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Words of Caution for Early Planting 03/30/10 12:13:23 PM
Planting Early May Blight Seedlings
March 23, 2010
As submitted by:
Loretta Ortiz-Ribbing, Ph.D.
Extension Specialist, Crop Systems
Macomb Center
ortizrib@illinois.edu
As the weather warms up it is hard to fight the desire to get into the field and start planting. However, remember a few words of caution. Many seedling blights can infect germinating plants early in the season, especially when the seed is exposed to less than desirable cool, wet soil conditions. Seedling diseases are not a problem every year in all areas, but they cannot be ignored during cool, wet springs, like those we have had for the past two years. Common organisms causing seedling damping-off and blights are those in the genera Pythium, Phytophthora, Rhizoctonia and Fusarium. All four organisms overwinter in the soil. One of the most common and earliest groups of fungi that attack corn and soybeans belong to the genera Pythium. Fungi in the genera Pythium and Phytophthora are called "water-molds", because they thrive in soils that are wet.
These soilborne organisms can infect seeds and seedlings alone or in combination so it is often difficult to distinguish which pathogen is the main problem. Disease caused to the seed or seedling by these pathogens can begin at planting and continue up through the early vegetative stages of crop growth. The presence of disease is typically noted as reduced germination and/or emergence which results in a thin stand. After emergence, another observable symptom can be damping-off that kills seedlings. Seed treatments may provide protection for 10 to 14 days after planting under cool, wet conditions, but sometimes the benefit is not apparent. This is because other considerations such as planting date, tillage, previous field history for disease, type of disease organism present, soil compaction, seeding rates, and tillage also impact disease levels. What's more, these factors and the level of disease are affected by the weather. Warm and dry conditions usually result in fewer seed and seedling disease problems, whereas fungicides generally provide the most benefit during cool and wet conditions. In addition, the compounds used as seed treatments do not work on all the different seed and seedling blight pathogens. Products containing only one active ingredient like metalaxyl or mefenoxam provide control of Phytophthora and Pythium. Products or premixes that contain additional compounds like fludioxonil, maneb, PCNB, or captan protect against Fusarium, Rhizoctonia, and other true fungal pathogens, as well. Be sure to check what seed treatment is being used. Keep in mind that seed treatments can help improve crop stand establishment, but they may not result in a yield increase.Other control measures are based on cultural practices that improve conditions for the seed and for seedling emergence. Improve drainage in low, wet areas of the field. Avoid planting too early when soils are wet and cold, especially in no-till or conservation tillage fields with heavy crop residues that tend to retain moisture. Soybean producers need to consider which fields have a history of seedling blights or which fields contain soils high in clay that have a tendency to retain soil moisture or drain slowly. In these cases, consideration should be given to using a seed treatment. Resistance is not an option for controlling Pythium in corn or in soybean, but race-specific resistant in soybean cultivars with Rps1c, Rps1d, Rps1k, or Rps3a genes are available for controlling Phytophthora. A little planning can go along way to aid with early spring planting.
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