The beet leafhopper and its control on beets grown for seed in Arizona and New Mexico

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Title:
The beet leafhopper and its control on beets grown for seed in Arizona and New Mexico
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Romney, Van E
United States -- Bureau of Entomology and Plant Quarantine
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U.S. Department of Agriculture, Bureau of Entomology and Plant Quarantine ( Washington, D.C )
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May 1942 E-567











THE BEET LEAFHOPPER AND ITS CONTROL, ON BEETS GROWN FOR SEED
IN ARIZONA AND NEW MEXICO

By Van E. Romney, Division of Truck Crop and Garden Insect
Investigations



INTRODUCTION


The commercial production of sugar beet seed on a large scale is a
relatively new agricultural industry in the western part of the United
States. The more important areas in which the seed is now produced include
the Salt River Valley in Arizona, Mesilla Valley in New Mexico, valleys
near Hemet and Ferris in southern California and Shasta Valley in northern
California, Virgin Valley in southern Utah and several mountain valleys in
north-central Utah, an area near Klamath Falls and the Rogue River and
Willamette Valleys in Oregon, and the Puget Sound area in Washington.

Damage from curly top is a limitation of importance to the production
of sugar beet seed in some districts. Curly top is a virus disease trans-
mitted by the beet leafhopper, Eutettix tenellus (Bak.). The crop in
Arizona and New Mexico is subject to beet leafhopper infestations in the
fall from the time the seed germinates until the foliage practically covers
the ground. Certain of the varieties grown in these areas are resistant to
curly top, and on these varieties the leafhopper has not been a serious
problem. However, many of the varieties are very susceptible to this
disease, and it is on these susceptible varieties that leafbopper control
may be needed.

SOURCE AND TIME OF THE FALL INFESTATIONS

Arizona

The beet leafhoppers which infest the beets grown for seed in the
Salt River Valley come from desert areas completely surrounding the valley,
as shown in figure 1. The leafhopper breeds on extensive stands of chinch-
weed (Pectis papposa Gray), and on Tidestromia languinosa (Nutt.) Standl.,
beginning in July and continuing until late fall. Figure 2 shows a 62-percent
coverage of chinch-weed and a 1-percent coverage of Tidestromia as they









occurred 12 miles northwest of Phoenix, October 16, 1939. Such stands are
common over the desert areas, although usually more plants occur along the
washes. The numbers of leafhoppers produced in the desert areas are governed
largely by the abundance of the summer plants, which in turn depends upon
the amount of rainfall during July, August, and September. Two generations
of the leafhopper usually occur over desert areas by mid-September, but when
heavy rains occur early in September, as they did in 1939 and 1940, addi-
tional reproduction occurs in the breeding area. October and November
rains, which germinate winter annuals in the desert, are important in
reducing the number of leafhoppers entering the seed-beet fields.

Beets planted after August 15 in the Salt River Valley of Arizona
have been found to be promptly infested to a small extent by the beet
leafhopper, and the number of insects increased gradually until mid-Septem-
ber. Such early infestations did not result in serious damage except in
poor stands of beets. From mid-September to mid-October, leafhopper numbers
in the fields usually have not increased, although an unusual condition
arose ?ctober 3-7, 1941, when a moderately light influx of leafhoppers
infested the fields from Atriplex elegans (Moq.) Dietr. which grew abundantly
in basins southeast of Phoenix, The largest infestations occurred about
October 25. In one season out of six studied, additional influxes occurred
late in November.

The desert foothills around Safford, Ariz., also contain stands
of chinch-weed which are responsible for beet leafhopper infestations
that occur in beets grown for seed in that valley. Very little is known
about infestations in that area. In 1940 and 1941, moderate numbers of
leafhoppers had infested the beets by late September, and later increases
did not occur.

