50

▲Growing Knowledge

An ongoing series provided by Oregon State University in partnership with OAN

Treating irrigation waterThese water treatment methods can be effective at eliminating damaging water molds in nurseries

42

▲

cutting rots, and Phytophthora species, which cause root rot, shoot dieback and foliar blight on a wide range of nursery plants.

Unless recycled water is disinfested before reuse, irrigation water may become an effective delivery system for these plant pathogens.

Water sourcesExtensive sampling in nurseries

indicates that surface water sources such as rivers, ponds, and reservoirs for storing runoff water are almost always contaminated with Phytophthora and Pythium species and should be disin-fested before use in irrigation.

Only water from municipal sources and well water are free of these plant pathogens. You should assume that recirculated water is contaminated and disinfest it on a routine basis, or you can test your water at frequent (month-ly) intervals and treat only if needed.

PARK

E

By Jennifer Parke and Paul FisherNursery and greenhouse growers

commonly capture runoff water and reuse it for irrigation. This conserves water and prevents the escape of nutri-ents and pesticides into waterways.

However, reservoirs also pro-vide a habitat for waterborne plant pathogens. The most serious of these are the water molds, which look like fungi but require water to complete their life cycles.

The most common water molds are Pythium species, which cause damping-off of seedlings and stem

Water storage ponds, such as this one located at Fisher Farms in Gaston, Ore., are common to the nursery industry. It's important that nurseries treat recovered water before using it again for irrigation.

FEBRUARY 2012 ▲ DIGGER 41

▲ TREATInG IRRIGATIon

Testing your water for Pythium and Phytophthora

You can test for the presence of Pythium and Phytophthora by baiting water with rhododendron leaves for seven days and then testing the leaves with field diagnostic ELISA kits. Details for baiting water samples are avail-able here: http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/rCNPv1/rncp-appendix7.pdf

ELISA kits use monoclonal or poly-clonal antibodies to detect the patho-gens, the same technology used in home pregnancy kits. Kits are available as dipsticks such as the ImmunoStrip® (Agdia®), or as lateral flow devices such as the Alert LF™ (Neogen Europe Ltd.).

Note that currently available ELISA tests for Phytophthora cross-react with several Pythium species, potentially leading to false positives. For this rea-son, the ELISA tests are best used to rule out the presence of Phytophthora species. If the Phytophthora test is positive, further testing by a university extension plant pathology lab is advised to make sure that Phytophthora ramo-rum is not present.

Water disinfestation methods Several methods are available for

effectively disinfesting irrigation water. These methods are summarized in a two-page table available for down-

A nursery technician prepares a leaf bait for an ELISA test to determine the presence of Phytophthora and Pythium pathogens in irrigation water.

PARK

E

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load from the Oregon Association of Nurseries website at www.bit.ly/oansystems. A summary of research on efficacy tests for different treatment technologies to control waterborne pathogens is available at www.watered-ucationalliance.org by selecting “grower tools” and “waterborne solutions.”

Water treatment systems differ in installation costs, operating costs, mode of action, space requirements, water volume treated, worker safety, and envi-ronmental concerns. No single system is best for all nurseries. A combination of filtration with chemical or ecological treatments is often needed.

Suspended solids (such as soil and organic matter) in the water reduce the effectiveness of disinfestation treatments. Total suspended solids should ideally be less than 20 mg/L. Higher amounts of suspended solids increase the risk of plugging emitters that can interfere with water disinfestation treatments.

For example, chlorine is deactivated by organic materials in the water. Pre-filtration is usually required to remove these materials (remnants of potting media, algae and plant debris) from the water. Effective UV treatment of water to kill waterborne pathogens also requires the water to be clear. For these reasons, filtration is often the initial step in various water treatment systems.

Water chemistry also affects the effectiveness of several disinfestation treatments. For example, the sanitiz-ing activity of chlorine is strongly dependent on pH. For water amended with either calcium hypochlorite or sodium hypochlorite, the optimal pH range is 6.0-7.5. Above pH 7.5, the chlorine would be in the form of hypochlorite, a weak sanitizer. Below pH 7.5, chlorine would be in the form of hypochlorous acid and is 20 to 30 times as effective as hypochlorite.

