Imperial County Agricultural Briefs

From your Farm Advisors

Features

May, 2006

Page

MELON POWDERY MILDEW CONTROL ……………………...…….. Thomas A. Turini 2

IRRIGATION & CROP GROWTH – TIMING IS EVERYTHING .. Rick Bottoms, Ph.D. 3

INSECTICIDE EFFICACY AGAINST WORM PESTS IN ALFALFA … Eric T. Natwick 5

BAILING RECOMMENDATIONS ……………………..…………..…… Juan N. Guerrero 10

CIMIS REPORT ..........................................................................Khaled Bali and Steve Burch 11

Melon Powdery Mildew Control T. A. Turini Melon powdery mildew on melons has been

controlled with resistant varieties and

fungicides for many years. However, there

is evidence that plant resistance breaking

races and fungicide resistant strains are

present. This places increased importance

upon careful monitoring, knowledge of the

fungicides available and their limitations.

All cantaloupe, honeydew, mixed melon,

watermelon and squash should be checked

carefully for powdery mildew even if you

are using a variety that has resistance to race

1 and 2 of the fungus. Races capable of

breaking race 1 and 2 resistance are present

in Imperial Valley (1).

Results of 5 years of fungicide trials are

presented in Table 1. These materials were

applied three times at 10 day intervals for

purposes of determining efficacy. However,

in a commercial setting use tank mixes and

fungicide rotations to reduce the chances of

a resistance development and increase the

likelihood of having a successful powdery

mildew control program.

Ag Briefs – May, 2006 2

Your powdery mildew control program may

benefit from tank mixing a contact material,

such as chlorothalonil, with a systemic

material. Also, if you use a material with a

high risk of resistance development and

multiple applications are required to control

the disease, follow the application with a

material with a different mode of action.

Note that Quintec is not currently registered

for use on cucurbits in California, but

registration is anticipated in the near future.

This is not an endorsement of any product.

Carefully read the label before writing any

pesticide recommendation.

Table 1. Performance of Fungicides against powdery mildew on upper leaf surfaces of ‘Golden

Beauty’ casaba melon at University of California Desert Research and Extension Center.

Fungicide trade name,

formulation and ratez Leaf surface with powdery mildew (%)

2001 2002 2003 2004 2005

Flint 50WDG 2 oz/ac 0.7

c 48.8

b 0.7

c 48.8

b 28.8

ab

Quadris 2.08F 15.4 fl oz/ac 14.7

b 41.2

b

14.7

b 41.2

b 20.0

bc

Cabrio EG 1 lb/ac 17.0 b 48.8 b 17.0 b 48.8 b 17.6 bc

Procure 50WS 8 oz/ac 0.7 c 3.6 e 0.7 c 3.6 e 7.6 cd

Rally 40W 112 4.0 oz/ac with

Latron CS7 0.06% by vol. 7.0

bc 12.8

d 7.0

bc 12.8

d 10.6

cd

Topsin M 70W 8 oz/ac 12.3

b 25.2

c 12.3

b 25.2

c 20.0

bc

Quintec 6.0 fl oz/acx 3.0 bc 2.0 e 3.0 bc 2.0 e 6.2 d

Microthiol Special 80W 6.0 lbs/ac 11.7

b 18.8

cd 11.7

b 18.8

cd 12.4

cd

Untreated 57.7 a 67.2 a 57.7 a 67.2 a 41.6 a z All materials were applied in the equivalent of 30 gallons of water per acre with a CO2-pressurized backpack sprayer at

30 psi. Materials were applied at 10-day intervals. y Arcsine transformed data was subjected to analysis of variance. Means followed by the same letter within a column do

not differ significantly as determined by Student-Newman-Keul’s Multiple Range Test on transformed data (P≤0.05). Non-

transformed means are presented. x Quintec is not currently registered for use in California

1. McCreight, J.D., M.D. Coffey, T.A. Turini and M. E. Matheron. 2005. Field evidence for a new race of powdery mildew

on melon. HortScience. 40.

Irrigation & Crop Growth –Timing Is Everything

Ag Briefs – May, 2006 3

Rick Bottoms Ph.D.

Water is often the most limiting factor in

plant growth and yield. However, certain

stages of growth are more sensitive to even

slight water stresses than others. Subjecting

corn plants to any water stress at critical

periods in the plant's life cycle can severely

reduce yields and those times are long

before ears are visible.

