VEGETABLES - World Food: Production and Use - page 139

control. Mulch can prevent weed seed germination or, if germination occurs, plants
cannot survive because the mulch blocks sunlight. Mulch also slows or prevents evap-
oration of water from the soil surface, thus saving it for plant use. Irrigation with mulch-
ing is an effective way to maximize the use of irrigation water. Mulching will also
change the soil temperature depending on the type of mulch used, and this can be
used to advantage to increase vegetable production.
If mulching is not done, weed control will be essential during the growing season
either by mechanically removing weeds or the use of herbicides. Weeds can be
removed mechanically by either or both mechanical or hand weeding. There are a
limited number of herbicides that can be used on vegetable crops, and those that can
be are used with caution.
Harvesting is generally done by hand, although there has been much development
work designed to produce both machines and crops that are suitable to mechanical
harvesting. For smaller areas hand harvesting or picking is done; however, on multihec-
tare areas mechanical harvesting will be used if possible. Once harvested, the edible
portion is washed and, frequently, stored in cool conditions until transported to
market, canned, or frozen. Under the proper temperature and moisture conditions,
which will vary from crop to crop, fresh vegetables can be stored for a significant
period of time without spoilage.
Vegetables are generally higher value crops, and so additional expenses incurred in
field preparation mulching and irrigation and harvesting are generally justified.

4.6 PROTECTION

Vegetables often require protection from insects. Chemicals, either natural or organic,
such as various bacillus preparations and pyrethrins and synthetic chemicals such as
malathion and the various carbamates are called insecticides and are used to control
insects. These are sprayed or dusted on vegetable plants, as per label instructions, †
as evidence of insect infestation is noticed. Care must be exercised to cease insecticide
application prior to harvesting. The recommended time between the last application and
harvest is usually indicated on the insecticide container. In addition vegetables must be
washed thoroughly before being cooked and eaten.
In the case of starting plants in greenhouses, it is important to make sure that insect
and disease-free media is used to start plants because plant roots are susceptible to
attach by various soil-borne insect and disease organisms.
Growing a different crop in a field each growing season is another way to control
insects and disease organisms. This is called crop rotation and has been an effective
strategy for improved crop production.

Organic insecticides, although natural, are not necessarily less toxic than synthetic chemical insecticides!
† Insecticides are generally limited in the number of vegetables on which they are allowed to be used. Indis-
criminate use is dangerous.