Copper ionization or copper sul-fate is also more effective below pH 7. If electrical conductivity EC is low (<0.20 mS/cm) then it may be necessary

44

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FEBRUARY 2012 ▲ DIGGER 43

▲ TREATInG IRRIGATIon

to increase the electrode surface area when ionizing copper.

Runoff source and placement of the pump inlet in the reservoir

A recent study in a Virginia nursery showed that baiting of Phytophthora species declined with increasing dis-tance from the source of water run-off into the reservoir. This suggests that the irrigation pump inlet should be placed as far away as possible from the source of runoff.

Bait colonization tended to be greatest when baits were at the water surface or near the bottom of the res-ervoir, suggesting that placement of the pump inlet at half the depth of the res-ervoir would result in the least uptake of Phytophthora.

The study can be downloaded

at http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0434.2011.01831.x/full.

Types of water treatmentThe various water treatment sys-

tems disinfest water by different modes of action:

Oxidizing agents react with chemical groups on organic matter, changing the chemical structure of this material. Organic matter includes peat, algae, bacteria, plant debris, and pathogens. Pathogens are killed after exposure to the oxidizing agent if it is present at a certain concentration and duration. The oxidizing agent, however, can be depleted by organic matter in the water. That is why water should be pre-filtered before it is treated with oxidizing agents. Oxidizing agents also react with iron and other met-als. Oxidizing agents include bromine, chlorine gas, sodium hypochlorite, calcium hypochlorite, chlorine dioxide, ozone, and activated peroxygen.

Ultraviolet (UV) radiation involves exposure of the water in tubu-lar chambers to UV light, which kills living cells (including pathogens) by disrupting their DNA. Particulates in the water disperse the light, reducing the effectiveness of UV radiation. Pre-filtration of the water is necessary.

Copper ionization is the release of copper ions into the water result-ing from an electrical charge passed between copper plates. Copper ions are toxic to most pathogens and plants, but the levels used to treat water are well below those which cause phytotoxicity. Copper is also sometimes delivered as a dissolved salt, such as copper sulfate.

Heat treatment is another method of disinfesting water, but it is energy intensive and therefore too costly for treating large volumes. A temperature of 203°F for 30 seconds is sufficient to kill most plant pathogens.

Slow sand filtration is a low technology approach for disinfesting water that has been extremely effective in eliminating Phytophthora from recir-culating water in commercial nurseries in

Learn more

An excellent source for learning more about water treatment methods is the educational resource section of the Water Education Alliance for Horticulture website (www.watereducationalliance.org). The Alliance is a collaborative program between the University of Florida, other researchers and industry partners, that educates growers about water quality and conservation. At the website growers can find key articles and videos about water treatment technologies and monitoring, interactive grower tools and current and previous newsletters. You can also register for upcoming webinars and workshops.

44 FEBRUARY 2012 ▲ DIGGER

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NATIVE NURSERY LLC

‘Roots to grow on’Phone: 541-757-6520 Fax: 541-738-2607 www.sevenoaksnativenursery.com

- Over 300 species grown from seed- Hard to find natives - Drought tolerant, high elevation- Quaking Aspen specialists - Highest Quality bareroot seedlings- Containers from 4”-25 gallon

Germany www.plantmanagementnet-work.org/pub/php/research/2008/recy-cle. A biofilm crust, or Schmutzdecke, develops on the surface of the sand filter. While this layer is important for the functioning of the filter, it must be maintained or the filter can become clogged. Slow sand filtration may not be rapid enough to supply the volume of water during periods of peak demand, requiring filtration and then storage of the clean water in a reservoir.

SummaryGrowers can minimize their risk

of exposure to plant diseases and reduce pesticide use by ensuring that their irrigation water is free of Pythium and Phytophthora species. Several different disinfestation meth-ods, including high technology and low technology solutions, are avail-able for use by greenhouse and nurs-ery operations of all sizes.

DisclaimerChemical names and trade names are

included as a convenience to the reader. Their use in this publication does not imply endorsement, nor discrimination against similar products or services not mentioned. Individuals who use chemi-cals are responsible for ensuring that the intended use complies with current regu-lations and conforms to the product label. Be sure to obtain current information about usage and examine a current prod-uct label before applying any chemical. For assistance, contact your state pesticide regulating authority.

