Annual ISU field day
KANAWHA – Despite being brought indoors due to heavy rains, the summer field day hosted by Iowa State University’s Northern Iowa Research Farm Association still provided opportunities for growers and ag professionals to learn all about what has been going on so far this growing season and what to be on the lookout from now until harvest.
The field day was held last Thursday.
Topics included information on crop diseases and management, crop pests and more.
Daren Mueller, assistant professor at ISU and ISU Extension specialist in plant pathology and microbiology, encouraged producers to take to social media, specifically Twitter, to help them track what diseases are popping up and where in Iowa fields.
This, he said, is a method commonly used by the Centers for Disease Control to help track diseases in humans, so they are better able to warn the public what kind of sickness and where that disease is popping up in the United States.
“We’re trying to do something like that with field crop diseases,” Mueller said, “so we’re hoping we get enough people to participate we can start pulling up that information.”
He added if a producer or agronomist starts seeing a disease in their corn or soybean fields to snap a picture, add the name of a disease, the county and state they reside in and upload it to Twitter using the appropriate Twitter handles: @soydisease or @corndisease.
For corn, a newer disease has been recently identified in 2016. It is known as “bacterial leaf streak.”
This disease, Mueller said, was first discovered in Nebraska in 2014. It is caused by a species of bacteria that also can cause diseases on sugar cane.
So far, South Africa is the only other country that has seen disease caused by this particular bacteria.
“It took plant pathologists and the USDA a couple of years to figure out what this was and to give it a name,” said Mueller. “So it’s a little head-scratching as far as trying to figure out why the heck we are suddenly seeing this disease in the central part of America when the only other place that this pathogen is from is the other side of the world.”
Last growing season, Mueller said a survey was conducted in the central part of the U.S. and neighboring states to Nebraska and were surprised to find the bacterial leaf streak growing in several states.
Bacterial leaf streak, he said, is now being found on corn leaves in the V4 and V5 growth stages for this growing season.
“It is one of the few disease popping up already and as it becomes more established, this could be an early season disease that we keep an eye on,” said Mueller, adding that by visiting cropdetectionnetwork.org, producers can find a lot of pictures of bacterial leaf streak that could help them identify the disease.
Otherwise, he advised to look for streaking down the leaf of narrow lesions that feature wavy margins and with yellow, tan or brown streaks.
“For me, the thing that makes it a little disconcerting is that there are several other diseases or disorders that can look very similar to bacterial leaf streak,” he said.
The main tool to use to help make the proper diagnosis, he said, is the sun.
“You have a leaf, and look at it holding it up to the sun,” he said. “We see more evidence of the disease, see the disease and then you will see a halo; a bright yellow halo that extends from the ends of the lesions.”
If producers or ag professionals believes they have found bacterial leaf streak in a corn field, Mueller urges them to share some samples.
“This is a new enough disease, and we are asking you guys that if you find it, to send samples into our plant and insect diagnostic clinic, or help it get to the hands of someone in our extension system,” said Mueller.
There is an importance of making sure that you are getting a proper diagnosis.
“That should be motivation right there to make sure you have the disease properly identified for that field,” he said.
Sudden Death Syndrome (SDS) is a fungal disease where pathogens live in the soil. It can cause a root rot where those pathogens, eventually later in the season, cause the toxins to move up the plant, killing it.
Mueller said one of the best ways to help combat the disease is seed treatments.
“Seed treatments should work on SDS,” he said.
Through several product evaluations of seed treatments, Mueller said the product ILeVO has shown a reduction in disease by 55 percent and a higher percentage of yield increases over other seed treatment products available.
“Right now, nothing is topping ILeVo, but keep your eyes open for new products coming out,” he said. “There is some stuff in the pipeline that looks promising.”
John Sawyer, professor and ISU Extension specialist in soil fertility and nutrient management, discussed some of the current research going on at ISU regarding sulfur deficiencies coming up in Iowa’s soils and applications of the mineral to corn.
