The corn earworm on lima beans and its control

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Title:
The corn earworm on lima beans and its control
Physical Description:
Book
Creator:
Brannon, Loyd W
United States -- Bureau of Entomology and Plant Quarantine
Publisher:
U.S. Department of Agriculture, Bureau of Entomology and Plant Quarantine ( Washington, D.C )
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aleph - 030285167
oclc - 779480140
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Full Text



August 1941


THE CORN EARWORM ON LIMA BEANS AND ITS CONTROL 1/

By Loyd W. Brannon, Division of Truck
Crop and Garden Insect Investigations




Introduction

The corn earworm (Heliothis armigera (Hbn.)), also knovn as the
tomato fruitworm and the bollworm, frequently causes severe dmnge to the
fall crop of lima beans in eastern Virginia as well as in runerous other
sections of the United States. It attacks this crop after corn in the
vicinity has dried out and is no longer attractive to the nPoths for egg
deposition. In the past five seasons in eastern Virginia an average of
approximately 15 percent of the bean pods on fall lima beans were damaged
by the insect. This, however, is not a true indication of the losses caused
by the insect, as it fails to take into consideration the large reduction
in yield resulting from injury and consequent shedding of blossoms and
young pods prior to harvest.

General Description of the Corn Earworm

The corn earworm is the young or immature form of a moth. The insect
overwinters successfully in the southern part of this country in the resting,
or pupal, stage. In the more northern part of-the country, where severe
winters are experienced, the insect does not successfully pass a winter.
Consequently, infestations which appear in the more northern States comre
from moths which developed in the more southern States and migrated north-
ward.


I/ A contribution from the Bureau of Entomology and Plant Quaran-
tine, U. S. Department of Agriculture, in cooperation with the Virginia
Truck Experiment Station.


E-547





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The egg laid by the moth is about half the size of the head of a
common pi. In form it is round and flattened on its bottom side. When
first laid the egg is yellow, but it appears white against the dark green
of bean leaves As soon as the young larva, or caterpillar, begins to
develop in the egg it darkens. and just before the egg hatches it becomes a
dusty-brown color.

The noe ly hatched caterpillar is whitish, with a black head, and
measures oily bout one-fourth inch in length. When fully developed the
caterpillar is about 12 inches long The full-grown caterpillars vary
greatly ir color, but in the main they are dark brown, striped with green,
yellow,. slate, ard black markings Oftentimes the type of food on which
the caterpillars feed affects their general color, and in such cases the
background color may be light green marked with yellow markings.

The pupa or resting stage. is light brown and has a form common to
many other moths.

The moth, v,hich belongs to the group of insects commonly known as
killers, has a wing expanse of about 1 inches. The ground color is usually
ochraceous or buff, ;,ith shades that vary from light olive green to reddish
brown.

Feeding Habits and Nature of Injury

The cor earworm attacks lima beans in the fall after corn in the
vici ity has dried out and is no longer attractive to the moths for egg
deposition Darage to lima beans is caused by the feeding of the earworms
on the blosso' aird pods Tn eastern Virginia the first eggs are usually
laid by the orb on bean foliage in the last part of August or the first
part of ept nber. the majority observed being laid on the upper surface
of the leaf Hatching occurs in from 3 to 6 days after the eggs are depos-
ited, te length of time depending on the temperature. Soon after hatching,
the slall worm, or caterpillar, begins to feed on the leaf upon which he
egg ,a' laid, later wandering about and feeding on the leaves blosso 1 s
and developingJ ods until about three-fourths of an inch in length before
honing in+o ard eeding on the contents of pods. The worms grow very
rapidly and im the fall months they usually reach full size in from 22 to
23 days after hatchig. The worm makes a round hole through the pod wall
a d of'me completely devours the contents of the pod. The hotes vary ii
size, ut normally they range in diameter from about one-fourth to one-half
i ch and my apiear at any point on the surface of the pod. Freqently ods
thus affected (o not contain larvae, since several pods are often davagd
by ome larva The injury gives the pods a very unsightly appearance, ieces-
s itatinu had culling prior to marketing the crop. In cases \herc ;,ormy
nds re ot oi-I led out prior to shipment. the worms present in Iods enclosed
tin: na 'ncr,' cxy leave these pods and enter worm-free pods, thus adding to
the 1aage vhile in transit When the worm attacks young pods it causes
many of those injured to drop,





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Control

The control measures offered in this circular are ba' i o t e
results of five seasons' work, much of which ha- been deta ile e&] 1'0,,her.2/
These experiments show that corn earworm damage on lima beans cac be appre-
ciably reduced by the use of cryolite (synthetic or natural) '0 eithe
as a dust, as a spray, or as a bait, if properly applied.

Dusts

Cryolite, undiluted
Apply from 12 to 14 pounds per acre per application.