Dr. Jennifer Parke is an associate pro-fessor (senior research) at Oregon State University in Corvallis where she con-ducts research on Phytophthora species in nurseries. She can be reached at Jennifer.Parke@oregonstate.edu. Dr. Paul Fisher is an associate pro-fessor and extension specialist in the Environmental Horticulture Department at the University of Florida in Gainesville. He can be reached at pfisher@ufl.edu.

Your contribution today helps prepare the nursery industry leaders of tomorrow. OREGON

NURSERIESFOUNDATION

The ONF is a nonprofit 503(c)3 corporation. Donations may be tax-deductible; consult a qualified tax attorney or accountant.

Contact the Oregon Association of Nurseries for more information503.682.5089 or 800.342.6401

FEBRUARY 2012 ▲ DIGGER 45

60 SAFE PROCUREMENT AND PRODUCTION MANUAL

Tabl

e 8.

3.2b

— A

sum

mar

y of

tre

atm

ent

opti

ons

for

wat

erbo

rne

path

ogen

s in

nur

sery

and

gre

enho

use

irri

gati

on s

yste

ms

(Pag

e 1

of 2

)

Trea

tmen

tAc

tive

ingr

edie

ntRe

adily

so

lubl

eIn

ject

ion

met

hod

How

It W

orks

Usua

l ran

ge in

co

ncen

trat

ion1

Not

es

Brom

ine

Ex

ampl

e:

Agrib

rom

™

1-Br

omo-

3-ch

loro

-5,

5-di

met

hyl-2

,4-

imad

azol

idin

edio

neNo

Tabl

ets o

r gra

nule

s are

pla

ced

in a

cont

aine

r w

ith w

ater

. The

supe

rnat

ant s

olut

ion

is in

ject

ed in

to th

e irr

igat

ion

wat

er.

Oxid

izing

age

nts

liste

d in

this

tabl

e in

tera

ct w

ith re

activ

e ch

emica

l gro

ups o

n or

gani

c mat

ter. T

he

oxid

atio

n of

org

anic

mat

ter r

esul

ts in

a

chan

ge in

the

chem

ical s

truct

ure

of th

e or

gani

c m

atte

r, and

dea

th o

f th

e pa

thog

en. T

he

oxid

izing

age

nt it

self

is al

so “

used

up”

du

ring

sani

tatio

n be

caus

e th

e ag

ent

chan

ges c

hem

ical

form

as i

t rea

cts w

ith

orga

nic m

atte

r. Pl

ant

path

ogen

s var

y in

th

eir s

usce

ptib

ility

to

the

agen

ts li

sted

in

this

tabl

e. So

me

plan

t pat

hoge

ns a

nd

type

s of r

esist

ant

inoc

ulum

stru

ctur

es

may

requ

ire h

ighe

r ra

tes o

f oxi

dizin

g ag

ents

and

/or

expo

sure

tim

es

than

thos

e lis

ted.

Th

e m

ater

ial b

eing

ox

idize

d ca

n in

clude

pa

thog

ens,

peat

, an

d fe

rtiliz

er sa

lts.

Beca

use

all o

rgan

ic m

atte

r in

the

wat

er

will

abs

orb

and

depl

ete

oxid

izers,

go

od p

re-fi

ltrat

ion

is es

sent

ial.

5–35

ppm

bro

min

e

Beca

use

of lo

w so

lubi

lity,

som

e tim

e is

requ

ired

for

the

undi

ssol

ved

tabl

ets o

r gra

nule

s to

repl

enish

the

brom

ine

in th

e st

ock

solu

tion.

Diffi

cult

to m

aint

ain

a co

nsta

nt co

ncen

tratio

n of

bro

min

e ov

er th

e co

urse

of

the

day,

espe

cially

with

hig

h flo

w ra

tes.

Req

uire

s a

spec

ial i

njec

tor r

esist

ant t

o co

rrosiv

e ch

emica

ls.

