8/9/2019 Polyester Covers Protect Vegetables from Whiteflies & Virus Disease; Gardening Guidebook for California

1/2

8/9/2019 Polyester Covers Protect Vegetables from Whiteflies & Virus Disease; Gardening Guidebook for California

2/2

Check uncovered , un t rea ted)

\

Pro t ec t ion rom w h i t e f ly -sp read v i rus d i seases by spun -bonded po l yes t e r i nc reased y i el dof zucch i n i squash 20-

f o l d ove r unp ro t ec t ed p l o t s . Lack o f p ro t ec t i on a l so l ed t o sheepnose and c rack i ng i n d i seased f ru i t.

cide, no cover) plots on Sep temher 1 4 and

20. Whitefly counts w ere ve ry high, rang -

ing from 94 to 911 and from 556 to 3,820

per plant on September 1 4 and September

20, respectively, including insecticide and

check plots. Endosulfan

or

comhinations

of other insecticides with endosillfan Drn-

vided the best control. Floating

row

cov

ers excluded whitefly from the zucchini

plants.

Virus disease ratings were made on

September 17 and 21, five and four days

after insecticide tre atm ents, respectively.

The virus ratings were based on the num-

ber of zucchini plants with let tuc e infec-

tious yellows o r squash leaf curl virus dis-

eas e symptoms per 10 plants examined in

each of four replicates. The virus ratings

TABLE 1. Pro jec ted p roduc t ion cos t s f o r

summer squash g rown under spup-hnnded

poly ester row covers wi th furrow i r r igat ion

c o s t

Sample cos t s

per ac re

ADDliCatiOn

of

covers 700

Removal

Total

1

800

.

Other preharvest costs 675

Harvest p ick , haul , grade. pack,

and sel l 500 cartons @ 7 75) 1,375

TOTAL COSTS 2 850

Total preharvest 1.475

Cost per car ton @ 500

Cost pel car ton @ 60C

cartons per acre 4

19

cartons Der acre 3.49

N O TE

Actual

c o s t s

m a y

v a r y W i t h

availability o f

spun-bonded poly ester and cultural practices We

estimate c o s t s Could be u p to 5 percent higher

ranged from 3.0 to 5.0: 30 to 50 percent of

the plants were showing virus disease

symptoms five days afte r the first insecti-

cide treatments

or

about eight days a fter

eme rgence Virus disease symptoms were

apparent

in

75 to 100 per cent of the z uc-

chini

plan ts

fniir days a fte r the second in-

secticide sppliration. only 12 days af ter

the seedlings emerged. 1Jnder f loat ing

row covers, virus disease symptoms did

not appear until the plants were large (18

inches tall) and were flowering.

When the floating row covers were re -

moved, very slight virus symptoms could

be seen in new growth of a few plants.

Whitefly counts were made on five leaves

of each of 10 plants in four replicates on

October

10 as the row covers were re-

moved

Very few whitefly adults were

found

on

plants that had been covered: the

average was 10 adults, significantly few-

e r than the 6,425 on untreated check

plants

Yield and economics

Zucchini fruit were harvested from the

insecticide-treated, row-covered, and un-

treated check plots from October 15 to

November 1 for a total of eight harv est

dates. Rows that had been covered pro-

duced a much greater yield than any of

the insecticide-treated rows or the un-

treated, uncovered check rows. Covered

rows yielded the equivalent of 369 carto ns

of zucchini per a cre com pared w ith the

check. which produced as little as 18 car-

tons per ac re, based on 18-pound carto ns.

TABLE 2. I n c o m e a b o v e c o s t per a c r e

__

I ncome a t f o l l ow ing p r i ces per box :

.

Boxes

per

a c r e 3 5 7 9 11 13 1

5

200 -1,425

-1,025 625

225

175 275

975

400 -1,375

575 225

1,025 1,825 2,625 3,425

600 -1,325 125 1,075 2.275 3,475 4,675 5.875

800 -1.275 325 1,925

3,525

5,125

6,725 8.325

1,000 1,225 775 2,775

4,775 6,775 8,775 10,775

1,200

-1,175 1,225 3,625

6,025 8,425 10,825 13,225

Yields f rom insec t ic ide- t r ea ted p lo ts

ranged from 25 to 153 cartons p r acre;

endosulfan and combinations of endosul-

f an wi th o ther insec t ic ides p roduced

yields from 128 to 153 carto ns per acre.

Rows covered with the polyester pro-

duced statistically greate r yield than any

o ther t r ea tment , as de termined us ing

mu ltifac tor analysis of v aria nce and Dun-

can's new multiple range test for separa-

tion of the m ean s at the 1perce nt level of

significance.

Before the squash leaf curl virus dis-

ease problem, low-desert-area growers

could produce more than 800 cartons of

squash per acre, averaging over 500 car-

tons in fal l production. Since this disease

and, later, lettuce infectious yellows be-

came prob lems , average y ie lds have

dropped to less than 300 carto ns per acre.

An economic analysis indicates that,

for a profit to be realized through use of

spun-bonded polye ster a s row covers,

m ark et prices must be higher than 5 per

carton (tables

1

and

2).

During the fall of

1984, squash prices reached levels as high

as 14 per carto n. With the cost of SBP

and labor costs to cover beds exceeding

800 per acre , it appe ars that spun-bond-

ed polyester floating row covers will only

be profitable for protection of high cash

value crops.

Conclusions

Currently only small acreages are

un-

der cultivation with spun-bonded polyes-

ter row covers in the Imperial and Coa-

chella valleys, but their use could become

common in southern California. Technol-

ogy for economical application, removal,

and disposal of the material is being de-

veloped, and other materials from which

tunnels or floating row covers could be

constructed may provide similar insect

exclusion and disea se suppression.

Eric

T.

Natwick is Entomology Farm Advisor Impe-

rial County and Alfonso Durazo III is Limited-

Scale-Agriculture Farm Advisor Imperial and Riv-

erside counties.

22

CALIFORNIA AGRICULTURE, JULY-AUGUST

1985