It might be time to consider a seed treatment for soybeans
Much like car buying, seed purchasing has gotten a lot more complex. After picking a model, there’s a host of options one can add to personalize it to his or her liking.
One set of options that seems to have become as ubiquitous as air conditioning is seed treatments. While corn attracts much of the attention here, University of Illinois’ plant pathologist Carl Bradley says soybean seed treatments can be a great weapon in protecting against seedling diseases.
• Illinois growers deal with four soybean seedling diseases.
• Seedling diseases primarily reduce yield by thinning stands.
• Seed treatments and variety selection offer some protection.
In Illinois, the main seedling diseases are caused by pythium, fusarium, rhizoctonia and phytophthora. Since seed sales reps soon will start stopping by to book orders, Bradley says it’s important to remember the efficacy of seed treatments against these diseases.
When thinking ahead to the 2011 crop year, don’t forget what diseases popped up this year. In many cases, these seedling diseases overwinter in the soil. Bradley says this means crop rotation can be a great defense against many of them. However, some have a very long life span and can actually survive a crop rotation.
The big 4
A number of different fusarium species can cause seedling blight and rot. One species can also cause sudden death syndrome. Fusarium prefers warm, dry conditions. While sudden death syndrome is easily identified, seedling blight and root rot caused by fusariam can be difficult to diagnose.
The fusarium species that causes head scab of wheat is also known to cause a seedling blight of soybean, Bradley cautions. When double-cropping into wheat stubble in a bad head scab year, he suggests using a seed treatment with a broad-spectrum fungicide that protects against fusarium.
Pythium flourishes in a cool, wet spring. It grows best when temperatures are below 65 degrees F. This means pythium could be worse in no-till fields, where soil temperatures are usually slightly cooler.
This spring’s warmer conditions created ideal soil temperatures for rhizoctonia. The disease is characterized by sunken, reddish brown lesions on the hypocotyl and roots. Bradley says rhizoctonia has been observed in some of his research plots this year.
Phytophthora also likes warmer soils, i.e. above 65 degrees F. Unlike rhizoctonia, the best defense against this disease is variety selection.
Bradley says some varieties include resistance genes against specific races of phytophthora. Other varieties include a “field tolerance” for phytophthora. While field tolerance gives a general protection against the disease, Bradley says farmers could still see yield loss from phytophthora under severe conditions, especially when using varieties with good levels of field tolerance but no race-specific genes.
Perhaps the best defense against phytophthora is to couple a seed treatment with a variety that has a high level of field tolerance. The treatment will protect the seedling for the first few weeks after emergence. After that, the variety’s field tolerance provides protection.
Each of these seedling diseases can cause yield loss as a result of reduced stands. Bradley and Vince Davis, U of I Extension soybean specialist, are conducting experiments to pinpoint the potential to cause yield loss. If the diseases thin stands, Bradley says the remaining plants can compensate by producing more branches, thereby producing more soybeans per plant.
Davis is conducting an experiment that compares four planting dates, three seeding rates and two row spacings. This is the experiment’s second year. He expects to start discussing results after the 2010 harvest. This could provide solid guidelines on target stands and planting recommendations.
This article published in the August, 2010 edition of PRAIRIE FARMER.