Chlo

rine

gas

Cl2

Yes

Chlo

rine

gas i

s bub

bled

thro

ugh

the

wat

er, w

here

it co

mbi

nes w

ith th

e w

ater

to fo

rm h

ypoc

hlor

ous a

cid

(HOC

l) an

d hy

droc

hlor

ic ac

id (H

Cl).

0.5–

2 pp

m fr

ee ch

lorin

e.

Hy

poch

lorit

e is

a w

eak

acid

an

d ca

n be

foun

d in

solu

tion

in tw

o di

ffere

nt fo

rm: O

Cl- a

nd

HOCl

.

Beca

use

the

HOCl

form

is

muc

h m

ore

effe

ctiv

e at

disi

nfec

ting

than

the

OCl-

form

, the

wat

er p

H sh

ould

be

cont

rolle

d, a

s sa

nitiz

ing

reac

tions

tend

to

be sl

ower

at h

ighe

r pH.

Haza

rdou

s gas

requ

ires s

pecia

l equ

ipm

ent,

vent

ilatio

n, a

nd h

andl

ing.

As w

ith a

ll ch

lorin

e ap

plica

tion

met

hods

, hig

her t

han

reco

mm

ende

d co

ncen

tratio

ns ca

n be

toxi

c to

plan

ts.

Sodi

um

Hypo

chlo

rite

NaOC

lYe

sLiq

uid

NaOC

l sol

utio

ns

(5–1

5 pe

rcen

t chl

orin

e) a

re in

ject

ed

dire

ctly

into

irrig

atio

n w

ater

.

Requ

ires a

spec

ial i

njec

tor t

hat i

s res

istan

t to

very

co

rrosiv

e ch

emica

ls an

d ha

s a v

ery

high

inje

ctio

n ra

tio. H

as a

lim

ited

shel

f life

. War

m te

mpe

ratu

res a

nd

sunl

ight

spee

d up

bre

akdo

wn.

Nev

er co

mbi

ne w

ith

ferti

lizer

s or o

ther

chem

icals

cont

aini

ng a

mm

oniu

m.

Calc

ium

Hy

poch

lorit

eCa

(OCl

)2Ye

s

Gran

ules

may

be

diss

olve

d in

wat

er,

or ta

blet

s can

be

erod

ed in

a fl

ow-

thro

ugh

feed

er fo

r mor

e au

tom

atic

chlo

rinat

ion,

at c

hlor

ine

conc

entra

tions

up

to 1

0,00

0 pp

m, d

epen

ding

on

the

feed

er a

nd o

pera

ting

cond

ition

s.

Calci

um h

ypoc

hlor

ite so

lutio

ns o

f up

to

appr

oxim

atel

y 21

per

cent

can

be p

repa

red,

but

du

e to

the

pres

ence

of i

nsol

uble

mat

eria

ls su

ch a

s ca

lcium

carb

onat

e so

lutio

ns o

f abo

ve 2

00 p

pm te

nd

to b

e clo

udy.

Sedi

men

t for

ms w

ith v

ery

conc

entra

ted

solu

tions

. At l

ess t

han

100

ppm

ava

ilabl

e ch

lorin

e th

ere

shou

ld b

e no

app

aren

t clo

udin

ess o

r sed

imen

t.

Chlo

rine

Dio

xide

Ex

ampl

es:

Ultra

-Shi

eld™

, Se

lect

rocid

e™

ClO2

Yes

Dry

pack

et o

r tab

lets

pla

ced

in w

ater

, Cl

O2 sol

utio

n ge

nera

ted

in st

ock

tank

.

Inje

cted

into

irrig

atio

n lin

es.

Cont

inuo

us in

ject

ion

of

resid

ual c

once

ntra

tion

of

0.25

ppm

or l

ess.

Twice

a y

ear

shoc

k tre

atm

ent a

t 20

to 5

0 pp

m d

epen

ding

on

prod

uct.

Stoc

k so

lutio

n sh

ould

be

used

with

in 1

5 da

ys to

min

imize

loss

due

to v

olat

iliza

tion.

M

axim

um st

ock

conc

entra

tion

of 5

00 o

r 3,

000

ppm

dep

endi

ng o

n pr

oduc

t.

