Horticulture Principles and Practices

7.6.1 SMALL ANIMALS
Rabbits, mice, gophers, bats, and moles are among the rodents and other small animals
that plague cultivated plants. They may attack plants from above or below the ground.
Moles, for example, damage lawns from underground. They may eat seeds when planted,
causing incomplete plant stand in the field, or they may eat mature fruits and seeds. These
mammals, especially the ones that bore holes in the ground, may improve drainage.
7.6.2 BIRDS
Birds cause damage similar to that effected by small animals. Fruits and cereal crops are
particularly prone to bird damage. On the other hand, birds feed on insects at all stages in
their life cycles, thereby playing a beneficial role in controlling some insect pests.
7.6.3 NEMATODES
Nematodes are unsegmented roundworms. They are microscopic plant parasites that attack
above- and belowground parts of plants, including vegetables, fruit trees, ornamentals, and
foliage plants. However, most that are parasitic on plants are soilborne. The most common
nematodes include root knot (Meloidogyne spp.) and cyst (Heterodera spp.). They are
spread by equipment, water, shoes, and other means. On the roots, they cause irregularly
shaped knots that interrupt nutrient flow in the plant. This amorphous growth is distinguishable
from the well-defined and usually round shape of root nodules produced in
legume-Rhizobia symbiosis (Figure 7–14). The plant may be discolored (abnormal
yellowing) and stunted in growth. Tuber crops may have disfigured and unsightly skin.
Many nematodes are inactive at temperatures below 10°C (50°F). A field infested
with nematodes can be managed by cultural operations to lower the population of the
parasites. When the populations are high, fumigation is most effective, even though it is
not possible to irradicate the pest from the soil. Nematodes are especially difficult to control
in dormant form (cysts or eggs).
7.6.4 SNAILS AND SLUGS
Nocturnal creatures, snails and slugs are similar in many respects, one distinguishing
feature being the lack of a shell in slugs (Figure 7–15). The presence of these mollusks
is betrayed by the slimy trail they leave behind as they move on the soil surface. They
feed on leaves and young plant stems. Because of their nocturnal habits, they hide during
the daytime in cool and moist places such as under rocks, debris, and mulch. Slugs
cause more damage than snails to horticultural plants. The most common garden snails
are the brown garden snail (Helix aspersa) and the decollate snail (Rumina decollata).
The former has a globular spiral shell and the latter a cone-shaped spiral shell. The most
common slugs in the home garden are the spotted garden slug (Limax maximus) and the
tawny garden slug (Limax flavus). The tawny slug leaves a trail of yellow slime. The gray
garden slug (Agricolimax reticulatus) is small and leaves a clear slime trail.
FIGURE 7–14 Nematode damage
as distinguished from root nodules
formed as a result of Rhizobia
infection.
Root nodules
by Rhizobia
Root nematode attack
7.6 Other Pests of Horticultural Plants 233