http://ucanr.org/NapaEGVM (Napa3County) 33333UC Cooperative Extension

http://ucanr.org/egvm&leafrollers3(Sonoma3County)

13California3Irrigation3Management3Information3System.33http://wwwcimis.water.ca.gov/cimis/welcome.jsp

Degree%day)accumulations)used)to)time)insecticide)treatments)

to)control)1st)generation)European)grapevine)moth.

Lucia&G.&Varela,&Monica&L.&Cooper,&Walt&J.&Bentley&and&Rhonda&J.&Smith

University&of&California&Cooperative&Extension

There3 are3 several3 degreeGdays3 models3 in3 the3 European3 literature3 that3 differ3 in3 the3

amount3 of3 accumulated3 heat3 units3 needed3 for3 each3 life3 cycle3 stage3 of3 the3 European3

grapevine3moth.33We3are3validating3the3predictions3of3these3models3with3field3observations3

of3 various3events3in3 the3life3cycle3 of3 the3insect3during3each3generation.3 Field3 validation3is3

critical.3 We3 have3 preliminary3 validations3 from3 data3 collected3 during3 the3 20103 season3 in3

California.3 Here,3 we3 provide3 some3 predictive3 degreeGdays.3 Once3 a3 week,3 we3 will3 post3

degreeGday3accumulations3from3several3CIMIS13and3PestCast3stations3around3the3State3and3

we3 will3 also3 post3 validations3 as3 the3 season3 progresses3 (Table3 1).3We3 strongly3 encourage3

you3 to3continue3 visiting3 these3websites3as3we3 fineGtune3 the3degreeGday3predictions3under3

California3conditions.33

DegreeGdays3 for3 this3 insect3 are3

accumulated3starting3from3January31st3with3a3

lower3and3upper3threshold3of310o3and330oC,3

respectively3 (50o3 and3 86oF).3 All3 of3 the3

literature3reports3degreeGdays3in3Celsius.3To3

enable3 us3 to3 more3 easily3 compare3 models,3

we3 will3 post3 degreeGday3 accumulations3 in3

Celsius.3To3obtain3degreeGday3accumulations3

in3Fahrenheit3(oDF)3from3values3provided3in3

degreeGdays3 accumulated3 in3 Celsius3 (oDC)3

multiply3by31.83(eg.3150oDC3=3270oDF).

Timing3treatments3for3the31st generation

If) applying) a) conventional) insecticide

for3 the3 first3 generation3 of3 European3

grapevine3 moth3 (EGVM)3 make3 the3

application3 between3 2503and3 350oDC3 (450G

594oDF).3 This3 is3 a3 period3 that3 spans3 from3

peak3 flight3 (=peak3 egg3 laying)3 to3 10%3 egg3

hatch.3

Central3 Valley3 growers3 opting3 for3 two3

applications3 for3 the3 first3 generation,3 make3

the3 first3 application3 at3 250oDC3 and3 the3

second3143to3213days3later.3

If)applying)organic)insecticides3for3the3

first3 EGVM3 generation,3 begin3 at3 approxiG

mately3 300oDC3 (540oDF)3 and3 continue3

weekly3depending3on3population3levels.33

Accumulated Degree-Days

Because arthropods are cold-blooded, 

their development is influenced by 

ambient temperature. Each species 

requires a specific temperature range for 

development to occur. If temperatures 

are too low or too high development 

stops. The minimum and maximum 

developmental thresholds have been 

determined for some species. In warmer 

weather organisms develop more quickly 

than in cool weather, but the overall 

amount of heat required to complete a 

given organism's development does not 

vary. The combination of temperature 

(between thresholds) and time is 

expressed in units called degree-days. 

One degree-day results when the 

average temperature for a day is one 

degree over the minimum threshold. The 

accumulation of degree-days begins with 

either an arbitrary date (eg. January 1st) 

or a biofix (a biological event). 

