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Extension Update from Jenny Rees

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Jenny’s REESources-July 31, 2016

Crop Update:  This past week was fairly eventful in regards to our crops.  We confirmed southern corn leaf rust in Thayer and Clay counties on Tuesday; Fillmore and Butler on Wednesday; and Adams, Nuckolls, Lancaster, Pierce, Polk, and Valley were added later last week.  The southern rust thus far has been low incidence with very small, tan, tightly clustered pustules on the upper sides of leaves, usually on leaves just below the ear leaf with a few right at it.  Many instances, the pustules were the area the size of a quarter while others had pustules covering the leaves.  Regardless, it was hard to find more than a few leaves in individual fields with southern rust on them.  Gray leaf spot is starting to move up from lowest leaves of plants now which makes sense counting back 14-21 days to the wind/rain/greensnap event and the conditions that allowed the fungus causing gray leaf spot to infect and eventually sporulate.  Unfortunately, I’ve been in a few fields sprayed at tassel that now have active gray leaf spot and southern rust in them as residual has run out or will soon and the fungicide didn’t make it deeper into the canopy.  There’s also been much misdiagnosis between fungal and bacterial diseases this year.  Thank you to all who attended the three Corn Disease Updates for our area of the State and hopefully these meetings were helpful for you!  Good news is that some of you in the dry pocket of Clay/Nuckolls counties since May and hopefully also in Thayer and Webster received some much needed rain for the non-irrigated crops.

For the high heat, pollination overall is surprisingly good; there’s some tip back but I haven’t seen major pollination gaps on ears in many fields.  As the corn grew taller, I think it was easy to forget our cold, wet early season and the uneven emergence in some fields.  Plant height overall may have seemed similar, but looking at nodes of plants from soil level up and ear height, the emergence issue can be quite evident.  It’s also evident in the unevenness in ear development in fields.  Later emerging plants are just pollinating while others are closer to brown silk-late milk depending on planting date and maturity.  I’m also noticing quite a bit of arrested ear development in various fields.  Essentially arrested ear development is when the ear grows abnormally compared to a ‘normal’ ear.  These can range from ears completely absent on plants, blunt ears which are very short, malformed ears that are ‘pinched’ in different locations, excessive silks that get trapped in tight-husked hybrids, excessive husks with ‘baby’ ears that never develop, zipper ears, bouquet ears, and ears with strange looking husks.  A few resources with photos that I like to use include one from Purdue:  https://www.agry.purdue.edu/ext/corn/news/articles.07/ArrestedEars-0904.html and a PDF small poster from Ohio State and I have hanging in my office:  http://u.osu.edu/mastercorn/files/2014/08/Abnormal_ear_poster_2015_April28-168l0pl.jpg.

So what caused this? Well, it’s important to look at the symptoms in your fields to help determine the potential timing of the damage.  I think there’s a combination of factors involved here and it’s a matter of piecing together what factors were true for your situation if you’re seeing this in your fields.  I would encourage you to check your fields as it’s always better to figure these things out now before harvest.  Things to ask yourself:  are there patterns of hybrids, planting dates, populations, nitrogen/water stress, herbicide chemistries + surfactants and timing, fungicide + surfactants and timing, greensnap or other weather-related events that are consistent across fields showing these symptoms?  Also, it’s important to determine if the remainder of the plant appears ‘normal’ to narrow this down to only ear development damage.  Plants exhibiting some form of arrested ear development will eventually turn a red/purple color due to sugar accumulation in the plant that would have normally been in the grain. Research from Purdue University found non-ionic surfactants (NIS) applied with or without fungicides from 12 leaf to just prior to VT resulted in arrested ear development; they recommended no use of NIS in any foliar pesticide application from V10-VT as late post-glyphosate applications have also been shown to cause this malformation.  Many of us also seen this from pre-tassel foliar fungicide applications to fields, particularly in 2007 when fungicide use in corn drastically increased after the devastating southern rust outbreak of 2006.  With uneven growth stages in fields and some fungicide applications aimed for VT, I hypothesize this may be one contributing factor in some situations this year.  Ears in field end-rows may have been further along (especially in non-irrigated portions) than ears further inside the field.  With uneven growth stages, I’m speculating, based on current growth stages, that some fungicide applications aimed for VT hit various plants in the field prior to VT.  Another potential factor:  Dr. Bob Nielsen from Purdue University has written several articles showing patterns of “cold snaps” or large temperature variations in short periods of time occurring during early ear formation (from V6-V10) tend to produce blunt ear syndrome.  This spring we did have a cold, wet spell followed by high heat stresses in June and hybrids may have responded differently to those temperature fluctuations.  I searched and couldn’t find anything research-based on this, and yet I’m also wondering about our greensnap/high wind event that occurred in many pockets of the State during that V10-V14 stage in fields.  Purdue, Ohio State, and Illinois all talk about weather-related or other stresses occurring between V12-V18 contributing to arrested ear development, but don’t specifically mention greensnap that I could find.  In talking to other agronomists and other Extension Educators focusing on crops, we’re tending to see a pattern of arrested ear development on fields with greensnap, perhaps with some hybrids more than others.  So perhaps there may be more to this if we find more people experiencing this type of ‘pattern’ in your fields as well.  Besides those things, spidermites and some western bean cutworm were also found this week.

I’m starting to see sudden death syndrome (SDS) in soybeans in fields between R3 (beginning pod) to R5 (beginning seed).  There’s nothing a person can do at this point.  Management for the future include resistant varieties, seed treatments in which research is showing promise, and also soil sampling (in SDS affected areas) for soybean cyst nematode which is synergistic with SDS.  I’ve also received questions on the small white moths we’re seeing flying right now.  According to Dr. Bob Wright, our Extension Entomologist, they’re the yellow wooly bear caterpillar and we should start seeing the larvae emerge sometime in August-so be scouting for those in the coming weeks.

Homeowner Questions:  There’s a number of homeowner questions I’ve received as well.  In general, many have involved spruce trees, so I will share a resource that will hopefully help for the time-being: http://byf.unl.edu/d861f891-f677-42f9-950c-82ae060372b9.pdf.    

York County Fair:  Hope you make plans to visit the York County Fair this week from August 4-7!  More information regarding this week’s events can be found at:  http://www.yorkcountyfair.com/.

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