Measuring Weather
Issues for Pesticide Applicators
Part 2 by Linda S. Wiles
Penn State Extension Educator

Long-term (seasonal) – to schedule crop species, cultivars
Short-term (8-14 day, 6-10 day, 3-7 day) – to schedule irrigation, maintenance, pesticide applications
See NOAA www.cpc.ncep.noaa.gov/products/forecasts

• 6-10 Day Forecast
• To schedule irrigation, fertilization, and chemical application
• Recommended by Hu and Hubbard from
University of Nebraska

Temperature –
77

Fahrenheit 25

Celsius 298.15

Kelvin
Wind Speed –
9 mph 7.82 kt 4.02 m/s 14.48 km/h 13.2 ft/s
3 Beaufort
Pressure –
29 inch mercury 982.05 milllibars 0.97 atmospheres
98205.25 pascals 982.05 hectopascals 1001.41 gm/sq.cm.
736.6 mm mercury 14.24 lb/sq.in

Order of Weather Measurements
1 st - Wind Direction
2 nd - Wind Speed

• Use compass to find magnetic direction
- where wind comes from
• Avoid steel objects while measuring
- they may cause false readings
• Use compass reading in degrees
- not just N, S, etc.

Compass Wind Direction Reading
• Face the wind
• Measure in degrees
• Automatic calculation

270

TO 360

NORTH
0

TO 90

WEST
270

180

TO 270

YOUR
LOCATION
SOUTH
180

EAST
90

90

TO 180


Wind Speed Recording Tips
• Hold unit so that it faces the wind
• Measure for several seconds
• Record at estimated height of spray (if possible)
• Wind speeds increase with higher altitudes

• Check accuracy prior to field use
• Protect from excess heat or cold (don’t leave in a vehicle)
• Keep away from magnetic fields
- belt buckles, knives, magnets, etc.

Current Average Maximum
• Current – check for gusts
• Average – evens out gusts + calm – time based
• Maximum – highlights problems - time based

• Measure temperature at time of application
• Avoid spraying in hot temperatures
– Esp. in high humidity
– If you must, use larger spray droplet size and lower equipment pressure

Hand-held Temperature Reading
• 
F air temperature in shade
• Height of unit
• Some include min/max

Relative
Absolute
RealFeel Temperature
 patented Accuweather.com
 index

Hand-held Humidity RH Reading
• % moisture of air in shade
• At high temperatures, air can hold more moisture
• RELATIVE measure

Enter T and Dew Point in

F or

C
72

F and 69

F Dew Point

90.31% RH

Wind Speed + Temperature + Humidity
↓
Wind Chill
Heat Index
Dew Point

• Measured in 
F
• = temperature
– >45 
F
– <3 mph
• Defined by
US National Weather Service

• Define: combines temperature + wind
Where:
T = air temperature in

F, < 70

F
V= wind speed in mph data at 5 ft. height, clear night

• How to calculate
Formula for WC (

F)
=
35.74 + 0.6215T – 35.75 (V 0.16
) + 0.4275T (V 0.16
) includes modern heat transfer theory

• Why important
Personal - Frostbite
Plants - Frost Pockets

• In 30 minutes with calm wind at -5

F
• In 10 minutes with 35 mph wind
• In 5 minutes with 45 mph wind at 0 to -5

F at -15

F

• Close to ground level, cold air trapped in low areas – possible 15 °F lower than higher ground
• Hand-held meters can track winter air inversions
• Cold weather protections can be implemented
• Reduced damage to fruit and landscape plants
Caplan, 1988

• 
F air temperature in shade
• = air temperature
< 70

F
• Human comfort measure

• Define: combines temperature + humidity
Where:
T in

F = ambient dry bulb temperature
R = % RH
[Canada’s Humidex uses dew point in 
K]

• How to calculate
Formula for HI (

F)
=
-42.379 + 2.04901523T +10.14333127R –
0.22475541TR – 6.83783 x 10 -3 T 2 – 5.481717 x 10 -2 R 2 +
1.22874 x 10 -3 T+R + 8.5282 x 10 -4 TR 2 – 1.99 x 10 -4 T 2 R 2
Multiple Regression Formula with +1.3

F; R.G.
Steadman, 1979

• Why important
Personal – Heat Disorders
Plants – Increased Phytotoxicity

Heat Index Physical Response
80-90

F
90-105

F
Lethargy
Sunstroke, Heat Cramps, Heat Exhaustion
105-130

F Above, + possible Heat Stroke
130

F+ Above, + likely Heat Stroke
If DIRECT SUN, add 15

F to HI

Likelihood of Heat Disorders -
NOAA
• Caution T > 80

F; any % RH
• Extreme Caution
-T = 82

F; 90% RH
-T = 90

F; 40% RH
• Danger
-T = 86

F; 90% RH
-T = 98

F; 40% RH
• Extreme Danger
-T = 90

F; 95% RH

• 
F air temperature in shade
• DP ~ T humid
• DP = T dew forms
• DP = T <32 
F, frost forms

