Great Lakes Fruit, Vegetable & Farm Market EXPO Michigan Greenhouse Growers EXPO

December 4-6, 2012

DeVos Place Convention Center, Grand Rapids, MI

Weather Risk Management in Tree Fruit

Where: Ballroom D

MI Recertification credits: 2 (1C, COMM CORE, PRIV CORE)

CCA Credits: CM(2.0)

Moderator: Steve Thome, MSHS Board, Comstock Park, MI

9:00 am Reflections on a Growing Season: Weather extremes, climate trends, and some

implications for tree fruit production in the Great Lakes region

Jeff Andresen, Geography Dept., MSU

9:30 am How to Best Use Frost Protection Methods in Tree Fruit

Robert Evans, USDA Northern Plains Ag Research Lab, Sidney, MT

10:00 am Frost Protection Methods in Michigan – Costs and Considerations

Amy Irish-Brown, Tree Fruit IPM Educator, MSU Extension

10:20 am MSU Enviro-weather: Decision-making tools for weather risks

Beth Bishop, Enviro-weather Coordinator, Entomology Dept., MSU

10:40 am Calibration of Personal Weather Data Loggers and What to Do with the Data Once You

Have It

Julianna Wilson, Tree Fruit IPM Outreach Specialist, Entomology Dept., MSU

11:00 am Session Ends

2012: A Year of Weather Extremes in the Great Lakes Region

Jeff Andresen, Dept. of Geography, Michigan State University 673 Auditorium Road, East Lansing, MI 48824

Email: andresen@msu.edu Phone: 517.432.4756

Weather conditions during 2012 across the Great Lakes region were heavily influenced by a series of

extremes, ranging from record warm temperatures to severe drought conditions to flooding. The unusual

weather presented serious challenges to many agricultural activities across the region. The 2012 growing

season was preceded by an unusually mild winter across Michigan and the Great Lakes region, with mean

temperatures during the December through February period generally ranging from 4-8°F above normal.

The winter of 2011-2012 was marked by 5 consecutive months of above normal temperatures back to

October of 2011, below normal seasonal snowfall totals, and much above normal extreme coldest

minimum temperatures. While the relatively mild conditions resulted in relatively less winter/cold

damage for overwintering crops, it also allowed a higher survival rate of some insect and disease

pathogens that typically succumb to low temperatures during the season.

Perennial and overwintering annual crops in the region emerged from their protective dormant states

much earlier than normal in 2012 due to an unprecedented heat wave during the middle of March. The

March 2012 heat wave began in earnest on the 11th and continued through the 23

rd of the month. The

event was associated with a massive subtropical upper air ridge across central and eastern North America

which led to strong southerly low level winds across the region and the transport of tropical-origin air

northward from the Gulf Coast region. A representative plot of daily temperatures at a site in

southwestern Michigan during the event is given in Figure 1. At its peak during the third week of March,

daily mean temperatures soared to 30-40°F above normal and observed minimum temperatures exceeded

the normal maximum temperatures by more than 10°F. The heat wave resulted in many new climate

records across the region. In Michigan, these included the warmest March ever for the state as a whole

with a mean temperature of 44.4°F, which was 13.7˚F warmer than normal and 3.2˚F warmer than the

previous record (1945). A new all-time state record for warmest temperature ever in March was also set,

with 90˚F at Lapeer on the 21st. Growing degree day accumulations surged during the second and third

weeks of March in response to the heat wave, quickly surpassing the levels of all other warm Marches

including the (previous) 1945 record.

In terms of impacts, the heat wave led to rapid early growth and development of crops across the region.

Rapid plant growth continued as highs rose through the 80’s and warm nighttime temperatures in the 50’s

and 60’s allowed plants to grow both day and night. By late March, phenological development stages of

most crops were at least 4 weeks ahead of normal, leaving them vulnerable to injury from freezing

temperatures. Unfortunately, no location in the Upper Midwest has ever experienced an abnormally warm

March which has not been followed by freezing temperatures during April, May, or June. On the 24th and

25th of March, the upper air jet stream pattern that produced the heat wave broke down and was replaced

by a troughing pattern across the North Central USA which led to the passage of a cold, dry Canadian air

mass through the region and freezing temperatures over most areas on the mornings of March 26th and

27th. Following the late March upper air pattern change, more than 15 freeze events (including at least 5

with minimums below 28˚F) occurred across the region, which is climatologically greater than normal.

