Category Archives: Diseases
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!
Interesting, memorable don’t seem to capture this year. While portions of Nebraska are flooding again, many growers in this part of the state and east would like some rain. Dr. Suat Irmak shares on understanding matric potential and water content thresholds on sensors for irrigation scheduling in this CropWatch article: https://go.unl.edu/miym.
Soybean: The large number of painted lady butterflies we experienced in late May/June was due to a wet season in Mexico that allowed for greater vegetative growth and survival for northern migration, according to Bob Wright, Extension Entomologist. The cooler conditions may have caused more to stay here instead of move north. Saw newly hatched to early instars of thistle caterpillar (the larvae of painted lady butterflies) this week. Yet, a tremendous number of butterflies are still laying eggs. A painted lady female can lay up to 500 pale green eggs on plants individually instead of in egg masses. The larvae hatch in around a week and can feed from 2-6 weeks depending on weather conditions. 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/v0ts. If your primary defoliator is thistle caterpillars, it’s important to use insecticides that can be effective on them once their ‘tents’ are built. The 2019 Guide for Weed, Disease, Insect Management gives information regarding products that may work better on pages 308-314.
Gall Midge in Seward County: My colleague Aaron Nygren found soybean gall midge in
Seward County north of Bee this past week. I was a few miles away so met him at the field. Being a new insect pest, little is known about it. Infected plants show signs of wilting from larvae feeding within the base of the stem. These plants will eventually die. To scout for soybean gall midge, focus on plants that are close to the field edge and adjacent to fields that were planted to soybean in 2018. If you’re seeing wilted/dying plants, particularly in early planted beans this year, please contact your local Extension educator. More information at: https://cropwatch.unl.edu/gallmidge.
Bob Wright is asking for help to understand distribution of the green June beetle, Japanese beetle, and brown marmorated stink bug. If you see these insects, please take a picture and upload it to: inaturalist.org, including information on where the photo was taken. You need to make an account with inaturalist.org before you can upload photos. And, if you’re unsure what these insects look like, you can view them at: https://go.unl.edu/uzd0.
Corn: Looked at numerous corn leaves but so far, only common rust in Nebraska. Southern rust was confirmed in southern Kansas and Missouri this past week. You can view U.S. counties where southern rust has been confirmed at: https://corn.ipmpipe.org/southerncornrust/.
As we approach tasseling: 1-Areas of fields that had water ponded this
growing season may show crazy top of corn. Crazy top symptoms include when the tassel appears strange and leafy. Plants can be barren, have barren kernels on ears, or have multiple ears at shank. 2-Automatic fungicide applications at tassel: I prefer waiting till disease warrants application & Nebraska research shows fungicide applications later in the season are effective. Be careful if you automatically spray at tassel! Canopy closure covered problems in fields, including uneven growth stages. Plants in the field may have tassels with others several growth stages behind. Arrested ear development primarily occurs on plants from 12-14 leaves when surfactants (particularly non-ionic) are applied with fungicides. So, it’s important to know your growth stages and consider what you’re applying. 3-Japanese beetles in corn threshold: Three or more Japanese beetles per ear with silks clipped to less than ½ inch and pollination is less than 50% complete. 4-It’s OK to fertigate pollinating corn. Avoid running pivot from 6 a.m.-Noon during pollination. Can apply 30 lbs N in 0.25″ water or up to 60 lbs N in 0.50″.
Linden trees and Japanese beetles: Last week I didn’t stress the importance of insecticides and impact to bees when spraying linden trees. ‘Sevin’ is effective but highly toxic to bees. It’s better to use heavy streams of water in late afternoon to knock Japanese beetles down (then drown in soapy water), pyrethroids, or permethrin like ‘Eight’ as those products are not taken back to the hives.
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
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
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.
This post shares observations of what I’ve been seeing in fields pre-harvest and during harvest during this 2018 growing season. Some of these problems stemmed from hail/wind damage and others insect damage. This is a longer post with the desire to have many resources available to you in one place. Hopefully this will be helpful for diagnosing concerns as harvest continues.