• Define: combines temperature + humidity
Where:
T in

F = ambient dry bulb temperature
R = % RH
[Canada’s Humidex uses dew point in 
K]

• How to calculate
Formula for TD (

F)
Set x = (1 — 0.01 RH) where RH is expressed as a number from 1 to 100.
Set T as temperature in

C
DPD is the difference between the temperature and dew point in

C
TD is the dew point temperature
DPD = (14.55 + 0.114T)x + ((2.5 + 0.007T)x) to the third power + (15.9 +
0.117T)x to the 14th power
TD [

C] = T — DPD.
TD [

F] = (TD [

C] × 9/5) + 32
Formula from Bill Murrell, Meteorologist, http://www.srh.noaa.gov/shv/Past_Questions_THREE.htm

• Why important
Personal – more accurate estimate of human comfort than RH
Plants – indicator for dew still present, disease issues

IF full-coverage needed, as for contact herbicides, fungicides or nonsystemic fungicides,
THEN drift-resistant fan nozzles are not suitable.

• 25-30°F or more night/day temperature difference
• Clear skies + Calm winds previous night
• Seasonally common spring and fall, possible year-round
MA Dept Ag, 2003

Weather conditions at the time of application should be listed on the pesticide application records.

90
80
70
60
50
40
30
20
10
0
9:0
0
A
M
10
:0
0
A
M
11
:0
0
A
M
12
:0
0
PM
1:0
0
PM
2:0
0
PM
3:0
0
PM
4:0
0
PM
5:0
0
PM
Temperature
Humidity
Wind

90
80
70
60
50
40
30
20
10
0
9:0
0
A
M
10
:0
0
A
M
11
:0
0
A
M
12
:0
0
PM
1:0
0
PM
2:0
0
PM
3:0
0
PM
4:0
0
PM
5:0
0
PM
Temperature
Humidity
Wind

100
90
80
70
60
50
40
30
20
10
0
9:0
0
A
M
10
:0
0
A
M
11
:0
0
A
M
12
:0
0
PM
1:0
0
PM
2:0
0
PM
3:0
0
PM
4:0
0
PM
5:0
0
PM
Temperature
Humidity
Wind

• 9 mph
• 15-16 mph
• 25 mph

3 Major Nozzle Patterns
• Hollow or Full Cone Spray
• Flat Fan Spray
• Solid Stream Spray

0 mph
• Highly diffuse spray pattern at 0 mph
• High potential for spray drift
5 mph
0 mph post-app

5 mph
5 mph
13 mph

• Use for – shrubs + bushes
• Rounded ring pattern
• Finely atomized spray
• Post-emergent herbicides, contact fungicides and insecticides

• Full Cone makes a filled in circle pattern
• Primarily for broadcast spraying
• Some banded applications

5 mph
13 mph
5 mph post-app

Flat Fan Spray – Post Application
0 mph
0 mph
9 mph
13 mph
13 mph

• Use for row treatment, systemic applications
• Pattern is elliptical inverted V
• Variations
– Extended range – use for more pressures
– Flooding – uses larger droplets
– Even – non-tapered for band application

0 mph
0 mph
5 mph
5 mph
9 mph 13 mph

• Use for spot and long range
• Common for application of liquid fertilizer

Diverts chemical from target
→ Reduces effectiveness
Deposits pesticide where not needed or wanted
→ Injury to susceptible vegetation
→ Harm to wildlife
→ Deposition of illegal residues on crops
→ Contamination of water supplies

Vapo r
Drift
Vapo r
Drift
Center of
Target
Target
Edges
Spray Drift
Beyond
Target
Vapo r
Drift
Vapo r
Drift

• Incorporate chemicals into the soil
• If very hot, select pesticide with strong sorption and low vapor pressure
• Irrigation to buffer weather effects
Joern & Lohman, Purdue

INVISIBLE!!
Can predict likelihood for specific pesticides
• higher vapor pressure numbers
(MSDS sheet)
• higher volatility
• vapor drift

• Use larger spray droplets
• Fine to medium soil
• Wet soil

• How far from application site
– If windy
– If extreme heat
– If extreme humidity
– Other

Both affected by irrigation or rainfall amount & timing relative to pesticide application.
Avoidable by monitoring weather

During After
• Record weather conditions DURING application
• Record weather conditions AFTER application

Before During After
Wind Speed 0-3.6 mph 0-13 mph 0-6 mph
Air Temp 82.9
Wind Chill 82.3
84.1
84.2
85.2
85.4
RH 79.7
Heat Index 91.4
Dew Point 778.2
59.4
89.2
67.8
70.4
94.0
67.0-67.8

