Monthly Archives: June 2025
Plant Nutrition and Disease
Tar spot of corn was found in several Nebraska counties. We are not recommending fungicide applications at this time due to the research from Purdue University and other states. They found it best to wait till disease severity was 5-7% and corn was from tassel to dough stage of development. More info. at: https://jenreesources.com/2025/06/17/tar-spot-of-early-corn-update/.
What to do now:
1-Scout fields and wait till a 5-7% threshold on leaves before applying fungicide
2-Observe fields as to which hybrids have more tolerance to tar spot
3-When irrigating, consider less frequent and deeper irrigations, https://go.unl.edu/vipj
4-Consider plant nutrition?
In managing pests and pathogens, few mention plant nutrition or alternative options. Healthy humans and animals are less prone to disease; why not the same with plants? A book called “Mineral Nutrition and Plant Disease” shares published research on roles of minerals in aiding or managing disease. It was written by Dr. Don Huber, Professor Emeritus of Plant Pathology from Purdue University and there’s an updated version that I have.
There’s a lot of unknowns about tar spot and its control. Dr. Huber shared that the tar spot lesions contain oxidized manganese in addition to the fungal spores. Several journal articles referenced the black “freckles” in Goss’ wilt and the vascular plugging in the systemic version also contain oxidized manganese. When manganese is oxidized, it creates a manganese deficiency in the area which doesn’t allow for photosynthesis. The area runs out of energy and can’t defend itself resulting in disease expansion. Many of us in ag understand that micronutrients are chelated in plants in the process of applying specific herbicides. Companies have developed products to help with chelation and to stimulate plants sooner from the shut-down that occurs from applying herbicides.
I’m wondering about the opportunity to use plant nutrition right now to help stimulate plant defense mechanisms? We may need fungicide at some point, but we don’t right now. I have no research on this, but to me, it makes sense. When we have early symptoms of a cold, we’re told to take zinc to stimulate our defense system. Manganese and Zinc both travel in the xylem and they aid in plant defense signaling. Addition of zinc and copper in particular can reduce manganese oxidation, aiding in plant defense responses. Thus, wondering if zinc, copper, and manganese may help with preventing and fighting tar spot? Boron and sulfur could play a role too. The addition of Calcium increases the oxidation, so it shouldn’t be used alone for this situation. Manganese, Zinc, Copper, Boron, Sulfur all aid in defending plants against pathogens.
If you’re interested in trying something in plant nutrition and would like to work with me via on-farm research, please let me know. I also need to share that many plant pathologists disagree with the thought of using plant nutrition: https://cropprotectionnetwork.org/publications/mythbusting-tar-spot-separating-fact-from-fiction.
For those in industry, many of you have products in trials that reduce the chelation processes and/or that help stimulate plants after being shut down (ex. from 10 days to 2-3 days) after a pesticide application. I’m curious if aiding crops out of chelation/shut down sooner helps with reducing pest/pathogen pressure? How can we better share what we observe with each other?
Tar Spot of Early Corn Update
Received several calls about tar spot yesterday and today. As of right now, it’s been confirmed by UNL at LOW incidence (1-2 lesions per leaf) in Saunders, Pierce, and Clay (on 6/16/25), Polk, and Seward Counties (on 6/17/25). I really appreciate Craig Anderson and Mike Byers bringing me leaf samples to confirm. I also appreciate those who were calling to hear of any confirmations from leaf samples.
There’s a lot of fear surrounding this disease, and still some unknowns. We haven’t seen tar spot in Nebraska this early. It would be helpful if consultants/agronomists would confirm samples to Dr. Tamra Jackson-Ziems, the UNL Plant and Pest Diagnostic Lab (tar spot testing is free), or a local Extension Educator so that we have the most accurate information to provide. Tamra will update the tar spot map at: https://cropprotectionnetwork.org/maps/tar-spot-of-corn.
We are NOT recommending fungicide application in fields where tar spot is confirmed in these early vegetative stages.
Reasons for not applying fungicide now:
1-Economics: Corn economics are already a struggle. When tar spot appeared in the early vegetative stages, research from Dr. Darcy Telenko’s lab at Purdue University showed it wasn’t economical to apply at V6-V7 as it didn’t suppress disease enough. It was economical when the corn reached tassel stage or beyond. I show the research data below and you will also see the chart on the website link I shared above. In this post, Dr. Telenko shares 7 years of experience dealing with tar spot when it occurs early in the season and how to make fungicide decisions.
*Some Quick Tips & Tools for Preparing for Tar Spot in Corn-Dr. Darcy Telenko
*Tar Spot: What to look for in corn and making an informed fungicide application-Dr. Darcy Telenko
*Crop Disease Forecasting Tool for Tar Spot
2-Applications: Dr. Tamra Jackson-Ziems shared that some products say “no more than 2 applications per year”. Using those active ingredients now would mean you could use them again around tassel but no later when you may need the fungicide to finish the season. (See Dr. Telenko’s posts above).
3-Resistance management and integrated pest management. The photo below shows the economic threshold is 5-7% leaf severity for tar spot before it’s economical to spray. We’re a long way from that threshold on leaves confirmed for tar spot thus far. Avoiding unnecessary fungicide applications and using two modes of action when fungicides are applied may help in delaying resistance.