(Photos above) Hail-damaged soybeans pre-harvest. The plants in this field weren’t pummeled into the ground, but from the road it was deceiving as to what the soybeans were actually like on these plants. The two smaller photos are all the soybeans found on 2 adjacent plants from the top soybean photo pre-harvest. There were a lot of aborted pods on stems and moldy beans in general. For those who combined hail damaged beans in the area, farmers shared they had everything from ‘lima’ beans to shriveled, moldy beans as you can see in these pics, which is also what we were anticipating may be found.
Cladosporium ear and kernel rot seen on kernels already affected by Fusarium, particularly in hail damaged fields. This is a lesser ear rot fungi and doesn’t produce a mycotoxin but can create increased damage to kernels. Was recommending taking grain damaged to this extent directly to the elevator.
Photos above shared by a Clay County farmer who observed kernel germination and Fusarium growth (mostly due to western bean cutworm damage) upon harvesting his field. Hormonal balance within the kernels shifts towards harvest. At full maturity, very little abscisic acid (ABA) is left in the kernel (in both corn and soybeans) which allows them to germinate in correct conditions after harvest. These conditions include moisture and temperatures above 50ºF. Presence of fungi such as Fusarium and Gibberella also increases gibberellins in the kernels allowing for kernel germination with presence of moisture as we’re seeing this harvest. Increasing air flow during harvest will hopefully blow most of these damaged kernels out the back of the combine.
- Corn Ear Rots, Storage Molds, Mycotoxins, and Animal Health, ISU, 1997. (Nice comprehensive resource available in PDF download via web search)
- UNL Corn Disease Profile III: Ear Rots
There’s over 25 species of fungi that can produce ear molds with the majority of them ceasing growth at 15% moisture within the kernel. Thus, we recommend drying grain to 15% moisture as quickly as possible to cease additional fungal growth within the grain bin. The table below shares the days required to dry corn to 15% moisture with 1.0 cfm/bu and various temperature and humidity conditions.
- Management of in-bin natural air grain drying systems to minimize energy cost
- Grain storage management to reduce mold and mycotoxins (ppt presentation)
- UNL CropWatch Grain Storage Resources
- Managing large grain bins for potential mycotoxin contamination
In 2018, we’re primarily seeing Fusarium and Gibberella species which have the potential to produce mycotoxins. Thus, the information below is directed at those fungal species and mycotoxin levels that can be associated with them. Again, the presence of fungi does not automatically mean a mycotoxin is present.
- Grain storage management to reduce mold and mycotoxins (ppt presentation)
- UNL CropWatch Grain Storage Resources
- Managing large grain bins for potential mycotoxin contamination
- Understanding Fungal Toxins UNL
- Sampling and Analyzing Feed for Toxins UNL
- Use of Feed Contaminated with Fungal Toxins UNL
- Feeding Storm Damaged Corn: A few thoughts from a Veterinarian
Also, there’s a new app called “Mycotoxins” and it’s another resource with ear rot pictures and mycotoxin information put out by several Universities produced for both Apple and Android devices.
Crop Updates: A great deal of timely information was provided in this week’s CropWatch at http://cropwatch.unl.edu including information about high heat and pollination, applying fertilizer during pollination, western bean cutworm scouting, forecasted yields, etc. Please check it out!
Several called me asking about applying fertilizer during pollination. I shared that while
I wasn’t aware of research, I personally was concerned about anything potentially interfering with pollination and that I do recommend 30 lbs of N at brown silk if needed or if you were originally planning split nitrogen apps. This is based on research from Purdue sharing today’s hybrids use 30-40% of their total Nitrogen from flowering through maturity. After discussing with Dr. Tom Hoegemeyer, Adjunct UNL Professor of Practice, he offered the following insights: “Pollination mostly occurs between 8:30 a.m. and Noon. Thus, as a precaution, I would not run a pivot on pollinating corn from 6 a.m. to Noon. When the temperature is 90°F to 95°F, the pollen is killed by heat and is seldom viable past 2 p.m. That leaves lots of time to run pivots, apply N, etc. when it won’t harm pollination. Silks tend to be viable for three or four days at these temperatures, so if a plant isn’t pollinated one day, generally the next day will work just fine. (If nitrogen is needed), I’d recommend that nitrogen go on as soon as practical. Corn nitrogen use is very high during the pre-tassel growth phase and again at kernel growth, from one to three weeks post pollination. About seven to ten days post pollination (before brown silk) lower N will start causing kernel abortion and serious yield loss in corn.” The UNL recommendation for fertigation is to use 30 lb of N with 0.25″ of water or 50-60 lb of N with 0.50″ of water.
