By Rodrigo Borba Onofre
As producers start planting soybeans in Kansas, it is important to consider common causes of seedling damping off and potential management strategies.
What causes poor soybean stand establishment?
Although there are a few diseases that may cause poor stand establishment, it is important to also consider other factors that may be causing poor stand establishment including herbicide damage, soil compaction, high residue, flooding, cold stress, drought, planting depth, and seed quality. The proper identification of what is causing poor stand establishment will be crucial for current and future management decisions.
What are the main soybean seedling diseases in Kansas and what seed treatments are effective?
The most common pathogens causing seedling diseases Kansas are: Phytophthora, Pythium, Fusarium and Rhizoctonia. Although they have different names, the symptoms can be similar. Each of these may result in post-emergence damping off (Figure 1). Although there are seed treatments that are effective against each of these diseases, it is important to remember that these species often require different fungicide products. It is important to carefully check the label of seed treatments and to select a seed treatment product with multiple active ingredients that have efficacy against these common pathogens.
For example, if Phytophthora and Pythium have been a problem in the past, products should be selected with the active ingredients mefenoxam, metalaxyl, or ethoboxam. For Rhizoctonia, the active ingredient sedaxane has shown excellent efficacy. Strobilurin active ingredients such as azoxystrobin, trifloxystrobin, or pyraclostrobin are effective against other fungal pathogens.
Figure 1. Characteristic symptoms of Pythium damping off.
Seed treatments are not the only tool in the toolbox for managing seedling diseases. Variety selection, crop rotation, high seed quality, proper drainage, and seed treatments all make up the best management practices for seedling diseases in Kansas. A combination of these factors will help ensure a high quality soybean stand.
What conditions favor seedling diseases?
Each disease has slightly different environmental requirements, but in general, seedling diseases are favored by planting into cool soil with poor drainage. Spotty occurrences of infected plants may be most pronounced in low or poorly drained portions of the field. Soybeans planted early, when soil temperatures are cool, should always consider a seed treatment to avoid early-season losses.
Are there any other diseases to consider when using seed treatments?
Seed treatments are not only effective against the pathogens that cause early-season emergence problems. There are two products on the market, ILEVO® and SALTRO™, that also provide protection against sudden death syndrome (Figure 2) and soybean cyst nematode. These products should be considered for fields with a previous history of either of these diseases.
To know if soybean cyst nematode is a problem in your field, take advantage of the soybean cyst nematode testing program offered by K-State Research and Extension. Contact your local extension agent for more sample submission information.
Figure 2. Classic foliar symptoms of soybean sudden death syndrome. Infection typically occurs early in the season, but foliar leaf scorch symptoms are most visible at reproductive growth stages.Source : ksu.edu