PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CONTROL
METHODS
(contd)
Burning before rolling
can greatly reduce the
populations of snails
and slugs
Barriers
– Rough mulches around plants act as a barrier to snails and slugs which require a
moist smooth surface on which to move. This has limited practicality as snails and
slugs (and eggs) must be outside the barriers when these rough mulches are put in
place and there must be no bridges across them. Suitable mulches include coarse
wood chips, coco mulch, bark, sawdust, sand or wood ash (2-3 cm deep), crushed
egg shells (keep in frig or microwave a couple of days before using).
– Mosquito netting can be placed over young seedlings.
– Copper repellent barriers, eg bands, tape, copper-coated pot feet, and rings and
paint strips 10 cm wide, can be used to band planter boxes and tree trunks.
Copper tape can be partially buried in the ground and copper can be spread around
legs of benches. When snails and slugs make contact there is a toxic reaction which
repels them. Do before warm weather when snails become active. Lines of lime,
copper sulphate are repellent and used to prevent migrations into crops.
– Tiny electric fences (10 cm above soil) are effective but extremely expensive.
– Do not use salt to destroy snails and slugs as it will increase media salinity.
Treating standing stubble
– Rolling, harrowing or slashing stubble kills resting snails by dislodging them
o
from vegetation onto the ground on a hot day (temperature > 32 C below 50%
humidity) forces them to move over hot ground, they die by desiccation. Best - soil
o
o
surface is > 40 C, day temp > 35 C, low humidity, nights warm and dry.
– Burning infested stubble or herbicide-killed pasture, precipitates wind erosion and
interferes with stubble retention methods of farming. There must be a sufficient fuel
load and few rocks for snails to hide under.
– Rakes on the front of harvesters could reduce contamination of harvested grain.
Robot-type machines are being researched overseas which sweep over the
ground identifying slugs by their shape, picking them up, dropping them in a hopper
at the rear of the machine. There bacteria digest the slugs at the same time as
releasing a gas to power the machine.
Keep pots off ground (about 3 cm) using easy-to-handle boards (30 cm x
30 cm) to allow snails and slugs to crawl underneath.
Home made baits.
Just because a
pesticide is a natural
botanical extract it
should not be assumed
improperly handled and
prepared, it can be just
as hazardous, if not
MOLLUSCICIDES.
Chemical control is most effective when used in combination with sanitation.
The main molluscicides are metaldehyde, methiocarb, iron-edta, iron
phosphate and copper. They can be expensive and their effectiveness is
influenced by soil and weather conditions.
Resistance. Exposure to prolonged periods of metaldehyde can induce resistance
in white bradybaena snails (B. similaris) overseas (Salmijah et al 2000). Some slug
species may be naturally tolerant to methiocarb.
On edible crops, check current registration status.
Barriers. Copper can be spread around the legs of benches.
Baits (page 236, Table 47).
– Taste deterrents. Some types of baits must be formulated with taste deterrents.
– Some types of baits are mould resistant. Decaying pellets on plants such as
lettuce can promote mould development.
– Pellets and granules are more weather resistant than powders.
– Defender (metaldehyde) breaks down rapidly in direct sunlight. It kills snails and
slugs by dehydration, as a snail's body is 90% water, when dead there is only an
empty shell! Do not water heavily for at least 3-4 days after application, as they may
rehydrate and recover. Toxic to non-target animals. Do not allow contact with any
edible portions of any food or feed crop. Phytotoxic to some plants, eg daylilies,
clematis, don’t apply to dry soil. Metaldehyde baits are less effective during damp,
overcast weather than those containing methiocarb, but are cheaper to purchase.
– Baysol (methiocarb) is an anticholinesterase compound, affecting the nervous
system of snails and slugs. Toxic to non-target animals.
– Multiguard (iron-edta) contains iron which is toxic to snails and slugs but has low
toxicity to non-target animals.
– Enviroguard (iron phosphate) contains iron which is toxic to snails and slugs but
has low toxicity to non-target animals.
– Socusil (buffered copper complex).
– To improve performance of baits mow, cultivate or spray weeds along tree and
fence lines prior to baiting. As snails congregate along crop edges, fencelines,
etc. It can be cost effective to apply baits in these regions, before they invade large
areas especially if numbers are large.
– Home gardeners would mostly use baits as snails and slugs are mostly hiding
underneath bricks and pots, where aerosols and sprays would not be effective.
Snails and slugs 235