Accumulated degree-days are used to 

predict when an insect will reach a 

certain stage in its life cycle. 
http://ucanr.org/NapaEGVM (Napa3County) March328,32011

http://ucanr.org/egvm&leafrollers3(Sonoma3County)

Explanation3for3this3treatment3timing MUST3READ

The3 best3 time3 to3control3 the3 first3generation3is3when3 the3highest3proportion3 of3larvae3

are3about3to3emerge3from3eggs.3We3know3larva3emergence3is3eminent3when3its3black3head3

(cap)3is3visible3inside3the3egg.3Peak3flight3is3when3the3majority3of3the3eggs3are3laid.3Shortly3

after3peak3flight3the3proportion3of3eggs3with3visible3black3caps3increases;3shortly3after3that3

larvae3begin3to3emerge.3

To3 accurately3 time3 insecticide3 applications3 for3 the3 1st3 generation3 of3 EGVM,3 the3 best3

approach3is3to3follow3the3flight3and3observe3egg3development.3This3practice3is3still3used3in3

many3regions3of3Europe.3Thus,3for3conventional3insecticides3the3application3is3made3at320%3

blackGcap3 egg3 stage3 and3 for3 organic3 or3 strictly3 larvicide3 insecticides3 when3 emergence3 is3

observed3(see3CAPCA3April320113article3in3our3websites3for3a3detailed3explanation).3

Because3EGVM3 populations3in3many3areas3 of3 California3are3 very3low,3 following3 flights3

and3observation3of3egg3development3is3not3feasible.3Therefore3we3are3providing3the3current3

best3estimate3to3time3the3application3using3degreeGdays.33

Given3 that3insecticides3are3combined3with3a3powdery3mildew3 treatment,3we3provide3a3

window3 for3applying3a3conventional3insecticide3between3peak3egg3laying3when3 few3blackG

cap3eggs3are3present3(250oDC)3and310%3emerged3larvae3(350oDC).3

The3majority3of3 the3insecticides3currently3on3 the3market3 for3conventional3and3organic3

production3 kill3 the3larvae.3 3 There3 are3 a3 few3 conventional insecticides3 that3 are3 primarily3

larvicidal3 with3 some3 ovicidal3 activity.3 3 To3 maximize3 the3 ovicidal3 properties3 of3 these3

ovicidal/larvicidal3 insecticides,3 they3 must3 be3 applied3 before3 egg3 deposition3 through3

presence3of3first3larval3stage.33

However,3 during3 the3 first3 generation3 applying3 an3 insecticide3 before3 egg3 deposition3 is3

not3practical3because3 the3 flower3cluster3is3 rapidly3expanding3 (thus3coverage3is3poor)3and3

the3egg3deposition3period3is3over343weeks.33Thus3if3a3single3treatment3is3used,3it3is3best3to3

make3 the3 application3 in3 the3 period3 following3 peak3 egg3 laying3 (250o3 to3 350oDC).3

Ovicidal/larvicidal3insecticides3in3addition3 to3 killing3a3 percentage3 of3 the3eggs3 have3a3long3

residue3that3will3last3through3larva3emergence3period.3If3opting3to3apply3two3sprays3against3

the3first3generation,3place3the3first3spray3at3250oDC3and3the3second3143to3213days3later.

Insecticides3registered3for3organic3production3are3larvicidal3and3should3be3targeted3for3

the3beginning3of3egg3hatch3(300oDC).3Due3to3the3short3residue3of3organic3materials,3two3or3

more3applications3are3warranted3starting3at3egg3hatch3and3continuing3weekly3for3as3long3as3

larvae3are3detected.3

Validations3from32010

Although3a3few3moths3emerged3as3early3as3February3in320103and32011,3some3European3

references3state3that3consistent3trap3catches3begin3at3approximately3150oDC3from3January3

1st.3Consistent3trap3catches3in3the3Napa3Valley3in320103started3in3midGMarch3at3150oDC3(see3

