By Anne Dorrance
The water has hopefully found its way off of the fields. Flooding for greater than 2 days may reduce soybean yield by as much 20% compared to 1 day flooding events on soils with higher clay content. If I do some quick math here – 20% from a field that typically produces 50bu/A soybeans – is 10 bu. Matt Roberts may have some issues with my math but this is approximately a $120 loss ($12/bu, estimated price for fall soybean). It is time to check the costs of your inputs to determine if you can put additional inputs into this crop. Fields where soybeans were submerged, covered with silt etc, will not recover, and those should be forgotten about. I think I have said this several times this year, work on the drainage issues for that field, that will be money better spent.
For those fields with less flooding, we have several issues that are “brewing”. Here is the link that has a nice set of pictures to help in the identification diseases discussed below. (There are also additional diseases to the ones listed) http://www.oardc.ohio-state.edu/ohiofieldcropdisease/t01_pageview3/Soybean_images.htm
- White mold. Plants with symptoms caused by Sclerotinia sclerotiorum, stem rot were found in NE Ohio. This is unusually early. In a previous article, several fungicides were listed. These were listed for preventative spraying at R1 growth stage. I don’t have any data on spraying fungicides once infections have developed to the point of symptoms. But we can tell you that Approach (DuPont) is not recommended for these situations. If your fields are at R2, have a susceptible variety and no symptoms, and this field is a historic white mold field, Approach may still be used. If your soybeans are at R2, symptoms are visible then one of the triazole fungicides, Domark (Valent) or Proline (Bayer), are alternative choices; we do not have any data from these situations so leave untreated strips. If you have a variety that has a good score for resistance to Sclerotinia. It is best to leave it alone, double check with your seedsman to see what they are saying about that varieties genetics.
- Frogeye leafspot: It is time to scout. If you find frogeye lesions in the field, conditions are expected to continue to favor repeat infections. Applications should begin at R3 followed by a second application at R5. So this would be a good year to protect your crop. Again, if the variety has a good score for resistance, a fungicide is not needed.
- Brown spot. Brown spot caused by Septoria glycines, is very prevalent in many fields this summer. But is still in the lower canopy and we have very thick canopies early this year. From previous studies, we documented that in the worst case scenario, brown caused no more than 5 bu/A and most times it was between 2 to 3 bu/A, @ the projected price of $12/bu that is only $24 to $36/Acre. Our studies showed that applications at R3 of a strobilurin were the most effective at reducing brown spot. However, the variety resistance package should keep this from moving up the plant. Going after the 2 to 3 bu will be dependent on what your input costs are for this field right now coupled with the amount of flooding injury that occurred. Visit the Enterprise worksheets on the AgManager Website to determine if this is a worthwhile decision. http://aede.osu.edu/research/osu-farm-management/enterprise-budgets . This is determining the economic threshold for this disease in this type of year.
- Soybean Rust. We have been scouting this year due to the weather patterns – but everything is negative to date. Soybean rust was found in central Alabama and in western Mississippi, which are both a long way off, and levels are still low. From the scouting that occurred in previous years, it takes at least 3 cycles of infection at 7 to 10 days each, prior to rust being detectable.
- Phytophthora stem rot. You can definitely tell this year where the Rps genes are not working and where the partial resistance levels are too low for Ohio conditions. The fields have a choppy appearance with holes randomly spaced in the field. And the plants will keep dying now throughout the summer, especially if we hit a dry spell. Go back and look at the seed catalogues and see what you bought for resistance to this disease – make a note to buy something with more resistance in the future.
Source : osu.edu