Technical Yearbook 2023

TABLE 1. Manganese norms (mg/kg) if samples are taken during set. Leaf blade

Petiole

Deficiency

Sufficient

High >250

Toxic >650

Deficiency

Sufficient

High >300

Toxic

<15

30 - 60

<20

30 - 60

>1 200

TABLE 2. Manganese norms (mg/kg) if samples are taken during véraison. Leaf blade

Petiole

Deficiency

Sufficient

High >300

Toxic >750

Deficiency

Sufficient

High >300

Toxic

<20

30 - 80

<20

30 - 60

>1 200

According to Deckers and other authors (1997), the use of Mancozeb could have been sufficient in maintaining the Mn

• Cold, wet periods in soils (e.g. during wet springs in the Coastal Region). • Soil that developed from rocks with low manganese levels. There are existing norms for the manganese content of leaf blades and petioles for wine grapes (Dawid Saayman, 2016). Deficiencies can be supplemented with a foliar nutrient consisting of a 0.4 - 0.6% Mn sulphate solution. The addition of a 0.5% urea solution will improve the uptake. There are also commercial products available which are specifically formulated to supplement manganese deficiencies. It is an expensive process to correct manganese deficiencies in the soil. Where the content of the soil is low (minimum 2 mg/kg for soils with pH (KCI) values of 5 - 6.5), 20 kg/ha Mn sulphate can be applied through the irrigation system, or in solution on the berms. Summary Manganese is a micro-element and is required in small amounts by the grapevine. It is however just as important as nitrogen, phosphorus and potassium which are used in large amounts. The prevalence of visual manganese deficiency symptoms has dramatically increased over the past two seasons in the Coastal Region. It is quite possible that the use of Mancozeb previously maintained manganese content at the required levels. Producers are advised to take leaf samples at set or véraison if Mn deficiency symptoms occur. Corrections can be made by means of foliar nutrient sprays. Where the Mn levels in the soil are very low, Mn sulphate can be applied through the irrigation system.  Reference https://www.wineland.co.za/manganese-deficiencies/

levels in grapevines. Role of manganese

According to Dawid Saayman (2016), manganese is involved in the activation of various enzyme systems; and inter alia plays a role in carbohydrate metabolism, phosphorylation, the citric acid cycle, etc. It is also essential for the formation of chlorophyll, as well as photosynthesis; deficiencies thus have a direct influence on sugar formation. It also combines with copper, iron and zinc to promote plant growth processes. Excess manganese can suppress the availability of iron and this situation often occurs in soils with low pH’s. Manganese deficiencies can lead to a decrease in secondary metabolites, including flavonoids (Chen and other authors, 2020). Cabernet Sauvignon vines on a high pH soil, which exhibited Mn deficiency, were treated with Mn sulphate foliar sprays for two seasons. The sugar content of the grape berries increased, as did the phenolic components from véraison to harvest. Wines made from the treated vines had better colour intensity. Correction of deficiencies Various crops are sensitive to manganese deficiencies, namely citrus, core and stone fruit, grapevines, strawberries, potatoes, legumes, oats and sorghum. There are also several factors that can be detrimental to the availability of manganese: • Soil with high pH levels (plant availability is minimal at pH of 7 or slightly higher). • Lime-rich soils. • Light sandy soils. • Soils low in potassium. • Soils with low organic material content. • Soils containing high levels of copper, iron and zinc.

For more information, contact Hanno van Schalkwyk at hanno@vinpro.co.za.

99

TECHNICAL YEARBOOK 2023