Some of the freezes were of the advective variety in which subfreezing temperatures were accompanied

by surface winds accentuating the magnitude of cold injury and causing fan-based frost protection

equipment to be much less effective than is normally the case. Crop damage from the freezes in late

March and April 2012 was significant across the region, especially to tree fruit.

Figure 1. Daily observed maximum (top/red) and minimum (bottom/blue) temperatures (°F) at the

Bainbridge Center, MI Enviroweather automated weather station, March 1st – April 30

th, 2012.

Climatological normal maximum, mean, and minimum temperatures (1981-2010) are provided in gray

and black for comparison. The 28°F line (black) is given for reference as it typically serves as an upper

threshold for significant cold damage in tree fruit at and following bloom.

Following relatively normal weather in late April and early May, a large upper air ridge of high pressure

developed across the center of North America and persisted for much of June and July into early August.

This feature led to persistent hot and dry weather across large portions of the Midwest and adjoining

regions. As of early August, 3-month precipitation deficits ranged from 1-3” over central sections of the

Great Lakes region to more than 6” across southern sections (Figure 2). Normal rainfall for this area is on

the order of 8-11 inches and the time frame is usually among the wettest 3-month periods of the year.

Plant available soil moisture levels in the top 5’ of the soil profile of impacted areas during the same

period fell to levels generally 1-5” below normal. The unusually dry conditions led to rapid use of soil

moisture reserves and ultimately to water stress in many unirrigated crops. The Great Lakes region

remained along the northern periphery of a much larger area of abnormally dry conditions stretching

across eastern and central sections of the CornBelt to the Lower Mississippi River Valley and westward to

the Rockies. At that peak time of the drought, 81% of the Midwest region was classified as ‘Abnormally

Dry’ with over 69% experiencing some level of drought conditions. In more than 38% of the region, the

drought conditions were characterized by the U.S. Drought Monitor as ‘Severe’ or ‘Exceptional’. In

sections of the Ohio Valley into the southern Great Lakes region, the dryness was as intense as that

recorded in 1988, the last major region-wide drought. In contrast, rainfall across northern sections of the

Great Lakes and Great Plains regions was much heavier and more frequent, with some areas reporting

more than 200% of normal values during the same time frame. Nationally, this year’s drought was the

most spatially extensive and severe since 1956.

During the drought, there were at least three major heatwaves; the third week of June, the third week of

July, and the first week of July, the latter of which was the most severe and included many 100ºF+ high

temperature readings and a number of new records across the region (including some new all-time high

Figure 2. Daily precipitation totals (bottom) and accumulated precipitation totals (top) at Lansing,

Michigan, June 5th – September 4

th, 2012. In the top figure, accumulated precipitation surpluses are

depicted in green and deficits in brown (figure courtesy of NOAA Climate Prediction Center, (figure

courtesy of National Weather Service Hydrometeorological Prediction Center,

http://www.cpc.ncep.noaa.gov/products/global_monitoring/precipitation/).

temperatures). Another other critical factor during the 2012 growing season was an elevated rate of

potential evapotranspiration (PET), the rate of combined plant transpiration and soil evaporation that

potentially occurs under full sunshine when water is not limiting. A representative plot of accumulated

potential evapotranspiration for the early May through early August for East Lansing, MI relative to a

long term average is given in Figure 3. During the first half of the 2012 growing season, rates of PET far

exceeded both actual evapotranspiration rates and normal PET rates. As can be seen in the figure, rates of

PET were abnormally high beginning in the middle of May (the first half of that month was wetter and

cloudier than normal), with a difference of 2.85” (21.6 % above normal) by the last week of July. The

difference during this period was due to several meteorological factors, including greater than normal

solar radiation levels (8.5% greater than normal), higher air temperatures (3.1°F higher than normal), and

lower humidity (10.6% lower than normal). Overall, in terms of crop water needs, this resulted in a

‘double whammy’: Not only were soils generally not able to supply sufficient water to meet crop needs

due to the extended dryness (e.g. topsoil moisture levels fell to or below wilting point levels), but rates of

PET based on atmospheric conditions were significantly greater than normal this year, which exacerbated

the impacts of the drought.

