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protection and yielded 83 percent large and medium heads. Calomel-talc powder
containing 4 percent calomel applied at the rate of a teaspoonful around the stem
of each plant on May 3 was also satisfactory, giving 100 percent commercial
protection and yielding 75 percent large and medium heads.



58 MASS. EXPERIMENT STATION BULLETIN 388

In 1941 twelve varieties of cabbage were plaiilefl to fictermiiie their nntural
susceptibility to cabbage maggot injury. The results indicated that the early
maturing varieties such as Golden Acre and the Savoy types were most sus-
ceptible, and the red varietie*^ most resistant. Dry weather in the latter part of
the growing season interfered with the records on head development, but Red
Acre with 64.83 percent large and medium heads withstood the maggot injury
and drought the best, while Golden Acre, which suffered the most maggot injury,
gave the poorest yield with 7.69 percent marketable heads.

Susceptibility of Cabbage Varieties to Cabbage Maggot Injury, Wnlthum, Mass., 194L

l^ery Susceptible (80 percent or more commercial injur>). Golden Acre,
Enkhuizen Glory.

Susceptible (65 to 80 percent conmiercial injur>). Super Curled Savo\-,
Cornell Early Savoy.

Moderately Susceptible (40 to 65 percent commercial injury). — Premium
Flat Dutch, All Head Early, Danish Drumhead, Pearly Jersey Wake-
field, Pcnn State Railhead.

Slightly Resistant (25 to 40 percent commercial iiijur\). - Mammoth Red
Rock, Red Drumhead, Refl Acre.

Control of the Squash Vine Borer. (W. D. Whitcomb, Waltham.) The field
infestation of the squash \'ine borer was 7.52 borers per vine, which is one of the
greatest infestations vwr recorded in the experimental field of Blue. Hubbard
squash at Waltham. Experimental sprays and dusts were applied July 7, 14,
21, and 28. The sprats were applied at 275 pounds pressure with a small power
sprayer, and the dusts with a plunger t>'pe hand duster. The most effective
treatments were a rotenone-copper ox\'chloride sulfate dust, white oil emulsion
I percent with nicotine sulfate 1-500 spray, and nicotine sulfate 1-250 spra\'.
Rotenone -talc dust containing 0.75 percent rotenonc and a dust containing 20
percent cryolite with 5 percent metallic copper were moderatel}' effective. Lead
arsenate 3 pounds with fish oil 1 pint in 100 gallons of water as a spray was in-
effective, this plot having an infestation only 12 percent less than the untreated
check.

Yield records showefl a significant increase in favor of the dusted plants, re-
flecting the beneficial action of a fungicide on the production of fruit. The plants
receiving the rotenone-copper o.xychloride sulfate dust yielded 594 pounds more
than the untreated check, an increase of 80 percent. As in previous experiments,
there was no consistent direct correlation between yield and borer injury. The
1941 experiments also strengthened the theory that an infestation of 2 borers or
less per vine before August 1 does not greatly reduce the yield.

Control of Onion Thrips. (A. I. Bourne.) The early spring was characterized
by abnormally warm weather in April and was followed by more normal tem-
peratures in May with very little rain during that period. This was followed by
weather somewhat warmer than normal in June and rains which, although for
the most part small in amount, were so frequent that field crops such as onions
made an early start and grew rapidly.

Such weather conditions would normalh' favor the early appearance and rapid
development of thrips but this was not the case in 1941. In the experimental
plots of seed onions, thrips appeared late and developed slowly. There were
practically no thrips on the plants throughout June, and by July 14 the average
population per plant was only 10 thrips. Very high temperature in early July
induced a rapid increase to the peak of 40 thrips per plant on July 21. Following
a rainfall of nearly one-half inch on the 25th and a heavy downpour during the
28th (1.9 inches) the number of thrips was reduced to approximately 12 per



ANNUAL REPORT, 1941 59

plant and remained at that low level until late August when the plants matured.
No blast was observed.

Throughout the Valley, fields of both set and .seed-grown onions were com-
paratively free from thrips. Results of tests of contact insecticides for thrips
control were inconclusive because of the scarcity of the insects even on the un-
sprayed plants. Fixed nicotine with a resin residue spreader gave good initial
control although its action was slower than that of nicotine sulfate, it was as
effective alone as when used with a spreader. A rotenone extract with resin
residue spreader had a high immediate effect and good residual action. Derris
powder (4 percent rotenone) gave excellent kill within 24 hours, and reinfestation
was slow. This was true regardless of the type of spreader used. Nicotine sulfate
and soap caused the usual high mortality of thrips within a few hours after appli-
cation but its residual effect was inferior to that of rotenone.

