Category Archives: Weather

Frost Watch for Tuesday Night into Wednesday Morning

I hate to start the season with a frost warning post, but this has become our new norm anyway.

The good news is that, based on the forecast so far, I do not think the cold weather expected Tuesday night into Wednesday morning will be a major concern for many of us. I checked the forecast across several apple-producing regions in Virginia, and temperatures appear likely to range between about 23 and 25°F from midnight through sunrise on Wednesday morning. Those temperatures could cause at least some level of injury in certain fruit crops, depending on location and, more importantly, the developmental stage of the trees.

Here in Winchester/Frederick County, peaches are generally between calyx green and calyx red, and most apple cultivars are still not much beyond green tip. At these stages, this event should not be a major issue for either crop. That said, conditions may be different in other parts of the state. In central Virginia, for example, some peach cultivars may already be at 20–50% bloom, and those blocks could see damage if temperatures fall below about 24°F for a couple of hours. The same concern applies to apple cultivars that have reached tight cluster, where some injury can occur around 24°F, especially when dew points are low.

So, is there anything you can do?

Yes — if your trees are at a stage that could be truly affected, and you have frost protection options available, this may be the time to consider using them. Based on the current forecast, this looks like a fairly typical radiative frost event, with light winds, mostly clear skies, and low dew points. Under these conditions, tools such as wind machines, propane heaters, and irrigation can all be effective. Both under-tree and over-tree sprinklers may help raise orchard temperature by a couple of degrees, but protection efforts would likely need to begin Tuesday night.

For more information on sprinkler use for frost protection, check out this previous post:
https://tree-fruit-horticulture.vaes.vt.edu/2023/03/07/sprinklers-for-frost-protection-what-you-need-to-know-before-turning-them-on/

As always, this post reflects what I can see in the forecast right now. Please continue to monitor your local weather closely and use your own judgment based on your site conditions, crop stage, and available frost protection methods.

Another, probably less devastating, frost event is expected tomorrow, April 18

Another frost/freeze event is expected from midnight today to 9:00 am tomorrow (Monday, April 18), with temp as low as 30 oF in some portions of central, northern, and northwest Virginia. On their webpage, the National Weather Service stated that “this frost and freeze conditions will kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing”. I can’t comment about plumbing, but I can probably provide insights into how this frost event would impact apples, peaches, and apples in the state. In our location in Winchester, VA, most apple cultivars, including Honeycrisp, Gala, Fuji, Reds, and Goldens, are between 20%- 90% bloom. Some early cultivars, e.g., Pink Lady and Zestar, are already post-bloom. For cultivars at early bloom and full bloom, 10% kill happens at temperatures below 28 oF for > 30 min; and 90% kill happens if the temp drops below 25 oF for >30 min. Based on the current forecast, the lowest temp in most of the locations I looked at in Frederick, Rappahannock/Maddison, Roanoke, Nelson, and Carroll counties, is 30 oF, which should not, theoretically, cause any significant damage to apple blossoms. For cultivars at post-bloom and petal fall, subfreezing temp (below 32 oF) can cause damage to the skin of developing fruitlets, leading to “frost rings”. Fruits with a frost ring will likely grow normally until harvest, but blossoms damaged by the frost will likely abscise within the next 2-4 weeks. Temperatures above 28 oF should not cause significant damage to flowers and developing fruits of peaches and sweet cherries.

Central Virginia MaluSim for 4 May 2015

Warmer temperatures and cloud cover from some rainstorms later in the week will cause a moderately stronger carbohydrate deficit for Central Virginia.

Peck Central VA MaluSim 5_4_15

Thinning applications made Tuesday through Thursday will result in the strongest response this week. Long term weather forecasts predict days in the 80’s and nights in the 60’s for the next 10 days. Carbohydrate levels will likely remain in the 0 to -40 range during that period.  To get the strongest response possible, make your applications when average fruit size is 8-12 mm in diameter.

Due to a technical glitch, I was unable to run the MaluSim model for Winchester. I hope to have the problem resolved Tuesday morning. I will post an update for Winchester as soon as possible.

Full MaluSim report:

Peck Central VA MaluSim 5_4_15.pptx

Fruit Bud Damage in the Winchester Area

The winter of 2013-14 will surely go down as one of the colder, snowier winters in recent years. Many growers have been asking about potential flower bud damage from the cold temperatures that we’ve had. As a general rule-of-thumb, peach and sweet cherry buds are hardy to about -10F, and near complete bud loss and perhaps some branch damage will happen when temperatures are below -20F. As I mentioned in a previous post, plants are not affected by wind chills, so we are talking about absolute cold temperatures, which will be warmer than the wind chill temperatures that are reported in weather reports. Apples and pears are generally hardy down to -25F. However, hardiness is much less when: there is a warm spell preceding the cold temperatures, when trees have already been pruned, when the cold temperatures persist for an extended period of time, or when trees were under water or nutrient stress in the previous season. Under these circumstances, peach and sweet cherry buds might be damaged at 0F or even warmer. During this past winter, peach buds may have been killed during multiple events.

