Manganese (Mn) is an important plant micronutrient and is required by plants in the second greatest quantity compared to iron. Like any other element, it can have a limiting factor on plant growth if it is deficient or toxic in plant tissue. It is similar to iron in many ways, and manganese deficiency or toxicity is often mistaken for iron deficiency or toxicity.
Function: Manganese is used in plants as a major contributor to various biological systems including photosynthesis, respiration, and nitrogen assimilation. Manganese is also involved in pollen germination, pollen tube growth, root cell elongation and resistance to root pathogens.
Deficiency: Manganese deficiency symptoms, which often look like those of iron deficiency, appear as interveinal chlorosis (yellow leaves with green veins) on the young leaves, and sometimes tan, sunken spots that appear in the chlorotic areas between the veins. Plant growth may also be reduced and stunted.
Manganese deficiency can occur when the pH of the growing medium exceeds 6.5, because it is tied up and unavailable for uptake. Deficiency can also occur from low fertilizer application rates, use of general purpose fertilizers (which typically have reduced micronutrient contents), excessive leaching or applying too many iron chelate drenches.
Toxicity: Manganese toxicity symptoms begin with the burning of the tips and margins of older leaves or as reddish-brown spots across older leaves.
Severe toxicity may result in spots becoming more numerous and larger, forming patches on the older leaves. At pH levels below 5.5, manganese is very soluble and toxicity symptoms are probable, especially in zonal geraniums, marigolds, lisianthus and New Guinea Impatiens. Manganese toxicity can occur if the fertilizer application rate is excessive.
Similarities to Iron: Manganese and iron are closely related, so manganese competes with iron and, to a lesser extent, with zinc, copper, magnesium and calcium for uptake by the plant. Maintain the manganese to iron ratio at 1:2 for best results, and test the growing medium to verify that all nutrient levels and pH are within their normal ranges.
Manganese and iron have similar visual deficiency and toxicity symptoms. Manganese and iron deficiencies both appear as interveinal chlorosis of the young leaves. The major difference is that as manganese deficiency progresses, tan areas develop between the veins while iron deficiency progresses toward an almost white appearance in the leaves. Iron and manganese toxicities have identical symptoms, so it is difficult to tell them apart.
One cannot make assumptions and institute corrective measures without laboratory testing to confirm there is a manganese deficiency. If you suspect there is an issue with manganese or iron, the prudent approach is to test the medium and tissue from both “normal” and “abnormal” plants and the nutrient solution(s) that are applied. This is the only way to know if manganese deficiency or toxicity is occurring.
Where to Find Manganese: Most commercial growing media contain a “starter” nutrient package that includes manganese and the other essential micronutrients, but it will satisfy the needs of a crop for approximately one week.
Constant feeding with water soluble, peat-lite fertilizers is the best way to ensure that all essential micronutrients, including manganese, are provided in the correct proportions.
Test your water prior to the production season and consult with your fertilizer manufacturer regarding the fertilizers required to complement your water quality. Some water sources contain manganese, but rarely enough to supply the needs of a crop.
Contact your Premier Tech Horticulture Grower Services representative for assistance in establishing the fertilization program that will work best for your crops.
Authored by Ed Bloodnick of Premier Tech Horticulture