Predaceous insects were comparatively scarce during the early summer, but
by mid-August syrphid flies and predaceous thrips had increased to considerable
numbers and contributed very greath' to the rapid decline, in late August, of a
very light but long-drawn-out attack of thrips. No evidence of fungus disease
of thrips was observed.

The Spray Residue Problem. (A. I. Bourne.) The more liberal limits of
tolerance established in the late summer of 1940 continued in effect for the ship-
ping season of 1941. While the present limits are calculated to allow the growers
greater latitude in their pest control program, the prolonged drought from late
July until harvest and the uncertainty as to the permanency of the present
limits made growers reluctant to enlarge their spray program, and for the most
part very few changes were made. In the spray program recommended by the
college foi 1941 the only significant change was the suggestion of a 75-25 sulfur-
lead arsenate dust as an alternate for the 2d cover spray.

Through the cooperation of the Control Service, analyses were made for lead
and arsenic residue on samples of Mcintosh collected from the sprayed plots at
harvest. These analyses showed the amount of residue to be in all cases well
below the present limits.

PVuit which had received the standard sclietlule recommended for the State
showed residues of .031 grains of lead and .013 grains of arsenic per pound of
fruit. Samples from the optional standard schedule in which no lime was used
in the cover sprays gave .026 grains of lead and .009 grains of arsenic per pound.
In the plots where wettable sulfur was used throughout the season, the lead
residue ranged from .023 to .037 grains per pound and the arsenic residue from
.005 to .015 grains. Lead arsenate was applied in the 2d cover spray (June 10)
at 4 pounds per 100 gallons; 3 pounds in the 3d cover (July 2); and 2 pounds in
the 4th cover (July 29). The fruit was picked September 15. While the total
precipitation for July was nearly normal, approximately half of it occurred in
one shower on the 28th. Records showed that during August and September
little more than half the normal rainfall occurred, a deficiency of 3.67 inches.
Fruit encountered unusually favorable conditions for the retention of spray
deposits and normal weathering off could not take place.

Even under such a severe test as the past season offered, lead and arsenic resi-
tlues were so far below present limits that there was a substantial margin of safety,
which would indicate that if these limits are retained the growers will have more
latitude for stiffening their spray schedule for late summer pests than they have
enjoyed since spray residues became a problem of major importance.

Apple Maggot Control. (A. 1. Bourne and W. D. Whitcomb.) Apple maggot
proved to be of relatively minor importance in 1941, not only in Massachusetts
but throughout most of the Northeastern States. In well-sprayed commercial



60 MASS. EXPERIMENT STATION BULLETIN 388

orchards the injury was negUgible, and even in the smaller home orchards which
received little attention the pest was not conspicuous.

This reduction is not believed to be due to any marked increase in energy on
the part of the growers or to any improvement in the handling of dropped fruit
or other precautionary measures. It is the general belief that adverse weather
conditions and especially deficient rainfall at the period of normal emergence
of the flies were the chief contributing factors.

In the emergence cages at Waltham the flies began to appear on June 19 which
is the earliest date since the observations were started. Although the cages were
operated in the same way as in the previous years, the emergence in the culti-
vated cage was greater than usual and that in the sod much smaller than usual.
This condition is apparently correlated with the deficiency of soil moisture this
year. The emergence record is as follows:

In Sun — Light Soil
Cultivated Sod

Degree of Emergence:

First fly June 19 June 24 '

25% June 30 July 3

50% July 7 July 9

75% July 12 July 15

100% August 7 July 27

Number of larvae in 1940 400 400

Number of flies emerged 1941 207 43

Percent emergence 51 .75 10.75

Insecticides for the Control of European Corn Borer. (A. I. Bourne and \V. D.
VVhitcomb.) The unsea.sonably warni weather throughout April promoted ab-
normally early pupation of the overwintering corn borer larvae. Seasonable
weather in May allowed development to progress normally and resulted in a
very early emergence of the spring brood of moths. On the other hand most of
the growers planted corn at the usual time, with the result that considerable
moth emergence took place before corn was above ground or at least when it was
too small to be attractive for oviposition. In addition, during much of the time
that the moths were present the temperatures at dusk were too low for moth
activity. As a result the infestation by first generation larvae was negligible
throughout the State. Growers harvested very clean corn even where no control
measures were practiced, and in fields which were sprayed or dusted there was
slight evidence of the borer.

