Question:

Are Solubor and Techmangum absorbed solely through the leaves and if so does it have a rain fast time. Or if it gets rained off will it be absorbed through the roots?

Jordan Answer:

My impression is that manganese is primarily foliar absorbed. Boron is foliar absorbed but also root absorbed even from foliar sprays. If the concern is wash off you could make a second spray with fungicide. I am copying David Hardy for addition insight.

Hardy (N.C. Department of Agriculture and Consumer Services):

Both soil and foliage for both nutrients as David knows but he is addressing the foliage app. Here are my thoughts. For Mn, the foliar rate (0.5 lb/ a) may not provide much benefit if rained off soon after application since it is so low a rate compared to soil app rates (10 lb / a). This would be especially likely if soil pH is elevated so availability is reduced. For B, I think differently. The rates of apps for foliar and soil applied are more similar and plant requirements are less as compared to Mn so if rained off, likely still effective. Soil pH would affect similarly. That’s my opinion. I am not sure of rate of foliar Mn uptake or any rainfast info. Don’t have that in my head and looked but did not see on label online. Copying Luke Gatiboni who is our new soil fertility professor to get his thoughts.

Gatiboni:

I’m on the same page as David, B and Mn have a moderate speed of absorption by leaves (slower than N and K, for example). It means you can have some of these going to the soil if you have rain right after the foliar fertilization. If your B and Mn are washed from the leaves to the soil, I would expect different things: maybe your B can be uptake by roots because B has low fixation to the soil particles, being available for absorption (As David said, the rates of B are similar when applied via the soil or foliar). Conversely, Mn can have a high fixation to the soil particles, especially in high pH. Because of this, the rates applied via soil are much higher than the foliar rates. It means that if you had your Mn washed to the soil, probably a significant part of this cannot reach the roots, especially in high pH soils.

Hardy:

Sorry my lead sentence was a bit quirky last night… I have been under the weather. David J answered this correctly. A few more thoughts. High water solubility for B may be why it is taken up from soil after wash off from foliage too. It would be washed down to the roots more so than Mn. For both of these nutrients, the degree of waxiness of the cuticle could affect uptake rate, slower uptake possibly in peanuts. Cox found in soybeans 2 apps were better than 1 app in correcting Mn deficiency. Catching early is important. Guess this is in peanuts.

Jordan:

Thanks everyone. Product selection is important. Looks like you are using products that have enough B and Mn to correct a deficiency. Many people are applying liquid products that do not have enough B or Mn as a single application to correct an issue. And I suspect most folks are only going to make a single application along with fungicide sprays. Folks are paying for convenience in many cases and are not getting enough product to make a difference. In 2020 Peanut Information we show how much product it takes to provide the equivalent rate of B and Mn delivered by the older, dry products.

Source of original question:

Thanks everyone. That does help clarify. I’ve always liked Solubor and Techmangum, they are aggravating but we know what we are getting.