Category Archives: Corn

Weather & Disease Update

It’s hard to say we don’t want more rain, but more and more we’re saying just that. We’re having showers nearly every day or every other day, sometimes as much as an inch and a half. It’s starting to show up in the field where cotton is getting ‘wet feet.’ Some of our rain has come with strong winds. Our largest field of tobacco took a hit from these winds knocking plants to the ground in some places. The only hope is to stand it back up as best as possible. It is still causing issues with topping since the flowers on the ground began growing straight up.

We have a good crop of tobacco this year, but it was hit hard from strong winds and rain. Some areas completely blown to the ground.

Flowers turned from wind affects topping

From UGA weather station in Cairo, here are the rain numbers since the beginning of May.

Disease Update

Here is our latest disease update from UGA Extension Pathologist Dr. Bob Kemerait:

Southern Corn Rust: I was stunned when agents in our disease diagnosis class visiting a field in Morgan County found a very active spot of southern rust. Unbelievable because until yesterday, it had ONLY been found lightly in Seminole and Marion Counties. Obviously, as we expected, southern rust could be present anywhere in Georgia now.  Why it has not “exploded” yet is a mystery to me given the conditions we have had, but CLEARLY the spores have spread across the state.

The corn in that field as at hard-dough/early dent, so it does not need to be treated; however growers with later planted corn not yet at R6/dough stages should be aware there is at least some threat.

Target spot of Cotton: Perfect weather but I am NOT calling for an automatic fungicide application at first or at third bloom.  BUT I am saying that every cotton grower SHOULD be aware that these can be important and critical timings. As cotton approaches bloom, I hope growers can put some eyes and boots in the field and begin looking for it, lower leaves first. Weather is very favorable- growers with a history of disease in the field and those with high-input, strong yield potential should be the growers with the greatest chance for benefit. Target spot will not steal the entire crop, but it will take away a valuable portion of the crop.

Consider:  Growth stage (blooming yet?)  history of disease, reports from scouting, (have early symptoms been found?), what’s the weather like now and what is the forecast?  What is the value to the growing in a preemptive application “to be done with it”?

White mold and leaf spot in Peanut: We are seeing some of both.  Growers, don’t get behind!

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Southern Rust In GA

Southern corn rust has been identified in Georgia (on June 5th) by Rome Ethredge in Seminole County. Corn was in the silking (R2) state. This is likely some of the earliest southern rust to affect our state. UGA Extension Pathologist Dr. Bob Kemerait has this update for growers:

  1. Weather condition for the past few days and over the next few days is predicted to have a significant chance of rain and humid conditions.  These conditions are quite favorable for the development and spread of rust diseases to include southern corn rust and Asian soybean rust.
  2. As of today, 5 June- Asian soybean rust has been found on kudzu in Miller County and on corn in Seminole County.
  3. My recommendations:  Corn in southern Georgia that is approaching tassel stage (or has reached) is now at some risk to southern corn rust.  The risk is likely not urgent yet, but finding rust now (fairly early in the season) and coupled with the current weather conditions does increase risk.
  4. Grower spraying for southern corn rust:  tebuconazole is effective, but combination products that include multiple modes of action (e.g. strobilurins, triazoles, SDHIs) have a broader spectrum of activity against disease AND have a longer protective window (e.g., 3 weeks versus 2 weeks.)

Insects

The picture above is corn in Thomas County that is also silking. We are very fortunate with our rain these past few weeks. During this stage (70-80 DAP) corn is still using 0.3 inches of water / day. We also need to watch for stink bugs. It is common to treat during the ear elongation / tassel state (VT) is 1 SB per 2 plants is present. Because they can hide from you, it is easiest to drive down the rows and check.

During policantion and blister statges (R1-R2), SB feed through the husk and damage individual kernels. Treat if you see 1 per plant.

Pyrethroids are fine to use when we’re seeing southern green SB. If brown SB are prevalent, use a high rate of bifenthrin to get about 75-90% control.

1st Instar Brown Stink Bug

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Corn Disease To Scout

Some of our dryland corn is now tasseling. The rest of our corn is very, very close to tasseling, and many growers will put out a fungicide. And this is okay. Should we have sprayed before now? UGA Extension Pathologist Dr. Bob Kemerait has found that early fungicide applications (V5-V6) on early planted (Spring) corn has no  benefit to yield and disease, but can have “some” benefit on later planted corn. This is likely because corn planted behind corn will be affected earlier in the growth stage.

Former Seminole County Agent, Rome Ethredge found northern corn leaf blight (NCLB) last week. In corn disease, we are mostly watching for southern corn rust and NCLB. We have sentinel plots in the county to help us watch for rust. Unlike NCLB, southern rust is reintroduced each year and spores essentially blow in and re-infect corn.

Lesions o NCLB appear as a cigar shape. Photo by Rome Ethredge.

Control of NCLB

Northern corn leaf blight is more prominent where we have corn behind corn, overwintering in the leaf litter as well as irrigated corn. We have less of both situations in Thomas County. In fields with a) susceptible varieties and b) favorable conditions, you can have some NCLB in the field and NOT need to spray. When do we pull the trigger on spraying NCLB?Dr. Kemerait says treat for NCLB when lesions get as high as 3rd leaf from the ear leaf.

 

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Corn Update

Both irrigated and dryland corn are looking okay. Dryland is looking as good as it can. We’ve had less rain as we move east in the county. Corn on the central and west side has had almost an 1nch of rain for the last few weeks. There is rain expected for the weekend also.

This corn is our rust sentinel plot in Thomas County and has only nitrogen burn from foliar fertilizer. You can also see a few spots from Gramoxone drift as we’re planting cotton. None of this is anything to worry about.

We’re past most of our weed control. There are only a few fields where preemergent herbicides didn’t get activated and we’re dealing with pigweed.

Etching done by thrips

Burn from gramoxone

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Field Corn Weed & Disease Update

Some of our earlier planted corn is moving through the v8 growth stage. In this field corn, we are nearly past the time for over-the-top herbicide applications without yield loss. We’ve been applying mostly one shot Atrazine+RU+Prowl H2O when corn has about 3 leaves. It’s working great. We have a one or two fields were pigweed got past it and hurting us.

Weed Control Update

Here is an update from UGA Extension Weed Scientist Dr. Eric Prostko:

Field corn weed control does not have to be difficult.  Just about any of the herbicide programs that growers are using in Georgia do a good job of controlling most weeds, especially Palmer amaranth, when applied to small plants (<3″ tall). Check out the following pictures from my field corn plots that I rated earlier today.  These herbicide treatments were applied 17 days after planting with a CO2-powered backpack sprayer calibrated to deliver 15 GPA at 3.5 MPH using AIXR 11002 nozzles.

The most troublesome weed in Georgia field corn, in my opinion, is annual morningglory.  Field corn growers who struggle with morningglory should seriously consider a post-directed/lay-by application of Evik (ametryn) sometime after their initial POST treatment was applied. (Check out page 70 of the 2017 UGA Pest Control Handbook for more information about Evik.) The minimum corn height for post-directed applications of Evik is 12″.  If Evik is tank-mixed with glyphosate, post-directed applications can be applied up until 48″ tall corn (RR2 hybrids).

 

Halex+Atrazine+Adept, Dr. Eric Prostko

Atrazine+RU+Prowl H2O, Dr. Eric Prostko

Laudis+Atrazine+MES, Dr. Eric Prostko

Revulin+Atrazine+Adept, Dr. Eric Prostko

Disease Update

This is from UGA Extension Pathologist Dr. Bob Kemerait on 5/1/17:

Our earliest planted corn crop is beginning to approach times where we need to consider use of a fungicide (or not).  Here are some notes…

  1. There is no need at this point to protect against rust. 
  2.  Some growers might put out a fungicide application as early as the V6-V8 stage to protect against leaf blights.  Before doing so (unless the grower simply feels better doing the application anyway) scout for detection of the easily diagnosed lesions of northern corn leaf blight.  Simply finding one or two scattered in the field is NO BIG DEAL. Finding the disease more widely scattered, on a susceptible variety, could be. DO NOT MIX AN ADJUVANT OR CROP OIL with fungicide applications made prior to tassel.  This can result in significant ear deformation.

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Sidedressing Corn

We are very thankful for timely rains without significant storms. We’ve had atleast 1.5″ of rain in the last 7 days. This has helped get our pre-emergent herbicides activiated. This is also good for dryland corn, as it approaches the critical V6 growth stage where much of its yield is determined.

Ground Equipment

It’s not time to sidedress. We want 1.2 lb of total N per bushel goal. UGA Extension Fertility Specialist Dr. Glen Harris recommends sidedressing at 12″ to 16″ height. If we’re using ground equipment, we’re putting out 50 to 75 lbs of N per at at / before planting on irrigated land and 20 to 50 lbs of N per acre in dryland. We put out the rest of the N at sidedressing.

Fertigation

You put out 40 – 60 lbs of N at or before planting and start ground or injected applications of 30 – 60 lbs of N per acre when corn is 8″ to 12″ tall. Keep this going every other week until the total required N is finished. You’ll need 3 to 5 applications during the growing season.

Sulfur

Corn requires about 20 to 30 lbs of Sulfur and we sometimes see sulfur deficiency. It looks similar to N deficiency except we see an overall yellowing of the corn plants. (N deficiency shows up in the lower part of the plant since it is plant movile.) To be sure of which deficiency, we need to take a plant tissue analysis. I talked about the proper way to do this for corn in this blog post.

Only on sandy soils do we split our S applications. Whatever we don’t put out at planting needs to be put out now. Research has shown that we want to correct our S deficiencies between 21 and 30 days old to not hurt yield.

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Corn Coming Up

We looked at a good bit of corn this week that is now coming up in a few different stages. This field was actually planted before our freeze two week back. It slowed germination but would not have any injury. Any corn with just a few leaves – in the V1 growth stage – still has the groing point below the soil surface, which protects the plants from freeze.

We’re just now getting our first herbicide shot, so we’re able to mix Prowl in for grass control. Buffalo grass is all througought this field. Since some grass has already emerged, UGA Weed Scientist Dr. Eric Prostko says it’s okay to add Round Up in with Atrazine + Prowl. It’s one of the best one-shots we have in corn. We had just enough rain last night to help activiate some pre-emergent herbicides.

V1 Growth Stage – The collar (white line) is present on the 1st leaf.

V2 Growth Stage – The collar is present on 1st and 2nd leaf.

 

 

 

 

 

 

 

 

 

 

At the V1 growth stage, the growing point is still below the surface of the soil. At this stage, three leaves are visible. The leaf collar is only on the lowest leaf. At V2, four leaves are visible, but the collar is only on the 1st and 2nd leaf. At this growth stage, corn water demand is close to 1/10″ a day.

 

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