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JenREES 7/24/22

Even though few, the raindrops Saturday night were so refreshing after a hot week! I don’t know that it’s even really that hot compared to past years, but the sun seems extra intense to me this year. Cooler temps are welcome this week!

Crop Update: There is very little disease pressure thus far in both corn and soybeans. For corn, the most common thing I’ve seen this year is physoderma brown spot/purple leaf sheath, which is something we don’t worry about in Nebraska. Bacterial leaf streak is common on certain hybrids as always and is one we don’t worry about. A fungicide will not help against it and won’t protect against it. Gray leaf spot is very minimal to date in lower canopy, if it can be found. Same for common rust. The closest southern rust has been found is in southern Arkansas. So short story, fungicide isn’t necessary yet unless one is saving a trip for corn insects. For corn insects, there are still hot areas of Japanese beetles feeding on silks in addition to corn rootworm beetles. Spidermites are also flaring in some fields. Also be aware that spraying a fungicide can flare corn leaf aphids as it kills the fungus that attacks them.

For soybean insects, there’s still some Japanese beetles feeding and some spidermites flaring. For disease, have seen very minimal phyllosticta leaf spot and frogeye leaf spot and not anything close to levels for spraying. Seeing lots of phytophthora root rot this year in fields that is continuing to kill plants and there’s nothing we can do about that this year. Fields with a history of white mold may have been sprayed to help reduce disease pressure.

Tar spot has not been found in Nebraska yet this year. A great resource to track diseases such as southern rust and tar spot is: https://corn.ipmpipe.org/diseases/. Click on the disease of interest to see a U.S. map of where the disease has been found. Suspect samples can be submitted to the Plant and Pest Diagnostic lab in Lincoln for free. You can also get your samples to me locally if you’d like. There’s been a lot of confusion so far with insect “poop” and tar spot. A quick field test is to either get your finger wet or spit on the leaf and rub the spot to see if it comes off. Physoderma and tar spot won’t rub off but insect excrement will.

Fungicides and insecticides are helpful when we need them. Everyone’s trying to make the best decisions possible. Concerned we let fear of ‘protecting the crop’ drive decisions. Crop prices continue to be volatile and economics should be considered. Sometimes fields are sprayed a second time when disease comes in later once the residual wears off (regardless of product and because the product only makes it so far into the canopy unless chemigated). In terms of resistance management, we have fewer modes of action with fungicides than herbicides available to us, and we use those same modes of action in all our crops. We already have resistance to the quinone outside inhibitor (group 11 formerly strobilurin) class of fungicides to frogeye leaf spot in soybean. Concerned it’s only a matter of time before this impacts us on the corn side too.

I realize I’m continually an outlier in saying to wait and not automatically apply at tassel. Based on the Nebraska research (shared last year here) and observation I feel we can wait till disease pressure warrants applications and allow them to help with stalk strength. I also realize this column would’ve been more timely last week with the spraying that’s occurred.

South Central Ag Lab Field Day Aug. 4 will begin with registration at 8:30 a.m. with program from 8:45 a.m.-3p.m. at the South Central Ag Lab near Harvard/Clay Center. There are several tracks to choose from throughout the day including the latest in weed, disease, insect, nutrient, irrigation management, and soil health. Free lunch and CCA credits available. More info. and RSVP at: https://go.unl.edu/scalfieldday


The first picture on the left has been common of both physoderma brown spot and insect poop. With physoderma brown spot, most often these purplish spots are more prevalent on the midribs, leaf axils, and leaf sheaths (as seen in the middle photo). Often the spots outside of the midrib are more yellow/tan in color and are often confused with southern rust. Photo 3 on the right-hand side was tar spot that was found in Oct. 2021 in York Co. Would recommend getting your finger wet or spitting on the leaf and rubbing the spot to make sure it’s not insect poop as several samples looking like the first photo have been that instead. Physoderma won’t rub off and neither will tar spot. Feel free to submit any suspect samples to the diagnostic lab for free.


