By Anne Dorrance and Felipe F. Sartori, Ohio State University Department of Plant Pathology
We have received many calls and samples concerning seed quality and I’ve also heard about the rejections at the elevators. I was in Florida a couple of weeks ago with my colleagues (soybean pathologists) from across the country and Ontario, Canada and we are not alone. We were not the only state where soybeans had plentiful rains through and after grain fill with some of the crop still out in the fields.
What is causing all of the low germination?
From the samples we have received, we are culturing the expected seed borne pathogens: Phomopsis, Diaporthe, Fusarium, and Cercospora spp. All of these will affect seed and seedling health if the seed is not treated with a fungicide that can control true fungi.
What types of fungicides are there?
On the seed, there are materials to control the watermolds (Pythium and Phytophthora), insects, SCN, and the true fungi Phomopsis and Fusarium. There is one seed treatment, Fluopyram, which only targets the SDS pathogen, Fusarium viruguliforme. Refer to the fungicide seed treatment table at https://u.osu.edu/osusoybeandisease/management/ for more.
Is it worth treating the seed?
In the old days, the recommendations were if you had a batch of seed that was less than 70% germination, that it should not be used the next year. Based on the samples we received, the infections were mostly on the outside of the seed and the seed germinated before it was colonized by the fungus. Seed treatments greatly improved germination and health of the seedling by as much as 40% to 50%. We have stored the seed under very dry conditions to inhibit any additional colonization of the seed, so that has helped. With seed supplies of some varieties going to be limited, and the seed treatments are working, we may have some room here if needed, but only the best soybeans should be used for seed.
Which fungicide seed treatment was most effective?
There are several fungicide active ingredients that are effective on Phomopsis and Fusarium seed decay: fludioxonil, fluzapyroxad, ipconazole, PCNB, penflufen, prothioconazole, pyraclostrobin, sedaxane, and thiabendazole (TBZ). Thanks to Syngenta Crop Protection and Valent, we were able to evaluate a couple of these compounds on some poor quality seed. Fungicide seed treatments (rate per cwt) that we evaluated were: 1) non-treated control; 2) thiabendazole 0.08; 3) thiabendazole at 0.16; 4) fludioxonil 0.08; 5) fludioxonil 0.16; and 6) thiabendazole 0.08 plus fludioxonil 0.08.
Interestingly, fludioxonil was not effective on one of the seed lots, as was ipconazole in another study (data not shown). But the combination of fludioxonil plus thiabendazole provided the most consistent increase in germination over the non-treated across the seed lots.
Pick the best conditions to plant in 2019
Soybean seed had a rough go of it at the end of the 2018 season and it will also have a rough go of it once it is planted. Once it is cleaned and sorted and has the right fungicide seed treatment on it, use the best days to plant the seed. Plant as close to May 1 as possible when soil temperatures (not air temperatures) are suitable and the rain that is forecast is reasonable, not an Ohio 4-inch to 5-inch dump like we’ve been getting. My fingers are crossed hoping we have a decent planting season this year.