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aspergillus-crown-rot-peanut-GA-19.jpg Bob Kemerait, UGA Extension
Aspergillus crown rot in Georgia peanuts 2019.

Record heat and getting dry. What is your crop’s disease risk now?

Understanding the relationship between hot and dry weather and diseases can help growers make best decisions for crop diseases.

We’re not even into June and crops are broiling in Georgia.

BJ Washington, a colleague at the University of Georgia Stripling Irrigation Park near Camiila, Ga., called me at 7:20 yesterday morning. 

“Bad news, Bob. We are going to have to replant your cotton study.  ou didn’t get a stand.  You don’t have to get angry with me. Blame it on the weather, but not on me.” 

Driving across the state, I see corn, cotton and peanuts punished by hot and dry conditions and this could impact our yield potential.  Weather forecasts have predicted temperatures to soar to nearly 100 degrees with only the slightest chance of rain during the final days of May and into early June. There are the obvious consequences of such on our crops: wilted, flagging plants, urgent need for irrigation, delayed germination in bone-dry soils, catastrophe when there is enough moisture to swell the seed but not enough moisture to establish the crop. 

However, there are other concerns as well to which growers should be attentive when hot and dry weather dominates the early season.  Hot and dry increases risk to some diseases and reduces risk to others.

Dry weather this early will affect the row crop farmers in obvious ways: the need for irrigation, the cost of irrigation, the impact on plant growth and development, the impact on plant stand.  The following are ways that early-season hot and dry weather may also impact our crops in ways that are less obvious, but equally important to the growers.

While seedling diseases are most often associated with colder and wetter soils at planting this is not always the case.  The most important seedling disease affecting peanuts in the Deep South is Aspergillus crown rot. This disease is absolutely most problematic when hot and dry conditions exist.  Damage from scorching soil wounds the tender shoot allowing infection to occur.  Aspergillus crown rot is more severe when the peanut crop is affected by the lesser cornstalk borer, which also thrives when early season is hot and dry.  Seed quality also impacts the potential for crown rot; lower quality increases risk.  Perhaps more importantly, white mold (southern stem rot) is most severe when conditions are unusually hot.  Peanut farmers should consider starting their white mold program earlier this year to protect the crop.

Complaints about plant stands have been common from cotton growers this year, and I am complaining too.  Typically seedling diseases, as caused by the fungus Rhizoctonia, are less severe in warm soils, but not always.  Rhizoctonia solani is active in warm soils, however the cotton seedlings often germinate and develop rapidly enough to reduce damage.  Lower-quality seed, short crop rotation, and other factors that slow crop development and increase pathogen populations increase risk to disease.  Poor cotton stands are not always the result of disease.  When seed is planted too deep, the seedling may struggle to emerge.  Planted too deep, struggling to emerge, and then encountering hot and dry conditions can be a death sentence.

Dry conditions do provide some benefits to growers.  As some of the corn crop approaches the tasseling growth stage, growers are deciding whether or not to protect their corn with fungicides.  To date, we have not found southern corn rust in Georgia and threat from northern and southern corn leaf blight diseases is very low.  Protecting a corn crop from disease with fungicides is important, but at this time risk is low and many growers can safely delay applying a fungicide to their corn crop. 

As another example, Asian soybean rust has been found in kudzu very early this year across the Coastal Plain. However, drought will help to keep the disease from early infection of our soybean crop.  Peanut growers may also be able to delay start of their leaf spot program.

Row crops and row crop growers in the Southeast are being punished now by the soaring temperatures and lack of rain.  As growers develop plans to grow their crop, they should also understand how these conditions can affect disease and disease management options.  It is too late for most growers to change planting-time decisions; however an understanding of the relationship between hot and dry and disease can help them make best management decisions for diseases like peanut leaf spot and white mold.   

The fact that it gets hot in Georgia is not a surprise. Songwriters have had that figured out for years.  Familiar lyrics include, “I was driving through Georgia in late July on a day hot enough to make the devil sigh,” (Tracy Byrd),  “Way down yonder on the Chattahoochee, it gets hotter than a hoochie coochie,”  (Alan Jackson), “But August was red-hot and Georgia was steamin’,” (Brian Fallon),  “red-hot Georgia clay,” (‘Georgia Girl’, a Bluegrass classic),  “Is this Georgia heat playing tricks on me, or am I really seein’ what I think I see?” (native-sons Luke Bryan and Billy Currington) and “On the hot dusty Macon road” (Jim Croce in his song “Walkin’ Back to Georgia”).  As noted by the Marshall Tucker Band, when you hear it in a song, it can’t be wrong…

As for me, I am getting ready to re-plant a cotton trial and dreaming about a song by Zac Brown, another Georgia artist.  The song is called “Colder Weather.”

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