During the second week of August, the massive upper air ridge that had dominated weather conditions for

much of the growing season flattened out, leaving the Great Lakes region under the temporary influence

of southwesterly flow aloft and an active storm track through the region. This pattern change led to the

passage of two major low pressure systems that brought significant rainfall (2.00-5.00”) to much of the

region. In some cases (e.g. the Saginaw Valley area of Michigan), heavy rains even led to localized

flooding only hours after drought conditions had stressed crops. Subsequent rainfall in late August and

early September (including the remnants of Hurricane Isaac) continued to help reduce the impacts of the

drought, but long term moisture deficits persist as of mid-September, especially across southern sections

of the region.

Figure 3. Observed potential evapotranspiration (PET) from May 1st – July 24

th, 2012 (top line) versus

the long term average (1996-2011, bottom line) at East Lansing, MI. Data courtesy of the Enviroweather

Project (http://www.enviro-weather.msu.edu).

Given a very mild winter season, the March heat wave, and a much warmer than normal summer, the first

8 months of the year (January through August) were the warmest such period on record at most sites

across the region. September and October were near or cooler than normal. Regardless, given how warm

the first two-thirds of the year were, 2012 is still on track to end up as one of the warmest (if not the

warmest) calendar years on record.

One concern expressed by many growers in the region is whether this year’s highly abnormal weather is

the result of simple weather variability or part of a longer term trend. Given that the mild winter, March

heat wave, and summer drought were directly associated with brief, unusual jet stream patterns, the initial

response is that it was simply a part of short term ‘weather’ variability. However, there is some evidence

to suggest the root cause is not so straightforward. For example, the early warm up this season does fit

with a trend towards earlier onset of spring (the seasonal warm up is occurring about 7-10 days earlier

now that it did in the early 1980’s). In addition, the factors involved with the flow and evolution of the jet

streams around both hemispheres are physically linked, even in potentially perturbed climates of the

future. Another key issue is the expected frequency of the occurrence of such extreme events in the near

future. Given how unusual this year has been and assuming relatively slow trends in climate over time,

one would not expect to see anything like it in many years. At the same time, we do have an example of

‘lightning striking twice’ in the historical records: The previous record warm March of 1945 across the

Great Lakes was followed by another much warmer than normal March in 1946. Thus, while we can

expect a more normal, (and hopefully) less stressful growing season in 2013, one can’t completely count

out the possibility of yet another weather-related challenge or two. Combined with your own tolerance for

risk, these factors should play a continuing role in your crop insurance strategy.

How to Best Use Frost Protection Methods in Tree Fruits

Robert G. Evans, PhD

Research Agricultural Engineer (Retired) 32606 W. Knox Road, Benton City, WA 99320 bcevans@pocketinet.com

Introduction

Methods and protection programs to minimize cold temperature injury to crops must be thought of as

combinations of many small measures that incrementally achieve relatively small increases in ambient air

and plant tissue temperatures to minimize the risk of cold temperature injury. Often, air temperatures only

need to be raised a couple of degrees to avoid substantial cold temperature crop injuries and orchardists

should be thinking of systematic and holistic programs in terms of risk management strategies to

minimize cold temperature damage to crops.

Any crop can be protected against any cold temperature event if economically warranted. The selection of

a frost management system is primarily a question of economics and risk. Risk can be defined as the

probability of suffering frost damage—a statistical measure. Growers must assess risk by quantifying and

characterizing risk (i.e., estimating the likelihood of occurrence as well as the nature and magnitude of

frost on their farm) and expected economic consequences. Risk assessment is not an exact science and is

largely based on experience. There are many assumptions to be made and a much uncertainty; however,

the process provides some guidance on where resources should be expended and how to make best use of

their frost management systems. However, keep in mind that the capacity of any system or combinations

of systems is likely to be exceeded at some point in time.

The questions of how, where, and when to protect a crop must be addressed by each grower after

considering crop value, markets, expenses, cultural management practices and historic frequency and

intensity of cold temperature events. Thus, the implementation of frost protection strategies must be

balanced against risk assessments of both the probabilities of annual and longer term costs of lost

production (including lost contracts and loss of market share) and possible long-term tree or vine damage

(sustainability)

This presentation will briefly present the concepts of: passive strategies for frost risk avoidance and active

strategies for frost management including supplemental heating (e.g., water and heaters), heating by

mixing (e.g., wind machines and fountains) and heating by conservation (e.g., covers and fogs). Most of

this discussion is directed towards active frost protection strategies.

