Virginia's Extension soybean specialist is encouraging growers to keep an eye out for manganese deficiencies this season.
Manganese availability to the soybean crop is directly related to high soil pH. Heavy rains through early July may make the minor element deficient in some fields.
“Scout your fields,” says David Holshouser, Virginia Tech Extension specialist. The characteristic symptom is yellowing between the veins on new leaves.
“If you suspect manganese deficiencies due to high pH and no symptoms have yet appeared, you may want to consider using a tissue sample,” Holshouser says in his July newsletter.
He recommends applying — a pound chelated manganese or 1 pound inorganic manganese per acre to foliage when symptoms appear. More than one application may be required to correct the deficiency.
If there's a deficiency in the field, don't use the lower rate on the label. It's a maintenance rate.
On recently limed soils, however, a lower, maintenance rate can be combined with another scheduled application such as a postemergence herbicide. Combining manganese with glysophate will result in reduced weed control of certain weeds.
When pH levels reach 6.5 or above, manganese deficiencies will likely occur, Holshouser says. Deficiencies can occur at 6.2 in saturated soils.
“pH can drop in just a few weeks once the soil dries and aerobic microbial and chemical activity begins,” Holshouser says. “On the other hand, in wet areas of the fields, the pH could remain high.”
The problem in the wet fields, however, isn't manganese deficiency — it's the lack of oxygen to the roots that also causes other problems, Holshouser says.
“Throwing good money after bad will not likely improve the situation to a great extent,” he says. “I cannot advise widespread spraying of manganese on saturated fields or areas within fields.”
If you were able to get your fields limed, you may be experiencing manganese deficiency, Holshouser points out. If you weren't able to get in the field to lime, the soils will likely become more acidic and a manganese deficiency is less likely.