Knowledge of these particularly sensitive

growth stages and evaporation transpiration

Ag Briefs – May, 2006 4

(ET) rates during these growth periods can

be helpful when deciding whether to irrigate

or delay for a few days. Research conducted

at the University of California and other

universities around the county have

identified these most critical times.

Corn growth stages until tasseling are

identified by leaf number (i.e. V1 to V18).

Each leaf is counted when the leaf collar is

fully exposed. At growth stage V9, the

potential kernel row number is being

determined, that is the thickness of the ear.

Corn plants at this stage may be only 4 feet

tall but avoiding water stress at this time is

most critical. At growth stage V12 through

V17, the length of the ear is being

determined. Any growth limiting stress at

this time will reduce yield. The largest yield

reduction from water stress occurs from

tasseling to 2 weeks after silking,

approximately 65-75 days after planting in

corn and 45-70 days after planting for

sorghum during the critical boot through

bloom stage. Plants can use up to 1/3 of an

inch of water a day during those critical

growth periods. No amount of additional

water can compensate for moisture stress

that occurs during these critical growth

periods.

Generally, the ET requirements during the

most sensitive growth stages are similar for

the various crops and range between 0.22 -

0.28” (0.56 to 0.71 cm) and .20 - 0.25” (0.51

to 0.64 cm) per day for corn and sorghum,

respectively.

For grain crops, yield is determined by both

the total number of seeds produced and by

the weight of each seed. Thus, any stress,

which causes a reduction in either the

number of seeds produced or the weight per

seed will result in yield reductions. Growth

stages, which are most sensitive to water

stresses, are usually the growth stages

during which either seed numbers or seed

weights are being established. Crop yield is

generally less impacted by water stress if the

stress occurs before the reproductive stages

of growth.

When considering late-planted corn

additional stress can be critical to irrigation

management. The growing point remains

under the soil surface until growth stage V6.

Around growth stage V3, excess water

(flooding) can kill the growing tip in a few

days especially when temperatures are high.

Inadequate moisture during any period of

growth can result in reduced grain yield.

Nutrient availability, uptake, and transport

are impaired without sufficient water. Plants

weakened by stress are also more

susceptible to disease and insects. Severe

moisture stress is indicated by leaf wilting

that is alleviated only when the plants

receive additional water.

Four consecutive days of visible wilting can

reduce potential corn yield by 5 to 10%

during the vegetative growth stage. In

addition, during silking and pollination,

yield reduction after four consecutive days

of wilting can be as much as 40 to 50% (see

Table 1). Moisture stress during this period

can result in a lack of synchronization

between pollen shed and silking at

pollination, because pollen grains may not

remain viable and silking may be delayed.

Table 1. Effects of Drought on Corn Yield. Stage of Percent yield development reduction* ----------------------------------------- Early vegetative 5-10 Tassel emergence 10-25 Silk emergence, 40-50 pollen shedding Blister 30-40 Dough 20-30 ---------------------------------------- Source: Classen, M.M , and R.H.. Shaw. l97C. Water deficit effects on corn. II. Grain components Agron J 62:652-655. Careful irrigation management is essential for optimum yields. This is especially critical in our warm

growing region. To help in irrigation scheduling, crop water use tables and actual evapotranspiration

rates contact Dr. Khalid Bali, Farm Advisor at the Imperial - UC Cooperative Extension office or on-

line at www.cimis.water.ca.gov. Remember -Timing is everything.