General Considerations

Advective (windy) freezes are relatively rare, which is somewhat fortunate because they are much more

difficult to protect against than radiation freezes. Most frost protection methods and systems are practical

and effective only under radiation situations. The formation of thermal inversion layers under radiation

frost conditions is a benefit and many protection methods use the inversion to furnish, trap and/or re-

circulate heat. In addition, a high dew point temperature is probably the most powerful and effective

mechanism available for reducing cold temperature damage to plants.

Successful frost protection programs are always a mix of several passive and active measures. Passive

methods can greatly reduce potential cold temperature damages. Active methods are necessary when

passive measures are not adequate, and consist of efforts to modify field microclimates in order to inhibit

the formation of ice in plant tissues. Careful consideration of various combinations of several potential

passive and active scenarios in the initial planning before planting will make active frost protection

programs more effective and minimize costs of using active methods without significantly increasing the

cost of orchard establishment.

Passive Frost Avoidance Strategies

Passive or indirect frost protection measures are risk minimization practices that decrease the probability

or severity of frosts and freezes or cause the plant to be less susceptible to cold injury. These include site

selection, variety selection and multiple cultural practices, all of which influence the type(s) and

management strategies of an integrated passive and active frost protection program. These strategies are

typically implemented well before the onset of a frost event.

The best time to protect a crop from frost is before it is planted, and good site selection is the most

effective passive risk avoidance strategy. The importance of good site selection in the long term

sustainability of a commercial fruit operation cannot be over emphasized. It will influence the overall

health and productivity of the plants through: soil depth, texture, fertility, water holding capacities, slope,

elevation, latitude, aspect (exposure), subsurface and surface water drainage patterns, microclimates,

disease and pest pressures and cold air sources. In short, a good site can minimize the potential extent and

severity of cold temperature injury and greatly reduce frost protection expenses and the potential for long

term damage to trees and vines. The availability of natural heat sources such as large water bodies and

rivers can also have a large effect on warming cold air masses, and can be an important factor in site

selection. Obtaining a good site with good air drainage, especially in a premier growing area, can be very

expensive, but it is often an investment with a very high rate of return.

One of the best ways to improve the effectiveness of active frost protection methods is to understand what

the sources are and defining where the cold air drainage moves into and out of a block. Ignoring cold air

drainage patterns leads to many potentially avoidable frost problems. Windbreaks, buildings, stacks of

bins, road fills, fences or other barriers, tall weeds, etc., can all retard cold air drainage and can cause the

cold air to pond in the areas behind them if not sited and maintained properly. The size of the potential

cold air pond will most likely be 4 to 5 times greater than the height of a solid physical obstruction. Thus,

the proper use and placement of windbreaks and other barriers to control or manage air flow in radiation

frost protection situations is very important. Weeds at field edges should be kept short. Remember that

wind management and frost management are not always compatible.

Active Frost Management Strategies

Active or direct frost management systems are systematic efforts to modify orchard or vineyard

microclimate to inhibit the formation of ice in plant tissues. These frost avoidance practices are

implemented just prior to and/or during the frost event. Their selection will depend on the dominant

character of an expected frost event(s) as well as the scope of passive measures used in the orchard

establishment and operation phases. Active frost management systems should be simple, durable and non-

polluting, and they must always work when needed.

Active frost management technologies will use one or more of three processes: 1) addition of heat, 2)

mixing of warmer air from the inversion (under radiation frost conditions) and 3) conservation of heat.

Options include various systems for overtree and undertree sprinkling with water, wind machines and

fossil-fuel heaters as well as various cover systems. Producers will commonly use two or more active

cold temperature modification techniques (e.g., wind machines and undertree sprinklers or heaters)

simultaneously in the same field depending on the severity of the event.

Addition of Heat

The addition of heat for frost management is basically limited to the application of water by the use of

various overtree or undertree sprinklers and to the use of fossil fueled heaters. Water-based methods are

generally the most economical. Heat from water is also more efficient than some other sources (e.g,

heaters) because it is released at low temperatures into the environment, is less buoyant, and may

selectively warm the coldest plant parts. However, water-based frost protection systems can create

problems with disease, saturated soils, runoff and leaching of nutrients and other agrochemicals.

Overtree Sprinkling. Overtree sprinkling is the field system which can provide the highest level of

protection of any single available system (except field covers/green houses with heaters), and it does it at

a very reasonable cost. It is the only method that does not rely on the inversion strength for the amount of

its protection and may even provide some protection in advective frost conditions with proper design and

adequate water supplies. The applied water must supply enough heat by freezing to compensate for all the

losses due to radiation, convection, and evaporation. Consequently, overtree sprinkling requires great

amounts of water, large pipelines and big pumps, which often limit its use. Most overtree sprinkler

systems are also used for irrigation and/or crop cooling for sunburn reduction.

Because of the large amounts of water required for overtree sprinkling for frost protection, some growers

have attempted to spread overhead water applications by wide spacing of sprinkler heads, cycling of

water applications on and off, or misting techniques to reduce the total water supply needs across a block.

However, these techniques do not apply adequate water directly to the plant canopy to account for

evaporation, and these systems are not recommended because of the high level of risk.

Undertree Sprinkling. Another commonly used frost protection method in orchards is the application of

water through undertree sprinklers. Research and experience has shown that the success of undertree

sprinkler systems (with and without wind machines) is influenced by the following factors (in

approximate order of importance): 1) the height and strength of the temperature inversion, 2) the amount

(mass) of water applied and the temperature of the applied water, 3) the volume of air flow moving into

the orchard (drift) which can remove much of the added heat, 4) the release of latent heat from the

freezing of the applied water (a very small contribution), and 5) the intercepted radiation heat fluxes from

the soil. Other important, but less significant, parameters are the height and type of a cover crop and water

droplet sizes. The relative contribution of any one factor will vary with site and existing climatic

conditions at the time. However, the expected maximum amount of temperature increase is about 3º to

4ºF using cold water (e.g., 36º to 42ºF) in the spring, depending on inversion strengths.

Many orchardists do not have the availability of the relatively large amounts of water required for

adequate frost protection with undertree sprinklers. The warmer the applied water, the lower the average

application rate required to achieve the same protection levels for a given inversion strength, and it is

possible to preheat applied water up to a maximum of about 110ºF and reduce total water requirements.

Research has shown that, depending on water temperatures and flow rates, applications of pre-heated

water with flow through boiler systems can be an economical and only use about 20% of the fuel required

for heaters. Applications of preheated water from 12 to 18 inch risers may also be effective as border heat.

Heaters. Heating for frost protection (addition of heat) in orchards and vineyards has been practiced for

centuries with growers using whatever fuels were available. Heaters were once the mainstay of cold

temperature protection activities, but are plagued by very low heating efficiencies, high labor

requirements and ever rising fuel costs. In addition, air pollution by smoke is a significant problem and

the use of oil-fired heaters has been banned in many areas. In addition, dense clouds of smoke do not

serve as barriers to radiation losses and provide no frost management benefit.

Current fossil-fueled heater technology was developed in the early 1900's through the 1920's. Propane-

fired heaters made their appearance in the 1950s. These designs were designed to maximize radiant

heating by greatly increasing the radiating surface area of the heater. However, the effectiveness of

radiant heat is proportional to the inverse square of the distance, and only nearby objects benefit. For

example, the amount of radiant heat intercepted 10 feet from a heater is only one one-hundredth of the

radiant heat at 1 foot from the heater. Most of heat is lost vertically.

Heaters are the applications of large amounts of heat in a very small area. Thus the primary

recommendation on the use of heaters in vineyards and orchards has been to use many small heaters

rather than a few large ones. Typically there are about 40 return stack oil heaters (without wind machines)

or about 60 propane heaters per acre. Heaters are often used in conjunction with other methods such as

wind machines or as border heat (two to three rows on the side where the drift enters the block), and with

undertree sprinkler systems, which greatly reduces the number of heaters and greatly lowers fuel costs.

Field measurements indicate actual efficiencies of both oil and propane heaters to be in the range of 10%

to 15%. In other words, 85% to 90% of the heat from both conventional oil and propane heaters is lost,

primarily due to buoyant forces of the hot exhaust gases taking the heat above the plants (e.g., stack

effect) where it is no longer able to be recaptured and reused.

Mobile Heaters. There are numerous variations of relatively large propane fueled heaters with fans that

are pulled around and around the block by small tractors. Their intent is to provide heat to protect the crop

as the machine is driven back and forth through the block. These are generally limited to small blocks as

the heater should return to each spot every 4 to 6 minutes to be most effective. The use of these devices

can be compared to trying to heat a room with a candle.

Heating by Mixing

Heating by mixing provides no new heat into the system. Wind machines and helicopters fall into this

general category. Although it does not introduce any heat into the system, one additional method

(“fountains”) is included because it also relies on a fan. These are briefly discussed below.

