• The main question being asked is, “should I spray a fungicide?”
A SEVERE case of frogeye leaf spot from a soybean plant in Kentucky.
Indications are the occurrence of frogeye leaf spot is pretty severe in some Kentucky soybean fields east of I-65, and especially in northeast Kentucky.
Most of these fields began to show severe symptoms this week, but were relatively clean a week ago.
The main question being asked is, “should I spray a fungicide?”
The answer depends on the extent of the disease and the average stage of the plants. If the crop is before, at, or near stage R5 (pods full size, but beans are very small) then spraying may be advisable as long as the disease is established throughout the field in question and the crop has good yield potnetial.
The closer fields get to the R6 growth stage (pods filled), the less likely spraying will be of any benefit.
If the disease is not already established in a field, there is a good chance it will only be a minor player, perhaps because the variety has some resistance.
There are many available varieties that are resistant to frogeye leaf spot. Growers with problems this season, should seek out and plant frogeye resistant varieties in problem fields the next time they grow soybeans.
In the meantime, spraying a fungcide is the only available option if frogeye is a problem now. If you have a field that meets the above criteria, it is important to spray ASAP.
If you must wait (three days or longer), the chances of success are limited.
Finally, as a result of some work funded by the Kentucky Soybean Promotion Board during 2011-12, we know that about half of the frogeye fungus populations in Kentucky are resistant to strobilurin fungicides.
Since most farmers cannot know if they have strobilurin-resistant or —sensitive strains — they must assume the strain of the forgeye fungus in their fields is resistant to strobilurins.
Thus, if a fungcide is sprayed, it should be either a triazole fungicide, such as TopGuard, or a strobilurin-triazole mix product, such as Stratego YLD.
Contact you local county Extension office, or your fungcide salesperson, for help in slecting the best, available triazole or strobilurin/triazole pre-mix for control of frogeye leaf spot.
If you encounter a field with widespread and severe frogeye, yield loss is sure to take place even if a fungicide is sprayed. However, if a crop still has 3-4 weeks before the pods are filled in, it still might be advisble to spray a fungicide in order to minimize losses in an otherwise good crop.
But the time to act is now!
Want access to the very latest in agriculture news each day? Subscribe to Southeast Farm Press Daily. It’s free!
More from Southeast Farm Press