INSECTICIDE EFFICACY AGAINST WORM PESTS IN ALFALFA

Eric T. Natwick

Insecticide efficacy studies for control of worm

pests in alfalfa were conducted during the

summer of 2004 and 2005 at the UC Desert

Research and Extension Center. A stand of

alfalfa, VAR. CUF 101, was used for both

experiments and plots were arranged in a

randomized complete block design with four

replications. In 2004, six insecticide treatments

were compared to an untreated control for

efficacy against beet armyworm, alfalfa

caterpillar and alfalfa looper. In 2005, six

insecticide treatments were compared to an

untreated control for efficacy against beet

armyworm, alfalfa caterpillar and alfalfa

webworm. Insecticide treatments and rates

fluid ounces or pounds of formulated product

per acre for are listed in Table 1 for 2004

(Spinosad, XDE-175 a spinosyn insecticide

under development and Lorsban 4E all from

Dow AgroSciences LLC; and Warrior an

insecticide from Syngenta Crop Protection

Inc.) and in Table 2 for 2005 (Intrepid 2SC,

Ag Briefs – May, 2006 5

Success, XDE-175 which is a spinosyn

insecticide under development and Lockon-

2EC all from Dow AgroSciences LLC; and

Steward an insecticide from DuPont

Agriculture and Nutrition). In 2004, plots

measured 35 feet by 50 feet and insecticide

treatments were broadcast applied September 2

using a tractor mounted spray boom with 19 X

TJ-60 11003VS nozzles at 20 psi delivering 29

gpa. In 2005, plots measured 13.3 feet by 50

feet and insecticide treatments were broadcast

applied July 28 using a tractor mounted spray

boom with 12 X TJ-60 11003VS nozzles at 35

psi delivering 47 gpa. Worm pest populations

were measured in each plot each year using a

standard 15 inch diameter insect sweep net

consisting of ten 180o sweeps 1, 5, 7, 14 and 21

days after treatment in 2004 and 1 day pre-

treatment and 1, 4, 7, and 14 days after

treatment in 2005.

In both 2004 and 2005, all insecticide

treatments controlled beet armyworm with post

treatment means that were significantly less

than the untreated control (LSD, P<0.05)

(Table 1 and 4). In 2004, Warrior had a beet

armyworm post treatment mean that was

significantly higher than that of any other

insecticide treatment and XDE-175 at 0.045 oz

per acre had significantly fewer beet

armyworms than both Lorsban and Warrior. In

2005, Success and XDE-175 had post treatment

means for beet armyworms that were

significantly lower that the mean for Lockon-

2EC.

Ag Briefs – May, 2006 6

In both 2004 and 2005 all insecticide

treatments controlled alfalfa caterpillars with

post treatment means that were significantly

less than the untreated control (LSD, P<0.05)

(Table 2 and 5) but there were no differences

among the insecticide treatments. In 2004, all

insecticide treatments controlled alfalfa loopers

with post treatment means that were

significantly less than the untreated control

(LSD, P<0.05) (Table 3) but there were no

differences among the insecticide treatments.

In 2005, all insecticide treatments controlled

alfalfa webworms with post treatment means

that were significantly less than the untreated

control (LSD, P<0.05) (Table 6) but there were

no differences among the insecticide

treatments.

XDE-175 is a spinosyn insecticide under

development by Dow AgroSciences LLC that

has is similar to spinosad (Success). This new

chemistry provided control of worm pests in

alfalfa at levels similar or superior to worm

control insecticides registered for use on alfalfa

in both experiments.

Ag Briefs – May, 2006 7

Table 1. Numbersw of Beet Armyworms per Ten Sweeps in Alfalfa, Holtville, CA, 2004.

Treatment oz/acre 1 DATxy 5 DATy 7 DAT 14 DAT 21 DATy PTMyz

Check --------- 150.25 a 66.75 a 70.25 a 15.50 a 4.00 a 61.35 a

*Spinosad 0.09 12.75 bcd 0.25 c 1.00 c 1.25 c 0.00 b 3.05 de

*XDE-175 0.09 21.50 b 2.50 bc 0.00 c 0.00 c 0.00 b 4.80 cd

XDE-175 0.045 9.5 cd 1.50 c 0.25 c 0.25 c 0.00 b 2.30 e

XDE-175 0.022 7.75 d 7.50 bc 0.25 c 0.25 c 0.00 b 3.15 de

Warrior 0.03 98.25 a 19.75 b 15.25 b 6.25 b 1.50 b 28.20 b

Lorsban 4E 1.0 18.75 bc 4.50 bc 4.00 c 9.75 b 0.75 b 7.55 c w Mean separations within columns by LSD0.05. x Days after treatment. y Log transformed data used for analysis; actual means reported. z Post treatment mean. *Not registered for use on alfalfa at the time of this publication. Table 2. Mean Numbersx of Alfalfa Caterpillar per Ten Sweeps in Alfalfa, Holtville, CA, 2004.

Treatment oz/acre 1 DATy 5 DAT 7 DAT 14 DAT 21 DATy PTMz

Check --------- 14.25 a 4.75 a 3.25 a 1.00 a 0.25 a 4.70 a

*Spinosad 0.09 1.50 b 0.25 b 0.00 b 0.00 b 0.25 a 0.40 b

*XDE-175 0.09 3.50 b 0.00 b 0.00 b 0.00 b 0.00 a 0.70 b

XDE-175 0.045 1.50 b 0.00 b 0.25 b 0.00 b 0.00 a 0.35 b

XDE-175 0.022 0.00 b 1.25 b 0.00 b 0.00 b 0.00 a 0.25 b

Warrior 0.03 1.75 b 0.75 b 0.75 b 0.50 ab 0.00 a 0.75 b

Lorsban 4E 1.0 5.50 b 1.25 b 0.25 b 0.25 b 0.00 a 1.45 b x Mean separations within columns by LSD0.05. y Days after treatment z Post treatment mean. *Not registered for use on alfalfa at the time of this publication.

