Farmers have a tendency to use foliar spray feeds containing a mixture of macro- and microelements, which they believe will reduce deficiency diseases. In many trials of these products I have never found a good response, even when deficiencies were present. Don’t waste your money. It is better to determine the specific deficiency and treat it on its own.
The best-known element deficiency associated with cauliflower is boron. The symptoms are brown sunken areas in the curd, which, when cut through down to the stem, shows a hollow area which tends to become darker. Unfortunately, by this stage it is too late to do anything about it.
The other symptom of boron deficiency, which applies to all brassicas, is holes in the leaves, which look as though they have been stretched until they start to tear. Hold the leaf up to the light and you will see areas where the cells are shrunken, as well as small light patches which are the first stages of the deficiency. All too often, holes in the leaves caused by newly hatched diamondback moths are blamed. However, these holes have smooth edges in contrast to the jagged holes of boron deficiency. This deficiency will affect all plants in the area, whereas moth damage may skip some plants.
Different varieties have different susceptibilities to boron deficiency, and the availability of boron can fluctuate depending on factors such as soil organic matter. It is sound practice to apply at least one boron foliar spray to the crop at an early stage. The usual rate is 1kg/ha of Solubor, but if symptoms have already appeared, 2kg/ha would be better. It is often preferable to add boron to the soil, but it is extremely difficult to apply 15kg/ha evenly, which is why most farmers go the foliar route.
The two vegetable crops that are known to suffer first from a boron deficiency are cauliflower and beet. If these are treated, there is usually enough spray left for the crops which follow in rotation. If you have had boron deficiency problems in the past, rather apply two foliar sprays.
The other element that is sometimes deficient in cauliflower is calcium. The leaves near the growth point become scorched, with a pale area adjacent to the scorching, and start to curl at the edges. Calcium foliar sprays are the only solution at this stage. This deficiency should not occur if fertilisation is done according to soil analysis.
Molybdenum deficiency, which was described in a previous article on cabbages, is another possibility. Almost without exception, this occurs where the soil pH is low. – Bill Kerr Contact Bill Kerr on (016) 366 0616 or e-mail [email protected].