Looking at the absolute cold temperatures from August 1 to present, we see that many of the fruit growing regions in the mid-west and Northeast likely have moderate to significant damage to their peach and sweet cherry crops.

US_freeze_py_mmin

Zooming into the Mid-Atlantic, we see that there were some areas along the western edge of Virginia that sustained temperatures below -10F this winter. Many other areas of Virginia have had temperatures in the minus single digits.

210_freeze_py_mmin

To get an idea of how much peach bud damage is in the Winchester area, last week my lab  collected 10 peach branches from each of seventeen different blocks of peaches. Many of the blocks were located at the AREC, but we also collected branches from some nearby farms. The branches were kept in a vase at room temperature for 24 hours, and then every bud on every branch was dissected from the tip to the base to look for damage. Healthy buds are green and look moist, while damaged bud are brown and translucent.

Table 1. Peach bud damage from the winter of 2013-14. Branches were collected on March 4 and analyzed on March 5.

Cultivar

Percent of Flower Buds Alive on Shoot

Total Number of Buds Dissected

Contender

 83.0 317

Laurel

 30.8 289

Loring 1

 0.5 195

Loring 2

 0.0 180

Loring 3

 91.0 144

Red Haven 1

 94.1 187

Red Haven 2

 92.5 253

Red Haven 3

 83.2 232

Red Haven 4

 96.0 173

Red Haven 5

 97.8 90

Red Haven 6

 86.6 313

Redskin

 0.0 197

Sentry

 65.0 163

Sugar Giant

 79.0 372

Sweet Breeze

 41.7 103

Sweet-N-Up

 45.9 204

Topaz

 50.0 142

From these data it is clear that there are both variety and site differences in bud damage. A few blocks are likely to have no or little fruit this year, but most blocks have the potential to set a full crop. Remember that it only takes 15-40% of the buds to make a full crop. The bottom line is that before you prune, it would be a good idea to assess how much damage you have in your trees. Only in situations where severe bud damage occurred should growers leave extra wood when pruning.

Penn State did a similar analyses of peach buds, and found that only 22-32 percent of the peach buds were dead at the Biglerville Fruit Lab.

Fruit Bud Damage from Cold Temperatures

Cold temperatures in the winter, such as we’re experiencing over the next couple-few days with a polar vortex can cause damage to plants, people, and livestock. Tmin forecast 1_6_14_midatlanticAt this time of year, fruit buds on our main tree-fruit crops (apple, peach, cherry, and pear) are still in their winter dormant state (endodormancy). During endodormancy, buds have a very low water content and tend to be more cold tolerant. However, absolute lows are not the only factor to consider. If warm temperatures precede a cold spell, then tree buds tend to be less cold tolerant and are more likely to be damaged. There is also considerable variation amongst species and cultivars. For this reason, critical temperature thresholds, like those developed for spring frost damage to flower buds, are not well defined. However, from an ongoing discussion among pomologists in the Eastern part of North America, the consensus seems to be that peach flower buds start to be damaged at -10F and complete crop failure and/or tree loss occurs at -20F. Cherry and plum flower buds are slightly more cold hardy than peach buds and damage will likely occur at -20F. Apple flower buds can withstand temperatures down to -25F. As of now, the forecast for most of Virginia does not show temperatures dropping below 0F. Hopefully, this means that fruit buds in Virginia will not be damaged by the polar vortex.

Plants are not affected by wind chills (plants do not lose heat to the wind). But people and animals will be impacted by the heat loss from the high winds that are accompanying this storm. I’ve seen several wind chill forecasts for Tuesday in the -10 to -20F range. If your pruning crews are outside, make sure they are dressed appropriately for the cold. Also, make sure that your farm animals at least have shelter from the wind. For more information on protecting farm animals and equipment from the cold, read Cory Childs’ (VCE-Warren Co.) blog post from earlier today.

 

 

Harvest Maturity Report for October 8

On Tuesday (October 8), we sampled York, Cripps Pink (Pink Lady), Winesap, Granny Smith, Stayman, Fuji (BC2), and Suncrisp (which had ReTain and NAA applications) apples from trees on or near the AREC for this week’s maturity report. Despite the summer-like weather late last week and over the weekend, apples are continuing to ripen slowly. Fuji, Suncrisp, and Granny Smith are all showing starch degradation, (though ethylene levels remain low) and should be picked soon. We starting picking our Fuji (BC2) trees today.