What to do now:
1-Continue to scout fields and wait till a 5-7% threshold on leaves before applying fungicide (see photo below)
2-Observe fields as to which hybrids have more tolerance to tar spot
3-When irrigating, consider less frequent and deeper irrigations
4-Consider plant nutrition? Manganese, Zinc, Copper, Boron, Sulfur all have a role in defending plants against pathogens. Will share more thoughts in another blog post.
Slide courtesy of Dr. Tamra Jackson-Ziems, UNL and Dr. Telenko, Purdue University. Fungicide application at V6-V7 resulted in negative economic return and similar disease pressure as the non-treated areas. Best fungicide timing for disease suppression occurred from tassel to milk and for economic return from tassel to dough.
Crop Updates 6/16/25
Wheat stem maggot in corn and herbicide injury issues have been my top questions the past few weeks. A team of us wrote a more detailed article of what we’re seeing and recommending regarding wheat stem maggot in CropWatch: https://go.unl.edu/atx9. Regarding herbicide injury, it perhaps is amazing this doesn’t happen more with all the traits we have. As spraying season continues, please double check fields for which traits are present to ensure the wrong herbicide isn’t applied to create potential crop injury. The one that has happened the most this season is glufosinate (Liberty) applied to non-Liberty link corn. The growth stage timing and rates of those applications make a huge difference on what we’ll see on corn survival.
Also, please always be checking growth stage of plants inside the field prior to herbicide applications. Crops have shorter internodes early on making them somewhat shorter than what we might expect. With June 21 coming this weekend as the longest day of the year, I’m anticipating we’re also going to see some blooms by this weekend/early next week with as many soybeans went in early this year.
As side-dress applications of nitrogen have been made in fields, it made me think of more on-farm research studies we’re conducting this year that might be of interest. They all involve using plant-based sensing from Sentinel Nutrient Management (also known as Sentinel Fertigation). Since not everyone who has irrigation systems wants to apply nitrogen through their system and because we have plenty of non-irrigated acres in the state, On-Farm Research is working with Sentinel to sense what the crop needed for side-dress applications this past year. There’s also opportunity for those with hi-boy machines to use this technology to apply nitrogen later in the season.
You’ve heard me share the on-farm research results about nitrogen savings using this sensing technology. In our area of the state, growers have used this technology in corn, soybean, and seed corn. This year, I know of growers also trying it in wheat and sorghum.
For on-farm research, I’m super excited to learn more from three studies that have had a history of cover crops and grazing! Each year, growers ask when to expect the nitrogen and other nutrients to be released from cover crops. Journal articles fairly consistently mention a 6-week time-frame. It ultimately depends on the Carbon:Nitrogen (C:N) ratio of the covers and rainfall to activate the biology. I’m excited to see if we can capture this time-frame better through satellite imagery using Sentinel Nutrient Management. The goal would be to see if we could better time nitrogen applications in addition to rates better using sensing technology.
Another question growers have asked is “how do we know how much nitrogen to credit after grazing cover crops?”. We hope to better answer this on two fields this year using sensing technology. Two of the on-farm research studies are following “Regen Years” where the land was planted to multi-species cover crop mixes and grazed all year instead of taking crops for grain. One is irrigated while the other is non-irrigated and both have nitrogen rate ramps associated with them. We plan to have a field day on the irrigated site in late July and will share more details later. Looking forward to what we will learn and sharing the results!
Reminder: June 25 Weed Management Field Day at UNL’s South Central Ag Lab near Clay Center, NE. Details at: https://go.unl.edu/qemk.
JenResources 6/8/25
Wheat Stem Maggot in Corn: Been seeing and hearing of some wheat stem maggot in corn for some fields where corn was planted green into rye. While I see this to a small extent each year, the last time we heard widespread reports was in 2017 (photos and info. at: https://jenreesources.com/2017/06/05/corn-concern-in-wheatrye-cover/). Symptoms include the corn whorls of plants looking wilted. Pulling out the whorl and carefully unfurling it may reveal the light-green maggot. Some key points: the maggot will move from dying rye or wheat into healthy corn. It will not move from plant to plant in corn unless the entire corn plant dies. What we have normally seen is the maggot kills the main stem of the corn plant; however, the plant produces tillers which then produce ears (not typical tiller ears). Because of that, replanting is not recommended. Our Extension Entomologists also don’t recommend spraying an insecticide once the maggots are in the whorls because they won’t have activity against the maggots inside the corn. There are no published thresholds for the maggot once it gets into the corn plant. Here’s an article UNL researchers published on timing and use of insecticides in cover crop/corn systems: https://www.mdpi.com/2075-4450/13/4/348.
Regen Ag Field Tours: A series of Regen Ag tours are available June-August. For now, I’ll share on two of them. On June 11, Doug and Traci Steffen are hosting a compost and covers tour on their farm near Crofton, NE from 1-3 p.m. RSVP at https://practicalfarmers.org/field-days.