Ozo

neO3

No

An e

lect

rical

arc

is u

sed

to

prod

uce

the

ozon

e fro

m b

ottle

d or

at

mos

pher

ic ox

ygen

. The

ozo

ne is

th

en b

ubbl

ed th

roug

h th

e w

ater

.

Resid

ual e

ffect

from

reac

tion

prod

ucts

(per

oxid

es,

orga

nic r

adica

ls).

Brea

ks u

p bi

ofilm

. 10

gram

s/hr/m

³.

Requ

ires p

rofe

ssio

nal d

esig

n ba

sed

on w

ater

an

alys

is. P

rope

r des

ign

prev

ents

ozo

ne fr

om e

scap

ing

into

the

atm

osph

ere

in h

azar

dous

conc

entra

tions

.

Activ

ated

Pe

roxy

gen

Ex

ampl

es:

Zero

Tol™

, San

iDat

e™

Hydr

ogen

dio

xide

/hy

drog

en p

erox

ide

(H2 O

2 ) an

d Pe

roxy

acet

ic ac

id/p

erac

etic

acid

(C

H3 COO

-OH)

Yes

A st

abili

zed

H2 O2 a

nd p

erac

etic/

pero

xyac

etic

acid

solu

tion

that

is in

ject

ed d

irect

ly in

to

irrig

atio

n w

ater

. Pe

roxy

acet

ic ac

id is

a

mor

e ef

fect

ive

bioc

ide

than

H2 O

2 alo

ne.

27 to

540

ppm

H2 O

2Re

quire

s a sp

ecia

l inj

ecto

r tha

t is r

esist

ant t

o ve

ry

corro

sive

chem

icals

and

has a

ver

y hi

gh in

ject

ion

ratio

, or t

he m

ater

ial m

ust b

e di

lute

d be

fore

inje

ctio

n.

CHAPTER 8: PLANT PRODUCTION: WATER MANAGEMENT 61

Tabl

e 8.

3.2b

— A

sum

mar

y of

tre

atm

ent

opti

ons

for

wat

erbo

rne

path

ogen

s in

nur

sery

and

gre

enho

use

irri

gati

on s

yste

ms

(Pag

e 2

of 2

)

Trea

tmen

tAc

tive

ingr

edie

ntRe

adily

sol

uble

Inje

ctio

n m

etho

dHo

w it

wor

ksUs

ual r

ange

in

conc

entr

atio

n1N

otes

Ultra

viol

et

(UV)

radi

atio

nN/

A

Wat

er is

exp

osed

to h

igh

dose

s of

UV li

ght i

n tu

bula

r cha

mbe

rs. M

ost

com

mon

are

low

pre

ssur

e m

ercu

ry

vapo

r lam

ps w

ith a

wav

e le

ngth

of

254

nm

, clo

se to

the

optim

um

rang

e fo

r kill

ing

path

ogen

s.

UV ra

diat

ion

disr

upts

the

gene

tic m

ater

ial i

n th

e ce

ll,

effe

ctiv

ely

killi

ng it

. Dos

e, ex

posu

re ti

me

and

turb

idity

de

term

ine

effe

ctiv

enes

s.

250

mJ/c

m2 e

limin

ates

mos

t pa

thog

ens.

No re

sidua

l ef

fect

on

path

ogen

s do

wns

tream

of t

reat

men

t.

The

effe

ctiv

enes

s of t

he la

mp

decr

ease

s w

ith a

ge. A

ny p

artic

ulat

e m

atte

r in

the

wat

er w

ill d

isper

se th

e lig

ht, m

akin

g th

e ap

plica

tion

of U

V ra

diat

ion

less

ef

fect

ive.

Good

pre

-filtr

atio

n is

esse

ntia

l. Of

ten

used

with

oth

er d

isinf

ectin

g m

ater

ial t

o ge

t som

e re

sidua

l effe

ct.

Copp

er

ioni

zatio

nCu

++Ye

sAn

ele

ctric

al ch

arge

is p

asse

d be

twee

n co

pper

bar

s or p

late

s, re

leas

ing

copp

er io

ns in

to th

e w

ater

.

Copp

er io

ns a

re a

toxi

n to

m

ost p

atho

gens

, inc

ludi

ng

Pyth

ium

, Phy

toph

thor

a,

Xant

hom

onas

, and

alg

ae.