In the experimental fields the plots sprayed with derris and Ultrawet showed
4 infested ears out of 660, 99.4 percent clean corn, 84.5 percent of which was
grade 1 or 2; in other words, 84 percent of the total yield was marketable grade.
A fixed-nicotine spray gave 97.1 percent clean corn, 84 percent of which was
marketable. In the plots dusted with derris there were 4 infested ears in a total
of 652, 99.4 percent clean corn, 90 percent of which was of marketable grade.
Dual-fixed nicotine dust gave 98.8 percent clean ears, and 84 percent of the total
yield was of marketable grade. The infested ears were so few that the grower
made no effort to salvage them. The unsprayed check plots yielded a total
of 682 ears, 48 of which were infested. In other words the infestation was so
light that 92.9 percent of the yield was free from borers. In the entire field, re-
gardless of treatment, only 83 ears out of 3,341 examined weve infested. No
attempt was made to spray late corn because of the scarcity of 2d brood larvae.

The infestation by the first generation of the European corn borer in the ex-
perimental planting at Waltham was so light that results of spray applications



ANNUAL REPORT, 1941 61

were not significant. In the check plot there were 5 infested non-salable ears
and 5 infested but salable ears in a yield of 203 ears. Hills sprayed individually
with a mist nozzle showed 1 infested but salable ear in 219 ears, and the block
sprayed with a spray gun from the border showed 2 infested salable and 2 in-
fested non-salable ears out of 226. Powdered derris root 3 pounds and Ultrawet
}/2 pound in 100 gallons was used June 17, 24, 30, and July 7.

The second generation planting at W'altham was not sprayed because of the
light infestation, and an examination on August 21 showed 15 infested ears or
1.34 percent In 1,118 ears examined.

On August 12 a part of this corn was treated for protection against the corn
ear worm, by applying a standard lubricating oil-pyrethrum solution to the
dried silk of the ears. No corn ear worm infestation developed but the treatment
injured the ears by preventing pollination of the kernels in the terminal portion of
the ear, indicating that this treatment is not satisfactory under all conditions.
(See page 55.)

Potato Spraying Experiments. (A. I. Bourne.) The weather conditions during
spring and early summer furnished a ver\' favorable start for potatoes and al-
lowed them to keep this initial advantage. The plots were planted on May 9.
The plants appeared promptly and growth was steady and rapid throughout the
summer. The plants were slightly damaged by a light frost on the night of
September 19-20 and were killed by a heavy frost on September 29-30. The
crop was dug September 30 to October 2. In all of the plots sprayed with bor-
deaux the plants were alive, green, and thrifty until killed by frost.

Leafhoppers were very few and no outbreak occurred at any time during the
season. Potato aphids became abundant in early July but were controlled by
the addition of nicotine in the spray of July 16 and never threatened thereafter.
Flea beetles were abundant throughout June and early July; the late July infes-
tation was not so heavy. In the experimental plots 11 applications were made
between June 11 and August 27. A new method of determining flea beetle injury
was devised by which the number of feeding punctures was correlated with the
amount of leaf growth. The plan was designed to show the amount of injury from
week to week as well as the cumulative damage throughout the season. On this
basis the amount of flea beetle feeding in the plots given a commercial spray of
basic copper sulfate and sulfur was 103.1 feeding punctures per square inch of
leaf surface; plots which received a basic copper arsenate-sulfur compound
showed 45.1 feeding punctures per square inch of leaf surface; and the plot which
received a neutral insoluble copper fungicide (double copper) showed 88.6 punc-
tures per square inch.

In all the plots sprayed with home-made bordeau.x mixture the damage from
flea beetle feeding was very much less than that in the plots receiving commercial
sprays. There was a slight advantage in favor of the low-calcium bordeaux,
and the addition of calcium arsenate in every case furnished added protection.

The length of life of the plants in the different plots was in exact proportion
to this index of beetle activity. The plants sprayed with basic copper sulfate
and sulfur began to die early in August and by the end of the month practically
all were dead. Plants in the plot given the basic copper arsenate-sulfur compound
succumbed somewhat later. The plants given the neutral copper fungicide re-
mained alive until mid-September. In all of the bordeaux-sprayed plots most
of the plants were alive and green until the frosts of late September.

