A36-Lancaster Farming, Saturday, April 13, 2002
Capitol Wagon
ALFALFA WEEVII
ARE HATCHES!
Del Voight
Extension Agronoi
Agent, Capitol Regii
The mild winter has
many insects to increase i
lation and, in some cast
age area crops. Already
many insects that are di
timothy, orchardgrass.
grains, and alfalfa. Thi
details the alfalfa pests
important today.
Area fields are infesi
both alfalfa weevils and pea
aphids, of which I will detail al
falfa weevils. Alfalfa weevils have
grown in population over the last
few years and have accounted for
huge losses in income for area
producers from their feeding on
the leaf portion of the plant, re
ducing the relative feed value
and protein content of the hay.
Weevils follow a life cycle re
ferred to as complete metamor
phosis (change). This means the
insect progresses through an egg,
larvae, and adult stage that ap
pear to be completely different in
appearance but are still the same
insect.
Adults hard-bodied, dark
:olored insects with a distinct
mout search for alfalfa fields
in the fall that have as many egg
laying sites as possible. Fields
that are mowed close to the
ground in the fall eliminate egg
laying sites for these adults (Di
vely, U. of Maryland). Those
same adults awaken in the spring
and begin laying more eggs in al
falfa fields. In general, the fall
laid eggs account for 20 percent
af the total hatch in the spring
and the spring-laid eggs account
For 80 percent of the total spring
batch. Adult females can lay
from 500 to 2,000 eggs, so there
:an be significant numbers if left
unchecked by growers.
You can walk through alfalfa
fields and find larvae feeding, the
result of the fall-laid eggs. Just
last week I received reports of
adults in area fields and laying
more eggs, which will end up as
the official spring hatch. These
;ggs should hatch in the next sev
eral days and begin feeding im
mediately.
Entomologists at Penn State
and other universities can predict
the activity of the pest and poten
tial damage through the use of
heat units. This method is simply
a measure of the accumulated
Adults hard-bodied, dark-colored insects with a dis
tinct snout search for alfalfa fields in the fall that have
as many egg laying sites as possible. Fields that are
mowed close to the ground in the fall eliminate egg-laying
sites for these adults.
Eggs overwintering in
the stem of the alfalfa
hatch into a pale green
worm with a distinct white
stripe down its back. The
first instar (stage) of the
weevil includes a pest that
is very small and hides in
the bud portion of the
plant.
heat from Jan. 1. By following
the heat, we can predict egg
hatch, larvae growth, and, more
importantly, the period which the
insect is no longer a problem.
Generally it takes from 14-21
days from egg to adult, depend
ing on heat accumulation.
This year we had first egg
hatch the last week of March, in
dicating the fall-laid eggs. Last
year this did not occur until the
April 19, showing just how far
ahead we are this year.
Eggs overwintering in the stem
of the alfalfa hatch into a pale
green worm with a distinct white
stripe down its back. The first in
star (stage) of the weevil includes
a pest that is very small and
hides in the bud portion of the
plant. The best indication of in
star activity in the field is small
shot holes that are visible around
the new growth of the plant.
Once the larvae get to the third
instar, at Vi toVt inch, they will do
massive damage to the plant and
in some cases can remove all foli
age from the plant.
Observing recent heat unit pat
terns and the next two-week fore
cast, it appears that the third in
star stage for fall laid eggs was
set to occur from April 14-April
21, 2002. This will be the time
that growers will need to have al
ready determined the need for
treatment. Spring laid eggs
should be active at this time as
well and growers will need to
time crop protection product ap-
Holstein Winners Announced
SENIOR TWO YEAR OLD
Rmotm Pmmi Gat* Unjot PBootopa
Clayton Wood, Uttlestown
Jr. All-fA Towtr-Vu« Im Ruttii*
Scott Walton, Carlisle
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Reserve McCullough* Adolph VoroM
Tobin Stuff, Mercersburg
Hon. HleiS# tteetMf HCMHf
Emily CkNtingt*; Centra Hall
JUNIOR THREE YEAR OLD
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Brian Hindman, Brockway
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Hon. Man. Graat-Viaw M Chrfstmu Mi*
Holly Miller, Hamsburg
plications to correspond with
these dates.
To scout for this pest, growers
should be collecting (randomly)
30 stems from the field. Using a
bucket, the scout will tap the
stems along the edge of the buck
et. The larvae will fall to the bot
tom of the bucket and can be
counted by the scout. If more
than 60 larvae are counted, then
a treatment is warranted immedi
ately. Another method is to ob
serve leaves, and if four out of 10
leaves have shotholes, then treat
ment is called for.
Widespread depletion of the
population is of major concern.
Fungal pathogens as well as par
asitic wasps need some weevils
around in order for them to sur
vive. These biological weapons
accounted for the massive drop
in weevil populations 15 years
(Continued from Page A2B)
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SENIOR THREE YEAR OLD
Jr. All-PA 8011-Stone H Mm Sotoiu
Andrew Stoner, Waynesboro
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Cttristi Knight, AlmiH*
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Jr. M-M MMMom Whip tMfy iay
Andrew Stoner, Waynesboro
AGED COW
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Jr. AH-M Hickory Green IsUr Petty
Scott Welton, Carlisle
ago. The fungal pathogen re
quires warm and damp weather
to infect larvae and kill them. If
the conditions exist, it could well
mean an application of an insec
ticide is not warranted. In addi
tion, parasitic wasps place eggs
inside the adult weevils and the
egg eats the weevil adult inside
out. If growers see large amounts
of either disease of these wasps,
then the avoidance of chemical
control may be the result.
If crop protection products are
needed, growers have many op
tions available to them. Applica
tions using synthetic pyrethroids
(contact insecticides) such as
Warrior, Baythroid, or Pounce
need to come in contact with the
insect to be effective. For this rea
son, growers need to increase ap
plication rates to a minimum of
20 gallons per acre and prefera-
FOUR YEAR OLD
Jr. Atl-P* Sintee-Acm Encor* Sunkhrt
Daniel Oliver, Gmenoastle
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IteMnw Turnpike-View Skytaefc Nrniy
Dustin Horning, Stevens
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Eric Hixson, CwmsMle
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Clayton Wood, Lrtdestown
bly with pressures exceeding 40
psi. Applications of organophos
phates (Furadan, Dimethoate,
Lorsban), which use both contact
and systemic pathways to insects,
require applications in wanner
weather to be highly active. For
this reason, growers need to allow
for warm weather (60 degree F)
to improve the effectiveness of
these materials. Also, carbamates
such as Sevin are effective but
also must come in contact with
the pest similar to synthetic py
rethroids.
Weevils are active now and
growers need to take action to de
termine the need for treatment.
This spring suggests a similar
pattern to spring 2000 and we
may see weevil activity on the re
growth of second cutting, so
growers must be scouting weekly
to determine additional control
measures.
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