Blog Archives

JenREES 8-26-18

Reminder of South Central Ag Lab Field Day August 29th from 8:25 a.m.-4 p.m. (Registration at 8 a.m.)! 10.5 CCA credits have been applied for. More information at: https://go.unl.edu/zvwx

Crop Update: The rain last weekend was a blessing to many. It along with cooler temperatures has allowed for deeper kernels and delayed corn maturity. In fact, if we were to stay at the high temperatures we were experiencing, the Hybrid Maize model was predicting maturity in our area anywhere from 1-3 weeks early. Now, it’s mostly just predicting one week early (for anything that isn’t already mature). It also is showing above average yields for non-irrigated corn where drought-stress and hail weren’t a factor. Irrigated yields are showing near average according to the model for most fields in the area. You can see all the graphs and read more in this week’s CropWatch at http://cropwatch.unl.edu. Corn has reached black layer in many of the hail damaged fields I’ve looked at and some of the drought-stressed fields will begin harvest in a few weeks. The rain also greatly helped the soybeans, even in drought-stressed areas.

However, the rain also greatly increased stalk rot in fields, particularly in hail damaged ones. We weren’t seeing a large amount of mold in the first 7-10 days post-hail  in hail damaged fields that were late dough to early dent. Now, nearly 21 days later, we’re seeing fungal growth increasing with the moisture and humidity within the husks of corn ears. It will be very important to check your fields to determine worst ones and worst areas of fields regarding stalk rot and kernel damage. Those areas should be harvested first if they’re being taken for grain and we’re recommending to fill any contracts with grain from those areas first. In checking for stalk rot, I prefer a ‘pinch test’ compared to a ‘push test’. With the pinch test, take your thumb and first finger and pinch the stalk internode that occurs between the lower nodes above the soil line. Do this for 20 plants in an area and get a percentage for those that crush. Then do this for several areas of your field. This gives you an indication of the level of stalk rot for your field and worst affected areas.

Cover Crops: With recent crop insurance determinations on these damaged fields, I’ve received an increasing number of questions regarding cover crop use. We’re already seeing weeds germinating in these fields due to open canopies, so weed control is one considerations for using a cover crop right now. Other reasons expressed have been for excess nitrogen uptake and also for a forage option. Dr. Mary Drewnoski, Extension Beef Nutritionist, Dr. Daren Redfearn, Extension Forage Specialist, and I talked through options to consider right now.

Always check with your crop insurance agent before seeding a cover crop into hail-damaged fields. It’s also important to check replant, forage and grazing restrictions regarding the herbicide program you used and any delay necessary before seeding a cover crop and any forage restrictions to grazing a cover crop. (See Replant Options and Herbicide Rotation Restrictions and Forage, Feed, and Grazing Restrictions for Row Crop Herbicides, both excerpted from the 2018 Guide for Weed, Disease, and Insect Management in Nebraska, EC130.)

In general, we’re at an interesting time for making cover crop decisions. Typically we use September 1 as the divider between planting small grains such as oats that will winterkill and winter hardy cereals such as rye or triticale (planted after September 1). Even with brassicas such as turnips, collards, or rapeseed, we’d recommend the cutoff for seeding to be within the next two weeks. Because of this time frame, mixes may be beneficial because they’ll take advantage of whatever weather we have for the rest of the season. Simple, inexpensive mixes may allow for at least something to become successfully established. So, for those looking at something to winterkill, oats could be planted yet this week as could a mix of oats and brassicas. However, after this week, we’d be looking at either adding something like rye or triticale to the mix or just switching to the more winter-hardy small grains. And honestly, while it isn’t mentioned in the table, if a person’s goal is cover the ground for weed management, bin-run wheat is also an inexpensive option. Your local seed supplier can provide seeding rates for cover crop options and we’ve provided a table with these options, depending on your goals, at http://cropwatch.unl.edu.