York harvest started for some growers last week, and I suspect many growers in the Northern Shenandoah Valley are focusing their attention to this variety right now. The Yorks that we tested (Ramey’s and Imperial) were very firm (19.9 lbs), have excellent color (84% blush), a fair amount of sugar (12.1 Brix), and only showed a minimal amount of starch degradation (~1.3).

Pink Lady apples are already showing high sugar levels (13.1 Brix), but they are still quite starchy and varietal flavor hasn’t started to develop. I’d say they are still a couple-few weeks away from harvest.

The remnants of hurricane/tropical storm Karen is predicted to hit the region tonight, and for the first time this harvest season we are forecasted to have a prolonged stretch of rainy weather. Although the rains might slow down harvest activities, it will help to size up the later cultivars.

Click the on the link at the end of this sentence to download a copy of the 2013 Oct 8 Maturity Report.

Harvest Maturity Report for September 10

We harvested apples on September 10 for this week’s harvest maturity. Due to our annual Field Day and running samples for a pre-harvest drop trial, we only ran Golden Delicious, Red Delicious, and two strains of Fuji. From these data and my observations from around Frederick County, it appears that sugar content (soluble solids) are starting to come up in Golden Delicious, while starch degradation is still optimal for long term storage. Red Delicious are starting to ripen, and some early coloring strains are already being picked. I expect Red Delicious harvest to be in full swing by early next week. Early strains of Fuji are ready for harvest, but later strains still have several weeks before they will be ready for harvest. On Thursday, we’ll be harvesting Daybreak Fuji from a tall spindle planting and Rising Sun Fuji from a rootstock trial.

I expect the heat over these past couple-few days will advance apple ripening faster than what we have seen up until this time, so keep checking blocks that are near to your ideal harvest maturity. The heat is forecasted to break on Friday after which we’ll return to more moderate temperatures for at least seven days.

Click the link to the right for this week’s harvest maturity evaluation data.

Harvest Maturity Report for September 3

We collected fruit on Tuesday for this week’s maturity testing. Most growers in the Winchester area are finished or near to finishing Honeycrisp and Galas and moving into the main cultivars. Golden Delicious harvest has started, but the fruit has not advanced in maturity very much over the past week and is still very variable based on location and planting system. Compared to last week, the Goldens have lost firmness, but not starch and they have not increased in soluble solids or ethylene. Most Red Delicious strains are still at least a week away from early harvests for long term storage. This is despite the deep red colors that are developing. Picking of early strains of Fuji is underway, and like the other red skinned cultivars appear to have very nice color and size this year. Empires are starting to ripen and can probably be picked sometime in the next week, particularly if the fruit is going to be stored for any significant amount of time.

Over the next week, we are going to remain in a relatively dry weather pattern with warm but not hot days in the 80s and cool nights in the 50s and 60s. These conditions are ideal for developing color on red skinned cultivars and allowing the fruit to hang on the tree until ideal maturity and flavor has developed. We can only hope that these conditions will continue for several more weeks.

Click on the below link to download a pdf of the complete harvest maturity report for September 3, 2013.

2013 Sept 3 Maturity Report

Annual End-of-August Maturity Testing

This it the 28th year that researchers at the Alson H. Smith, Jr. AREC have recorded Golden Delicious and Red Delicious apple maturity data from orchards based in and around Winchester. Including 2013, data for Empire has been taken for twelve years and Gala for six years. In recent years, we have also added other commercially important cultivars to the analyses in order to generate long term averages. These data provide an interesting insight into the current season’s harvest, and can help growers make decisions on when to pick different blocks.

As discussed in a previous post, bloom date was about three weeks later than in 2012 and fairly close to the long-term averages. This should mean that harvest dates will be relatively “normal” or at least more similar to harvest dates in the late 1990’s through early 2000’s than they have been in the last several years.

As of this week, most growers in the Northern Shenandoah region are finishing up picking Ginger Golds, and have started picking Gala and Honeycrisp. Some growers in Central Virginia are finishing Gala and starting with Golden Delicious.

Many of the Golden Delicious blocks that we tested this week had very nice fruit finish, with minimal russet. Golden Delicious maturity was quite variable in the blocks that we tested, and it appears that some blocks will be ready to harvest within the next week, while others are probably 7-10 days away from being ready to harvest. The use of ReTain by some growers may explain some of this variability.

With the cool nights that we have experienced in August, red skinned cultivars have developed better than average color. However, be sure to check the starch and sugar levels before picking to be sure that the apples are mature enough to pick. Many Red Delicious apples that we tested this week had great color but very little starch degradation and soluble solids were only at 9-10 Brix.

