Source: Ohio State University Extension
By Anne Dorrance, Ron Hammond, Andy Michel
Dec. 4, 2013 — If we could predict or know that the planting season during 2014 would be like it was in 2012 (the dry spring), then we would say don’t treat your seed at all. But if the season is like this past year, wet, the combinations of seed treatments did a much better job and at the higher rates. There have been lots of questions over the past few days on what fungicides to apply; what rates to use; and are insecticides always necessary. Here we try to parse it all out for you.
Metalaxyl (Numerous companies) & Mefenoxam (Syngenta):
These products are targeted for most of the water molds. Damping-off, seed rot, and poor stands are the primary symptoms that occur in the field, but at the end of the year – yield benefits can be measured. The two active ingredients are applied at totally different rates. For Metalaxyl – typical rates are 0.2 (low), 0.75 (medium) or 1.5 (high) fl oz/cwt and mefenoxam is applied at 0.16 (low), 0.32 (medium), and 0.64 (high) fl oz/cwt.
Our data from fields with optimum disease conditions, both at the research branches and on farm have shown that the higher rates provide for significantly higher stands (thus no replant), as well as higher yield at the end of the season. Some companies have begun to drop the rate, which is fine for other states and areas of Ohio where the soils are better drained and there is little pressure from Phytophthora.
However, for producers that farm poorly drained fields, no-till, continuous soybean or soybean/corn rotation, and have a history of replant are the most likely to see the added benefit of higher rate of seed treatment. Work with your seed dealer to figure out which active ingredient he has and then which rate is most appropriate for your field conditions and history.
Several active ingredients of this chemistry have been added to the seed treatments over the past few years. They have a limited spectrum of activity, but for the most part they are contributing to better stands and yield under Ohio’s conditions. Some of the strobilurins have activity towards some but not all of the Pythium spp. This is giving an added benefit to the soils with poor drainage, no-till and where even with the high rate of metalaxyl or mefenoxam, control was not optimal.
Some of the strobilurins are also good on Phomopsis, a fungal disease that is seed borne. Seed lots with less 70% germination should not be planted, but those with 70 to 90% germination can see an improvement in germination when treated with pyraclostrobin (BASF) but not azoxystrobin (Syngenta) or trifloxystrobin (Bayer). I have no idea why there is specificity here, but there is.
Fludioxinil (Syngenta): This product is sold as Maxim and has and continues to have excellent activity towards Fusarium and Rhizoctonia as well as seed borne Phomopsis and Sclerotinia.
Sedexane (Syngenta): Newer product and new mode of action on the market also has good activity towards Rhizoctonia.
Ipconazole (Valent): Another new seed treatment compound that has good activity towards Fusarium and Rhizoctonia.
Penflufen (Bayer/Pioneer): A new seed treatment compound targeted towards Rhizoctonia sold as EverGol Prime.
Insecticides (thiamethoxam [Syngenta], clothianidin [Bayer and Valent], and imidacloprid [Monsanto]): There are these three insecticides that are widely used as soybean seed treatments, usually in combination with one or more of the above fungicides. They are labeled for numerous insects, including soil pests such as seedcorn maggot, white grub, and wireworm, and early season foliar insects such as soybean aphid and bean leaf beetle.
However, our experience is that the only soil pest of significance on soybean in Ohio is seedcorn maggot, and then only when a green, living cover or manure is incorporated into the soil prior to planting. This is the only scenario we have see seedcorn maggot issues. None of the other soil pests appear to occur in Ohio on the crop. Although these seed treatments will offer control of the foliar insects that are listed, they are seldom if ever needed.
Although bean leaf beetles will occur on early planted soybeans, they are almost never reach economic levels, and even then, can always be controlled with a foliar insecticide spray following scouting. If growers are planting soybean for seed or food grade purposes and have had problems with bean pod mottle virus, they might consider a seed treatment to potentially offer suppression of the virus, albeit it will not be controlled.
With soybean aphids, growers should realize two things. First, Ohio aphid populations are on a two-year cycle, and few aphids are observed in even numbered years, which should be the case in 2014. Second, most aphids show up in our fields in later June, not in May. Thus, there are usually no aphids to “control” even in the odd numbered years early in the season. At most, a grower might delay aphid population growth in mid-summer by a week when using a seed treatment. But if conditions are right for aphids to achieve economic levels, a foliar treatment will still be necessary; you will still be paying for and making two insecticide treatments.
Thus, growers should consider whether or not insecticide seed treatments are really necessary prior to spending the additional money for an insecticide treatment that perhaps is not necessary nor that effective.