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This week has brought us the confirmation of plant diseases in corn and soybeans. Southern Corn Rust (SCR) was confirmed in Decatur County on June 4th and in Mitchell County on June 6th. Soybean rust was confirmed on June 5th in Telfair County and in Tift County on June 6th. Growers should consider these findings in their fungicide decisions.

Following are comments from Dr. Bob Kemerait, UGA Plant Pathologist, on Southern Corn Rust.

  1. Finding southern rust NOW in Decatur Co is very important because a) some of our most intensive corn production is in that part of the state, and b) much of the corn there is tasseling, which is a critical growth stage at which to consider applying a fungicide.
  2. Just because we now know rust is present in Decatur Co does not mean the disease will spread quickly in that field or to other fields. All I know is that a) the match is lit, b) the conditions are favorable for spread, and c) potential losses to this diseases can be as high as 80 bu/A in my experience (but typically not that high).
  3. If you do not catch southern rust early, you likely will not catch it all.
  4. I cannot promise that if you apply a fungicide and that your neighbor does not that you will make more yield than she does or that she will even have rust in her field. What I CAN promise you is that given threat from rust (in my experience) I would rather have a fungicide in place rather than farm on “luck”.
  5. There is no single fungicide choice for southern corn rust. The key is to get there early, before disease is well-established, and consider using a product mixture that includes more than one mode of action.
  6. Highest risk now is corn at tassel or beyond, in counties like Seminole, Decatur, Early, Miller, Mitchell, Grady, and Baker. Counties neighboring these counties- Thomas, Colquitt, Terrell, Calhoun, Webster, Dougherty, Worth, Tift, Randolph should be watching carefully to see how rust continues to be found.
  7. We want to be proactive in fighting any rust disease, but judicious use of fungicides is always best and that always includes careful decisions for most appropriate application date.

Finding soybean rust on kudzu now is important; finding more southern corn rust is urgent. Why the difference? Because right now we are finding the most important disease of corn in Georgia as corn in an area where the crop is intensively produced at a stage of growth of increased susceptibility. Corn growers in southwest GA are at a stage where they must make a decision. Does every corn grower in GA need to spray a fungicide now for rust? Absolutely not. Should every corn grower in SW GA carefully consider their options? Yes they should.

We have been checking peanut stands for the last couple of weeks. Some stands are ideal, while many are decent, and some plant stands are less than desired. Weather conditions have affected us greatly in the month of May. As planting is finishing, spraying time is here. Check out the latest information from Dr. Eric Prostko, UGA Weed Scientist, on weed control in peanuts.

Peanut growers should be seriously thinking about beginning their POST herbicide applications as early as 30 DAP. Some peanut growers will choose to use Cadre (imazapic). Others may not want to use Cadre due to crop rotation/carryover concerns. Here are a few things to consider:

1) Growers who will be using Cadre need to consider the fact that much of the Palmer amaranth in Georgia is resistant to the ALS-inhibiting herbicides. Thus, it’s a a a good idea to tank-mix Cobra (lactofen) or Ultra Blazer (acifluorfen) with Cadre to address this particular issue. If Cobra or Ultra Blazer are not included, it will be too late to control those pigweeds once a grower discovers that they are ALS-resistant.

2) If a grower cannot use Cadre, then Cobra or Ultra Blazer are the best options for pigweed. When pigweed plants are small (2″-4″), there is not much difference in control between Cobra or Ultra Blazer. However, Cobra is more effective on larger weeds (>4″). But, Cobra will cost about ~$9/A more than Ultra Blazer. It is important to remind growers that if Cadre is not used in peanut, it is very likely that yellow/purple nutsedge and sicklepod/coffeeweed will be a problem.

3) If sicklepod is also present in the field, Butyrac (2,4-DB) should be included in the tank-mix. I recently heard from a grower in Middle Georgia that there was a rumor floating around that I only recommended 12 oz/A of 2,4-DB in peanuts. To set the record straight, I recommend the use of 12 oz/A of 2,4-DB, if needed, when it is tank-mixed with Gramoxone (paraquat) + Storm (bentazon + acifluorfen) + Group 15 when applied early-postemergence (i.e. cracking spray). I usually recommend 16-24 oz/A of 2,4-DB when it is applied POST with Cadre or Cobra or Ultra Blazer.

4) Because pigweed and annual grasses are such a problem in most peanut fields, it’s also a good idea to think abut including a Group 15 herbicide that will provide additional residual control of these weeds. Group 15 herbicides include the following: Anthem Flex (pyroxasulfone + carfentrazone), Dual Magnum (S-metolachlor), Outlook (dimethenamid-P), Warrant (acetochlor), and Zidua (pyroxasulfone). Not much difference in weed control between the Group15 herbicides but Anthem Flex and Zidua have provided slightly better residual control of Texas panicum in my research trials over the years.

5) When Dual Magnum or Outlook are included in POST tank-mixtures, additional adjuvants are not recommended because these are EC (emulsifiable concentrates i.e. oil-based) formulations. NIS (0.25% v/v) is recommended if any of the other Group 15 herbicides are used since they are not EC formulations.

6) Check out Figure 1 below. These pictures were taken from my plots on June 3, 2024. Since the Palmer amaranth population at this location is ALS-resistant, I am getting much better control with the Cadre + Cobra or Ultra Blazer tank-mixes.

7) Note that I have included the estimated prices/A for each of these treatments. These are average prices that I have obtained from several dealers so they will very likely be slightly different for every grower.

If we can be of assistance at Worth County Extension, please let us know.

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