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JenREES 7-7-19

Crop Updates:  I really appreciate all those in ag industry who share what you’re seeing in the fields; it’s a blessing to have a great network of people looking at fields in different areas of the state and sharing what we’re all seeing!

Western bean cutworm (WBC) moths were seen in corn whorls the past week. They’re

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Western Bean Cutworm Moth courtesy UNL CropWatch

also showing up in UNL light traps in addition to industry ones. To view the UNL light trap reports near Clay Center, please go to: https://scal.unl.edu/ltr2019.pdf. The light trap near Mead is currently having black light issues, but the report can be viewed at: https://go.unl.edu/2usz and the light trap report from North Platte is at: https://go.unl.edu/a56b. WBC moths prefer laying eggs on upper leaf surfaces in corn that is in the late whorl to early tassel stage. UNL entomologists recommend scouting at 25% of moth flight. It’s unknown how larval survival will be impacted by corn growth stage at this time. Larvae survival is highest when they have fresh tassel tissue and pollen to feed on before moving down to developing ears and silks. Larval survival is lowest when only vegetative tissue is available to feed on. So, the delayed planting and growth in some fields may allow for less western bean cutworm damage in 2019. However, our entomologists say that air and soil temperature can also impact insect development leading to slower development of the insects. UNL Entomologists Tom Hunt and Bob Wright, along with University of Minnesota researchers, developed a degree-day model to predict when WBC moths will emerge to begin mating and laying eggs. In a recent CropWatch article, they were predicting 25% moth flight to occur for the following dates/locations: July 7th in Lincoln; July 11 in Hastings and Ithaca; July 12 in Grand Island and York; July 13 in Clay Center; July 15 in Holdrege, and July 23 in North Platte. Corn expressing VIP3A proteins are highly effective for WBC control. Corn expressing Cry1F (Herculex) proteins may provide some WBC feeding suppression but shouldn’t be relied upon for control. The current UNL economic threshold for treatment is 5-8% of corn plants with eggs or larvae.

Common Rust in Corn: The rainfall, humidity, and wet canopies have allowed for

 

increased common rust to be seen in corn this past week. I was seeing larger numbers of pustules on lower leaves of plants, but this week could also see pustules occurring in upper canopies. Pustules of common rust are typically brick red in color, larger, more separate, and can appear on both the upper and lower leaf surfaces. Southern rust typically has smaller, orange to tan colored pustules occurring in tight clusters on upper surfaces of leaves. However, the past few years, we’ve seen common rust looking more orange in color, including this year. The best way to confirm for sure if it’s common or southern rust is to check the spores under the microscope, and I’m happy to do that. The spores of common rust will be circular in shape whereas southern rust spores are more oval to football shaped. Samples can also be submitted to the UNL Plant and Pest Diagnostic lab. So far, every sample I’ve looked at has been common rust. Southern rust hasn’t been found further than Georgia and Louisiana to my knowledge right now. We don’t typically recommend fungicides for common rust. It will be important to continue scouting for diseases with the humidity and leaf wetness we’re experiencing this year.

Lawn and Garden Questions: The wet weather has allowed slime mold (gray-black fungal growth on leaves) in patches in lawns in addition to mushrooms in lawns and landscapes. They are harmless and fungicides aren’t effective. They will go away upon drying out and with warmer weather.

Bagworms are out and it’s time to control them if you have them. The following gives more detailed info on their life cycle: https://go.unl.edu/rgju and this YouTube video shows what you’re looking for this time of year on your trees:  https://jenreesources.com/2015/06/27/bagworms-in-evergreens/.

Japanese Beetles may be causing holes in Linden trees or rose leaves. They are

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Green June Beetle (left) and Japanese beetle (right). Photo via Purdue Entomology.

green/brown beetles with white hairs that look like rows of white spots near each wing. Kelly Feehan in Platte County shares that “applying insecticides to lawns to control grubs will not prevent beetles from feeding on landscape plants. The product ‘Milky Spore’ sold to kill them, does not work. On landscape plants, hand picking or knocking beetles into a bucket of soapy water around 7 PM is the best time of day to do this as it prevents plants producing a distress pheromone that attracts more beetles. Japanese beetle traps work very well – IF you want to attract them to your yard – so traps are best NOT used. If a Linden tree has Japanese beetles, know these trees CANNOT be treated with Imidacloprid or other Neonicotinoid insecticides.” Carbaryl (Sevin) is effective to use for Lindens and landscape plants where it’s not feasible to remove beetles by hand.

Corn Disease Diagnostic Workshops

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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:

2013-07-30 09.31.26

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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