First of all, do you use any glyphosate or has there been a history of regular use of glyphosate on your property in the past? It is not uncommon in orchards, where this is the case, to find severe manganese and/or iron deficiencies in the trees. This is because glyphosate reacts with these cationic micro-nutrients to form glyphosate-metal complexes which binds up the metals and renders them unavailable for plant uptake. Even if glyphosate has not been applied to the soil for some time, it has a half-life in soil of anywhere between several weeks to years.

Furthermore, soil problems such as high pH due to high magnesium, sodium, potassium or calcium, can also severely limit the uptake of manganese, as can high pH water (which may be the case if using alkaline bore water for example). Even very high soil levels of zinc and copper, (which is also very common in citrus orchards), will limit the uptake of manganese. Therefore, I would persist with the manganese foliar applications whilst you are trying to overcome the limitations in the soil. At what rate were you applying the foliar manganese? What sort of chelating agent did you use? Did you use a good spreader and sticker with the application? And what time of the day was the application applied?

I would try our Manganese Shuttle™ at 5 L/ha or, if you are certified organic, try manganese sulphate at 3-5 kg/ha with Fulvic 1400™ at 2 L/ha and incorporate a good spreader/sticker such as Cloak™ Spray Oil at 1.5 L/ha. This application will probably need to be repeated a couple of times at 3-4 week intervals. A reliable leaf test should always be taken before and after application to determine the effectiveness of the spray. You can include other sulfur based inputs in this application, but avoid incompatibilities such as calcium nitrate, potassium nitrate, MAP or MKP. Also, avoid spraying in the middle of the day as this is when humidity is lowest and plants are less responsive – very early in the morning or late afternoon/evening is the best time to foliar spray.

Hope this helps,

Kind regards,

Julie