Yellow or red tops in corn plants: For a month now, we’ve observed yellow tops in cornIMAG5726 plants. Plants that contain ears and are turning yellow from the top to the middle of the plant can be occurring because of anthracnose top dieback or another disorder called ‘top leaf death or dieback in corn‘. Some plants with this discoloration truly do have anthracnose spores present on the stalk and sheaths. However, there have been other situations where I couldn’t find the presence of anthracnose spores. In those situations, the plants were often on compacted areas of field edges, always had a nice ear on the plant, and sometimes had tillers as well. Dr. Bob Nielsen at Purdue mentioned they had found what’s called ‘top leaf death’ in corn in situations where they experienced more drought or heat stress. Those plants had leaf discoloration similar to anthracnose top dieback, but without the presence of the spores. So, for those situations where I’m not finding anthracnose spores, I’m calling it this top leaf death disorder. You can read more about this at: https://www.agry.purdue.edu/ext/corn/news/timeless/topleafdeath.html.


Table 1. Cover crop considerations for late-season hail-damaged crops
COVER CROP USE/GOAL WHEN TO PLANT HOW TO SEED RATE
(PER ACRE)
ADDITIONAL NOTE
OATS Weed Management By Sept. 1 Drill best. Can fly on. 30-40 lbs *
OATS/RYE MIX Weed Management By Sept. 1 Drill best. Can fly on. 30 lbs each *
OATS Forage By Sept. 1 Drill best. Can fly on. 80-90 lbs *
OAT/RYE MIX Forage By Sept. 1 Drill best. Can fly on. 30-40 lbs of rye and 50-60 lbs oats *
BRASSICAS (TURNIP, COLLARD, RAPESEED)-NOT OILSEED RADISHES Cover ground, forage, nitrogen uptake By Sept. 1 Fly on for quicker establishment. 5-6 lbs  —
RYE Weed management, cover ground, forage, nitrogen uptake After Sept. 1 Drill best. Can fly on. 50-60 lbs  *
*If adding a brassica to any of these small grain options, only 2 lb/ac is needed. Rapeseed isn’t as well known, but is an inexpensive and good option for consideration.

Corn Disease July 2015

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.

Anthracnose has been observed in fields for a good month now.  It is mostly seen on lower leaves of plants, particularly in fields where we've had high amounts of rainfall, standing water, and/or hail.  I haven't seen it moving up the plant very far yet.  There are fungicides labeled for this, but we rarely recommend fungicide treatment for anthracnose.

Anthracnose has been observed in fields for a good month now. It is mostly seen on lower leaves of plants, particularly in fields where we’ve had high amounts of rainfall, standing water, and/or hail. Lesions are tan in the center and have a wavy yellow colored margin.  I haven’t seen it moving up the plant very far yet. There are fungicides labeled for this, but we don’t often recommend fungicide treatment for anthracnose.

We saw this disease in the Saronville/Sutton area last year.  This year, we are seeing it throughout Nuckolls, Thayer, Clay, and Adams counties...and most likely others too.  Some hybrids (and have seen this across companies) are highly affected by this bacterial disease.  We have informally called it

We saw this disease in the Saronville/Sutton area last year. This year, we are seeing it throughout Nuckolls, Thayer, Clay, and Adams counties…and most likely others too. Some hybrids (and have seen this across companies) are highly affected by this bacterial disease. Neither last year, nor this year, has the pathogen causing this disease been confirmed. Plants will have vein-limited lesions in streaks on the leaves. It is often confused with gray leaf spot early on.  Take a hand-lens and looking closely, you will see wavy margins on the lesions which doesn’t usually occur with gray leaf spot.  Over time, these lesions become elongated and can coalesce with other lesions. Also looking closely with a handlens or microscope, one finds the leaf tissue eventually becomes transparent. While other diseases can look similar to it, under the microscope, no fungal spores are found other than secondary ones. Putting an infected leaf in water reveals cytoplasmic streaming in which the bacteria is escaping the leaf tissue. (The pathogen causing Goss’ wilt also does this, but this disease is not the same as Goss’ wilt). Fungicides will not cure bacterial diseases and the products advertised for targeting bacterial diseases haven’t been researched for this disease.  This is the primary disease we are seeing in our area right now-and it looks nasty in some fields!  Unfortunately there’s nothing we can do about it.  If you are considering testing one of the products for bacterial diseases, please let me know as I’d appreciate testing it with you via on-farm research.