Rece

nt a

dvan

ces i

n co

ntro

ls pr

oduc

e co

nsist

ent c

oppe

r le

vels

and

relia

ble

resu

lts.

0.5

to 1

ppm

Cu

for p

atho

gens

. 1

to 2

ppm

for a

lgae

and

bio

film

.

Less

effe

ctiv

e if

wat

er p

H is

abov

e 7.

5.

Choo

se a

syst

em w

hich

act

ivel

y co

ntro

ls co

pper

out

put a

ccor

ding

to fl

ow a

nd

EC. A

pplie

d co

pper

conc

entra

tions

are

w

ithin

U.S.

drin

king

wat

er st

anda

rds

and

a fra

ctio

n of

pla

nt to

xicit

y le

vels.

Heat

tre

atm

ent/

past

euriz

atio

nN/

AW

ater

is h

eate

d to

spec

ific

tem

pera

ture

, and

was

te h

eat i

s re

cove

red

to p

re-h

eat i

ncom

ing

wat

er.

Path

ogen

resis

tanc

e to

hea

t var

ies.

Effe

ct

larg

ely

inde

pend

ent

of w

ater

qua

lity.

An e

xam

ple

treat

men

t is

203

F fo

r 30

seco

nds.

No

resid

ual e

ffect

on

path

ogen

s do

wns

tream

of t

reat

men

t.

High

ene

rgy

use

mak

es it

exp

ensiv

e fo

r lar

ge fl

ow. T

o pr

even

t sca

ling

of

heat

exc

hang

ers f

rom

har

d w

ater

, pH

need

s to

be re

duce

d to

4.5

, the

n ra

ised

agai

n as

nee

ded

for i

rriga

tion.

Bes

t for

lo

w-fl

ow, h

igh-

sani

tatio

n ap

plica

tions

.

Slow

sand

fil

tratio

nN/

A

Wat

er m

oves

pas

sivel

y th

roug

h sa

nd

bed

that

supp

orts

a b

iolo

gica

lly

activ

e la

yer (

Schm

utzd

ecke

or

biofi

lm cr

ust)

on th

e fil

ter s

urfa

ce.

Clea

n, fi

ltere

d w

ater

is st

ored

in

a co

vere

d re

serv

oir u

ntil

use.

Sand

filtr

atio

n w

orks

thro

ugh

a co

mbi

natio

n of

phy

sical

rem

oval

of

parti

cles a

nd b

iolo

gica

l act

ivity

of t

he

biofi

lm cr

ust.

Effe

ctiv

e at

elim

inat

ing

Phyt

opht

hora

spp.

from

wat

er.

An e

xam

ple

rate

of

filtra

tion

is 30

-90

m3 /h

r. A

filte

r bed

are

a of

260

m2

and

1 m

dee

p ca

n yie

ld

appr

oxim

atel

y 40

,000

m

3 filte

red

wat

er/m

o.

Whi

le th

e bi

ofilm

crus

t or S

chm

utzd

ecke

is im

porta

nt fo

r the

fu

nctio

ning

of t

he fi

lter, i

t mus

t be

mai

ntai

ned

by p

erio

dic r

akin

g or

the

filte

r can

bec

ome

clogg

ed. S

low

sand

filtr

atio

n m

ay n

ot

be ra

pid

enou

gh to

supp

ly th

e vo

lum

e of

wat

er d

urin

g pe

riods

of

peak

irrig

atio

n de

man

d. S

pace

lim

itatio

ns m

ay a

lso li

mit

the

size

of th

e sa

nd fi

lter a

nd th

e vo

lum

e of

wat

er th

at ca

n be

trea

ted.

Not

es1.

De

sired

conc

entra

tion

depe

nds o

n th

e ap

plica

tion

(e.g

. sho

ck tr

eatm

ent v

ersu

s con

tinuo

us tr

eatm

ent o

f clea

n w

ater,

and

the

spec

ific p

atho

gens

targ

eted

). S

ee p

rodu

ct la

bel a

nd m

anuf

actu

rer’s

instr

uctio

ns fo

r you

r app

licat

ion.