Figure31).3As3of3this3writing3we3have3passed3150oDC3in3Oakville,3Napa3County3and3yet3few3

moths3have3been3caught.3

Some3 references3 cite3 peak3 first3 flight3 at3 250oDC3 ±3 563 (Coscolla3 1989).3 Depending3 on3

weather,356oDC3may3be3±363days3at3this3time3of3year.3In320103peak3flight3in3Oakville3was3on3

April3193at3250oDC3and3coincided3with3the3first3observation3of3eggs3in3the3black3cap3stage.33
http://ucanr.org/NapaEGVM (Napa3County) March328,32011

http://ucanr.org/egvm&leafrollers3(Sonoma3County)

CAUTION3when3using3degreeGday3accumulations

1) You3cannot)use3programs3that3accumulate3degreeGday3on3a315Gminute3interval.3DegreeG

day3models3were3developed3in3the31980’s3when3methods3of3accumulating3degreeGdays3

over3a3period3less3than3243hours3were3not3available.3You3need3to3use3the3minimum3and3

the3maximum3for3the3day.

2) Do)not)project)more) than)1)week) ahead.3Programs3 such3as3 the3UC3 IPM3degreeGday3

calculator3 use3 30Gyear3 averages3 of3 daily3 minimum3 and3 maximum3 temperatures3 to3

project3future3degreeGdays.3These3projections3are3helpful3when3projecting3short3periods3

(a3week3or3so),3but3are3not3intended3for3projecting3future3conditions3over3three3or3more3

weeks.3 Daily3 temperatures3 differ3 from3 a3 30Gyear3 average,3 thus3 the3 farther3 into3 the

future3the3prediction3the3lower3the3accuracy.333

3) Continue) to)check)with) these)websites) as)we) validate) the)models.)Field3 sampling3

and3validation3are3critical3components3of3these3models.3In32010,3we3found3that3some3of3

the3 most3 accurate3 predictors3 were3 not3 based3 solely3 on3 the3 flight.3 For3 example,3 to3

accurately3predict3the3start3of3the32nd3flight,3we3needed3to3know3pupation3date3for3the31st

generation3larvae.3

Figure3 1.3 Male3 moths3 caught3 in3 Napa3 County3 during3 the3 first3 European3 grapevine3 moth3

flight3in32010.3Egg3laying3was3first3observed3at3the3end3of3March;3peak3flight/blackGcap3was3

first3observed3on3April319;3and3emergence3was3first3observed3in3early3May.3Moth3catch3data3

provided3by3USDA,3APHIS,3PPQ3European3Grapevine3Moth3Program.33
http://ucanr.org/NapaEGVM (Napa3County) March328,32011

http://ucanr.org/egvm&leafrollers3(Sonoma3County)

Table31.3DegreeGdays3accumulated3from3January31,320113in3Celsius*

Station** County DegreeGdays33(2011)

3/13 3/20 3/27 4/3 4/10 4/17 4/24 5/1 5/8

Oakville3#77 Napa 160.0 171.1 177.7

Carneros3#109 Napa 153.8 169.2 179.9

Suisun3Vly3#123 Solano 147.8 173.5 198.1

Windsor3#103 Sonoma 129.5 136.9 142.4

Santa Rosa3#83 Sonoma 120.7 129.1 134.9

Bennett3Vly3#158 Sonoma 134.2 139.2 143.6

Hopland3#106 Mendocino 142.2 148.0 151.6

Ruddick3Ukiah Mendocino 136.0 140.1 142.3

Lodi3West3#166 San3Joaquin 115.6 132.2 142.0

Cressey3#41 Merced 93.2 113.1 121.0

Del3Rey3(DELF) Fresno 117.3 141.6 152.1

*Generated3using3University3of3California3Integrated3Pest3Management3Program3(UC3IPM)3

degreeGday3calculator,3with310o3and330oC3as3minimum3and3maximum3thresholds,3

respectively.3http://www.ipm.ucdavis.edu/WEATHER/ddretrieve.html

**All3stations3are3in3the3CIMIS3or3PestCast3Networks3and3daily3minimumGmaximum3

temperature3data3reside3on3the3UC3IPM3web3site.