Crop News


F) Seed treatments: the range of what they control - Anne Dorrance, Dennis Mills, Maggie Ellis

There has been a lot of activity in the past few years focused on identifying new seed treatment fungicides and insecticides for soybeans. These are great tools for Ohio’s challenging planting conditions but a few things should be considered.

What seedling pathogens are most prevalent in Ohio.

1. Based on several surveys that we have done in the state, Phytophthora sojae and Pythium spp. are the primary component to a long list of seed and seedling pathogens. Both of these pathogens are classified as water molds, in that they require free water to form spores which can then infect seedlings. To make it a bit more interesting Phytophthora sojae is not controlled by the 0.16 fl oz of ApronXL or the 0.2 fl oz of Allegiance, the high rate is needed when there is high disease pressure. In addition, some of the Pythium spp. are also not controlled by these two fungicides, but are limited by compounds azoxystrobin and pyraclostrobin.

2. Rhizoctonia and Fusarium graminearum are two additional soil borne pathogens that can also infect seeds and seedlings after planting. Infections caused by Rhizoctonia have a brick red color on the hypocotyl and brown roots while Fusarium infections tend to be bright pink and “fuzzy”. The mycelium is quite visible on the decaying plant tissue. These fungi are controlled by different active ingredients, specifically fludioxonil, PCNB and a new active ingredient ipconazole.

3. Phomopsis is a seed borne fungal disease of soybeans. This is an intermittent problem due to variety susceptibility as well as rains during harvest. Seeds that are infected have a chalky appearance. But this is one that for some seed lots the germination can be immensely improved with the addition of seed treatment. Lots that start with 70% germination should not be used for seed. We are still in a “catch-up” phase to look at which materials provide good control. In the most recent seed treatment fungicide chart you will see ND – to indicate we are still working on this. Fortunately we had a couple of our own seed lots that we use for experiments get hit with Phomopsis this year so we can begin to evaluate this parameter.

A new seed treatment chart will soon be posted on Ohio Field Crop Disease website
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/ which illustrates what some of the new products will control based on the date that we currently have. (posted now on the West Ohio CropWeather blog: http://westohcropweather.blogspot.com/2010/02/soybean-seed-treatments-for-ohio.html)








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