New Mexico

The foothill areas on both sides of the Mesilla Valley, N. Mex.,
are known to be important as a source of beet leafhoppers which infest
sugar beets grown for seed in that valley. Four annual host plants are
important in this general area, which include chinch-weed (Pectis sp.),
Tidestromia sp., Trianthema portulacastrum L., and Acanthochiton wrightii
Torr, In addition to these four summer plants a perennial peppergrass
(Lepidium alyssoides A. Gray) also grows throughout the summer breeding
areas in New Mexico and Texas (fig. 1), and the abundance of this plant
greatly influences the numbers which infest the beets in the fall.

Rather large infestations in seed-beet fields in the Mesilla Valley
have occurred by late September, although the more severe infestations have
occurred after late October.

NUMBERS REQUIRED FOR INJURY

The density of the beet stands and the rate at which the soil is
covered by beet leaves are important factors in determining the amount of
curly top injury which will result from a given number of beet leafhoppers.







-'3 -


A stand of 700 to 1,000 beets per 100 feet of row in the Salt River Valley
of Arizona has required a fall infestation of from 125 to 150 leafhopper
adults or-nymphs per 100 feet of row to induce about 20 percent total curly
top by the following April or May. This amount of disease or more is appar-
ently required before the yield of seed is measurably reduced in stands of
this density, but thin stands cannot tolerate this amount without a loss
in yield. Observations made during two seasons in the Safford, Ariz.,
district indicate that somewhat similar numbers would be required to induce
injury in that area. A stand of 600 to 800 beets per 100 feet of row in the
Mesilla Valley, N. Mex., has required a fall infestation of from 75 to
100 beet leafhoppers per 100 feet of row to warrant insecticidal control
measures. More growth takes place in the fall and winter in Arizona than
in New Mexico, and the average stands in New Mexico are thinner. The
resulting difference in soil coverage in the two areas is probably largely
responsible fo.r the difference in numbers of beet leafhoppers required to
cause conspicuous injury. With thinner stands in both districts, smaller
numbers of leafhoppers may induce pronounced injury.

CONTROL OF THE BEET LEAFHOPPER

Cultural Methods

Beet leafhopper control by cultural methods has been found effective
in reducing curly top injury in nonresistant varieties. Early planting
(late August to early September), good stands, and care conducive to rapid
growth until the leaves almost completely shade the soil have greatly reduced
curly top in seed-beet fields of the Salt River Valley, Ariz. Under favor-
able conditions early-planted beets there may almost completely cover the
soil by late October when large leafhopper influxes occur. The field shown
in figure 3 was first irrigated (planted a few days earlier in dry soil)
September 2,'1940. On October 25, or 53 days later, the beet leaves shaded
about 98 percent of the soil surface. Such fields as this have been found
to be unfavorable environments for the beet leafhopper. By the time the
foliage covers about 80 percent of the soil in the fields, beet leafhopper
adults begin to leave them, and fields with 90 to 98 percent of the soil
covered with leaves have invariably been found to contain small numbers of
leafhoppers. Furthermore, leafhopper reproduction does not occur in fields
where the foliage is dense. Fields with poor stands or poor growth (fig. 4).
or both, are subject to October and November infestations, and there may be
late fall reproduction in them during milder seasons, sucb as 1939-40.
Such fields may be severely damaged.

Good cultural practices will also reduce losses from curly top in
nonresistant varieties in the Mesilla Valley of New Mexico, but they have
not been so effective in reducing beet-field leafhopper populations there
as in the Salt River Valley of Arizona. Moderate leafhopper infestations
have occurred in the Mesilla Valley as early as mid-September, when the beets
were still small, and under such conditions insecticidal control measures
are needed. Owing to a colder climate in New Mexico than that in Arizona.
it is more difficult to obtain the rapid growth of the beets necessary for
early soil coverage. Some seasons the seed beet fields in the Mesilla






-4-


Valley are subject to large leafhopper inrestations during late October and
at later intervals; therefore every effort should be made to obtain a dense
leaf growth by that time in order to avoid the necessity of insecticidal
control.

Data from the Safford, Ariz., district are limited, but the indica-
tions are that control of curly top by cultural practices in that district
will be a little more difficult than in the Salt'River Valley, since beets
in that area make slower fall growth and are subject to damaging beet
leafhopper infestations in September while the beets are still small.

Chemical Control

During seasons when unusually large or early leafhopper infestations
occur, cultural practices should be supplemented by chemical control.
This holds true generally for the Mesilla Valley and Safford districts and
for fields with poor coverage in the Salt River Valley.

Pyrethrum-in-oil / spray applied at the rate of 6 to 9 gallons per
acre was found to be very effective in controlling the beet leafhopper in
seed-beet fields. The machine used is illustrated in figure 5. Six gallons
per acre proved sufficient for a reduction in leafhopper populations of 90
percent or greater, when there was little wind and temperatures were between
500 and 750 F. It was found necessary to increase the quantity of spray as
the temperature rose above 750 F., until at temperatures above 900 F. as much
as 9 gallons per acre were required to kill 90 percent or more of the leaf-
hoppers. An increase in wind velocity decreased the efficiency of the
spray, but winds up to 8 to 10 miles per hour 4 feet above the ground were
not too great to permit spraying.

1935-36 Experiments.--Tests of the effectiveness of commercial appli-
cations of the pyrethrum-in-oil spray were arranged by having unsprayed
strip plots left in six separate commercially sprayed fields and comparing
these with sprayed strips of similar size in the same fields. The results
are give;- in table 1. Fields 1, 2, and 3 were sugar beets in the Mesilla
Valley of New Mexico, and fields 4. 5, and 6 were table beets southeast of
El Paso, Tex. The sugar-beet fields were sprayed once, fields 2 and 3 in
late November and field 1 in mid-December. The table beets were sprayed in
early December and again in late February. The plot sprayed once in field 6


l/ Formula: 10 parts white oil -- a highly refined petroleum oil
having a viscocity of 90 to 100 seconds. Saybolt at 1000 F., and an un-
sulfonated residue of 94 percent.

20 parts kerosene -- a good grade of commercial kero-
sene complying with Federal Specification VV-K-211.

1 part pyrethrum extract -- an extract of pyrethrum
flowers in petroleum oil having a pyrethrin content of not less than 2.0
percent (or 2.0 grams of pyrethrins per 100 cc.).







-5-


was ruined by root rot, and therefore two strips sprayed twice were compared
with the unsprayed in this field.

Beet leafhopper infestations in the fields were large by late October
and no marked increase occurred until late December. Even though the appli-
cations were not timely, the yield of seed from plots sprayed once was
increased in all cases, with an average of 33 percent, over the unsprayed
plots, and there was an average increase of 60 percent in the plots sprayed
twice. Curly top injury was reduced indirectly by reducing the numbers of
leafhoppers, and this was responsible for the increases in yield in the
sprayed plots. There was considerable curly top damage even in the sprayed
plots, and the yields were not large. The viability of the seed was very
poor in all the plots, but slightly higher in the sprayed plots. Populations
of plant bugs ( ygus spp.) were high in these fields in the spring, and the
results of later investigations2/ indicate that the low percentage of viable
seed was at least in part due to these insects.

1937-38 Exneriment.--This experiment was conducted just northwest of
Buckeye, Ariz., and consisted of 16 plots, approximately one-half acre in
size, arranged as a Latin square, with 4 treatments. However, owing to the
fact that leafhopper numbers were so reduced by rapid leaf growth by late
November that no additional treatments seemed worthwhile, the experiment
was left with 8 plots sprayed October 30, 1937, to be compared with 8 un-
treated plots. The rate of application was 10 gallons per acre because the
temperature during the application ranged from 880 to 890 F. and the wind
velocity 4 feet above the ground was 7 to 8 miles per hour. Leafhopper
counts 24 hours later showed a reduction in populations of 94 percent for
adults and 99 percent for nymphs.

Results from the single application of October 30, 1937, are given
in table 2. The beet plants averaged 1,031 per 100 feet of row in the plots.
Owing primarily to dense leaf growth, the numbers of leafhoppers in the
unsprayed plots decreased from 401 per hundred feet of row on November 1 to
96 on December 21 and to 77 by January 21. Leafhopper numbers in the
sprayed plots increased slightly during this same period. On November 1 the
beet leaves covered about 40 percent of the soil surface, on November 30
they covered about 80 percent, and by December 21 approximately 95 percent
of the soil surface was covered with beet foliage. Curly top counts made
May 23-25, 1938, showed a 34.2-percent decrease in the total curly top and
a 58-percent decrease of severely diseased plants in the sprayed plots as
compared with the unsprayed plots. The average yield of clean seed from the
sprayed plots exceeded that produced by the unsprayed plots by 55.1 percent,
The seed stalks averaged 230 per 100 feet of row in the sprayed plots, and
192.9 per 100 feet of row in the unsprayed plots. There was no significant
difference in the percentage of viable seed from the sprayed and the un-
sprayed plots.


g/ Hills, Orin A., and Romney, V. E. A Progress Report on Hemip-
terous Insects Affecting Sugar Beets Grown for Seed in Arizona and New
Mexico. U. S. Dept. Agr., Bur. Ent. and Plant Quar., E-552. October 1941.






-6-


The average increase in seed from the sprayed plots over the unsprayed
plots amounted to 359 pounds per acre, which was worth $30. The cost of
spraying at the 10-gallon rate was approximately $5 per acre, which leaves
a net gain of $25 from the spray application.

1939-40 Experiment.--This experiment involved 20 plots measuring
100 by 123 feet (0,23 acre) and was conducted near Coldwater, Ariz. Ten
randomized blocks with 2 treatments (sprayed and unsprayed) each were sprayed
on November 6 and 7 with 6 gallons of pyrethrum-in-oil per acre. The
temperature was 680 to 760 F., and there was no wind. Within 24 hours there
was a 92-percent reduction in adult beet leafhoppers, and at this time
nymphs were scarce. The beet leaves covered about 45 percent of the soil
surface on November 8, just after spraying, and by December 20, 70 percent
of the soil surface was covered by the foliage.

The results of this experiment are given in table 3. The stand
averaged 580 plants per 100 feet of row in the plots, which would be rated
as only a fair stand. The leafhopper population 24 hours after treatment
(Nov. 8) averaged 332 per 100 feet of row in the unsprayed plots and 28 in
the sprayed. By December 20 the leafhopper numbers in the unsprayed plots
decreased from 332 to 217 per 100 feet of row, while at the same time those
in the sprayed plots increased from 28 to 72 per 100 feet of row, which was
probably due to a shifting of leafhoppers from the unsprayed to the sprayed
plots. Curly top counts made April 19-20, 1940, showed a 39.5-percent de-
crease in total curly top and a 52.3-percent decrease of severely diseased
plants in the sprayed plots as compared with the unsprayed plots. The
average yield of clean seed from the sprayed plots exceeded that produced
by the unsprayed plots by 22.1 percent. More seed stalks were produced in
the sprayed plots than in the unsprayed plots. An average of 319 seed stalks
per 100 feet of row was found April 19-20, 1940, in the sprayed plots,
and 210.5 per 100 feet of row in the unsprayed plots. There was no differ-
ence in the viability of the seed from the sprayed and unsprayed plots.

The average seed increase of 219 pounds per acre due to the one spray
application was worth $18.62, The cost of the treatment at the 6-gallon
rate was approximately $3.50 per acre, or a net gain of $15.12.

THE 1940 CROP IN ARIZONA AS AFFECTED BY CURLY TOP

The winter of 1939-40 was abnormally warm in Arizona. The Weather
Bureau at Phoenix recorded the following departures from the mean monthly
normal temperatures in degrees Fahrenheit for November to March inclusive:
+4.60, +5.60, +4,40, +1.7', and +4.10. This extremely warm season.was
favorable for leafhopper activity and reproduction, especially in fields
with poor coverage. This was the first time in six seasons that beet leaf-
hopper reproduction occurred in the Mesa and Tolleson districts during the
winter months.

On the basis of beet leafhopper populations in the seed-beet fields
in the Mesa and Tolleson districts in late October 1939, it did not appear
that serious curly top injury would occur, and very little commercial






-7


spraying was done. However, approximately two-thirds of the seed-beet crop planted
in the Salt River Valley in the fall of 1939 did not have good leaf coverage at
that time, owing mainly to interference with field operations by rains in early
September. This situation and the mildness of the winter resulted in a greater
amount of curly top damage than had been noted in other seasons. The conditions in
a field southwest of Mesa were typical of a number of fields in the valley. It
had 80 adult leafhoppers per 100 feet of row in late October in a stand which
averaged only 271 plants per 100 feet of row. The field passed the winter with
not more than 75 percent of the soil covered by foliage. By early March there was
an average of 60 adults and 90 nymphs per 100 feet of row. There was 55 percent
total curly top in this field by late April. It is important to note, however,
that of 17 fields studied in the Mesa and Tolleson districts in the spring of 1940
only 5 had more than 20 percent curly top infection, Many observations had brought
out the fact that in good stands there must be more than 20 percent total curly
top by late April for the disease to be a major factor in reducing seed yields.
Evidently other factors of importance besides curly top contributed to the abnor-
mally low average yield and poor germination of the 1940 seed crop.



Table l.--Results obtained by commercial applications of pyrethrum-in-oil for
control of the beet leafhopper, as indicated by strip-plot experiments in New
Mexico and western Texas


Adult leafhoppers per Plants Severely Yield Increase Seed
100 feet of row having diseased of in yield balls
Field Treatment Shortly curly beets per seed over with
No. after first Feb. top 100 feet per untreated viable
application 1-2 of row acre checks seed


Number Number Percent Number Pounds Percent Percent

Sprayed 12-14-35 16 28 57.7 205 1,173 44.5 35.0
Unsprayed check 166 182 89.7 566 812 32.8

Sprayed 11-22-35 --- 66 57.7 222 567 22.5 40.8
Unsprayed check 223 300 91.7 372 463 35.8

Sprayed 11-29-35 28 42 53.7 186 777 28.9 36.3
Unsprayed check 123 145 78.2 246 603 34.8

Sprayed 12-8-35 4 566 -- 131 721 28.7 --
Sprayed 12-8-35 and 2-22-36 --- -- 122 1,022 82.5 35.0
Unsprayed check 297 825 --_ 261 560 31.0

Sprayed 12-9-35 10 280 74 583 39.8
Sprayed 12-9-35 and 2-23-36 --- --- 69 607 45.6 27.0
Unsprayed check 150 440 136 417 15.0

Sprayed 12-10-35 and 2-22-36 .- --- ---- 280 34.6 -
Sprayed 12-10-35 and 2-22-36 26 550 92.1 186 372 78.8 20.8
Unsprayed check 391 750 98.5 441 208 17.5


1.



2.


3.



4.






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Table 2.-- Results obtained by one application of pyrethrum-in-oil for control


the beet leafhopper, as indicated by eigh
October 30, 1937, near Buckeye, Ariz.


t replications of two treatments


Plants Plants Yield of Seed
Treatment Beet leafhopper adults and nymphs with with clean balls
per 100 feet of row curly severe seed with
top 1/ curly per viable
Nov. 1 Dec. 21 Jan. 21 top acre seed

Number Number Number Percent Percent Pounds Percen

Sprayed 9 26 34 41.1 10.8 1,011 78.0

Not sprayed 401 96 77 62.5 25.3 652 75.9



Difference required for
significance at the 5-percent level 8.5 4.9 144 2/


1/ Curly top counts by systematic samples made May 23-25, 1938.

a/ Not significant.


Table 3.--Results obtained by ohe application of pyrethrum-in-oil for control ol
the beet leafhopper, as indicated by 10 replications of 2 treatments madE
November 6-7, 1939, near Coldwater, Ariz.

Plants Plants Yield of Seed
Beet leafhopper adults and nymphs with with clean balls
Treatment per 100 feet of row curly severe seed with
top curly per viable
Nov. 8 Dec. 20 top acre seed

Number Number Percent Percent Pounds Percen

Sprayed 28 72 43.5 23.2 1,208 69.6

Not sprayed 332 213 71.9 48.6 989 69.6



Difference required for
significance at the 5-percent level 5.0 4.5 102 ---


I/ Curly top counts by systematic samples made April 19-20, 1940.







-9-


SUMMARY

In the fall, beet leafhoppers infest fields of beets grown for seed
in Arizona and New Mexico and transmit curly top, a disease which reduces
the seed yield. The insects come from surrounding desert breeding areas.
Several summer annuals serve as host plants for the leafhopper, and in
New Mexico a perennial peppergrass is also of importance. In the Salt
River Valley of Arizona large infestations usually do not occur in good
stands of beets until late October. In the Mesilla Valley, N. Mex., and
Safford, Ariz., districts rather large infestations often occur by late
September.

The number of leafhoppers required to induce injury is in general
greater in Arizona than New Mexico. Fields in the Salt River Valley of
Arizona planted before September 10, with stands ranging from 700 to 1,000
beets per 100 feet of row, have required fall leafhopper infestations of
from 125 to 150 per 100 feet of row to induce a conspicuous amount of curly
top damage by the following April. Fields in the Safford, Ariz., district
will probably require somewhat similar numbers. Fields in the Mesilla
Valley of New Mexico, however, with stands ranging from 600 to 800 beets per
100 feet of row, have required only from 75 to 100 beet leafhoppers per
100 feet of row to warrant insecticidal control measures.

Curly top injury can be prevented to a large extent in the Salt
River Valley of Arizona by planting the beets early and giving adequate
care to get the soil surface in the field practically covered with foliage
by late October. Such fields become unfavorable environments for the beet
leafhopper. In the Safford and Mesilla Valley districts the crop has been
subjected, in some seasons, to moderate September infestations before good
coverage was obtained. Owing to colder climates it is also more difficult
to get enough fall growth in these districts to afford complete coverage.

A pyrethrum-in-oil spray applied in the fall at the rate of 6 to 9
gallons per acre has given better than 90 percent reduction of beet leaf-
hopper adults and nymphs within 24 hours. Such reductions in leafhopper
numbers have reduced curly top and resulted in increased yields of seed.
The viability of the seed was not significantly affected by the spraying.

Curly top was only partially responsible for the poor beet seed crop
in Arizona in 1940.









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Figure 1.-Map showing cultivated districts (black areas) in which beets are grown for seed where
curly top is a problem some seasons, and summer breeding areas (shaded areas) of the bete


























Figure 2.-Photograph showing a 62-percent coverage of
chinch-weed (Pectis) and a l-percent coverage of
Tidestomia 12 miles northwest of Phoenix, Ariz.,
October 16, 1939, which is typical of simmer host-plant
conditions in the breeding areas of the beet leafhopper,
especially along the lowlands of washes.


Figure 3.-A field of beets in the Salt River Valley of
Arizona photographed October 25, 1940, 53 days after plant-
ing. The foliage covers about 98 percent of the soil sur-
face, tbW creating an environment which is unfavorable for
the beet leafhopper.

























Figure 4.-A field of beets in the Salt River Valley of
Arizona photographed October 25, 1940, 32 days after plant-
ing. The foliage covers about 40 percent of the soil-6-w-
face, which is not sufficient at this season of the year to
repel the leafhopper. This type of field is therefore sub-
Ject to large infestations of the beet leafhopper during
outbreak years.


Figure 5...-Spray machine used to apply a pyrethrum-in-oil
spray for control of the beet leafhopper. The machine is
Shown praying a comparatively thin stand of beets in the
Salt River Valley of Arizona in October 1940.




UNIVERSITY OF FLORIDA

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