Much of Ohio’s soybean production ground is on soils with poor to fair drainage, high clay content, and reduced tillage systems. Any one of these factors alone or in combination contributes to the environmental conditions that favor infection of seeds and seedlings by watermolds. Reduced tillage systems favor pathogen build-up in the very place that the seed is planted each year. Both soybean and corn are attacked by a great diversity of Pythium spp.; some of which are favored by cool, wet soil conditions and others by warmer but also wet soil conditions. Of course for soybean, Phytophthora sojae can be recovered from all of Ohio soils and this is favored by warmer temperatures and wet soils. True fungi, Fusarium spp. and Rhizoctonia solani, are also pathogens of soybean and corn, but for these the amount of inoculum that is present in the field and adequate moisture for pathogen growth is all that is needed to favor infection of both corn and soybean.
Host resistance is the primary means by which we manage many grain crop diseases, but there is little effort put into screening for resistance towards Pythium spp., Fusarium spp. (other than F. virguliforme which causes sudden death syndrome of soybean) and Rhizoctonia solani in comparison to other diseases. This is where seed treatments aimed at watermolds and true fungi can play a big role for fields which are high risk these seed and seedling pathogens. This protects the seed and seedling when they are the most susceptible, since for some of these diseases host resistance is not expressed in the early plant growth stages (partial resistance to Phytophthora sojae). How do you know if your field is at risk? It is a very simple question to answer:
- How many times in the past 10 years have you had to replant? If it is more than 1, then you are always at risk.
- Are you planting into a field that had head scab of wheat or Gibberella Stalk rot of corn? If the answer is yes, then it is important to add fungicide seed treatments specific to Fusarium graminearum to limit stand losses.
With a seed treatment, it is important to note that no one seed treatment active ingredient will provide protection against all of the pathogens that attack seeds and seedlings. As you examine the list from your seed dealer – you will see a long list of active ingredients, each of which is targeting a small portion of the total grain crop pathogen complex that Ohio farmers must deal with on an annual basis.
We are sure your next question is which seed treatment package is best. In reality the companies have been testing numerous combinations, formulations, and sites to get this right. None of them are perfect, there are a growing number of Pythium spp that can get past the protection, but they are in the minority. We do have a number of Pythium spp. which are resistant to metalaxyl/mefenoxam and we know for Phytophthora sojae that more metalaxy/mefenxoam (0.75-1.5 fl oz metalaxyl//0.32-0.64 fl oz mefenoxam) is better. So for those fields having a different active ingredient, such as ethaboxam or adding a strobilurin will pick up a few more of these Pythium spp. For example, in the seed treatment trials during 2015- we can’t separate the difference among the seed treatments when there was very high disease pressure (Figure 4– graph). All of the seed treatments had significantly higher yields than the non-treated.
Some of you may recall that AD was in a challenge to test the need to add more metalaxyl on top of the Acceleron base seed treatment that was marketed for Ohio. In two years of testing, none of the plots that received extra metalaxyl had significantly higher yields in the 3 locations in 2015 nor the 3 locations in 2014 (see C.O.R.N. 2014-38). Just as in 2014 and now in 2015, I’ve lost the challenge again. As promised we will not request or recommend that additional metalaxyl be applied over the top of what is already in the Acceleron base treatment as it is was marketed in Ohio during these two years.
