Texas Corn: Rains, Humidity Promote Increased Disease Development

    Southern corn rust.

    Our above average rainfall this season has obliged most of our grain crops. Although many of our Hale & Swisher fields are later than we would prefer, irrigation systems have remained quiet for the most part. This has saved untold millions of gallons of irrigation water while maintaining a solid yield potential.

    These wetter than normal conditions also come with a down side, particularly in corn. Corn diseases in our area are running high. This stands to reason as most of these diseases are fungal related and require moisture and humidity to spread and certainly for the spores to germinate. Continually keep driblets of water present on the leaves and the diseases thrive.

    On a usual year, the only disease we can count on seeing in our area corn year in and year out is Common Rust. This pathogen is not usually economic for us but can become economic in the right conditions. With the additional rains, morning dews, and higher humidity, the conditions have certainly been right for Rust this season. For most of our Plains Pest Management scouting program corn acres, I am estimating a 2 – 3 fold increase in common rust as of this week.

    That is not the only pathogen we are finding in the field, and certainly not all we are getting reports of.

    We are also identifying Southern Rust, Northern Corn Leaf Blight, Grey Leaf Spot, and a handful of other ‘blights’ to lessening degrees. Several of these lesser blights have flared on a few spots or in some cases for just a few days and ceased when conditions dropped back below “ridiculously wet” with little impact made other than the knee nocking turmoil of potential trouble brewing in the field.

    The Southern Rust and Northern Corn Leaf Blight look to have more staying power this season with the conditions we have, and potential to become economic if they have not already. In our older or more developed program corn fields the impact of all of these diseases has been minimal so far, but these fields have all been treated with fungicides in a preventative manor recently before any real harsh problems developed. This is not the case for all area fields.

    Last week we were getting reports from across Hale, Floyd, and farther south that Northern Corn Leaf Blight (NCLB) looked to be hitting post tassel corn pretty hard with long term affects to be felt in yield and harvestability later. Emergency treatment applications were soon abound for those scouting closely enough to catch and identify the problem in time. The NCLB now seems to have slowed this week with “the line in the sand drawn” through good scouting and slightly dryer conditions predominating the area.

    Still a growing concern today is Southern Rust. Clay Golden, independent crop consultant based in Floyd County, spoke with me recently about what he is seeing in Floyd County.

    “We have quite a few fields that we treated with fungicide two weeks ago and quite a bit for NCLB last week. There are a few fields treated two weeks ago that are now in the dough stage. We have Southern Rust rebuilding now (that residual from our treatment is running out). We really don’t want to, but we might be forced into making a second application in a few spots if the trend continues.”

    I also spoke with Dr. Jason Woodward, extension plant pathologist district 2, this week about the increase in corn disease pressure this season. Dr. Woodward explained,

    “The wetter weather has increased the corn disease pressure throughout the region and there has been a lot of fungicide go out to combat them. Much of the older corn in the Lubbock area has reached dent stage and I feel pretty confident stating that those fields should be on the downhill side of the rust and blight risks. Even if those post dent fields have an increase in disease it might not be an economic situation as that field starts to dry down, especially if they have already been treated.

    “On the other hand, the whole region has quite a bit of late corn that hasn’t even tasseled yet. Those fields are going to be a major concern for disease issues as we move forward if the moist weather persists. As the days start growing shorter, the nights cooler, and morning dew becomes common, in conjunction with a continued wet weather pattern, and we could see some major issues with several of these corn diseases over the next few weeks and months on those younger corn fields as they progress through key and later reproductive growth stages…

    “Now that many of these diseases are present in the region at a noticeable level, I might even expect to see even higher disease problems in pivots compared to say drip fields where we will be making applications of water to the plant even if the much appreciated rain patterns slow.”

    This situation described by Dr. Woodward certainly holds true for the late corn fields in our scouting program corn acres and looks valid throughout Hale, Swisher, & Floyd with greater than normal late corn acres due to be hitting those key reproductive stages soon. We really do not want to chase away any future rainfall that we know we will need but we should be aware of the potential problems that could arise with the blessings of a good rainfall pattern.

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