In this update, we will discuss topics: Local small grain situation, Current soil temperatures, Cover crop termination timing and corn planting, Questions about calcium in peanuts. and The SmartIrrigation App. and When do I take the cows off my small grains and still harvest them for baleage or grain?
Local small grain situation: The local oat and wheat crops range from fully tillered to jointing. Powdery mildew is starting to be noticed in area wheat fields. Powdery mildew, caused by Blumeria graminis f. sp. tritici (syn. Erysiphe graminis) is an obligate, host-specific fungus that attacks wheat exclusively according to the UGA publication Identification and Control of Powdery Mildew of Wheat in Georgia. Planting resistant wheat varieties is the best way to control wheat losses to powdery mildew. On all but the most susceptible varieties, powdery mildew confined to the lower leaves has little or no effect on yield as these leaves often naturally senesce before heading. However, protecting the flag leaf is critical to attaining high yields. Powdery mildew infections and development declines rapidly when daytime temperatures consistently reach 72–75 °F (22–24 °C) and the relative humidity (RH) falls below 85%. Typically, these conditions happen before flag leaf emergence in the wheat-growing areas of Georgia. Therefore chemical control is only warranted on highly susceptible varieties in powdery mildew-conducive years. The UGA Pest Management Handbook provides options for fungicides.
What are the soil temperatures? This has been an interesting weather week. The table below shows the average 2, 4, and 8-inch temperatures from the UGA Weather Station at the Sunbelt Expo from February 25 until March 2, 2024. The table also provides the average soil temperatures at those soil depths for the last three years to compare to.
Cover crop termination timing and corn planting!
I have been getting a question or two about cover crop termination timing and corn planting. Dr. Eric Prostko, UGA Corn Weed Specialist, suggests that generally, the optimum timing for cover crop control in field corn is 10-14 days before planting. Planting into green cover can result in corn yield losses (up to 10% in some trials).
1) What is the plant-back restriction for field corn following an application of 2,4-D?
Plant-back restrictions for field corn after a burndown application of 2,4-D are 7 days (16 oz/A) or 10-14 days (>16 oz/A)
2) If a grower cannot wait to plant field corn in 7-14 days after an application of 2,4-D, what other burndown options are available?
Roundup (glyphosate) or Gramoxone** (paraquat) + Atrazine 4L (32 oz/A) is my first choice. There are no field corn plant-back restriction for these treatments.
Questions about calcium in peanuts. This week I got a couple of questions about calcium requirements in peanut. Dr. Glenn Harris has educated everybody on this subject in the past. Let’s do some reviewing.
To review, UGA Extension recommends using gypsum when you take a pegging zone soil sample (4 inches deep) soon after peanut emergence and when the results say you have either 1) less than 500 lb Ca/a or 2) a Ca:K ratio of less than 3:1. If either of these criteria are not met then we recommend applying 1000 lb/a gypsum m at early bloom (approximately 30-45 days after planting). All peanuts to be saved for seed get 1000 lb/a gypsum automatically since calcium levels in the nut are critical to good seed germination.
Can I use lime instead of gypsum? Yes, but lime needs to be applied before planting since the calcium in lime is not as soluble as the calcium in gypsum. So timing is important. Also if you deep turn you need to deep turn before applying lime so you don’t bury it. So placement is important. The calcium needs to be in the “pegging zone” (top 4 inches). And technically, lime should only be used when you either need a pH adjustment (below 6.0) or start around 6.0 so the lime will not raise the soil pH too high.
What about “liquid lime” ? There is a product currently available called “Topflow” that has been field tested at a 12 gal per acre rate, surface applied at planting. This may not provide as much calcium to the pegging zone as 1000 pound per acre of gypsum and won’t raise the soil test calcium as much but can be considered an alternative if you cannot get gypsum. Even though it is a liquid, it is still lime so it needs to be applied before or at planting.
What about other “Liquid Calcium’s” ? Well, it depends on which “liquid calcium: you are talking about. For example, recent research has been conducted showing 10 gallons per acre of calcium chloride (or 20 gallons of calcium thiosulfate) through the pivot during peak pod fill (around 75 days after planting) can have some benefit. Again, this is not as good as a timely gypsum application but can be viewed as an ‘emergency” or “insurance” application. The calcium in both of these products is basically 100 % soluble and therefore can be applied during peak pod fill. Also, calcium chloride should be the more affordable option but check on price and availability.
