Agriculture Reference
In-Depth Information
inability to absorb them, foliar sprays provide a very rapid response, and after
2-3 weeks improvement can be noticed. Pineapple in Hawaii is sprayed at
regular intervals with an iron solution to correct a defi ciency; even though the
soils are high in iron, most is unavailable to the plant.
Many fertilizer preparations contain microelements that are sprayed on
to the foliage from one to four times a year. Spray application frequency is
dependent on the micronutrient, the species and the defi ciency severity. Foliar
fertilizations should not be performed at fl owering time or when the fruits are
very small. Some micronutrients are applied as sulfates, such as zinc sulfate,
but since this is an acid product, it has to be mixed with lime to avoid leaf
damage. Urea, which has a high biuret content, can also cause severe burns.
Soluble forms of single essential micronutrients and mixtures of a number of
micronutrients, as their sulfates, nitrates and chlorides and complexed with
chelating compounds (EDTA), are available commercially. These products can
be tried and used if satisfactory results are obtained.
For best results, foliar fertilization by spraying young leaves will make it
easier for the product to be absorbed, since the leaf cuticle is thinner. If the
spray drop size is small, repeat applications at lower concentrations enhance
uptake. Since a liquid is applied to the foliage, the more foliage it covers and
the longer it stays as a liquid the more nutrients will be absorbed by the plant.
Application during cooler, high-moisture and calm air conditions is the best
to obtain maximum benefi ts, with early-morning sprays being recommended.
Covering both sides of the leaves, especially the underside, with the greater
number of hairs and pores and less wax, aids in foliar nutrient uptake. The
addition of a spreader sticker to the foliage fertilizer mix can also increase
uptake. Some foliage spraying can be done in combination with disease
and insecticide sprays after checking for compatibility. Phosphates are not
compatible with salts of copper, manganese, zinc and iron; copper fungicides
should not be mixed with sulfates, nitrates or chlorides. If a new product or
procedure is being used, test the mixture on some plants before spraying the
whole fi eld.
CROP PROTECTION
Fruit crops can be af ected by insects, mites and nematodes, and diseases
caused by bacteria, fungi, viruses and similar organisms. Vertebrate enemies
such as rats, squirrels, monkeys, birds and bats can also be a problem. Since
fruits are expected to be without blemishes, and more so if they are for export,
the tolerance is zero for damage. It is not possible to obtain blemish-free-
quality fruit without using pesticides. For many tropical fruit crops, there
are few approved pesticides, and the residues tolerance is low, and varies
with market.
