Agriculture Reference
In-Depth Information
crop yields. For example, neglect of weeding results in a 20-40% decrease in
pineapple yields. In situations with adequate moisture in the soils, weeds are
not a factor in competing with the crop for water. Some weeds can also cause
sanitary problems that can af ect the crop, this in addition to the negative
aesthetic aspect. Weeds are an important problem in climates where there
are year-round crop-growing temperatures that favour continuous growth.
This weed problem is especially acute in tropical and subtropical climates,
except for subtropics with cooler winters, or the arid tropics and subtropics.
Weed control is particularly troublesome during the fi rst 2-3 years of orchard
establishment, when the trees have not yet developed substantial canopies to
shade weed growth.
In arid areas with drip irrigation and little or no rainfall, weed problems
are not very dii cult to solve, since weeds will only be found in wet areas
around a dripper and these can be eliminated mechanically or chemically.
However, if sprinkler, furrow or basin irrigation is used, weeds will be
widespread and control measures will have to be used frequently. Weeds can
be controlled by non-chemical and chemical means. Both approaches have
advantages and disadvantages, but if done properly can produce similar
results. The approaches can also be combined. The non-chemical control
involves either weed elimination or cutting weeds back to reduce competition.
Annual weeds are controlled by the use of hoes, pulling them manually,
fl ooding the land, the use of mulches, and mechanical tilling or discing the
soil. Mechanical cultivation should be avoided, though very ef ective, due to
the damage it causes to the superfi cial feeder roots. Weed height reduction
is achieved by periodically cutting the weeds back with a machete and with
mowers or many types of brush cutters.
The chemical approach relies on herbicides or weed killers, which can
belong to dif erent chemical groups. Herbicides can be selective and non-
selective; in both categories some are for foliar application and others for
soil application: The chemicals can work by contact or can be translocated
to other parts of the plant (systemic). Contact herbicides kill only the tissue
that they contact, while the systemic herbicides applied to the soil or the
foliage will be absorbed by the roots or aerial parts and move into the plant,
reaching the places where they will have their lethal ef ect. Some herbicides
are applied to the soil before the weed seeds germinate and thus are called pre-
emergence, while the post-emergence herbicides are applied once the plant
has germinated. Pre-emergence application, either before or immediately after
planting, is ef ective, the least costly and a desirable management practice.
Some of the techniques used for chemical weed control consist of using
a contact herbicide for annual weeds and a systemic herbicide for perennial
weeds. Sometimes a pre-emergence herbicide can be used before the start of the
rainy season. Several herbicides are on the market and dif erent approaches for
their use can be taken. An analysis should be made to be sure about the most
convenient application procedure. Annual weeds should be eliminated when
 
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