Cryolite, 80 pounds
Talc or sulfur, 20 pounds
Apply from 18 to 20 pounds per acre per application.

When prepared from commercial brands of cryolite containi- 85 per-
cent of sodium fluoaluminate, the second formula gives a sodium fluoaluwiiate
content of approximately 68 percent in the finished dust mixture If the
sodium fluoaluminate content of the cryolite is greater or less than 85 per-
cent, the proportions of the ingredients must be varied accordingly

Spray

In general, cryolite dust mixtures, made according to ther of the
above formulas, have given better results than sprays in corn ecorfI Con-
trol. If the use of a spray is desired, however. the vaterial should be
applied according to the following formula:

For large areas For small areas

Cryolite 4 pounds 4 ounces (12 level tablespoonfuls)
Water 50 gallons 3 gallons
(Based on cryolite containing 85 percent of sodium flucalurinate)

Bait

Cryolite, 1 pound
Cottonseed meal, corn meal, or soybean meal. 10 pounds
(Based on cryolite containing 85 percent of sodium fluoainaLuinate)
Apply 80 pounds per acre per application

Sulfur is recommended in preference to talc as a dilnent Tor cryolite
i., i stances where the potato leafhopper, the common red spider, or powdery


/ Bran&on Loyd W, Control of the Corn Earworm on Fordhook Lima
Bca..s in Eastern Virginia. U. S. Dept. Agr Circ. 506, 14 pp ilus 1939.




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nildei. is present along with the corn earworm In the case of the spray,
wettable sulfur may be added to the cryolite at the rate of 2 to 4 pounds
to 50 gallons of water.

The baits should prove of considerable value in instances here the
grower is not equipped to dust or spray, or in cases where the bean foliage
has attained such dense growth that the use of horse-drawn equipment would
be impracticable. They should be broadcast by hand lightly and evenly over
the leaves of the plants at the same time intervals as for dust or spray
applications. If the Mexican bean beetle is present in injurious nbers
along with the corn earworm the dust or spray should be used in preference
to the baits, as these baits are not effective for control of the Mexican
bean beetle.

To secure thorough coverage of all parts of the pla ts a d o rake
the treatments effective simultaneously for control of the Mcexcan bean
beetle the insecticide should be directed to both the upper ?
surfaces of the leaves This may be accomplished by making minor adjstvents
to the nozzles of dusters and sprayers equipped for control of th Mexican
bean beetle._/

Treatments should be begun when the majority of the silks on ears
of field corn in the vicinity of late plantings of lima bea.s hve dried
out, for it is usually at this tim& that the orn earworm moths Vei l gying
eggs o hems, Tin eastern Virginia this usually occurs in the last part of
August or the liT'st part of September. at which time late pla.ti of ma
bears are generally in full bloom Treatments should be begu' e~r!]er in
case the worms are observed on the foliage in injurious numbers or ii
becomes necessary to control the Mexican bean beetle.

As orf earworm 'ioths are continuln]ly emerging ar(d del e
which are riot affected by the t reatet .i .. C_ since new ute oliage
is constantly developing, treLets i siI_ be repeated 6t pproxi. tely
2-week iiatervalsi Three treatments ur i usually necessary, ep Jl ot
abu ;di ce of the ia t In or t' L( avo the dtanger of harmful fluorine
rescues on thi edi le v tios oi the ma rket or'oduct, treat: t i s ~ld he
U 9.n~t 2 v.)eks i ] rii to9 ha aies!. Dvs should be applied C n I little
or o C is blowg If rtin occur vhi 48 hours after e et is
give, the application should be repeated ;ioon as conditions ii permit.

Note e I o C re e te xper J indicate tha tue cr3olite
treatjeats ] ~ is above are. also &f'-ctiv. in reducing cor- cnr .or. damage
on sWap bQa8s On account of Ih fl..uoi:ne s idue hazard cvoli 1 should
not. be aoj)iid n< sj be ais afte r the Lods have begun to fo m D y making



3/ iowa d Neale .. Br~nnon. ,o)d IV and MasonL W 1orto C The
Mcxi a. Bea Beete +n the ;at a j ts Cu rol. U S. Dept. i I- r .rs'
Bull 1624 (rev.), 21 p,., illus. 1936.






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careful applications prior to this time, however, damage to this crop ray
be appreciably reduced. In instances where the corn earworm is pres t in
injurious numbers along with the Mexican bean beetle, cryolite should be
used in preference to the rotenone-bearing materials, such as derris and
cube, for the combined control of the two insects, as the derris and cube,
although highly effective for control of the Mexican bean beetle, are not
effective for control of the corn earworm.

Information regarding the purchase of the insecticide materials
mentioned above may be obtained through local dealers in agricultural
supplies, seedsmen, drug and department stores, or through the county
agricultural agent, State agricultural experiment station, or State depart-
ment of agriculture.




UNIVERSITY OF FLORIDA

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