Experts Offer Tips On How Fruit Growers Can Combat Cold Temperatures

If you’re a fruit grower in the upper Midwest, mid-Atlantic, or Northeast, you don’t need to be told how damaging the April freezes have been, especially following mild March temperatures.

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The last time growers in those regions experienced a spring like this was in 2012, when the apple crop in Michigan was almost completely wiped out. That year, USApple reported Eastern and Midwestern crops were down 31% and 79%, respectively.

Recently, growers in Pennsylvania are going so far as to set fires in their orchards to save their crops.

But it’s not just apples and other tree fruit crops that have been affected; grapes are also being hit.

Posts on GrowingProduce note products such as Promalin, which can help, but must be applied at the right time.

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In light of all the recent problems, if you believe you have already sustained damage, Lynn Kime, Penn State Senior Extension Associate, says a call to your crop insurance agent may be in order.

If you believe the recent low temperatures may have damaged your crop, you have 72 hours to report the event to your insurance provider. If you have not documented the temperatures at your farm, Kime notes the National Oceanic and Atmospheric Association (NOAA) provides weather information three days prior to the date you access their web site and enter your ZIP code.

In addition, Penn State Extension Tree Fruit Production  lists critical temperatures for fruit crops at various bud stages.

Mark Longstroth, Michigan State University Extension Fruit Educator gives advice on what should be of concern to growers.

In addition, Mary Concklin, University of Connecticut Visiting Associate Extension Educator — Fruit Production and IPM, posted the following frost/freeze protection options:

Row Covers
Row covers are spun bonded polypropylene and vary in weight from 0.45 ounces to 4 ounces. Cloth sheets also work for small areas. Research has shown using two layers of a 1-ounce weight row cover provides somewhat better frost protection than a single layer of 2 ounces cover, likely due to air between the layers. Heavier covers (3 ounces to 4 ounces) work for frost protection but restrict light too much and need to be removed as soon as temperatures are above freezing. Be sure to anchor the row covers for the winds. If you have the swing arm trellis for blackberries, lower it to the ground and put the row cover back over it. A double layer where growth is already underway is advisable. Avoid placing plastic over the rows unless it is suspended and will not touch the plants. Wherever the plastic touches the plant — leaf or flower — the plant tissues will be killed in freezing temperatures.

Straw
Straw is a very good insulator, which is one reason it is used for winter protection of strawberries. If you have removed the straw from your strawberry beds, put it back on. Adding a row cover on top is an added measure of security.

Overhead Watering
Overhead watering works based on the principle of latent heat of fusion — as water turns to ice, heat is released. This heat maintains the plant tissue at just above freezing. If at any time during the night the water stops while the temperature is below freezing, the process reverses —heat is removed from the plant tissue and the tissue will freeze. To avoid this, watering must continue until the air temperature rises above 320F and the ice has started to melt.

Overhead watering may be combined with the use of row covers or used independently and requires a calibrated emitter system to be sure the required amount of water is constantly being provided. Positives are a proven track record of maintaining the temperature of the flower buds above critical temperatures. The negative is that it may lead to saturated soils and root diseases; if the water stops at any point when the air temperature is below the 320F, the buds will freeze; and limb breakage from heavy ice buildup.

Keep in mind, in a windy situation, you will not be able to maintain an even distribution of the water.

Under-Tree or Surface Watering
As the water cools, it releases heat into the environment around the trees and plants and also increases the relative humidity which reduces radiated heat loss. Advantage: the sprinklers do not need to be as precisely calibrated as they are for overhead sprinklers; if the system shuts down during the night the impact is not the same as with over-head watering.

Potential problems: saturated soils; increased root rot problems.

Wind Machines
This method carries an initial high expense, but on sites that are frost-prone this method will pay for itself. A temperature inversion and wind speeds less than 5 mph are required for this system to be effective. There are several models, mobile and stationary, tall for tree fruits and lower for vegetables and small fruits. Acreage covered varies by model and the strength of the temperature inversion, generally 1 acre to 20 acres. May be used in combination with supplemental heat for large areas, or when the temperature is expected to be down to the low 20s, or with a weak temperature inversion.

