Farmers often have difficulty with identifying nutrient deficiencies in cabbages. I recognise them because of my experience in dealing with them over the years. Some deficiencies are uncommon and even many fertiliser company representatives cannot identify them. Some representatives take chances and tell the farmer what they think the deficiency could be instead of admitting they don’t know.
As brassica is an expensive, high-value crop to grow, farmers should base their fertilisation on soil analysis. a deficiency occurs later, the analysis will help to eliminate or identify elements by referring to the pH alone.
In my early farming days, had picked up a deficiency and called in the experts. An individual with a PhD who worked for a fertiliser company couldn’t help. then sprayed a small trial, each with a number of micro-elements and had an answer in days. It was a molybdenum deficiency. The pH was low and therefore this element was unavailable. This deficiency causes chlorosis ( yellow blotches) and cupping of the leaves with severe stunting. manifests as patches in the land. As a foliar spray, 50g to 100g of sodium molybdate per hectare solves the problem.
Magnesium deficiency is uncommon, but manifests when magnesium is low and too much potassium is applied. An indistinct chlorosis starts on older leaves, but with less cupping. Potassium deficiency manifests as a dark discolouration of older leaf edges.
Calcium deficiency shows up as a burning and/or yellow discolouration of the margins on tender, young leaves. Cauliflower is more susceptible than cabbage. deficient calcium level may cause leaves to break off in the developing head and may result in dead leaves when cut open. This is called tip burn and can be a physiological problem associated with certain varieties in early summer when there are rapid weather changes.
Phosphorous deficiency causes leaves to develop a purple/reddish hue. is often confused with a nitrogen deficiency where the phosphate levels are marginal and the leaves develop a pink colour. If the leaves are a dark colour with a reddish tinge, it is a phosphorous deficiency. the pink colour matches the light-coloured areas, it is a nitrogen deficiency.
Boron deficiency leads to leaves “tearing” and leaves a specific pattern. Plants in the area will have these symptoms too. Many confuse this with damage caused by DBM larvae. Trace elements can be rectified by boron foliar sprays. Foliar sprays of nutrient mixes are useless in this case. – Bill Kerr
Contact Bill Kerr on (016) 366 0616. |fw