The summer was marked by a prolonged drought, and the lack of sufficient mois-
ture interfered very seriously with the growth of the tubers and yields were
proportionally reduced.

The yield records, however, showed a direct correlation with the amount of
flea beetle injur\'. In the plots which received the commercial sprays, yields



62 MASS. EXPERIMENT STATION BULLETIN 388

of 308 to 346 bushels per acre were recorded, while plots in the same field which
received bordeaux mixture yielded 420 bushels per acre. The plot which received
the low-calcium bordeaux plus calcium arsenate gave the highest yield — 474
bushes per acre, 76 percent of which was of number 1 grade.

Introduction of Parasites of Oriental Fruit Moth in Peach Orchards. (A. I.

Bourne.) The work of rearing parasites of the oriental fruit moth was con-
tinued in 1941. By agreement with the Department of Entomology of the
Connecticut Experiment Station, Mr. A. DeCaprio was again placed in charge
of the collection and shipment of breeding material for both institutions. Para-
sitism was comparatively high in the New Jersey strawberry fields in 1941 and
the season was early. Mr. DeCaprio, by benefit of his experience in past seasons,
was able to locate superb fields for collection. Cool weather during the shipping
period and rapid transit allowed the material to arrive at the laboratory in Am-
herst in very good condition.

The strawberry leaf roller larvae were very nearly full grown when collected
so that very little migration took place after arrival in the laboratory. Emergence
of the parasites was such that all the orders from growers were filled by June 30,
and within the next few days a sufficient number of parasites emerged to duplicate
all original orders, fill late orders, and in most cases duplicate these. The surplus
material for distribution was made possible by the very proficient work of Mr.
DeCaprio in collecting breeding material, the very accurate estimates of para-
sitism, and the improved technique in the laboratory. Fifty-eight growers in
9 counties received a total of 140 colonies. More than half the growers received
their orders in half colonies to facilitate more uniform distribution in large orchards
or for use in small, isolated blocks.

The warm weather, the unusually large number of hours of bright sunshine,
and the few rainy days during the period of liberation offered very favorable
weather conditions for the parasites.

Naphthalene and Similar Compounds as Greenhouse Fumigants. (W. D.

Whitcomb and Wm. Garland, Waltham.) A complete series of experimental
fumigations with a mixture of monochlor naphthalene oil 3 parts and commercial
flake naphthalene 1 part indicated that the vaporization of % to 1 ounce of the
fumigant in 1,000 cubic feet constitutes a lethal atmosphere which will kill 80
percent or more red spiders if they are exposed for three hours. These results
were obtained when the experiment was made at a constant temperature of
70° F. and a relative humidity of 50 percent, and also at 75° F. and 60 percent
humidity. At the higher temperature and humidity the mortality was about
3 percent higher, especially at the shorter exposures.

A mortality of 30 to 40 percent resulted when the spiders were exposed for
three hours to ^ to ^ ounce per 1,000 cubic feet, and an exposure of one or two
hours to a lethal atmosphere killed only 15 to 25 percent. Potted carnations heav-
ily infested with the common red spider mite supplied the. experimental material,
and the fumigant was vaporized at the rate of l-i ounce per 1,000 cubic feet each
hour for six hours. An infested plant was entered and removed each hour during
the fumigation.

Control of the Common Red Spider on Greenhouse Plants. (W. D. Whit-
comb, Wm. Garland, and W. E. Tomlinson, Jr., Waltham.) Life history studies
of the red spider on different host plants at constant temperatures were con-
tinued. Most of the studies were on potted snapdragon and showed that the
time required for development at 60°, 70° and 80° F. was approximately in a
3:2:1 ratio as follows:



ANNUAL REPORT, 1941 63-

Average Number of Days at —

60° F. 70° F. 80° F.

From oviposition to hatching 14.48 7.71 3.81

From hatching to adult — male 15.70 9.46 5.35

female 19.17 11.00 6.25

From oviposition to adult — male 30 . 94 1 6 . 95 9 . 23

female 31.41 18.62 10. CO

Oviposition records showed that although the female spiders laid about a&
many eggs at 60° F. as they laid at 70° and 80° F. in this experiment, they re-
quired about ten times as long to lay them.

Studies of red spider development on various host plants continue to indicate
that there is some plant character which determines the rate of spider develop-
ment, and studies to determine this are planned.