Last week also brought questions regarding thresholds and difficulty in finding Western Bean Cutworm egg masses with moth flights at their peak. You can view light trap data from UNL’s South Central Ag Lab thanks to Terry Devries at: https://scal.unl.edu/ltr2018.pdf. There’s also a great article in this week’s CropWatch on how to scout for them, insecticide options, and additional recommendations. Thresholds for western bean cutworm are 5-8% of corn plants in the field containing egg masses or larvae. Egg masses can be difficult to find during pollination with pollen hiding them. ‘Typically’ egg masses are found in the top third of the plant on the upper sides of leaves and near midribs or leaf axils. However, with higher heat, I tend to find them closer to the ears and have even seen masses laid on the ear husks and on the backsides of leaves (not common). While larvae are generally known to move up the plant to feed at the tassels, I’ve seen high heat force larvae into ears earlier. It typically takes 5-7 days for larvae to hatch and the egg masses turn purple just prior to hatching. A number of insecticide options are available for both aerial application and via chemigation; these products are listed in the CropWatch article.
With insecticide applications occurring in corn for both western bean cutworm and also corn rootworm beetles, many have also called or talked with me about the recommendation of fungicide applications. Right now, I haven’t found gray leaf spot above 3 leaves below the ear leaf in several counties. There’s been some mis-diagnosing bacterial leaf streak as gray leaf spot. Southern rust was just confirmed in a Kansas county this week, but we still have yet to confirm it in Nebraska. Even the longest residual products won’t get us through August if a fungicide application occurs now. I can appreciate that economics are tight so the thought is to save an additional application cost by applying a fungicide now with the insecticide. And, I can appreciate economics are tight regarding why apply a fungicide right now when disease pressure doesn’t warrant it? Perhaps, at least those of you with the ability to chemigate could consider waiting till disease pressure warrants it for your field, if it does. Always in the back of my mind is the need for late-season protection with southern rust eventually showing up and gray leaf spot often worse then.
My perspective is from a resistance management and research-based one. We have 5 total modes of action for fungicides with 2 of them being in nearly every fungicide product we use in corn, soybean, and wheat because they work against foliar fungal pathogens. At some point, our pathogens will also adapt, as we’ve seen our weeds and insects do…it would be like losing our ability to control gray leaf spot and southern rust similar to palmer amaranth on the weed side. In Nebraska, Dr. Tamra Jackson-Ziem’s research has not shown an automatic yield increase to fungicide application in the absence of disease. And, it has also not shown an automatic yield increase when applied at tassel. In a high heat and low disease year like 2012, there were no statistical yield differences with fungicide application vs. the untreated control. Even in years with some disease pressure such as 2008-2010, she found no statistical yield differences between when various products were applied from Tassel through Dough stages. In high disease years, her research shows the benefit of fungicide application for reduced disease pressure and increased stalk strength. Fungicides are great tools to help us with disease pressure and stalk strength. Just would encourage all of us to consider when we really need to apply them and to understand that research in Nebraska does not automatically show increased yields with the use of them or with the timing of Tassel/Silking vs. later in the year. Also, hybrids may vary in their response due to disease susceptibility and other factors. Not all her data is listed at this site, but you can view it for yourself at: https://go.unl.edu/ni3y.
Bagworms: I’ve been seeing shelter belts and various trees turning brown from heavy
bagworm infestations. Please be checking your trees if you are noticing them turning brown. Additional information can be found at: https://go.unl.edu/rgju.
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
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
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 email@example.com.
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.
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.
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.
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.