What if I get delayed getting gypsum? Or how late is too late to put out gypsum? Again, gypsum should be applied at “early bloom” or approximately 30-45 days after planting. Since “peak pod fill” is around 60-90 days after planting you can still see benefit from gypsum applications made any time before 60 days after planting. It can also depend on water or irrigation since you need water to dissolve the calcium and get it through the hull into the developing kernels.
Does every field of peanuts in Georgia need gypsum? Probably not, so if supply is short or budgets are tight how do you decide which fields get gypsum? First, any peanut being saved for seed should automatically receive 1000 pound per acre of gypsum, regardless of soil test calcium levels. Second, any field where results from a pegging zone test show you need gypsum should get it. Remember, if the soil test calcium (Mehlich 1 Extractant) is 500 or higher and the calcium to potassium ratio is 3:1 or higher in a pegging zone sample then the soil test calcium will be considered adequate and no gypsum will be recommended. This is based on research field trials looking at yield and grade. Research also shows that
gypsum is even more important in dryland compared to under irrigation since water will be more limiting in dryland and less soil test calcium will be available.
Can I base my gypsum or calcium needs on a Fall soil sample? You can, and this is better than nothing, but it is still better to base your calcium needs on a pegging zone sample. Soil samples taken in the Fall were likely taken at a deeper than the pegging zone. Also, calcium can leach out of the pegging zone between a Fall sample and early bloom and give you a false sense of security. Finally, if you take a fall soil sample and then deep turn before planting peanuts you can very possibly turn up soil into the pegging zone that is low in calcium.
How important is gypsum for peanut production? This probably should have been the first question answered. And the answer …. It is very or extremely important! Since peanuts as a deep tap-rooted legume can fix nitrogen and scavenge residual soil phosphorous and potassium, calcium is the most critical element. Lack of calcium in the pegging zone to be absorbed through the hull can result in “pops” or no kernels which obviously reduces yield. Calcium deficiency on peanut can also lead to pod rot.
And again, calcium is critical to germination for peanuts saved for seed for next year.
The SmartIrrigation App. Dr. George Vallidis, UGA Ag Engineer, sent out notifications about the SmartIrrigation app last week. If you are using this app to help make irrigation decision please down load the CropFit App.
UGA The SmartIrrigation Corn, Cotton, and Soybean Apps have been incorporated into the new SmartIrrigation CropFit App. The CropFit App maintains all the functionalities of the original apps and adds new functionalities which should make irrigation scheduling more efficient. For example, you can now delineate the perimeter of your field by dropping pins and the CropFit App will extract your field’s soil properties directly from the USDA NRCS Soil Survey – no more guessing about your field’s soil type. We plan to terminate the SmartIrrigation Corn, Cotton, and Soybean Apps by June 2024.
Please download the SmartIrrigation CropFit App from the app stores before the growing season begins. Your account and all your current and past fields from the standalone SmartIrrigation apps are automatically available in the SmartIrrigation CropFit App if you login with the same credentials.
The links to install SmartIrrigation CropFit on iOS and Android devices are listed below. You can also search for it in the App Store or Play Store as “SmartIrrigation CropFit”.
Android:https://play.google.com/store/apps/details?id=co.austn.si.cropfit
When do I take the cows off my small grains and still harvest them for baleage or grain? I had a couple of calls about when to pull cattle that are grazing small grains and still cut the small grains, such as oats and wheat, for grain or baleage. Cattle need to be pulled off at jointing (Feekes 6.0) or the first hollow stem. Once the second node has formed, the cattle will remove the growing point, and small grains such as oats, triticale, and wheat will not regrow. According to the publication Growth Stages of Wheat: Identification and Understanding Improve Crop Management, At 6.0 the first node is swollen and appears above the soil surface. Above this node is the head, or spike, which is being pushed upwards to eventually be exerted from the boot. The true stem is now forming. The spike at this stage is fully differentiated, containing all potential spikelets and florets or seed forming branches.Growers should look carefully for the first node to emerge. It can usually be seen and felt. A sharp knife or razor blade is useful to split stems to determine the location of the developing head. The stem is hollow in most wheat varieties behind this node. Last week, numerous oat and wheat fields were at Feekes Stage 6.0, or jointing. Stages of development can vary from field to field due to planting date, variety, and fertility. Dr. Lisa Baxter provided a great illustration of Feekes Stage 6, or jointing.
Have a great week.
Jeremy M. Kichler
Colquitt County Extension Coordinator