1. Minimize pesticide in non-target areas
2. Minimize pesticide loss
3. Minimize exposure to operators or bystanders

1. Minimize pesticide in non-target areas

Reduce possible injury to wildlife
Reduce possible injury to sensitive crops
[from contaminated water]

2. Minimize pesticide loss

To ↑ pest control
To ↓ costs

3. Minimize exposure to operators or bystanders

Health problems ↓
↓ Liability issues

4. Minimize damage to beneficial insects
 organic/natural control maintained


Fewer pesticide applications needed

• “Studies have shown that the equipment and its operation are responsible for 68-
90% of the physical drift problems, while weather accounts for 1032%.” quote from D.B. Smith 1982,
Fate of Pesticides in the Environment, in “What Happens to the
Pesticides We Apply?”, Commercial Pesticide Applicator Exam
Preparation Class, Laura Pottorff, Colorado State University,
Adams County

• Temperature and precipitation
• Plants are affected
• Plants can alter these
Noah Diffenbaugh, Purdue University,
May 2005, Geophysical Research
Letters (Live Science)

Possible Now –
Improved Local Weather Forecasts
• Weather Forecast Model
• + Photosynthesis/Transpiration Vegetation Model
•
+ Improved soil moisture mapping
• = Temperature, Humidity and Thunderstorm Predictions
Yields 5 to 50% greater accuracy
Dev Niyogi, Purdue University, March 2006 (Live Science)

Future - Fine-Tuning Effects of
Solar Radiation
Effects: physical properties of pesticides biophysical processes of organisms
Controlled by: sun’s angle day length cloudiness
Rozenzweig, et al

Hand-held Devices ($6 -$700)
↓
↓
↓
Sophisticated Computerized Logging
Devices ($160 - $1,500)

•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Climate Change and U.S. Agriculture: The Impacts of Warming and Extreme Weather Events on Productivity, Plant Diseases and Pests, by Cynthia
Rosenzweig, et. al, Harvard Medical School Center for Health and the Global Environment
“Climate Predictions: How to Interpret and Use Them,” by Q. Steven Hu and Kevin Hubbard, University of Nebraska-Lincoln Extension
Noah Diffenbaugh, Purdue University, May 2005, Geophysical Research Letters (Live Science)
“Effects of Cold Weather on Horticultural Plants in Indiana,” Larry A. Caplan, Vanderburgh County Horticulture Agent, December 1988
Fate of Pesticides in the Environment, in “What Happens to the Pesticides We Apply?”, Commercial Pesticide Applicator Exam Preparation Class, Laura
Pottorff, Colorado State University, Adams County
“Instrumentation to Document Environmental Conditions during Pesticide Applications,” by Robert Wolf and Patricia A. Hipkins, Kansas State and
Virginia Tech
Dev Niyogi, Purdue University, March 2006 (Live Science)
“Pesticides and the Environment,” Brad Joern and Becky Lohman, Purdue Pesticide Programs
Predicted Effects of Climate Change on Agriculture: A Comparison of Temperate and Tropical Regions, by Cynthia Rosenzweig and Diane Liverman
“Predicting the Weather,” United States Search and Rescue Task Force
“Thermal Inversions,” MA Dept. of Ag Resources, Pesticide Bureau Technical Information Bulletin, May 2003 Version
“What happens to the Pesticides We Apply?”, Commercial Pesticide Applicator Exam Preparation Class, Laura Pottorff, Colorado State University,
Adams County
Beaufort Wind Scale http://www.spc.noaa.gov/faq/tornado/beaufort.html
Brunton A,B,C,D Compass System Instructions
EPA “In Case of Pesticide Poisoning”
EXTOXNET http://extoxnet.orst.edu/pips/ghindex.html
Kestrel

3000 Pocket Weather Meter instructions www.nkhome.com
NOAA National Climactic Data Center http://www.ncdc.noaa.gov/oa/ncdc.html
NOAA Calculators http://www.crh.noaa.gov/gid/?n=wxcalc
Penn State Core Pesticide Manual
Plymouth State University http://vortexplymouth.edu/
Solo
 Operator’s Manual and Parts List www.solousa.com
TeeJet
 “A User’s Guide to Spray Nozzles
University of Illinois www2010.atmos.uiuc.edu
Radio http://www.findradio.us/displaystate-PA.htm
Television http://www.globalcomputing.com/GetTV_Map1.cfm?stateid=PA
Web Site www.weather.com www.accuweather.com
Airport http://www.fly.faa.gov/flyfaa/nemap.jsp

Grant support for program development from Penn State Pesticide Education
Assistance by Michael Wiles
Review by Karen Wilkins, Jeanne Dunstane, Katharine Kresge
Concept, PowerPoint text, charts, diagrams, photos and design by Linda Wiles, July 31, 2007
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
Penn State is committed to affirmative action, equal opportunity, and the diversity of its workforce.

Thank You
& Enjoy this Summer Evening