Agriculture Reference
In-Depth Information
A plant growth regulator will speed up, stop, retard, prolong, promote,
start, or in some other way influence vegetative or reproductive growth of a
plant. These chemicals are sometimes called growth regulators or plant regu-
lators. They are used, for example, to thin apples, control suckers on tobacco,
control the height of some floral potted plants, promote dense growth of or-
namentals, and stimulate rooting.
A defoliant causes the leaves to drop from plants without killing the
plants. A desiccant speeds up the drying of plant leaves, stems, or vines.
Desiccants and defoliants are often called "harvest-aid" chemicals. They usu-
ally are used to make harvesting of a crop easier or to advance the time of har-
vest. They are often used on cotton, soybeans, tomatoes, and potatoes.
V.
MOLLUSKS
Mollusks are a large group of land and water animals including slugs,
oysters, clams, barnacles, and snails. They have soft, unsegmented bodies and
often are protected by a hard shell.
A.
SNAILS AND SLUGS
Land snails and slugs are soft-bodied and have two pairs of antennae-like
structures. Their bodies are smooth and elongated. Snails have a spiralshaped
shell into which they can completely withdraw for protection when disturbed
or when weather conditions are unfavorable. Slugs do not have a shell and
must seek protection in damp places.
Snails and slugs feed on plants at night. They tear holes in foliage,
fruits, and soft stems, using a rasp-like tongue. They may eat entire seed-
lings. As they move, snails and slugs leave a slime-like mucous trail which
dries into silvery streaks. These streaks are undesirable on floral and ornamen-
tal crops and on those portions of crops to be sold for human food.
Snails and slugs deposit eggs in moist, dark places. The young mature in
a year or more, depending on the species. Adults may live for several years.
They overwinter in sheltered areas. They are active all year in warm regions
and in greenhouses.
Figure 3.17
shows a land snail and
Figure 3.18
pictures a
soft-bodied slug.
B.
SHIPWORMS
Shipworms are marine mollusks which cause extensive damage by boring
into wood which is in contact with salt or brackish water. Of all the marine