Ag Briefs – May, 2006 8

Table 3. Mean Numbersx of Alfalfa Looper per Ten Sweeps in Alfalfa, Holtville, CA, 2004.

Treatment oz/acre 1 DATy 5 DAT 7 DAT 14 DAT 21 DATy PTMz

Check --------- 4.75 a 4.00 a 2.50 a 2.00 a 0.25 a 2.70 a

*Spinosad 0.09 0.00 b 0.00 b 0.00 b 0.00 b 0.00 a 0.00 b

*XDE-175 0.09 1.50 b 0.00 b 0.00 b 0.25 b 0.00 a 0.35 b

XDE-175 0.045 1.25 b 0.00 b 0.00 b 0.00 b 0.00 a 0.25 b

XDE-175 0.022 0.00 b 1.00 b 0.00 b 0.00 b 0.00 a 0.20 b

Warrior 0.03 4.75 a 0.00 b 0.00 b 1.00 ab 0.00 a 1.15 b

Lorsban 4E 1.0 2.25 ab 0.50 b 0.00 b 0.75 ab 0.00 a 0.70 b x Mean separations within columns by LSD0.05. y Days after treatment z Post treatment mean. *Not registered for use on alfalfa at the time of this publication. Table 4. Numbersv of Beet Armyworms per Ten Sweeps in Alfalfa, Holtville, CA, 2005.

Treatment oz/acre 1 DPTw 1 DATx 4 DAT 7 DAT 14 DATy PTMz

Check --------- 5.25 a 2.00 a 2.00 a 5.75 a 2.50 a 3.06 a

*Intrepid 2SC 6.0 3.75 a 0.75 a 0.00 b 0.25 bc 0.00 d 0.25 bc

Intrepid 2SC 8.0 3.50 a 1.75 a 0.00 b 0.00 c 0.75 bc 0.63 bc

*Success 6.0 6.25 a 0.25 a 0.00 b 0.00 c 0.00 d 0.06 c

*XDE-175 5.8 2.25 a 0.25 a 0.00 b 0.25 bc 0.25 cd 0.19 c

Lockon-2EC 32.0 2.75 a 1.25 a 0.25 b 0.75 b 1.00 b 0.81 b

Steward 6.7 3.25 a 0.50 a 0.25 b 0.50 bc 0.00 d 0.31 bc v Mean separations within columns by LSD0.05. w Days Pre-treatment. x Days after treatment. y Log transformed data used for analysis; actual means reported. z Post treatment mean. *Not registered for use on alfalfa at the time of this publication.

Ag Briefs – May, 2006 9

Table 5. Mean Numbersw of Alfalfa Caterpillar per Ten Sweeps in Alfalfa, Holtville, CA, 2005.

Treatment oz/acre 1 DPTx 1 DATy 4 DAT 7 DAT 14 DAT 1 DPTz

Check --------- 4.00 a 3.00 a 4.25 a 6.00 a 3.50 a 4.19 a

*Intrepid 2SC 6.0 2.75 a 0.75 a 0.00 b 0.00 b 0.25 b 0.25 b

Intrepid 2SC 8.0 3.75 a 0.25 a 0.25 b 0.00 b 0.00 b 0.13 b

*Success 6.0 4.75 a 0.50 a 0.00 b 0.00 b 0.00 b 0.13 b

*XDE-175 5.8 4.25 a 0.50 a 0.00 b 0.00 b 0.25 b 0.19 b

Lockon-2EC 32.0 3.75 a 0.25 a 0.00 b 0.00 b 0.00 b 0.06 b

Steward 6.7 2.50 a 0.25 a 0.00 b 0.00 b 0.25 b 0.13 b w Mean separations within columns by LSD0.05. x Days Pre-treatment. y Days after treatment. z Post treatment mean. *Not registered for use on alfalfa at the time of this publication. Table 6. Mean Numbersw of Alfalfa Webworms per Ten Sweeps in Alfalfa, Holtville, CA, 2005.