2.

All t

he m

etho

ds m

entio

ned

abov

e ar

e no

n-sp

ecifi

c and

will

reac

t with

any

type

of o

rgan

ic m

atte

r, whe

ther

it is

a p

atho

gen,

alg

ae, o

r a p

artic

le of

pea

t. In

all c

ases

, the

clea

ner t

he w

ater

is b

efor

e th

e ap

plica

tion,

the

mor

e ef

fecti

ve th

e di

sinfe

ction

m

etho

d is

at re

mov

ing

path

ogen

s.3.

Br

omine

, chlo

rine p

rodu

cts, o

zone

, per

oxya

cetic

acid

, and

hyd

roge

n pe

roxid

e are

stro

ng o

xidizi

ng a

gent

s. M

etal

micr

onut

rient

s (co

pper,

iron

, man

gane

se, a

nd zi

nc) a

re ea

sily o

xidize

d (p

artic

ularly

iron

). It

is lik

ely th

at lo

ng-te

rm ex

posu

re (g

reat

er th

an 2

0 m

inute

s) of

met

al m

icron

utrie

nts t

o th

ese o

xidizi

ng a

gent

s will

decre

ase t

heir

solub

ility.

Chela

ted

micr

onut

rient

s sho

uld b

e only

sligh

tly le

ss a

ffecte

d th

an su

lfate

s.4.

Ul

travio

let ra

diat

ion

is a

phot

o-ox

idizi

ng a

gent

. Res

earc

h by

Cor

nell U

nive

rsity

on

phot

o-ox

idat

ion

of ir

on in

ferti

lizer

solu

tions

indi

cate

s tha

t the

gre

ater

the

light

exp

osur

e, th

e les

s iro

n th

at w

ill re

mai

n in

solu

tion.

5.

Quat

erna

ry a

mm

oniu

m co

mpo

unds

such

as G

reen

-Shi

eld®, P

hysa

n 20

™, o

r Tria

thlo

n™ a

re lis

ted

for d

isinf

ectio

n of

wal

kway

s, be

nche

s, to

ols,

flats,

etc

., bu

t are

not

for u

se w

ith ir

rigat

ion

wat

er.6.

Liq

uid

hydr

ogen

per

oxid

e/hy

drog

en d

ioxid

e (H

2O2)

solu

tions

(35–

50 p

erce

nt H

2O2)

are

not E

PA-re

giste

red

for w

ater

trea

tmen

t in

gree

nhou

ses,

and

are

less e

ffect

ive a

nd st

able

com

pare

d w

ith re

giste

red

activ

ated

per

oxyg

en p

rodu

cts.

Chem

ical n

ames

and

trad

e na

mes

are

inclu

ded

in th

is pu

blica

tion

as a

conv

enien

ce to

the

read

er. Th

e us

e of

bra

nd n

ames

and

any

men

tion

or lis

ting

of co

mm

ercia

l pro

duct

s or s

ervic

es in

this

publ

icatio

n do

es n

ot im

ply n

dorse

men

t, no

r di

scrim

inat

ion

agai

nst s

imila

r pro

duct

s or s

ervic

es n

ot m

entio

ned.

Indi

vidua

ls w

ho u

se ch

emica

ls ar

e re

spon

sible

for e

nsur

ing

that

the

inte

nded

use

com

plies

with

curre

nt re

gula

tions

and

conf

orm

s to

the

prod

uct l

abel.

Be

sure

to o

btai

n cu

rrent

in

form

atio

n ab

out u

sage

and

exa

min

e a

curre

nt p

rodu

ct la

bel b

efor

e ap

plyin

g an

y che

mica

l. For

ass

istan

ce, c

onta

ct yo

ur st

ate

pesti

cide

regu

latin

g au

thor

ity.

Tabl

e m

odifi

ed b

y J. P

arke

, Ore

gon

Stat

e Un

iversi

ty, w

ith p

erm

issio

n fro

m F

isher,

P. (e

d.) 2

009.

Wat

er Tr

eatm

ent f

or P

atho

gens

and

Alg

ae.W

ater

Edu

catio

n Al

lianc

e fo

r Hor

ticul

ture

. 57

pp.