Wind Machines. Wind machines, or fans as they are often called, are used in many orchard and vineyard

applications. These technologies (including helicopters) rely on mixing the warmer air from the thermal

inversion into the colder air near the ground to raise air and plant temperatures and mixing it with the cold

air below to minimize cold air stratification in the block and reduce the potential for frost damage.

Wind machines consist of large propellers on stationary towers which pull vast amounts of warmer air

from the thermal inversion above an orchard. They have greatly increased in popularity because of energy

savings compared to some other methods, and they can be used in all seasons. Wind machines pull warm

air from the thermal inversion up to about twice the height of the fan hub. Consequently, the higher the

fan’s hub, the more heat that is available (up to a point); however, the hub height should be at least 2X the

height of the crop.

A single, large wind machine can help protect 10 to 12 acres under calm, radiation frost conditions. The

actual amount of protection or temperature increases in the orchard or vineyard from wind machines

depends on several factors. As a general rule, the maximum that the air temperature can be increased

within the orchard canopy is about 50% of the temperature difference (thermal inversion strength)

between the 6 and 60 ft levels with standard machines.

A wind machine should be located only after carefully considering the prevailing drift patterns and

topographic surveys. In reality, the protected area is usually an ellipse rather than a circle due to distortion

by wind drift with the upwind protected distance about 250 to 350 ft and the downwind distance about

400 to 460 ft. Thus, these devices are often placed in the upper third of a block. Several wind machines

are often placed in large orchard blocks with synergistic benefits from carefully matching the head

assembly rotation direction and spacing. Non-rotating wind machines may also be located so as to push

cold air down hill out of particularly cold problem areas.

Undertree sprinkler systems (heated or not) are very compatible with wind machines and their respective

individual heat contributions are additive. Some of these systems are being used in conjunction with both

wind machines and with heaters. There are fewer risks, less disease problems and lower water

requirements than with overtree systems because the water does not come in direct contact with the buds.

The total number of heaters needed may be reduced by at least 50% by dispersing them into the

peripheral areas of the wind machine's protection area. A small amount of the heat which is normally lost

by rising above the trees may be mixed back into the orchard by the wind machines and heat is also added

from the inversion by the fan. The wind machines are usually turned on first and the heaters (or undertree

sprinklers) are used only if air temperatures continue to drop.

Helicopters. Helicopters are an expensive (and sometimes dangerous) variation of a wind machine which

can also be used under radiation frost conditions. They can be very effective because they can adjust to

the height of an inversion and move to cold spots in the orchard. The amount of area protected depends

on the thrust (down draft) generated by the helicopter. Generally, the heavier (and more expensive) the

helicopter, the better their capability to raise orchard air temperatures during radiation frost events and to

protect larger areas. A single large helicopter can protect areas of about 40 acres under the right

conditions, but they are generally limited to just one farm. However, due to the large standby and

operational costs as well as safety considerations associated with night time flying, the use of helicopters

for frost protection is limited to very special cases or emergencies.

Fountains. “Fountains” are relatively new devices that have come into limited use within the past 15 years

that uses the principle of selectively extracting cold air from the coldest areas and mixing it high in the

inversion layer. Their purpose is to prevent cold air from the drift from accumulating to depths where

they can cause damage to buds. These devices only pump existing cold air and no new heat is introduced

from the inversion or elsewhere. These large, stationary machines come in electric and tractor powered

versions. The axis of the propellers is parallel to the ground inside some type of shroud, usually sheet

metal. The horizontal fan is located near the top of the shroud.

These machines are generally sited near the lowest elevations in an orchard or other areas where cold air

pools. The horizontal fan pulls in cold air and forces it directly upward at high velocities into air above.

However, this cold air does not dissipate or disappear and it is not carried away from the orchard. Rather,

the cold air from the orchard floor is inefficiently mixed with the warmer air in the inversion, and because

this air remains colder and heavier than the air in the inversion layer, it begins to settle back to the

ground. Limited research has shown that after a short period (e.g., 1-2 hours), this circulation pattern

creates an effect very similar to a water fountain spraying vertically upward into the air with the water

falling back to the ground under gravitational forces. Consequently, this process serves to re-circulates

the cold air that was pushed up earlier and has resettled back to the ground as well as the cold air drift that

continues to accumulate in the vicinity. Thus, over time the cold air pool deepens and frost injury can still

occur.

Conservation of Heat

Measures that conserve heat include covers, fogs and foams. Fogs and foams are not practical for orchard

applications. However, overhead fabric covers for hail or sunburn protection of an orchard or vineyard

(conservation of heat) may also provide frost benefits, but these are very expensive (e.g., $10,000 to

$20,000 per acre). Undertree sprinkling, heaters and even flood irrigation may also be used under the

covers, which greatly increase the effectiveness of all methods by reducing radiation losses and trapping

some of the supplemental heat.

Additional References:

Evans, R.G., 2009. The ABCs of Frost Management. Proceedings of the 104th Annual Meeting of the

Washington State Horticulture Association. Dec 1-3, 2008.Yakima, WA pp. 79-96.

Evans, R.G. and T.W. van der Gulik, 2011, Irrigation for Microclimate Control. Chapter 29. L. Stetson

and A. Dedrick, eds. Irrigation. 6th Edition. The Irrigation Association. Falls Church, VA. pp 1015-1036.

Burning Organ

ic 

material

Heaters

Cold Air Drain

®Helicop

ters

Wind Machine

s / Fan

sMicroSprin

klers

Sprayable Frost 

Materials

Coverage

Depe

nds o

n air m

ovem

ent

Oil‐Fueled

: 40 he

aters/acre         

Prop

ane‐Fueled

: 60 he

aters/acre

Approx. 10 acres

Large = 40

 to 60 acres                

Smaller =

 25 to 40 acres

Approx. 10 to 13 acres

limite

d by

 well size

               

(35 GPM

 for 1

0+ hou

rs)

unifo

rm

Power Options

NA

oil, diesel or p

ropane

Gas, Electric, PTO

fuel

Gas, Electric, PTO

, Diesel          

(most n

ew are propane

)electric

NA

Unit C

ost

cost of o

ld hay bales or 

brush piles is u

sually 

minim

al

Oil‐Fueled

: App

rox. $50

 each = 

$2,000

/acre                       

Prop

ane‐Fueled

: App

rox. $10

0 each 

= $6

,500

/acre

Approx. $13

,500

Rental cost:                         

Large = $1

600 pe

r hou

r per bird

       

Small = $70

0 pe

r hou

r               

(+travel & fu

el time)  

Approx. $16

,000

‐$35

,000

well, irrigation system

 plus e

xtra 

$100

0 pe

r acre for 

microsprin

klers

$10 to $25

 per acre

Fuel Con

sumption for 

One

 Hou

rNA

Oil‐ and

 Propane

‐Fue

led: 1 

gal./hr/heater 

Approx. 1

 gal./hr

includ

ed in

 rental

Approx. 13 gal./hr

electricty cost

fuel fo

r tractor

Installatio

n Co

stcost of o

ld hay bales or 

brush piles is u

sually 

minim

almovem

ent to site

cost to

 move ‐ grower 

installed

minim

um hou

rs fo

r stand

byCe

men

t Pad

 + Installatio

n (often

 includ

ed in

 total unit cost)

adde

d on

 to irrig

ation system

 install costs

time of ope

rator

Mainten

ance Cost

tend

ing to burn

Significant ‐ he

aters sho

uld be

 cleane

d after 2

0‐30

 hou

rs of u

seMinim

al: O

wne

r Maintaine

dNA if hired in.

can be

 covered

 und

er con

tract, 

but m

ostly

 minim

al unless a

 gearbo

x goes

adds m

ore tim

e for m

icrosprin

kler 

care th

an re

gular trickel irrigation

some materials are hard 

on sp

rayers

Auto‐Start Available

NA

NA

Yes

NA

Yes

Yes??

NA

Enha

nces Other Frost 

Protectio

nYes: W

ind Machine

sYes: W

ind Machine

sYes: W

ind Machine

s, 

Sprin

klers, Heaters

??Yes: Heaters

perhaps

perhaps

Quiet Factor

Yes, but can

 cause sm

okey 

cond

ition

sYes, but can

 cause sm

okey 

cond

ition

sNo                         

(63‐66

dB)

Not re

ally

No                              

( 90 dB

)Yes

No                    

(sprayer/tractor noise)

Special W

eather 

Concerns

Not in

 high winds or d

ry 

cond

ition

s.Yes

Yes

Less coverage if it is very cold. The

y can move vertically to

 find

 the warm 

air inversio

ns.

Yes/No

Yes

No

Dua

l usage

 factors 

recycling

NA

NA

for fun

 if you

 fly on

emight help with

 fruit finish

irrigation in su

mmer     coo

ling 

effect in

 dormancy to

 prevent 

bud break???

NA

Frost P

rotection Metho

ds in

 Michigan – Co

sts a

nd Con

siderations

Amy Irish‐Brown, Tree Fruit IPM

 Edu

cator, Michigan State University

 Exten

sion, 

Decembe

r 4, 201

2 ‐ W

eather Risk

 Sessio

n

MSU Enviro-Weather Decision-Making Tools for Weather Risks

Beth A Bishop MSU Enviro-weather Coordinator

bishopB@msu.edu (517) 432-6520

Although the weather during the 2012 growing season was unusually devastating to many fruit

crops, even in more “normal” years, crop managers must make many decisions to adapt in

response to weather. Minimizing weather risk requires knowledge. Growers need to know the

current weather conditions and have an idea of what they will be in near future. Growers must

also understand the cumulative effects of previous weather conditions. In 2012, for example, the

unusually high temperatures early in the year pushed development of crops and insects far ahead

of normal.

Michigan State University’s Enviro-weather Program provides growers with weather-based

information to help with crop management decisions. MSU’s Enviro-weather Program provides

real-time and past weather information and predictions to help grower’s make optimal

management decisions. Enviro-weather consists of a network of 71 weather stations throughout

Michigan (and six weather station on Wisconsin’s Door Peninsula). Each weather station is

equipped with at least 12 research-quality sensors, a data logger, and a cell modem, which is used

to transmit data. Every 30 to 60 minutes during the growing season data is sent to a central server

on the Michigan State University campus. The data is checked for quality, is organized and

archived in a database. The data is used in on-line tools, weather summaries and tables, pest and

predictive models, and crop-management applications that are accessible via the Enviro-weather

website (www.enviroweather.msu.edu).

When a user accesses the Enviro-weather website, he or she will see a map of Michigan with the

location of Enviro-weather stations indicated by yellow dots. Users can view current conditions at

any of the weather station locations simply by moving the mouse

pointer of the dot and a box will pop up.

A number of weather applications and

summaries are available on Enviro-weather

by selecting a station by clicking on it.

Users are taken to the “station page”, which

shows a number of applications that use the

data from the selected weather station.

Applications and models that are specific to a particular crop can be accessed by clicking on the

commodity list at the top of the page. This will bring up the commodity page, which has a list of

crops in the left column. Clicking on the crop will show the list of tools and applications that are

specific for that crop

Enviro-weather provides a number of insect and disease predictive models and crop maturity

models for fruit. For example, the apple maturity model will predict the harvest date for three

apple varieties based on bloom date. The fireblight and apple scab tools predict when growers

should treat for these diseases based on local weather conditions. The grape berry moth tool

predicts the beginning of egg laying (and thus treatment window). The oriental fruit moth and

codling moth tools predict when treatment is required based on accumulated degree-days

(accumulated heat) from a particular biological event (biofix).

The most impactful weather events of 2012 were the early heat/April freeze and the summer

drought. Enviro-weather has specific tools to help growers deal with frost/freezes and to help

with decisions about water use.

The Overnight temperatures tool (accessible from both the station page and any commodity page)

provides growers with three separate summary tables. The first shows hourly average

temperatures for the previous night at the selected station and other Enviro-weather stations in the

region. The second table lists forecasted low temperatures for the next night. The third table

shows late afternoon dew points for predicting potential frost in calm clear conditions.

Enviro-weather also offers a “Frost Alarm” service for a small yearly fee. Subscribers to this

service are notified 24 hours a day, 7 days a week by email and/or text message of potential

frost/freeze conditions in their area.

Enviro-weather also provides applications to help grower’s assess water-balance in their crops.

Water-use tools are listed on Enviro-weather’s commodity pages and include

an irrigation scheduler program and checkbook. The “potential

evapotranspiration” tool displays a summary table listing daily rainfall,

temperature and potential evapotranspiration for the selected

Enviro-weather station location. The tool also displays a

week’s worth of forecasted values so growers can evaluate the

future water needs of their crop.

Enviro-weather is constantly growing and improving to meet

the needs of Michigan agriculture. If you have a comment or a

question about the program, please contact Beth Bishop,

Enviro-weather Coordinator at eweather@msu.edu or (517)

432-6520. Enviro-weather is funded by MSU Extension, MSU

AgBioResearch, Project GREEEN and generous contributions

from industry and private donors.