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Tuesday, March 25, 2008 8:54 PM CDT
Now is the time to give your soybeans the best start, manage root rot
By SUZANNE BISSONETTE
Our bizarre winter weather continues. I have recently spent considerable time on the winter speaking circuit talking about some of the diseases that aren’t as flashy as some of our more recent exotic pest introductions to Illinois, but are diseases that year to year cause considerable chronic losses in the field. Some of the more important players in this group are the seedling root rot pathogens. For soybean, the worst seedling rots are caused by fungi. There are a number of fungicides for you to choose from that are labeled for use on soybean. The majority of soybean seed sold is untreated. Treating your own soybean seed is not an easy undertaking but it can be very beneficial to establishing a vigorous stand. Will you need a fungicide seed treatment for your soybeans this season?
Several fungal seedling blights cause serious problems in soybeans. Diseases such as Pythium root rot and the seedling phase of Phytophthora root rot can outright kill seedlings. Other common seedling diseases such as Rhizoctonia and Fusarium root rots usually are not quite as dramatic but can place the seedlings under considerable early season stress. Seedling death or poor root establishment due to infection by any of the diseases will probably lead to the need for replant.
Several factors lead to an increased risk for serious seedling blight. First is the past disease history of the field. These seedling diseases all reside in the soil, you cannot rotate away from them, and with the right environmental conditions they will be active. Environmental conditions that pose a high risk for seedling blights include above normal rainfall the week before planting and above normal rainfall 96 hours after planting. Also, if low areas of the field remain flooded for 48 eight hours after a 1 inch rainfall this presents an extremely conducive condition for disease development.
Several production practices also can lead to higher risk for seedling disease. No till and conservation tillage pose more risk than conventional tillage. Double cropping soybeans and seeding at less than 55 pounds of seed per acre also have increased risk. Do you like to get your soybeans planted early? Seedbeds with delayed germination or emergence are also at increased disease risk.
The quality of the seed is very important as well. This is an issue of concern this year that has been brought up several times to me in my travel this winter. If cold germination tests for your seed were less than 70 percent or less than 85 percent for a warm germination test you will have increased risk for disease. There is only disease resistance to Phytophthora seedling blight. But, be careful. Make sure the variety you have selected has resistance to the seedling phase of Phytophthora. Varieties listed as tolerant have tolerance to the adult plant phase of Phytophthora but not to the seedling blight. Also, selection of a Phytophthora resistant variety will not protect you from other seedling diseases.
Consider all these factors, as well as the cost of replanting, to determine if a fungicide seed treatment would be beneficial to your soybean production this season. So, sure it’s cold out in the field now, but what better time to finalize your management decisions about how to give your soybeans a good start this spring.
Master Gardeners seminar
at Lawn and Garden Show
The U of I Extension Master Gardeners from Coles County will be sponsoring a seminar on Saturday morning during the Lawn and Garden Show at the Cross County Mall. If you are a gardener who competes with wildlife, you will want to attend the presentation at 10:30 a.m. on Saturday in the former Sam Goody storefront. Learn tips for controlling the pests in your home landscaping. Find out which species are protected. There will be time for questions and answers. See you Saturday morning at the mall!
Suzanne Bissonnette is an integrated pest management educator for the University of Illinois Extension.
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