Goss' wilt (bacterial disease) has been observed in fields as well.  I typically notice it along field edges, pivot tracks, pivot/well roads or hail-damaged fields as plant wounds in general allow an entry for bacterial pathogens.  However, research has shown that the bacterial pathogen causing Goss' wilt can enter through the leaf stomates as well.  Leaf miner damage can be observed at the top of this photo, and often, but not always, I notice this occurring together in fields.  There is nothing we can do for Goss's wilt if you have this disease in your fields right now.  There are products targeting bacterial diseases on the market.  If you're interested in trying these, please consider an on-farm research experiment to prove the efficacy to yourself and help us obtain data.

Goss’ wilt (bacterial disease) has been observed in fields as well. I typically notice it along field edges, pivot tracks, pivot/well roads or hail-damaged fields as plant wounds in general allow an entry for bacterial pathogens. However, research has shown that the bacterial pathogen causing Goss’ wilt can enter through the leaf stomates as well. Leaf miner damage can be observed at the top of this photo, and often, but not always, I notice this occurring together in fields. There is nothing we can do for Goss’s wilt if you have this disease in your fields right now. There are products targeting bacterial diseases on the market. If you’re interested in trying these, please consider an on-farm research experiment to prove the efficacy to yourself and help us obtain data.

Physoderma brown spot typically doesn't occur in our area until tasseling (which is where we are at now in some fields).  However, I was seeing this as early as two weeks ago on some hybrids.  The pathogen causing this disease is a fungal-like pathogen that moves with water.  You will notice a purple/brown color on midribs of leaves, leaf sheaths, stalks, and tiny yellow/brown/purple spots on leaves.  This disease isn't considered yield-limiting or of significance to us in Nebraska.  Some confuse this disease with southern rust, but there are no pustules produced with Physoderma brown spot.

Physoderma brown spot typically doesn’t occur in our area until tasseling (which is where we are at now in some fields). However, I was seeing this as early as two weeks ago on some hybrids. The pathogen causing this disease is a fungal-like pathogen that moves with water. You will notice a purple/brown color on midribs of leaves, leaf sheaths, stalks, and tiny yellow/brown/purple spots on leaves. This disease isn’t considered yield-limiting or of significance to us in Nebraska. Some confuse this disease with southern rust, but there are no pustules produced with Physoderma brown spot.

The larger, rectangular lesion is typical of gray leaf spot found in some lower leaf canopies right now.  It is easy to confuse with anthracnose as both diseases appear a little different on various hybrids.  Gray leaf spot will be vein-limited while anthracnose is more blotchy in appearance.

The larger, rectangular lesion is typical of gray leaf spot found in some lower leaf canopies right now. It is easy to confuse with anthracnose as both diseases appear a little different on various hybrids.  Gray leaf spot will be vein-limited while anthracnose is more blotchy in appearance.  Comparing gray leaf spot with the unknown bacterial disease, the lesion edge will be straight for gray leaf spot and wavy for the bacterial disease.

Northern corn leaf blight is a disease we're hearing a lot about but I have yet to see it in our area.  Most have been mistakingly calling the unknown bacterial disease shown above northern corn leaf blight, but there's truly a difference as you see these photos.  Compared to gray leaf spot, northern corn leaf blight will be more cigar-shaped instead of forming a rectangle.  As this photo taken from the Mead, NE area shows, lesions are often forming in close proximity to each other on the leaves in Nebraska right now.  This disease is one to watch as it has been expanding on certain hybrids in some fields, particularly in eastern, Nebraska.  However, I still haven't seen it in our area and haven't received any confirmations of it being found in our area.

Northern corn leaf blight is a disease we’re hearing a lot about but I have yet to see it in our area. Most have been mistakingly calling the unknown bacterial disease shown above and even Goss’ wilt, northern corn leaf blight, but there’s truly a difference as you see these photos. Compared to gray leaf spot, northern corn leaf blight will be more cigar-shaped instead of forming a rectangle. As this photo taken from the Mead, NE area shows, lesions are often forming in close proximity to each other on the leaves in Nebraska right now. This disease is one to watch as it has been expanding on certain hybrids in some fields, particularly in eastern, Nebraska. However, I still haven’t seen it in our area and haven’t received any confirmations of it being found in our area at this time. (Photo courtesy of Aaron Nelson, Nelson Precision Agronomics).

%d bloggers like this: