As we close in on the 4th of July, we need to consider our possible fungicide applications on corn and soybean.
Weather is one of the big drivers for foliar diseases in both of these crops. The worst-case scenario is not a mid-afternoon thunderstorm which delivers 1+ inches of rain but then the sun comes out and dries the leaves. Late evening storms where the leaves remain damp all night or even a heavy fog or dew that sticks around until after 10 a.m. probably does more to promote infection and disease development than the afternoon storms. Of course, a front that sits over us and we are cloudy with any type of moisture for several days is the worst-case scenario, i.e. favors disease spread and development the most. These scenarios are certainly true for corn and soybean this time of year.
Most of our corn has tasseled and silked but, in most fields, we continue to have very clean corn, no sign of southern rust in South Carolina. The latest reports from Georgia continue to have rust primarily in the southern half of the state, i.e. not along the South Carolina border.
Preventative sprays work the best. The latest weather forecasts for the next week have the possibility of wet weather of several types. So, this is probably a good time to spray.
As many of you know, we have experienced a very dry April and May throughout most of the state. With that being said, we did receive quite a bit of rainfall in the beginning on June (6.5 inches in Blackville) which helped our dryland crop.
Now that we have or are starting to dry out across the state, do not slack on irrigating corn now if it is needed. Most of the corn in the state has tasseled or is beginning to tassel.
Estimated water use in corn from tassel (VT) through early dent growth (R5) stages is approximately 0.3 inches of water per day. Therefore, if we do not receive any rainfall around 1 inch of irrigation should be applied every 3-4 days to meet the water use demand on our corn.
At Tassel Nitrogen
I have received a few calls about a “Tassel Shot” of nitrogen through the center pivots. A few things to consider before applying any additional N through irrigation. How much nitrogen has already been applied to the field? If a yield goal for that particular field is only 150 bushel/acre and 180-200 lbs of N have already been applied, additional N through the irrigation may not be warranted. If the additional N was part of the original fertility plan or insufficient nutrients have been applied previously and corrective measures are needed, and yield potential is good, then my recommendation would be to apply no later than R1 (silking) if this practice is going to be pursued. Remember, 70-80% of total nitrogen uptake has occurred by the tassel (VT) to silk (R1) growth stage.
Pulling a tissue sample for analysis at or prior to tassel is a good indication of total nitrogen in the plant prior to applying any additional nitrogen.
Here is the link for the Clemson Ag Service Lab: https://www.clemson.edu/public/regulatory/ag-srvc-lab/plant-tissue/index.html
Last week I started getting reports of late MG IV soybeans in the Lee County area that have flowered and are putting on pods. As soybeans switch from vegetative growth stages to reproductive growth stages, they become more susceptible to many foliar diseases. So R3, early pod development (see table below), is when we start making decisions on whether to spray. With the weather forecast for multiple chances for rain over the next week or two this might be a good time to spray, especially if pods are visible. As stated above, a dew that remains long into the morning probably enhances disease more than an early afternoon thunderstorm.
Most of the soybean fungicides provide 2 to 3 weeks or more of protection. Fungicides with more active ingredients tend to provide longer protection, some past 3 weeks. There is a table with the fungicides available for South Carolina in the “2021 South Carolina Soybean Guide” on pages 47 to 49. For a comparison of fungicides for efficacy on foliar diseases of soybean see “Fungicide Efficacy for Control of Soybean Foliar Diseases” produced by the North Central Regional Committee on Soybean Diseases (NCERA-137) and published by the Crop Protection Network (CPN-1019-W) Fungicide Efficacy for Control of Soybean Foliar Diseases (soybeanresearchinfo.com). If you have never used it, try the Crop Protection Network. It has a lot of good information on crop production for many crops.
If it is soybean rust you are worried about, we have not detected it in South Carolina on soybean or kudzu this year. It has been detected on kudzu in Georgia.
The labels for all foliar fungicides on soybean state they cannot be applied after R-5, i.e. once R-6 has been initiated. Below is a table of growth stages to refresh your memory.
Reproductive growth stages for soybean. For a visual version of this table see page 7 of the new “2021 South Carolina Soybean Production Guide” which is available at www.clemson.edu/extension/agronomy/index.html
Reminder: The 2021 South Carolina Soybean Production Guide is now available online at: