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Full text of "Control of the grape leafhopper in California"

CALIFORNIA 
AGRICULTURAL EXTENSION SERVICE 

CIRCULAR 72 

FEBRUARY, 1933 



Control of the Grape Leafhopper 
in California 



J. F. LAMIMAN 



Cooperative Extension work in Agriculture and Home Economics, College of Agriculture, 

University of California, and United States Department of Agriculture cooperating. 

Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. 

B. H. Crocheron, Director, California Agricultural Extension Service. 



THE COLLEGE OF AGRICULTURE 
UNIVERSITY OF CALIFORNIA 
BERKELEY, CALIFORNIA 



Digitized by the Internet Archive 

in 2011 with funding from 

University of California, Davis Libraries 



http://www.archive.org/details/controlofgrapele72lami 



CONTROL OF THE GRAPE LEAFHOPPER 
IN CALIFORNIA 

J. F. LAMIMANi 



The grape leaf hopper, Erythroneura comes (Say), has become in- 
creasingly injurious to grapes in the San Joaquin Valley in recent years. 
So severe have been its attacks during the period from 1928 to 1931 that 
extensive investigations and experiments have been conducted during 
the past two seasons to develop more modern and effective insecticides 
and other methods of dealing with the pest. 

As a result of the combined effects of climatic conditions and leaf hop- 
per damage, it is estimated that the crop of raisin grapes was reduced 
from 295,000 tons in 1930 to 157,000 tons in 1931. If we assume that 40 
per cent of this loss was the result of leaf hopper injury (55,000 tons at 
$60.00 per ton) this insect cost the grape growers more than $3,000,000 
for that year. 

HISTORY AND DISTRIBUTION 

The grape leafhopper is a native of North America and occurs in all 
the important grape-growing areas of the United States. However, its 
attacks are most serious in the Great Lakes region and in the states of 
Arizona and California. 

While this leafhopper occurs in all the grape-growing regions of 
California, it is most serious in the Sacramento, San Joaquin, and Impe- 
rial valleys, and the greatest losses are occasioned in the southern por- 
tion of the San Joaquin Valley. 

In California this insect has been known to occur since 1875. In 1908, 
Quayle 2 gave an excellent account of the life history and control with 
the materials then known to be effective. Since that time, the increase 
of leafhopper damage and the advent of new materials have necessitated 
additional experimental work to determine the best present-day methods 
of control. 

The past history of this insect indicates that its attacks occur in a 
series of fluctuations in which periods of abundance are followed by 
periods of low populations. These fluctuations are influenced by the 



i Junior Entomologist in the Experiment Station. 

2 Quayle, H. J. The grape leafhopper. Calif. Agr. Exp. Sta. Bui. 198:177-216. 



1908. 



California Agricultural Extension Service 



[Cir. 72 




C<* 6u^q 



1933] 



Control of the Grape Leafhopper 



number of overwintering leafhoppers and the rapid building up of the 
spring population. They may be reduced by weather conditions (wet 
and cold seasons), and by parasitism during the late summer. 



SEASONAL LIFE HISTORY 



The grape leafhoppers pass the winter as adults (figs. 1 and 2) , which 
may feed on various plants growing in or near the vineyard during 
warmer weather. In cold weather these overwintering adults will be 
found hibernating under leaves, dead grass, weeds, and old paper trays ; 



MAR. 


APR. 


MAY 


JUNE 


JULY 


AUG. 


SEPT 








OVER 


WINTER 


ING 




1 \ii^\™ 


LTS * - - - , _ 






FIRST 


1 










^\. EGGS^-^.^ 








BROOD 


\. NYMPHS ^^\. 








\. ADULTS^^-\^ 








SECOND 


BROOD 










^\. EGOS ^^ 








"V 


\ NYMPHS 








\^ 


ADULTS 












THIRD 


BROOD 










^\. EGGS 








NYMPHS 




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\^adulTS 





Fig. 2. — Diagram representing the life history of the grape leafhopper in rela- 
tion to the time of appearance and length of the various stages of the three broods. 
Note that as the season advances the overlapping of the broods becomes more 
complex . 

in brush and straw piles; in debris along ditches and fences; and in 
alfalfa fields, dry tule ponds, and old cotton fields. While these adults 
have been reported as occurring from one-half to one mile from the 
nearest vineyard, the majority of them are found in or close to a vine- 



6 California Agricultural Extension Service [Cir. 72 

yard. In spring, February to March, they leave their various winter 
quarters and move to green vegetation to feed, and attack the vines as 
soon as they begin to leaf out. Thereafter feeding is confined to the 
grapevines until the leaves drop in the fall. 

Egg laying begins about two weeks after the overwintering hoppers 
attack the vines, which period is usually about April 7-15, in the Fresno 
area. The young of the first generation begin to appear about May 1, and 
one to two weeks later in the Lodi-Stockton area. About 18 days are re- 
quired for maturity. The young of the second generation appear the 
latter part of June and those of the third from the middle to the last of 
August. 

In autumn, when the leaves drop, the adults seek the winter quarters 
mentioned above. During favorable seasons, this winter population may 
be very abundant as was indicated by a number of counts made during 
the winter of 1931-32, which varied from less than 100 to 1,800 indi- 
viduals per square foot of debris. 

GENERAL LIFE HISTORY 

Adults. — The grape leaf hoppers (fig. 3) do' not migrate in the true 
sense of the word but disperse from one locality to another, while mov- 
ing from winter hibernation to green vegetation in February and March. 




Fig. 3 




Fig. 4 



Fig. 3. — The adult grape leaf hopper, Erythroneura comes (Say). (Greatly 

enlarged.) (After Quayle.) 

Fig. 4. — Egg of the grape leafhopper in the tissue of the leaf. 

(Greatly enlarged.) 



1933 ] Control of the Grape Leafhopper 7 

They move to the vines as soon as there is suitable green leaves for feed- 
ing, but seek protection in trash or other cover beneath the vines in 
periods of cold weather. 

The only adult activity observed during the summer months was the 
flying from vine to vine during the evening but not for any great dis- 
tance. 

Eggs. — The eggs of the grape leafhopper are laid singly in the epi- 
dermal tissue of the upper and lower surfaces of the leaf. Each egg is 
minute, about % o inch in length, and is difficult to see without the aid 
of a magnifying glass* As it occurs in the leaf tissue it may be recog- 
nized as a small bean-shaped blister 3 (fig. 4) . 

The egg-laying period may be prolonged several weeks, especially in 
cold weather, resulting in an overlapping of generations. Each female 
deposits about 100 eggs which have an incubation period of 17 to 20 days 
in the spring. This period is shorter during the summer months. 

Nymphs. — The young leafhoppers, known as nymphs, resemble the 
adults in general form, though they are smaller and lack wings. They 
have the same feeding habit of sucking the sap from the leaves. 

When first hatched from the egg, the young nymph is very small and 
semitransparent with red eyes. There are five successive nymphal stages 
(fig, 5), each resembling the other except for size and developing wings. 

The developing wings, in the form of wing pads become more pro- 
nounced in the third, fourth, and fifth stages. Development from the 
time of hatching requires from two to three weeks. 

The nymphs feed almost without exception on the lower surface of 
the leaves although the eggs may be found in almost equal numbers on 
both surfaces. 

Theoretically the first eggs of each generation may develop, in the 
Fresno area, as indicated in the tabulation below, with the maximum 
number of each stage occurring about two weeks later than the respec- 
tive dates given. 

Generation Eggs Hatching Adult 

First April 7-15 April 24-May 1 May 20-25 

Second June 5-10 June 25-30 July 1-8 

Third July 25-30 August 10-15 August 25-30 



s The small droplets of crystalline material found chiefly on the veins of the new 
growth, especially in the spring, are hardened drops of sap and should not be mis- 
taken for eggs. 



California Agricultural Extension Service t Cl R- 72 




Fig. 5. — The five nymphal stages of the grape leafhopper. Note developing wing 
pads on the last three. Control measures should be applied when the first few nymphs 
reach the two most advanced stages. (Greatly enlarged.) 



NATURE OF INJURY 

The most important injury produced by the grape leafhopper is that 
resulting from the extraction of sap through the innumerable feeding 
punctures made by the mouthparts of these insects. This injury first 
appears as scattered, small, white spots, which become more and more 
numerous until a pale-yellowish blotching, due to the removal of the 
chlorophyll, results. Eventually the leaves dry up and fall prematurely. 
The damage produced is in direct proportion to the number of individ- 
uals present and the degree of injury increases with the increase in 
population. 

Unless the overwintering adults are exceedingly abundant, the injury 
produced by them is negligible ; but their offspring, which develop on 
the first six leaves of the new growth, may produce early defoliation in 
the crown of the vines. This defoliation, which increases as the season 



19 33] Control of the Grape Leafhopper 9 

advances, frequently exposes the ripening grapes to sunburn injury, 
causing heavy losses in table varieties. Defoliation also reduces the sugar 
content of raisin grapes, reducing the crop in quantity and lowering the 
quality. In addition, the presence of leafhopper excrement on the table 
grapes is objectionable. 

According to most authoritative estimates, the tonnage of raisin and 
table grapes has been reduced 25-30 per cent in some seasons as the 
direct result of the injury produced by this leafhopper. This estimate 
does not include the loss from lowered quality and the decreased vigor 
of the vines which may be intensified by long periods of high tempera- 
ture and inadequate soil moisture. 



FARM PRACTICES IN RELATION TO LEAFHOPPER CONTROL 

While the control of overwintering grape leafhoppers by burning or 
cleaning up the hibernating places has not proven entirely satisfactory, 
this method may furnish a degree of relief in some localities. When 
serious infestations occur over large adjacent areas and when only a 
few vineyardists resort to this method, results are likely to prove very 
disappointing. 

Many of the adults may be destroyed by plowing while the tempera- 
ture is below 50° F, when the adults are inactive on weeds or in the litter. 

Observations indicate that in wet weather succulent covercrops grow- 
ing in a vineyard do not harbor large numbers of overwintering adults 
in comparison with adjacent areas of dead grass, trash, etc. This is evi- 
dently because of the cool, moist conditions produced by the growing 
covercrop. Such a covercrop may be utilized as a trap crop by leaving 
unplowed strips when the covercrop is turned under as the buds of the 
grapevines begin to swell in the spring. Fall cultivation in conjunction 
with a covercrop planted early decreases places for the adults to over- 
winter. 

After the litter has been destroyed (fig. 6) in October or November, 
a trap strip of barley or rye or a combination of the two, not over 2 feet 
wide may be planted throughout the vineyard at intervals of 4-8 rows, 
depending upon vineyard practice (fig. 7) . In February or March when 
the insects become active and move to green plants and just before vine 
growth begins, all other vegetation in the vineyard and along fences, 
roads, and ditch banks, should be plowed under or destroyed. 

The success of a trap crop depends upon the destruction of the over- 
wintering adults while they are feeding on this crop and before vine 



10 



California Agricultural Extension Service 



[Cir. 72 



growth starts in the spring and upon the area treated, as the larger the 
acreage the less will be opportunity for reinfestation from surrounding 
vineyards. Sufficient irrigation and fertilization produce vigorous vines 
and often prevent serious injury though populations may be high. 




Fig. 6. — Clean-cultivated vineyard. Trash has been plowed under during the 
dormant season to remove overwintering quarters for adult leaf hoppers. 




Fig. 7. — Trap crop and vineyard in proper condition for treatment 

the spring. 



1933 ] Control of the Grape Leafhopper 11 



CONTROL MEASURES 

Success in the control of the grape leafhopper depends on the selec- 
tion of the specific means most effective against the life stage of the 
insect chosen for treatment. There are periods during which no one 
treatment is sufficient owing to the presence of several different stages 
of the insect (fig. 2) . The selection of the period for treatment will nat- 
urally be dependent also upon the degree of infestation and the antici- 
pated damage. Any treatment, to give the most satisfactory results, 
must be applied before serious damage has been produced. Thus the 
individual grower always has the responsibility of closely observing the 
conditions within his vineyard with a view to determining the period 
and material to select for control measures. Any method adopted will 
be greatly aided by utilization of the best farm practices to increase the 
health and vigor of the vines. 

Regardless of what materials may be used in the suppression of the 
grape leafhopper, effective control is dependent upon thorough, prompt, 
and timely applications of the same. Failure is most often traceable to 
the improper use of a control measure especially in regard to strength 
of material and manner of application. Weather conditions also have a 
bearing on the effectiveness of a particular treatment and are discussed 
under the various materials. 

Spraying represents the oldest method for the control of the grape 
leafhopper and now includes both liquid and vapor sprays, the latter 
utilizing air as the diluent and carrier of a concentrated insecticide. 

Liquid Sprays. — Nicotine sulfate as a liquid spray, with whale oil 
soap or other type of spreader or in combination with bordeaux mix- 
ture, has long been the recognized control and is still practical in spite 
of numerous limitations. The most effective combination is made accord- 
ing to the following formula : 

Nicotine sulfate (40 percent) 1 pint 

Casein spreader % pound 

Water 100 gallons 

Such a spray destroyed 95-97 per cent of the first brood nymphs. It also 
gave a slight indication of being effective against eggs, but this aspect 
needs further investigation. 

In place of the casein spreader, % gallon of liquid whale oil soap may 
be substituted, though this material at times produces a slight scarring 
of the fruit. 



12 



California Agricultural Extension Service 



[Cm. 72 



Experiments conducted with pyrethrum extracts (alcohol, acetone, 
or pyrethrum-soap emulsion) in water, during 1932, resulted in 93-95 
per cent control of the first brood nymphs. As these extracts (commer- 
cially sold as Evergreen, Red Arrow, etc.) vary so greatly in pyrethrum 
content, the recommendations as to dilution, given by the manufac- 
turer, should be followed and checked by field experience. 

The above sprays, in the proper concentration and application, are 
the most effective methods used in nymph control if applied when there 
is a maximum number of first brood nymphs, normally from May 20 to 




Fig. 8. — Spraying for nymphs of the grape leafhopper with angle 
nozzles. (Photograph by J. L. Quail.) 

June 1 in the Fresno area. If the application is too early, many eggs will 
remain to hatch later ; and if too late, many adults will have developed. 

A power sprayer, capable of maintaining 200-250 pounds pressure, 
with angle nozzles attached to rods 3-4 feet long, is necessary for the 
proper application of these sprays (fig. 8). Set or boom nozzles (fig. 9) 
may be used but care must be taken that thoroughness is not sacrificed 
for speed. 

Because of many limitations, liquid sprays will have their greatest 
use when applied in combination with other insecticides for other vine 
pests, such as red spider, which require liquid sprays for control. The 
principal limitations are : 

1. These sprays are contact insecticides and must be put on the under- 
sides of the leaves where the nymphs are feeding. 



1933] 



Control of the Grape Leafhopper 



13 



2. They are effective against the nymphs only and should not be used 
after the grapes are larger than buckshot because of possible injury to 
the "bloom" of the grapes. 

3. They should be applied at the rate of 100-200 gallons per acre, de- 
pending upon the quantity of foliage, and 4 to 8 acres per day is the 
maximum to be covered with 2 to 4 nozzles. 

4. The chief limiting factor is the slowness of application. 

Vapor Sprays. — During the 1931-32 season, equipment (figs. 10 and 
11) was developed for the vaporization of concentrated insecticides. 




Fig. 9. — Spray boom used in the application of liquid sprays. 
(Photograph by J. L. Quail.) 

Of these sprays, one containing oil and an oil extract of pyrethrum was 
found to be effective against both nymphs and adults, especially the 
latter when they are forced to fly through the vapor. This material 
consisted of : 

Highly refined kerosene 87% gallons 

Neutral oil (90 per cent unsulfonatable residue and 60 sec. 

Saybolt viscosity) 10 gallons 

Petroleum oil extract of pyrethrum (containing 2 grams of 

pyrethrins per 100 cc 4 ) 2% gallons 



4 The concentration of 2 grams of pyrethrins (killing agents in pyrethrum) per 
100 cc of oil extract is equivalent to 20 pounds of pyrethrum flowers (containing 0.9 
per cent pyrethrins per pound), to the gallon. Because even the best grade of pyre- 
thrum flowers may vary from 0.2 per cent to 2.3 per cent pyrethrins per j>ound, the 
ratio of pounds per gallon is not a satisfactory standard for an oil extract of 
pyrethrum. 



14 



California Agricultural Extension Service 



[Cir. 72 



This combination, applied with the equipment using the paint-gun 
type of nozzle (fig. 10), destroyed 87-90 per cent of the overwintering 
adults when applied, April 15-17, 1932, at the rate of 2 gallons per acre. 
Later in the season the effectiveness of this type of spray decreased as the 
vine growth increased, so that an application of 5 gallons of pyrethrum- 
oil spray per acre early in August gave only 35 per cent control of the 
adults, where the populations were as high as 18,000 individuals per 
vine. 

Experimental evidence indicates that this material is of greatest value 
when applied against the overwintering adults before egg laying has 




Fig. 10. — Vapor spraying with compressed-air type of equipment. 
Vines in proper condition for the treatment of overwintering adults 
before egg laying. (Photograph by J. L. Quail.) 

started in the spring and when the new growth is not over eight to twelve 
inches in length. Repetition may be necessary if the adults continue to 
move in. 

Pyrethrum-oil sprays are new materials and, while very effective, are 
still under investigation with a view to their improvement and reduc- 
tion in cost. 

Use of Dusts. — In recent years, dusts, calcium cyanide or nicotine, 
have been widely used in the control of the grape leafhopper due to 
speed of application and the ease of adapting regular vineyard equip- 
ment. 

It is obvious that these materials cannot be used successfully in wind 
or even light breezes because a dust cloud cannot be confined to the area 
under treatment. Convection currents, set up in the vineyard as the 



1933] 



Control of the Grape Leafhopper 



15 



result of hot, dry soil, are equally undesirable. These smaller currents 
of air are difficult to detect and are seldom recognized by the grower. 
Irrigation prior to treatment cools the soil and reduces them to a 
minimum. 

Calcium Cyanide Dust. — Calcium cyanide dust may be applied for 
the overwintering adults, either in the trap crop or after they have con- 
centrated on the vines early in the spring. 

This material is effective against all active stages of the grape leaf- 
hopper, and is the most successful material for late summer treatment. 







ill ^ 




. ;\r:,_ 


1 * f, ^ < 




mjj ' IPKiKlPV 


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1 








m : W^^^fif/9;:^ : - :i. . " v '3- '.'../ '-' .. ;,.. " 


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Fig. 11. — Vapor spraying with blower type of equipment. 
(Photograph by J. L. Quail.) 

However, it must be used when the atmospheric conditions are such that 
a lethal concentration of the gas may be maintained in the area treated. 
This is after midnight when convection currents are at a minimum. 
(Conditions may be determined by building a smudge fire in the vine- 
yard. When the smoke settles or drifts very slowly, dusting should pro- 
ceed, but if smoke drifts or dissipates rapidly, dusting should not be 
done.) For the application of calcium cyanide dust, motorized power 
equipment is recommended, using "H-dust" (or coarse calcium cyanide) 
at the rate of 20 pounds per acre with the outlets directed toward the 
ground so that a greater part of the dust will fall with the insects. Thus 
large acreages can be treated in a short time, with a concentrated blanket 
of dust over the entire area treated. 



16 



California Agricultural Extension Service 



[Cm. 72 



Iii some districts atmospheric conditions prevent or hinder open dust- 
ing and this material may be applied under tents made of light drill, or 
good grade cotton sheeting, 15 feet wide and from 60 to 120 feet long 
(fig. 12) . These tents should only be used when the new growth has ma- 
tured sufficiently to prevent breakage of the shoots as the tents are 
pulled over the vines. The dust, known as "A," or fine calcium cyanide, 
should be applied at the rate of 20 pounds per acre, under the tent as it 
is being pulled forward. The treatment for each setting of the tent 
should be about four minutes. By this method, three men with two tents 
can treat 6 to 9 acres per day. 







Fig. 12. — Tent method of applying calcium cyanide dust in the 
control of the grape leaf hopper. (Photograph by A. F. Kirkpatrick). 



In 1931, vineyards treated the first two weeks in April, remained free 
from injurious numbers of leafhoppers for the entire season. In 1932, 
calcium cyanide dust applied in July gave 90-95 per cent control of 
adult populations of 10,000 to 33,000 per vine. 

The best results with calcium cyanide dust have been obtained in late 
summer, at the time when the adults or nymphs were most abundant 
and the fewest eggs were present. Failure with this material can usually 
be traced to improper weather conditions. 

As calcium cyanide dust produces a poisonous gas it should be han- 
dled with care. This material should not be applied with horse-drawn 
dusting machines or in the immediate vicinity of farmyards containing 
poultry or livestock, as these are susceptible to the gas released. The 
operators of commercial dusting equipment should have an adequate gas 
mask available in case of accident. 



1933] Control of the Grape Leafhopper 17 

Nicotine Dust. — Dusts containing a sufficient concentration of nico- 
tine (not less than 4 per cent actual nicotine), are successful in the con- 
trol of the first three nymphal stages of the grape leafhopper. Experi- 
ments conducted during 1932 show that a good nicotine dust should be 
free-flowing and should release a large part of the nicotine within a 
short period of time. Too much emphasis cannot be placed upon the 
necessity for treatment before the nymphs have entered the fourth and 
fifth nymphal stages (fig. 5) . 

Satisfactory results may be obtained with either a good grade of nico- 
tine dust as prepared commercially or with the following homemade 
material, which contains an activator to release the nicotine : 

Nicotine sulfate (40 per cent) 10 pounds 

Hydrated lime 80 pounds 

Sodium carbonate (activator) 10 pounds 

This dust gave 92-95 per cent control of the active nymphs and may 
be made as follows : Adapt a 50-gallon wooden barrel for the mixing of 
this dust, according to the directions with each can of nicotine sulfate 
(Blackleaf 40). Place the lime in the barrel and then add the nicotine 
gradually instead of all at once. After turning about five minutes add 
the activator (sodium carbonate) and turn for another five minutes. The 
success of the homemade mixture depends entirely upon the thorough- 
ness of mixing. 

Do not mix more than will be used the same day. After taking the 
material from the mixer place it in an airtight drum until used, but use 
it the same day. 

Use 15-20 pounds per acre depending upon the size of the vines and 
apply it just before the first nymphs get their wings. The best results 
are obtained with the material at temperatures of 90° F, or over, with a 
minimum of wind and where vineyards have been irrigated before treat- 
ment. Nicotine dust has the advantage that it may be applied with the 
hand or power machines ordinarily used for sulfur. The material must 
be directed so that the vines are completely enveloped by the dust. 

Second applications about two weeks after the first may be necessary 
for complete control, and thoroughness in application is essential. 

Air Sweepers. — Quayle reported experiments with types of suction 
machines and blowers for the purpose of collecting the leafhoppers 
which were flying in the immediate vicinity of the vines, but these de- 
vices were considered impractical. However, during 1931, there was a 
revival of this type of machinery and a variety of designs were built and 
used for the mechanical removal and destruction of the adult leafhop- 
pers (fig. 13). 



18 



California Agricultural Extension Service 



[Cir. 72 



At best these machines were only effective against the adults, and then 
only when the vines were shaken to dislodge them. The most effective 
types may aid in the reduction of the adult population if used through- 
out the season, but use must begin as soon as the leafhoppers move to the 
vines in the spring. Counts made of adult populations before and after 
using several of these machines showed a variation of from 30 to 70 
per cent control. 




Fig. 13. — One type of mechanical suction machine or air sweeper. 
This machine has a canvas curtain which drops over the row oppo- 
site the fan. 



Natural Enemies. — Although a number of insects have been recorded 
as destroying grape leafhoppers, none of them are found in sufficient 
numbers to reduce the large summer populations. 

Early in July, 1931, Mr. A. F. Kirkpatrick reported an egg parasite, 
Anagrus epos Girault, which was found in abundance throughout the 
balance of that season in most leafhopper-infested vineyards. In spite 
of the attacks of this parasite, the leafhoppers continued as a serious 
menace to most vineyards during late summer and fall and adults were 
very abundant at the time of the first frosts. 

During 1932 no parasitized eggs were observed until early in July 
after the second brood eggs had been laid. Following this there was 
found an increasing number of parasitized eggs. Thus by August 15, 
50-60 per cent of the eggs (third brood) observed were found to be 
parasitized. This parasitism undoubtedly greatly reduces the number 
of overwintering leafhoppers but the parasite probably occurs in active 
numbers too late in the summer to be an efficient check. 



1933 J Control of the Grape Leafhopper 19 



SEASONAL CONTROL PROGRAM 

The following program represents a full season's control, which in 
total should seldom, if ever, be necessary, and indicates the most effective 
measures at various seasons of the year. 

1. Clean cultivation followed by covercrops in the fall. 

2. Planting of the trap crop and treating it with calcium cyanide dust 
or pyrethrum-oil sprays to destroy the overwintering adults before vine 
growth starts. 

3. Early spring treatment of adults with calcium cyanide dust or 
pyrethrum-oil sprays after movement to vines. 

4. Two nymphal treatments with nicotine or pyrethrum sprays or 
nicotine dust. 

5. Treatment of first brood adults with calcium cyanide dust or pyr- 
ethrum-oil spray. 

6. Treatment of second brood nymphs with nicotine dust. 

7. Calcium cyanide dust treatment of adults before harvesting crop. 
Treatments 3 and 4 or both are exceedingly effective and are usually 

sufficient, if thoroughly applied, for practical control. 



SUMMARY 

The grape leafhopper is the most serious grape pest in California in 
the San Joaquin and Sacramento valleys. The degree of injury to vine- 
yards may be severe enough to reduce the crop 40 per cent. 

This insect overwinters in the adult stage in a wide variety of situa- 
tions, and moves to the vines as soon as the foliage appears in the spring, 
and feeds on the vines until fall. 

Three broods develop during the summer months, the first nymphs 
appearing about May 1. 

Control may be had by the application of one of a number of materials, 
as nicotine or pyrethrum sprays, pyrethrum-oil vapor spray, and nico- 
tine or calcium cyanide dusts. These must be applied under definite 
conditions. These insecticides may be advantageously supplemented by 
various farm practices. 

The egg parasite, Anagrus epos Girault, destroyed over 50 per cent 
of the third brood eggs in 1932, and thus reduced the number of over- 
wintering adults. 



20 California Agricultural Extension Service [ Ci R- 72 

Vineyardists, in order to maintain their vineyards in the best condi- 
tion and produce the highest quality product, should prevent the grape 
leafhopper from developing in destructive numbers. 

By following such phases of the suggested yearly control program as 
fits his situation, a grower can keep his losses at a minimum. 



ACKNOWLEDGMENTS 

The author wishes to acknowledge the assistance of Mr. J. L. Quail, 
Assistant Farm Advisor of Fresno County, in securing locations for 
experimental plots and in checking results ; of Dr. H. B. Walker, Mr. 
Roy Bainer, and Mr. 0. C. French, for their suggestions in relation to 
equipment used in experimental work; to Mr. Perez Simmons of the 
United States Department of Agriculture Entomological Laboratory, 
for laboratory space. Thanks are also due to Mr. G. L. Smith and Mr. C. 
E. Norland for assistance in checking experimental work; and to vine- 
yardists of Fresno County, namely, Messrs. H. R. Keller, J. J. Nielsen, 
H. H. Nielsen, Merle Smith, P. D. Turnbull, and others for the use of 
their vineyards in the experimental work. The drawings were made by 
Miss Dorothy Harris. 



16m-2,'33