Treatment oz/acre 1 DPTx 1 DATy 4 DAT 7 DAT 14 DAT 1 DPTz

Check --------- 4.00 a 1.00 a 3.25 a 3.50 a 3.50 a 2.81 a

*Intrepid 2SC 6.0 1.75 a 0.50 a 0.00 b 0.50 b 0.50 b 0.38 b

Intrepid 2SC 8.0 3.00 a 0.25 a 0.00 b 0.00 b 0.25 b 0.13 b

*Success 6.0 2.50 a 0.25 a 0.50 b 0.50 b 0.25 b 0.38 b

*XDE-175 5.8 2.75 a 0.25 a 0.00 b 0.50 b 0.00 b 0.19 b

Lockon-2EC 32.0 2.75 a 0.50 a 0.00 b 0.00 b 0.00 b 0.13 b

Steward 6.7 2.00 a 0.00 a 0.00 b 0.00 b 0.25 b 0.06 b w Mean separations within columns by LSD0.05. x Days Pre-treatment. y Days after treatment. z Post treatment mean. *Not registered for use on alfalfa at the time of this publication.

Baling Recommendations Juan N. Guerrero

From March through June, about ⅓ of the year,

about 40 to 45% of the annual alfalfa hay

tonnage is baled in the desert southwest.

During this extremely busy time of year, it is

important to remember the principles of good

hay making.

1. Time of Day – Theoretically afternoon

swathing should yield the highest quality hay.

During the day plant carbohydrates accumulate

in the plant and these same carbohydrates are

respired at night. Swathing in the afternoon

will maximize soluble carbohydrates in the

plant, decrease the NDF% (very good), and

increase the hay quality test. However, during

this very busy time of year it is often difficult

to only swath in the afternoon. Changing

swathing schedules from 11AM to 7PM might

do the trick, if feasible.

2. Wide Swaths – Wide swaths promote faster

drying rates.

3. Raking – Raking at 40 to 50% hay moisture

is recommended. Raking increases the drying

rate. Raking at 50% moisture will result in only

a 3% loss in dry matter and only a 5% loss in

leaves. Raking at 20% moisture will result in

dry matter losses of about 12% and leaf loss of

about 21%! Raking at 20 to 25% moisture can

be tragic.

Ag Briefs – May, 2006 10

4. Bale Moisture – As the year progresses, the

baling window in the day decreases. During

June and July, there may be only enough

atmospheric moisture that hay baling is only

possible for several hours in the early morning.

Bale moisture monitoring meters are available

that read bale moisture in the baling chamber

of the baler. Theoretically, alfalfa hay should

be baled at 14 to 18% moisture. Baling at

higher than 20% moisture might result in

moldy bales. Baling at lower than 12%

moisture results in leaf loss, lower quality hay,

and hay that becomes very brittle. Baling hay at

the appropriate moisture (14 to 18%) with

plenty of leaves means little if it stored

roadside for several months. Untarped hay over

four months can shrink down to 5% moisture

by the end of September. Tarping hay during

summer roadside storage will retard hay shrink,

enough to pay the tarp bill.

Current hay prices are relatively high now, so

maintaining and protecting hay quality is cost

effective. However, increased fuel prices have

increased production costs, even more reason

to sell the highest quality hay possible.

CIMIS REPORT Khaled Bali and Steve Burch* California Irrigation Management Information System (CIMIS) is a statewide network operated by California Department of Water Resources. Estimates of the daily reference evapotranspiration (ETo) for the period of May 1 to July 31 for three locations in the Imperial County are presented in Table 1. ET of a particular crop can be estimated by multiplying ETo by crop coefficients. For more information about ET and crop coefficients, contact the UC Imperial County Cooperative Extension Office (352-9474) or the IID, Irrigation Management Unit (339-9082). Please feel free to call us if you need additional weather information, or check the latest weather data on the worldwide web (visit http://tmdl.ucdavis.edu and click on the CIMIS link). Table 1.Estimates of daily Evapotranspiration (ETo) in inches per day

May

June

July

Station 1-15

16-31

1-15

15-30

1-15

16-31

Calipatria

0.32

0.36

0.39

0.40

0.39

0.38

El Centro (Seeley)

0.31

0.34

0.36

0.38

0.38

0.37

Holtville (Meloland)

0.32

0.35

0.38

0.39

0.39

0.38

* Irrigation Management Unit, Imperial Irrigation District.

Ag Briefs – May, 2006 11