Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1939-06-17

Sugar beet webworm moths, the
larvae of which strike heavy yield
ing crops in the rich irrigated val
legs of Montana, are reported in
such alarming numbers that unless
the moths prove sterile, the only
hope of preventing serious damage
is by immediate control
The warning is issued by j. H. Pep
per, entomologist for the Montana
agricultural experiment station, after
a personal survey Of the Gallatin val
ley and adjoining territories and a
study of reports that indicate rather
widespread infestation. He has re-
cetved reports OF heavy moth flights
from Sidney to Conrad.
Although the sugar beet webworms
prefer Russian thiStleS and lambs
quarters, sugar beets and practically
every truck crop are readily attacked,
Pepper says. Damage may be expected
from now on, but In areas where moths
are sterile, nc. eggs will be laid and
no damage viii be done.
Because no survey has been made,
Pepper is urging farmers and garden
ers to report outbreaks at once to his
office. The insect now is in the moth
stage In central Montana but young
larvae or worms may have already
Matched In other parts of the state.
Moths Easily Identified
The moths can be identified easily,
a one-inch wing spread. The wings at
rest are mottled with light brown and
are held back over the body giving the
insect a triangular appearance. When
disturbed the moths rise in swarms
but quickly settle down. They are most
active at night and attracted by light.
Moths begin to lay eggs week or
so after their appearance. The eggs
may be found on the underside Of
leaves of Russian thistle, lambs quar-
ter, sugar beets etc. The eggs are
pearly white and usually overlap in
a single line.
When the young worms hatch they
are about as big around as a pin, about
one-fourth inch long, dull, darkish
green with a darker head. They can
be found easily by observing the web
which will be found attached to the
underside Of the leaf after the worms
drop to the ground.
Whenever moths are found, farmers
are urged TO make careful inspection
of weed patches particularly around
gardens. Damage done by webworms
can be found by looking on the under
side Of leaves. The worms eat out tiny
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der surface of the leaf has been
scratched or scraped. The tips of
damaged Russian thistle leaves turn
black.
Control Measures
Control must be started right after
the worms hatch or 1t will not be eff
fective, Pepper warns Cut and burn
infested weed patches near fields and
gardens as soon as the young worms
are observed. These weed patches also
may be sprayed with an arSentcal
poison such as sodium arsenite This
poison acts quickly and Is dangerous
to stock, and should never be used on
gardens or sugar beets because 1t in
iures the plants.
When worms are small they can be
controlled by thorough disking of weed
patches.
Another means is water. The worms
cannot cross streams, so irrigation
bitches should be kept filled If pos
sible, gardens can be protected by sur
with a water filled ditch.
The worm also may be killed by
spraying with Paris green at the rate
Of q to 3 pounds per so gallons Of !
water. This spray Is recommended for
moderate infeStations Of fields. When |
used on garden crops, all vegetables |
should be washed before eating.
Pyrethrum and rotenone dustS gave |
kills only in early stages Of
worm development. After worms be-
eame a half-inch long 1t was less ef-
'ective and did not kin fully developed |
worms, according to experiment sta
ion results. These dllStS have gained |
,avor because they temporarily knock
tut" mature worms, but as they revive |
md continue to do damage the dugts |
ire only recommended against the
earlier stages.