“The sulfur deficiencies are here,” Sawyer said. “They have been here, so it’s not an increasing concern, but something we have really had to deal with the past few years and will continue to do so in the future.”
He added research has included some on-farm sulfur trials in corn and alfalfa.
The research is newer, as prior to 2005, there were no signs of sulfur deficiencies in the state.
Sawyer said research has shown that in sulfur uptake with a 200 bushel per acre corn yield, there is approximately 8 pounds of sulfur in the grain, and the vegetative part of the plant holds about 5 pounds of sulfur uptake.
“This will vary, but there will be about 13 to 14 pounds of sulfur per acre of total uptake above the ground,” said Sawyer.
Compared to a corn plant’s nitrogen uptake, Sawyer said sulfur is easily managed.
“You can see the difference in pressure on the soil system to supply nitrogen compared to sulfur,” he said. “And we can easily meet the sulfur needs with our soil supply or with an additional application of sulfur, and studies have been showing a yield increase with additional sulfur applied.”
Almost 50 percent of trials conducted on sulfur have responded with a significant response of a yield increase.
The main source of sulfur in Iowa’s soils is through organic matter, according to Sawyer.
“Just like nitrogen, that sulfur supply becomes available to a crop through mineralization,” he said.
Sawyer also explained there is a large pool of sulfur in most soils through either subsoil sulfate, rock degradation, accelerated gypsum in the soil, atmospheric deposition and manure.
He said those areas that may require a sulfur application could include course texture soils, eroded soils, low organic matter soils, reduced till or no till soils; soils with a high amount of crop residue; cold temperatures in the spring and where alfalfa was the prior crop.
Also, those soils with no manure application may also see the chance of having a larger response to a sulfur application.
“It does not guarantee it, but that tends to be where we see that happen,” said Sawyer.
Erin Hodgson, associate professor and ISU Extension specialist in entomology at ISU, discussed the two main insects that could affect Iowa’s producers this year: soybean aphid and the corn rootworm.
“With the soybean aphid, we don’t know what to expect every year,” she said. “It’s erratic. The time when it will hit the soybean and making the decision to make a treatment varies each year. It’s a pest that is on your mind and you should be thinking about.”
Hodgson said she brings up the potential of a soybean aphid issue because they are already beginning to show up in research plots and producer’s fields.
“It’s a week or two earlier than we would normally see them,” she said. “It’s not a huge number of aphids, so don’t freak out right now, but we have been seeing a handful where one or two percent of the plants are affected. Seeing aphids a little bit earlier and that does set us up for possibly more treatments than we could normally see.”
Soybean aphids can be treated with a pyrethroid insecticide. However, Hodgson said there have been some populations in northern Iowa that did not respond to a pyrethroid last year, showing a potential resistance.
“So that is on the horizon, but that one field doesn’t make a trend, but to know there were fields in southern Minnesota that have seen resistance failures and confirmation of resistance for a couple of years now, so that makes sense some of those northern tier counties in Iowa are seeing it.”
“The corn rootworm is probably the most important pest that we have here as far as economic injury potential in our state,” Hodgson said.
She shared some bad news in that research is showing all four Bt traits that have been made to help fight corn rootworm have been confirmed resistant.
“It’s not widespread, it’s not in every field, but somewhere all four traits have been confirmed resistant,” she said.
The larvae, she explained, will be feeding for the next few weeks. Then they will pupate and turn into adults. That is the time, she said, producers should be out scouting for any potential injury.
“You want to see the injury fresh because it is not very easy to tell what is rootworm versus other things in October,” she said. “You want to look at fresh injury – browning, pitting and scaring.”
Hodgson said, regardless of seed treatments, genetics, or soil insecticides use, to look at it all.
“Management implication for the next growing season are determined this year,” she said. “How intense the rootworm is makes the decision for next year.”
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