pustules are typically orange.  This was found on one leaf in a field near Trumbull. Just because southern rust has been found in the area, we don’t recommend automatically spraying. Scout your fields and consider disease pressure, growth stage, and economics. Long season corn and late-planted fields have the potential for most damage.  Secondary common rust sporulation has also been confused as southern rust as the secondary pustules tend to look like this.  It’s important to obtain microscopic confirmation to know for sure if you have southern rust in your fields.

Spores of southern rust appear elongated vs. common rust appear as near perfect circles.

Microscopic Observation:  Spores of southern rust appear elongated vs. common rust appear as near perfect circles.

Another common problem is old common rust lesions being confused as gray leaf spot.  The color of this lesion is a tan-gray, typical of gray leaf spot.  Using backlighting or a handlens, you can see the pustules within this lesion confirming it is common rust and not gray leaf spot.  I've had many calls that gray leaf spot was up the entire plant in their fields and after looking at fields, have found it to be common rust in most situations.  It's important to know what disease you truly have to make the best decision on fungicide application.

Another common problem is old common rust lesions being confused as gray leaf spot. The color of this lesion is a tan-gray, typical of gray leaf spot. Using backlighting or a handlens, you can see the pustules within this lesion confirming it is common rust and not gray leaf spot. I’ve had many calls that gray leaf spot was up the entire plant in their fields and after looking at fields, have found it to be common rust in most situations. It’s important to know what disease you truly have to make the best decision on fungicide application.

Have also received questions on soybeans, particularly in dryland.  Soybeans are drought stressed-often showing it in pockets within dryland fields right now.  Closer observation shows plants aborting pods and losing lowest leaves.  Spidermites can also be viewed on leaves in some of these patches.

Have also received questions on soybeans, particularly in dryland. This photo is showing drought stressed soybeans-often occurring in pockets within dryland fields right now. Closer observation shows plants aborting pods and losing lowest leaves. Spidermites can also be viewed on leaves in some of these patches.

Dryland corn showing stress as well.  June rains were making for dryland crops with potential, but also led to shallow rooting.  Crops could use a drink right now....but would prefer no more ice and hail.  The storm that hit Clay County so hard occurred one year ago today.

Dryland corn showing stress as well. June rains were making for dryland crops with potential, but also led to shallow rooting. Crops could use a drink right now….but would prefer no more hail and tornadoes. The storm that hit Clay County so hard occurred one year ago today.

Corn Disease Look-Alikes

Physoderma brown spot

Physoderma brown spot on corn. While the small, speckled lesions may look like southern rust, under hand lens or microscopic observation, there are no raised pustules as would be the case with southern rust. Also notice the brown/purple discoloration on the midrib which is also noticed on the stalk as well where the leaf color meets the stalk.

Fair week tends to be time for tasseling in corn and considerations for watering and fungicide application are being made.  Regarding diseases in corn, there has been confusion about a few diseases, particularly about a disease called physoderma brown spot which some have confused for southern rust.  The fungus causing physoderma brown spot feeds on pollen and debris on leaves and does not cause harm to the corn plants themselves.  Because the spores of this fungus move via water (it’s closely related to oomycetes), numerous lesions can appear on leaves in bands or areas where water collects.  While the lesions may look like early southern rust, there will be no pustules present and often purple colored lesions will also be observed in the midrib, leaf sheath, stalk, and outer husks.

Differentiating Rusts:

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Southern rust in corn. We currently have not seen southern rust in Nebraska in 2014. Notice how you can see raised pustules in this picture compared to the photo of physoderma brown spot above.

When differentiating between southern rust vs. common rust, there are several criteria to consider and this NebGuide is a great resource.  Typically common rust will have brick-red pustules randomly scattered on the upper and lower leaf surfaces that are larger in size.  It is common rust that we are currently seeing in our fields.

Bacterial leaf blight showing up heavily in some hybrids.  The UNL Plant and Pest Diagnostic Lab is determining species and we will share more information in the future.  There is no control for this disease at this point.

Bacterial leaf blight showing up heavily in some hybrids. The lesions are red-brown in color, long and skinny and mostly vein-limited.  Older lesions spread outside the veins and are buff in color-sometimes they are being confused as gray leaf spot.  The UNL Plant and Pest Diagnostic Lab is determining species and we will share more information in the future. There is no control for this disease at this time of the season.

Southern rust in our area tends to have very small, raised, tan-orange pustules on the upper leaf surface of leaves in localized areas on mid-upper leaves.  These pustules are tightly clustered on the leaves. However, color and size are relative as sometimes the two diseases can look alike.  Microscopic observation is the best way to differentiate the two diseases.  Fungal spores from Puccinia sorghi causing common rust will be near perfect round circles whereas fungal spores fromPuccinia polysora will be oblong in shape.

We do have some gray leaf spot in the lower canopies and I haven’t seen much northern corn leaf blight in the fields.  But we do

have a bacterial leaf blight that is affecting quite a bit of leaf tissue on some hybrids.  These lesions are long and skinny appearing at first to be limited to the veins.  There’s been concern about these lesions being severe gray leaf spot but it’s not and there’s nothing you can do about the bacterial disease.  Please don’t mistake this bacterial disease as a fungal one and trigger a fungicide application too early.

Fungicide Application Timing

We tend to see southern rust in our part of the State each year; it’s a matter of time.  Triggering a fungicide application too early may result in no residual for when you need it if/when southern rust occurs.  Every year some producers make more than one fungicide application due to blanket applications at tassel or shortly after followed by another fungicide application when southern rust occurs later in the year.  Consider good fungal resistance management and apply fungicides when disease pressure warrants them in your fields and also consider economics for your situation for proper fungicide application timing.

Southern Rust

Several of us had been watching the USDA IPM Pipe Map for weeks.  It wasn’t showing southern rust moving and only Georgia2013-07-30 09.31.26 was really lit up.  Yet, I had heard reports in Texas and Oklahoma at one point.  Spots were evident on corn leaves when backlit-so they were bound to develop into something.

That something has showed itself to be southern rust last week as it was confirmed in 11 Nebraska Counties:  Kearney, Adams, Clay, Nuckolls, Thayer, Fillmore, Gage, Platte, Polk, York, and Boone.  I’d like to thank all the crop consultants and ag industry professionals for sharing information on what we all were seeing and for submitting samples.  2013-07-30 11.44.36

So the common question was, why didn’t the map show anything south of us?  Federal funding was no longer available for this site and scouting efforts associated with it.  Many Extension Plant Pathologists weren’t aware that the site was even still online and were sharing information via other means instead.  The map for Nebraska will continue to be updated, but for surrounding states, it is advised to consult with your local Extension Plant Pathologist.

Differentiating Rusts:

When differentiating between southern rust vs. common rust, there are several criteria to consider and this NebGuide is a great resource.  Typically common rust will have brick-red pustules randomly scattered on the upper and lower leaf surfaces that are larger in size.

For southern rust, we’re seeing very small, raised, tan-orange pustules on the upper leaf surface of leaves in localized areas on mid-upper leaves.  These pustules are tightly clustered on the leaves. Fungal spores of Puccinia sorghi, the pathogen causing common rust. However, color and size are relative as sometimes the two diseases can look alike.

Microscopic observation is the best way to differentiate the two diseases.  Fungal spores from Puccinia sorghi causing common rust will be near perfect round circles whereas fungal spores from Puccinia polysora will be oblong in shape.

Disease Progression:

With the cooler weather last week, we were unsure how the disease would progress. Southern rust likes sustained temperatures in the 80’s-90’sF with humidity and leaf wetness.  So we encourage scouting for it.

We saw how southern rust can be devastating to fields in the past regarding removing photosynthetic tissue leading to cannabalization of the stalk.  In determining a fungicide application, consider Physoderma brown spotdisease pressure in your field, stage of growth, pre-harvest intervals, and length of time for fungicide residual in addition to economics.

Look-A-likes:

Other plant samples brought in contained diseases such as physoderma brown spot (which isn’t a significant yield limiting disease of corn).  Because the spores of this fungus move via water (it’s closely related to oomycetes), numerous lesions can appear on leaves in bands or areas where water collects.  While the lesions may look like early southern rust, there will be no pustules present and often the purple colored lesions will also be observed in the midrib, leaf sheath, stalk, and outer husks.

Southern vs. Common Rust in #Corn

In early July, southern rust caused by the fungal pathogen Puccinia polysora was discovered in Hall, Adams, Clay, Fillmore,  Thayer, and Burt counties in Nebraska.  Most farmers in south-central Nebraska remember the corn season in 2006 walking out of fields orange and the slow harvest due to downed stalks.  Since then, southern rust has been a disease of concern and fungicides are used to prevent and also treat it when it’s found in fields.  

I promised when we were first discovering southern rust this year that I’d post pics, so while delayed, here they are!  It is often confused with common rust which we see earlier every year.  Common rust typically has pustules (raised fungal spores) that are brick red in color, larger, and on the upper and lower leaf surfaces.  The pustules tend to be more spread out.  

Southern rust typically has very small pustules that are clustered on predominately the upper leaf surface and are tan to orange in color.  This year, southern rust pustules tend to be more tan in color than orange but are still distinctively different with their smaller and clustered appearance.  Both fungal rust pathogens arrive in Nebraska each year via wind from the south.  Southern rust prefers warm, moist conditions which, in spite of our dry spell, is typical within our pivot and gravity-irrigated fields in the area.  At this time we are recommending if you find southern rust in your field to consider treating with a fungicide.  Please be sure to read and follow all label directions including paying attention to pre-harvest intervals.  A list of corn fungicides and efficacy can be found here by scrolling down to the corn section.

Additional information and pictures of these diseases can be found here.

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