JenREES 7-8-18

Crop Update:  A few diseases started showing up the past few weeks in various portions of eastern and south central Nebraska.  Phytophthora root rot in soybean is perhaps the

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Phytophthora root and stem rot in soybean. Notice wilted plant with leaves hanging on turning yellow/brown.  Also notice characteristic brown lesion from base of plant up a good six inches on this plant.  This affected plant is surrounded by healthy plants.

most common in both areas.  We normally think of this disease as seedling damping off and death; however, it can also affect plants later in the season.  What surprised me was how much we are seeing it this year in higher ground and sidehills instead of the typical lower ground we often see it on.  Dr. Loren Giesler, Extension Soybean Pathologist said that in situations where we’ve had dry conditions followed by heavy rains (as we have this year), especially on clayey or soils prone to compaction, Phytophthora can also affect plants.  He has a few videos along with additional information at the following website:  https://go.unl.edu/tdfh.  Symptoms characteristic at these growth stages include wilting of plants during the day with leaves eventually turning yellow-brown-gray and remaining on the plants.  Also, look for a brown stem lesion that goes from the soil line upward about 4-6″.  Some of these plants are also snapping off at the soil line. For those experiencing Phytophthora this year, future management includes:

  • Using resistant varieties including a combination of good partial resistance and an Rps gene. Partial resistance alone will not be as effective during early growth stages or under high disease pressure.
  • Cultural practices include anything that can improve soil drainage and compaction.
  • Seed treatment fungicides containing mefenoxam or metalaxyl should be used and you may need to consider a higher rate of them.

Regarding corn diseases, bacterial leaf streak (BLS) has greatly increased on more

bacterial leaf streak

Bacterial Leaf Streak (BLS) in corn.  Lesions are elongated and skinny staying between the leaf veins, similar to gray leaf spot (gls).  However, leaf margins are wavy and diagnostics under the microscope show the presence of bacterial streaming from the leaf veins.  With gray leaf spot, there will be the presence of fungal spores.  Thus, the importance of correct diagnosis when considering fungicide applications.

susceptible hybrids since rain events.  Early lesions can look very similar to gray leaf spot, so it’s important to correctly identify the two.  The margins of BLS are wavy vs. those of gray leaf spot are more blunt.  Both can have yellow margins when backlit by the sun.  Fungicides are not effective against BLS and hybrids do vary in their tolerance to this disease.  It’s important to scout fields as we may see an increase in fungal diseases due to the humidity, leaf wetness, and recent rain events.  Southern rust has taken awhile to develop in the southern U.S., which is somewhat unusual, yet many states have been in drought this year too.  As of July 5th, southern rust has been confirmed in Georgia with one suspected sample in a Missouri county.  You can watch the map at: http://ext.ipipe.org/ and follow @corndisease on Twitter for the latest on corn disease findings in the U.S.

Trees:  With numerous wind storms, the following resource has a lot of great information regarding pruning storm damaged trees correctly and questions to ask tree care services regarding tree pruning:  https://go.unl.edu/94fm.

Agronomy Youth Field Day:  All youth ages 9-18 years old are invited to the 3rd Annual Agronomy Youth Field Day. Youth will have exciting educational experiences while discovering Science & Agronomy/ Irrigation / Mechanized Agricultural careers for producing Nebraska crops! The field day will be held Wednesday, August 8 from 9 a.m.-3 p.m. at Nebraska College of Technical Agriculture Educational Center in Curtis, NE.

Hands-on activities (for all age levels) will focus on pest management, equipment technology, crop growth, soil management, precision farming & center-pivot irrigation technology. Several Nebraska Extension Cropping & Water Systems and 4-H Youth Development Educators along with Nebraska College of Technical Agriculture in Curtis Agronomy / Ag Mechanics Department professors will be sharing the researched based information with the students.

Participants will gain important life skills while discovering the science behind producing Nebraska crops. The six-hour field day is a great opportunity for ALL the youth to learn more about the agronomy industry and increase their basic understanding of science, ag literacy, a technology & STEM while exploring careers. Parents/Adults are welcome and lunch will be provided.

Reserve your spot today by registering online at:  https://go.unl.edu/agronomyyouthfieldday  by August 3, 2018. For more information (or if trouble with registration) contact Nebraska Extension Frontier County at 308-367-4424 or email 4-H Educator Kathy Burr at kathy.burr@unl.edu.

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