NC Update on Thur and Fri Morning Frost, and Other Concerns (Including Hail Damage) (11:45am, Tue, 3/21/17)
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Figure 1. This photo of hail damaged fruit from this past weekend was provided by Georgia Love, NCDA Agronomist (shot taken in Robeson Co). If you get hail damage, be sure to use a fungicide afterwards to reduce growth of fungi that take advantage of the wounded tissue to colonize the berry (so-called opportunistic and secondary pathogens). Mild temperatures and sunshine are key to drying down, and dry weather allows the wounds on green berries to readily heal. Green fruit that has been ‘nicked’ by the hail is still marketable at a fruit stand when ripe.
Switch is a more broad spectrum fungicide with 12 hr REI and 0 day PHI. If Switch cannot be used, a broad spectrum product like captan would also work well. Keep in mind that you should not apply Switch more than twice a season due to resistance management (p. 8 2017 Strawberry IPM Guide ). Switch will be fine even up to 48 hours later for the lower field that doesn’t dry as quickly.
> Sanitation (may need extra labor to do this) – vip to strip most seriously damaged fruit; it is better to deposit the fruit in large buckets and remove from the field
> Nutrition: calcium is the most important nutrient to plant cell walls, and I would continue to fertilize as usual, but use calcium nitrate as N source…There does not seem to be much documentation about how much fertilizer to apply after a hail storm, but after the experience we had in 2015, it seems more important to maintain fertility than to be concerned about “bumping up” your fertilizer program. I would also pull some tissue samples to make a scientific determination of nutrient status following this episode.
> As hopeless as the situation may seem, you would be surprised at how quickly the crop can turn around if the hail is not too severe. Again, green fruit that has been ‘nicked’ by the hail is still marketable at a fruit stand when ripe. Hail damaged fruit is much more difficult to market off the farm. Customers can be offered a slight discount on hail damaged berries.
NC – it does now appear that FROST is a possible threat this coming Thursday (3/23) and Friday (3/24) mornings, as we talked about in this week’s OUTLOOK (issued Monday). In Kenansville, for example, the minimum according to AWIS may be 31 F on Thursday and 31 again on Friday. Dew points are relatively high and frost will form easily once air temp in canopy drops below 32 F. The Clayton Skybit shows the canopy temp will be below 32 on both Thur and Fri mornings. If you are using row covers, these should be re-applied in the mid-afternoon. A single 1to 1.25 oz cover should suffice. I would look for white frost as your cue to initiate protective measures with sprinkling.
IN CONTRAST TO LOCATIONS LIKE KENANSVILLE (IN EASTERN NC Kenansville), PLEASE BE ADVISED THAT SOME AREAS WILL BE RUNNING LOWER DEWPOINTS WED/THUR (LIKE GREENSBORO GREENSBORO), AND THERE IS POTENTIAL FOR BLACK FROST IN THESE AREA AS DEWPOINTS ARE IN UPPER TEENS AND LOW 20S. IN GREENSBORO THERE IS ALSO ONLY GOING TO BE A MINIMUM OF ONLY 31 AT BETWEEN 6 a.m. AND 7 a.m., AND SO THE RISK OF DAMAGE TO OPEN BLOOMS SEEMS MINIMAL – AT THIS TIME! ALL OF THIS CAN CHANGE! IF RUNNING SPRINKLERS FOR PROTECTION, BE SURE TO TURN ON A WET BULB OF ABOUT 32 (AIR MAY BE 38). OR, USE YOUR DIGITAL THERM TO GUIDE YOU –> WHEN IT READS 31-32 START RUNNING. IT COULD BE THAT THERE IS NO ACTUAL THREAT IN A LOCATION LIKE GREENSBORO ON BOTH TO THESE NIGHTS IF THE MINIMUMS ARE 31 (THUR) AND 33 (FRI). IT COULD GO EITHER WAY!