Spraying experiments with eleven advertised insecticides recommended for
combating the red spider mites on roses were applied at weekly intervals in three
series, using a greenhouse power sprayer at 275 pounds pressure. Of these, one
material was very effective and outstanding; two were moderately effective
and satisfactory; and eight were unsatisfactory. (See page 55.)

The most effective material is described as Technical Mannitan Monolaurate
to which 1 percent rotenone and 1.8 and 2.6 percent other derris extractives have
been added. When diluted to 1-400 this was the only spray material which
reduced a natural infestation of 25 to 50 spiders per leaf to less than 5 live spiders
per leaf, and consistently killed 90 percent or more of the spiders without injury
to the plants. When diluted 1-600 this material was less effective but gave sat-
isfactory control.

The other satisfactory materials, which combined rotenone and emulsified
dispersing oils, reduced the infestation 60 to 80 percent and permitted 10-18
live spiders per leaf after treatment.

Unsatisfactory materials included rotenone combined with chlorinated hetero-
cyclic hex>'lamine, powdered derris root and sulfonated castor oil, a commercial
flour paste, monochlor naphthalene soap emulsion, a commercial preparation
containing castor bean extract (ricin), and rotenone combined with hydrous
aluminum oxide. Several of the rotenone sprays which gave unsatisfactory
control of the red spider mite on roses gave excellent control of the same pest
on potted carnations.

Three applications in March of a dinitro dust containing 1 percent dinitro-
ortho-cyclo-hexylphenol killed 90 percent of the red spider mites and reduced an.
infestation from 25 to 2.4 live mites per leaf without injury to the foliage.

Biology and Control of the Apple Leaf Curling Midge. (W. D. Whitcomb,
Waltham.) Although a strong northeast storm occurred on June 5 while the
midge flies were still plentiful and might have been blown a considerable distance
to the southwest, no new infestations outside of the previously known infested
area were discovered or reported. However, this midge was found within the
infested area in several orchards where it was not known to be present before 1941.

In the insectary the transformation to flies was 22.54 percent from maggots
collected in June 1941, 45.41 percent from maggots collected in July and 11.11
percent from maggots collected in August.

In the observation orchard at Westford the infestation was very heavy during
May and June but, because of the drought and absence of late summer growth
even on watersprouts, it was below normal in late July and August. Records
of 2117 bud tips on Baldwin trees examined at regular 3 and 4 day intervals
between May 9 and September 12 showed that eggs were laid on 1712 or 80.87
percent of them. Oviposition was concentrated in three distinct periods when.



64 MASS. EXPERIMENT STATION BULLETIN 388

eggs were found on every bud examined, namely May 27 to June 10, July 1 to 8,
and July 22 to August 5. During the first two periods 100 tips were examined
at each observation; but in the last period the number of tips available averaged
less than 10, contrasted with 1940 when a large number of tips was available
until about August 25. In 1941 the first eggs were found on May 9 which is 15
days earlier than in 1940.

Maturity of larvae and their emergence from rolled leaves was concentrated in
three definite periods on June 17 to 24, July 8, and July 29. These periods gen-
erally correspond with the rainfall rather than with the development of genera-
tions which was extended and overlapped by abnormal weather conditions.
The relative abundance of the midge throughout the summer is indicated by the
number of larvae collected in 5 bands as follows: June 17, 2280; July 8, 244; and
July 29, 790.

In a newly infested orchard at Waltham containing 96 trees of 7 varieties of
approximate equal exposure to infestation, 893 infested buds were collected on
June 12. The average number of infested tips per tree of each variety was:
Delicious, 42.00; Rhode Island Greening, 8.75; Baldwin, 7.58; Mcintosh, 4.54;
Gravenstein, 3.16; Northern Spy, 0.33; and Wealthy, none. In this collection
63.29 percent of the infested tips were found on the Delicious trees. Another
collection on July 9 yielded 532 infested tips on the same trees, making a reduc-
tion of 40.42 percent due to destruction of the maggots in the infested tips at
the previous collection. ,

Similar collections from a nearby orchard where 396 infested tips were col-
lected on 54 small trees showed an infestation of 11.94 tips per tree or 57.32
percent of the total on Starking; 6.00 per tree on Golden Delicious; and 3.58 per
tree on Baldwin. In a block of young trees, 2 Milton trees had an average of



Online LibraryMassachusetts Agricultural Experiment StationBulletin - Massachusetts Agricultural Experiment Station (Volume no.379-398) → online text (page 36 of 77)