Helicopters
The aircraft utilize the temperature inversion the same as the wind machine. Their mobility is an advantage which enables them to cover several small frost pockets or one large area as long they return to the starting point every 4 to 5 minutes. The larger the aircraft, the more air it will move and the larger an area it will be able to cover. The larger aircraft will also be more expensive. These cannot be used in conjunction with any type of added heat that emits smoke for obvious safety reasons. Refer to the pilot for the types of lighting needed to mark the areas to be covered.

Return Stack Heaters
Heaters hold approximately five gallons of fuel with 20 to 40 heaters needed per acre, placing more on the upwind side of the block. They are effective when used alone as well as in combination with wind machines. Light every second or third heater initially and then light the rest. This will allow heat to begin moving through the field without a big burst of heat that may puncture the inversion layer.

Open-Burning of Straw bales, Wood piles, etc.
Avoid large fires (bonfires) as these will penetrate the inversion layer allowing the heat to leave the fruiting zone. When that happens, the only place there will be heat is right next to the fire. Small fires work best. Disadvantage of open burning — smoke. The smoke will hang over the field even after the sun is up but will not allow the heat from the sun’s rays to penetrate the smoke to warm the field keeping it colder longer. If the smoke is not there, it will have moved to your neighbor’s property. Be sure to check with your local fire department in advance for a burn permit. Don’t bother with tires — you will never get a permit for them.

Finally, if you are still in need of advice, but – and that’s a very big “but” indeed — you have retained your sense of humor, check out the following. With apologies to David Letterman, here are the “Top ten tips for possibly minimizing frost-induced losses in apples this spring,” by Jeff Alicandro, a longtime independent crop consultant with agr.assistance in North Rose, NY. (Emphasis is Alicandro’s.)

  1. Keep prayin’ — Keep (or start) attending Saturday or Sunday Mass — ASAP if not sooner.
  2. Luck out — Dust off your lucky rabbit’s And face it — as a fruit grower by definition you are already one lucky guy or gal — so let’s hope your good fortune continues.
  3. Keep planting on sites with good air drainage (yes this is Monday morning quarterbacking).
  4. Remember to start up that wind And go buy another unit — if there are any left.
  5.  Burn some old tires if it makes you feel Oops — no longer legal in many parts of North America — and never worked all that well anyways.
  6. Dormant copper fungicide sprays may help just a little bit by reducing bacterial populations which can serve as ice nucleation sites — but don’t use copper fungicides excessively or any fruit which does survive will be ugly.
  7. Good fruit bud vigor can help survive marginal frosts — but there isn’t much you can quickly “pump into” your buds or flowers this spring to greatly increase frost tolerance — at least not that I have seen. Higher tree zinc and potassium levels may give a bit of an edge in marginally frosty
    • Zinc can be supplied thru foliar applications of safe complexed zinc products — as well as with Polyram (14% Zn) or ziram(16% Zn) fungicides in scab Other mancozeb fungicides also supply a bit of zinc.
    • Vitazyme biostimulant programs can also help to improve bud hardiness and increase fruit set. But this program can’t start just 2 days before a frost event.
  8. Application of Perlan or Promalin PGRs can potentially increase APPLE fruit set when applied in bloom shortly after a frost event (within 24 hours).
    • This cost-effective PGR program ($50/acre) performed VERY well in several states in the record early 2012 spring — while results with wind machines were iffy at
    • Promalin and Perlan are of course typically applied during bloom in the Eastern U.S. to improve fruit typiness and fruit size on ‘Red Delicious,’ ‘Gala,’ ‘Braeburn,’ etc.
    • Leftover supplies of these PGRs hold up pretty well for a few seasons in spray sheds — plus there are some return programs in place in case we luck out and stay frost-free.
  9. Hold off on applying any pre-bloom soil-applied nitrogen for now in bearing orchards — until it appears that maybe this season gets back toward “normal.” Spreading fast-acting nitrate-based calcium nitrate (Yara) can very effectively be delayed until full tight cluster to early pink and still bolster spur leaf N status to promote strong apple fruit Fertilizers based on urea, ammonium sulfate or ammonium nitrate have zero chance of getting into spur leaves and fruit buds anywhere near that quickly. And calcium nitrate also supplies 1.2 pounds of fast-acting calcium along with every lb. of readily available nitrate N.
  10. That’s all I got — and I know it ain’t much — refer back to No. 1 and No. 2 above as required.

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