Crop Updates: An increase in disease pressure has been the theme the past few weeks. Sudden death syndrome is increasing in soybeans, but there’s also brown stem rot (BSR) and frogeye leaf spot in some fields. The foliar discoloration is the same for SDS and BSR with the yellow/brown discoloration between leaf veins. You can tell the difference by pulling a plant out of the ground. SDS is usually easy to pull as the taproot is rotted. Splitting the stem open, the root will show rot at the soil line but the stem pith will be white and healthy. With brown stem rot, the pith will have brown discoloration. The addition of stem borer can make it more difficult to tell the difference sometimes. Unfortunately there’s nothing one can do for SDS or brown stem rot now as both are caused by soil borne fungi. I would recommend taking soil samples for soybean cyst nematode (SCN) in areas currently impacted by SDS as the combination of diseases is synergistic in impacting yield loss. You only need 0-8” samples and they can be taken during soil fertility samples if you don’t want to take them now. The samples are free via your checkoff dollars and they can be sent to the Plant and Pest Diagnostic Lab at UNL in Lincoln.
In corn, foliar disease is increasing in mid-canopies. Most concerning are the number of stalk rot samples/situations I was called to the past week. They all appear to be bacterial stalk rot thus far. Symptoms include watersoaked nodes and below the nodes with plants breaking off/falling over. Damaged nodes are from the soil line to upper canopy. The bacteria disintegrates these stalks creating a stringy appearance within them where the nodes break and when slitting open stalks. It also has a distinct foul smell. This is more of a problem in wet years such as this and hybrid susceptibility varies. The bacteria doesn’t typically transfer from plant to plant. I have photos of what I’m seeing on my blog at https://jenreesources.com.
There have been multiple late-season hail events in the area. For those fields hit by the August 6th storm, the rainy, cool conditions have allowed for increase in mold on the hail damaged side since many of those damaged ears were at milk stage. However, I’m also seeing mold damage on some back-side of ears in hybrids with tighter husks. The white/pink fluffy growth on the hail damaged side is caused by Fusarium/Gibberella fungi. The presence of these fungi does not automatically mean mycotoxins are present; they do have the potential to produce mycotoxins. The green fungal growth in ears are caused by secondary and minor fungal pathogens that don’t produce mycotoxins. The white fungus overtaking ears on some tight-husked hybrids is diplodia which can cause for light test weight but does not produce a mycotoxin. It will be important to continue to watch grain quality over time prior to harvest.
Wild and Burcucumber on Trees has also been a huge question. Do Not apply 2,4-D to trees for
control as that has been the most common question! The simplest way to kill wild and burcucumber is pull or hoe the plant at its base below the tree. There’s not much to the plant root and the vines will then die on the tree!
It’s been a hard year for our growers and livestock producers with continued challenges. Seeking to end this column on a positive note, this year is the 10th year of the Nebraska State Fair in Grand Island and the 150th Fairabration. I’m grateful for the focus on agriculture, families and youth! And, it’s encouraging to me to see youth learning life skills whether competing in public speaking, working with and showing livestock, or studying and competing in contests such as weed and grass ID at the State Fair. 4-H is where I got my start and it’s exciting for me to wonder at the futures these 4-H and FFA youth have ahead of them as they continue to work hard and put into practice the life skills they are learning! Hope you can make it out to the State Fair at some point!
*End of News Column. Bacterial stalk rot photos below.
Radio advertisements, email blasts, and other media are warning of corn diseases and the need for fungicides. Two months of humid, wet weather has allowed for disease development. It’s important to know what diseases truly are in your field before spraying a fungicide, particularly with today’s economics. Here’s what we’re seeing in fields right now in the Clay, Nuckolls, Thayer, Adams county area. Based on the diseases we’re seeing, we would recommend you scout your fields to know whether you have mostly bacterial or fungal diseases present. Consider disease pressure, where on the plant the disease is occurring, growth stage, and economics. We have had southern rust show up in 10 of the last 11 years I’ve been serving in this area. If you spray a fungicide at tassel, you may not have enough residual to ward off southern rust when it appears later, potentially resulting in the need for a second application. In our area thus far, I’m not seeing enough disease pressure in many fields to warrant a fungicide at tassel; consider delaying an application till later for economic and resistance-management reasons. Ultimately this decision needs to be done on a field by field basis. Please also see this UNL CropWatch article regarding fungicide application and corn growth stage. Although I don’t have a photo of it, I’ve also seen common rust in the mid and lower portions of corn canopies thus far.
Happy New Year! Wishing all of you and your families a wonderful 2015! As I look back at 2014, there are several ag-related observations that I noted throughout the year.
The first observation continues to be the way communities and people in this County/area pull together in difficult times. Whether after tornadoes/wind storms or helping other farm families who had an injured family member or had lost a family member, it’s just a blessing to see the way people pull together to help each other in time of need. It was also a blessing for many who were unable to harvest in 2013 due to the August 1st storm, to harvest fields in 2014, and for many in the area to experience really good irrigated and dryland yields this year.
The dry winter of 2013/14 allowed for very mellow ground during planting time. Often seeding depth ended up ½-1” deeper than intended. The dry winter also didn’t allow for good residue decomposition leading to problems during planting and ensuing stand emergence. Cutting off residue and high rains in May led to unintended consequences of replant situations when residue was moved off of farmers’ fields onto neighboring fields, suffocating emerged plants in portions of fields. I’m not sure what the solution is for the future other than it really needs to be something worked out with neighboring farmers, but perhaps mentioning it here opens an opportunity for future conversations.
Cover crops have been incorporated into more operations in recent years, yet the ultimate goal for using them remains important in determining what species/crops are used in the fields. We also realized the importance of determining amount grazed prior to turning cattle into fields (whether for grazing cover crops or crop residue), as high winds in winter 2013/14 in overgrazed fields led to soil blowing throughout the winter.
The May frost showed us emerged soybeans at the cotyledon stage held up well to the frost compared to the corn. We also again watched Goss’ wilt show up systemically by 6 leaf corn that was injured early by frost or hail in fields where Goss’ wilt had been a problem in the past. We need more research/understanding of this disease. Wheat continues to show us its resiliency as it winterkilled in portions of fields, withstood drought-stress, and then made up yield in the last 4-6 weeks.
Perfect pollination conditions coupled with high solar radiation, low night-time temperatures, and timely rain events were keys to the bountiful corn crop we experienced this year. Soybeans were more of a mixed bag. In walking fields and in conversations with farmers, I think the disappointment in some irrigated yields could be attributed to early/over-irrigation, disease problems, and planting date. UNL on-farm research showed on average a 3 bu/ac yield increase when soybeans were planted in late April to first week of May (regardless if growing season was warm/dry or cold/wet like it was this year) and those I’ve talked to who achieved 80+ bu/ac in the area this year planted in that time-frame. I’m curious if there’s something to planting a 2.4-2.5 maturity early vs. a 3.0+ maturity early as some area producers are seeing strong yields from a shorter season hybrid planted early the past few years. So if you’ve also seen this and/or are interested, that will be an on-farm research project to try next year. Please let me know if you’re interested!
Here’s wishing you a healthy and prosperous 2015!
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.
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.
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.
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.
Several of us had been watching the USDA IPM Pipe Map for weeks. It wasn’t showing southern rust moving and only Georgia 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.
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.
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. 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.
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 disease pressure in your field, stage of growth, pre-harvest intervals, and length of time for fungicide residual in addition to economics.
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.
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.