How Much of a Safety Margin Does a Row Cover Provide? (March 26, 2014)

— Written By

DID YOU KNOW WE HAD NEARLY AN IDENTICAL BLACK FROST CONDITION ON MARCH 21-22, 2014

FROM AN ACTUAL REPORT FILED ON THIS WEBSITE LAST YEAR (WHILE THE INFORMATION WAS STILL FRESH)

CONCLUSION TO THIS REPORT: Everyone has a different tolerance for risk. But, after running this experiment last March at Clayton we learned that with a minimum temp of around 20.6 F that about 25% of the open blossoms beneath the covers were damaged, but another 75% lived. And, the blossom temperatures were as cold as 29 F.

FULL REPORT: https://strawberries.ces.ncsu.edu/2013/03/question-about-dew-points-and-relevance-of-dp-to-different-frost-protection-scenarios-3-30-13/

Re-capping Research Station Experience (3/21-3/22/13)

Over at the Research Station in Clayton, Rocco Schiavone tracked temperatures the same evening, and like Karma, we did not turn on the sprinkling and relied on the 1.2 oz row cover. Minimum temperatures of 20.6 and 20.7 were recorded for blossoms 1 and 2, at 7:15 am (Table 3). Then, at this same time, blooms 3 and 4 (both covered with 1.2 oz), gave readings of 29 and 29.9 (Table 3). At 7:40 the No. 3 blossom dropped to 28.2.

Overall, we had about 9 F elevation in blossom temperature due to row cover, but it wasn’t quite enough protection.  About 25% of the open blossoms beneath the covers were damaged, but another 75% lived. And, the blossom temperatures were as cold as 29 F.

Bloom conditiion/time 6:45 7:00 AM 7:15 7:40 8:00 8:30 9:15
No. 1 bloom exposed( East exp) 21.4 20.6 21.9 31.4 35.6 50.9
No. 2 bloom exposed(NE exposure)) 21.7 20.7 25.4 33.9 43.5 42.1
exposed ave. 21.6 20.7 23.7 32.7 39.6 46.5
No. 3 bloom covered 1.2 oz 30 29.2 29 28.2 30.2 30.3 48
No. 4 bloom covered 1.2 oz 30.8 30.1 29.9 30.9 36 44.4 58.8
covered ave 30.4 29.7 29.5 29.6 33.1 37.4 53.4

Table 3. Data compiled by Rocco Schiavone at Clayton Central Crops, 3/22/13.

6:45 7:00 7:15 7:40 8:00 8:30 9:15
Outside Air temp (no covers)
Station 1 – 3″ height 26.4 24.5 22.9 25.4 28.8 33.4 39.8
Station 2- 3″ 26.4 25.6 25.7 28.4 30.7 34.2 38.5
Station 3 – 3″ 25.4 24 22.3 24 27 33.9 37.9
3 ft height 22.6 22.3 24.7 31.1 35.2 36

Table 4. Air temperatures only (3 inch height and 3 ft). At 7:15 am the lowest recorded air temperature at Station 3 was 22.3. At this same time, the lowest recorded temperature for an uncovered (exposed) blossom was 20.6 (Table 2), or about 1.7 F lower than air temp.

CONCLUSION: WITH A ROW COVER (1.25 OZ) ALONE YOU COULD BE AT RISK FOR SOME CROP DAMAGE IF CANOPY TEMP HITS 20-21 F. IF YOU HAVE IRRIGATION SYSTEM, YOU CAN PREVENT THIS INJURY BY IRRIGATING ON TOP OF COVERS

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Dr. E. Barclay Poling
Interim Executive Director, NC Strawberry Association Inc.
& Professor Emeritus (Strawberry Plasticulture Researcher)
Department of Horticultural Science
Campus Box 7609, 162A Kilgore Hall
NC State University
Raleigh, NC 27695-7609
 

Written By

Photo of Dr. Barclay PolingDr. Barclay PolingFormer Professor and Extension Specialist, Strawberries and Muscadines (919) 515-5373 (Office) barclay_poling@ncsu.eduHorticultural Science - NC State University
Posted on Mar 26, 2014
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