On July 8 from 10 a.m.-Noon, Junior Pfanstiel is hosting a covers and corn tour on his farm near McLean, NE. Lunch is also included. Junior alternated 4 rows of corn with 4 rows of multi-species cover crops throughout his field with the goal of obtaining the same yield on fewer acres while also having grazing acres. Please RSVP to: (402) 254-6758.
Roundup: Homeowners, Please read the active ingredients on jugs before purchasing and using Roundup products. I’ve had several situations where homeowners have bought “Roundup” thinking it was the traditional “glyphosate”, but instead the active ingredient was “triclopyr”. The problem? They work differently. Glyphosate is a non-selective herbicide that doesn’t move in the soil or from plant to plant. It only works on the plant it comes in contact with. Triclopyr is a growth regulator herbicide (same family as 2,4-D and dicamba) that mostly affects shrubs, stump treatment, and broadleaf weeds. It has minimal activity on grasses. It has soil residual activity, on average for 30 days, but can be as much as nearly a year depending on how the microbial life break it down. It can volatilize (move off-target to other broadleaf plants after application) and it can be excreted through the roots of plants that were sprayed to nearby, non-sprayed plants impacting them.
Because of this, some people who have used Roundup containing triclopyr have reported issues with growing vegetables, flowers, their grape vines, raspberries, and around fruit trees. Triclopyr symptoms on plants looks like a “strapping” of leaves where they become bubbly and elongated, but it’s a different look than 2,4-D damage. Plants grown in soil treated with triclopyr may have kinked stems and appear stunted. More info. on triclopyr: https://purduelandscapereport.org/article/the-summer-of-triclopyr-mounting-evidence-for-off-target-damage/. A great resource explaining all the different “Roundup” products on the market: https://www.purdue.edu/fnr/extension/when-roundup-isnt-roundup-purdue-landscape-report/.
Early Corn Growth Stages
Determining Corn Growth Stage: Grateful for the rain showers! With the cooler weather, corn plants appear shorter due to shortened internodes but are further along in development than one may think. Correct growth staging of corn using the collar method is important. Some herbicides have application restrictions of V8 (8 leaves), particularly when certain adjuvants are used. These restrictions are in place to protect developing corn ears.
Be sure to growth stage plants correctly counting collars (leaves pull away from the main stem like a collar around one’s neck). Start counting leaves at the base of the plant with the smallest rounded-tip leaf with a collar as #1. From there count every leaf with a true collar. Leaves that are still wrapped in the whorl around the main stem without exposed leaf collars are not counted. Plants around V6 (6 leaves) start losing the lowest leaf.
The growing point emerges above ground between V5-V6. After that point, splitting the stalk becomes the most accurate way to determine plant growth stage when lower leaves are absent. To stage using this technique, dig a plant inside the field (past the endrows) without breaking the stalk. Carefully split the stalk down the middle through the root ball. At the base of the stalk is an inverted triangle that contains Nodes 1-4 (but they can’t be differentiated). Next look for the white area above that (about ½-3/4”) followed by the next visible band. The white area is the internode with the band being the 5th node (V5). There’s about an inch of internode between V5 and V6. After that, internode length is more dependent upon air temperature instead of soil temperature. Every leaf is attached to a node. Pull off the fully collared leaves and follow them back to where they break off at a specific node. Count the nodes on the stalk to the highest collared leaf that breaks off at a node to determine the growth stage. Once you determine the correct growth stage, you can consider painting a known leaf stage on certain plants (ex. paint the 6th leaf) and then count successive leaves from there when the field is checked. This avoids you having to split more stalks in the future.
Crop Share Survey: The economics team is asking landowners and tenants for input into a Crop Share Survey to better understand lease structure, shared expenses, and educational needs for those utilizing crop share leases in Nebraska: https://go.unl.edu/2025cropshare.
Toxic Plants Webinar Series regarding how the plants impact livestock health will be held June 11, 18, and 25 from 7:30-8:30 p.m. each evening. More info. and register at: go.unl.edu/toxicplants
June 17-18 Tractor Safety Training in York: This is an opportunity for youth to learn how to safely operate farm machinery and receive a farm husbandry certification if they’re 14-15 years old. For more information and to register, please visit: go.unmc.edu/tractor-safety-training
June 17th Prairie Strips Tour: Pheasants Forever is hosting a field day at Logan View School near Hooper in conjunction with UNL Extension from 9:30 AM to 2:30 PM, focused on prairie strips and their role in agricultural productivity and natural resource outcomes. RSVP at: nebraskapf.com/habitat-tours.
June 25 Weed Management Field Day will be held from 9 a.m.-1 p.m. (Reg. 8:30 a.m.) including lunch at UNL’s South Central Ag Lab near Clay Center. The event is free but pre-registration is needed for lunch count at: https://go.unl.edu/qemk. The event will demonstrate weed control options in soybean, corn, and sorghum. Management options that will be demonstrated include: various herbicide programs including ones with overlapping residual, timing of hairy vetch termination for weed control in sorghum, planting date and metribuzin based herbicide program in soybean, termination timing of cereal rye after corn planting, volunteer corn management in Enlist corn, and evaluating Surtain for weed control and crop safety in corn and popcorn.
JenResources 