Below are the data from this year’s end-of-August apple maturity sampling. In each year, the samples were taken around August 25 (August 26 this year) and consist of apples from the AREC and a few local growers. Thanks to Dave Carbaugh and Abby Kowalski for collecting and testing the fruit. Please refer to my post from last year if you need help interpreting the different maturity indices. You can also download a pdf of the 2013 Annual August Maturity Report.

Golden Delicious Maturity Report 1986-2013

 

  
Year

Background Color (1-4)*

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)**

Ethylene (ppm)

Bloom Date
1986

2.2

19.5

12.7
1987

20.0

12.2
1988

18.6

11.0

1.5
1989

17.7

10.3

2.0
1990

18.0

10.5

1.6
1991

1.8

19.7

12.0

2.1
1992

1.8

20.1

12.0

1.6
1993

1.9

19.8

11.6

1.5
1994

2.3

19.8

12.0

1.7
1995

0.9

18.8

10.9

2.1
1996

2.9

19.6

11.2

2.9
1997

2.0

21.8

11.7

2.0
1998

2.5

19.2

12.2

2.1
1999

1.9

20.3

11.7

1.4
2000

1.8

17.5

11.9

2.5
2001

1.9

20.1

11.0

1.4
2002

2.2

21.2

11.4

2.1
2003

2.6

20.3

11.1

1.2
2004

2.3

18.2

12.3

2.0
2005

1.8

20.1

11.4

1.7
2006

1.9

18.5

12.4

1.8
2007

1.6

18.0

12.3

1.6
2008

2.1

18.3

12.9

1.6

22-23 Apr
2009

1.8

17.2

12.4

1.7

22-Apr
2010

1.6

18.6

12.9

1.4

13-Apr
2011

2.1

20.1

12.9

1.2

20-Apr
2012

2.5

18.5

13.0

1.3

0.00

2-Apr
2013

2.2

18.3

11.9

2.2

0.17

25-Apr
Mean

2.0

19.2

11.9

1.8

17-Apr
Max

2.9

21.8

13.0

2.9

25-Apr
Min

0.9

17.2

10.3

1.2

2-Apr
* 1 = green, 2 = light green, 3 = yellowish green, 4 = yellow.
** 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

Red Delicious Maturity Report 1986-2013
Year

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date

1986

72.0

18.8

11.2
1987

68.0

19.8

10.8
1988

54.0

18.4

10.0

1.6
1989

69.0

18.6

8.7

1.6
1990

73.0

18.1

8.9

1.5
1991

69.0

18.8

10.4

1.6
1992

76.0

20.8

10.2

1.3
1993

68.0

21.7

9.5

1.7
1994

68.0

19.7

9.5

1.9
1995

68.0

19.2

9.1

1.6
1996

62.5

19.3

8.9

2.0

25-Apr
1997

66.7

22.4

9.4

1.2

25-Apr
1998

81.9

19.3

9.9

2.5

15-Apr
1999

65.5

19.8

10.5

1.9

28-Apr
2000

87.4

16.2

9.6

2.3

11-Apr
2001

61.0

20.5

8.3

1.8

28-Apr
2002

60.2

21.4

9.4

2.1

22-Apr
2003

58.4

20.4

8.5

1.9

22-Apr
2004

88.2

16.7

10.0

2.3

20-Apr
2005

73.7

18.7

9.2

2.0

24-Apr
2006

63.8

18.7

10.7

2.0

16-Apr
2007

81.1

18.1

11.0

1.7

22-Apr
2008

86.6

18.1

9.4

2.0

22-Apr
2009

79.2

17.5

10.2

1.9

24-Apr
2010

65.9

18.2

11.5

1.7

8-Apr
2011

67.5

19.8

11.5

2.1

21-Apr
2012

92.1

18.2

11.9

1.8

0.03

29-30-Mar
2013

91.3

18.4

9.8

2.0

0.25

23-Apr
Mean

72.1

19.1

9.9

1.8

0.1

20-Apr
Max

92.1

22.4

11.9

2.5

0.3

28-Apr
Min

54.0

16.2

8.3

1.2

0.0

29-30-Mar
* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

 

Gala Maturity Report 2008-2013

 

  
Year

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date

2008

93.5

18.3

13.6

5.6

21-Apr
2009

86.8

17.5

13.4

4.5

22-Apr
2010

78.0

16.3

14.9

6.4

9-Apr
2011

77.5

19.4

13.7

4.9

19-Apr
2012

91.1

18.0

13.2

4.1

7.13

29-30-Mar
2013

91.1

18.0

12.4

5.4

1.71

23-Apr
Mean

86.3

17.9

13.5

5.2

4.4

15-Apr
Max

93.5

19.4

14.9

6.4

7.1

23-Apr
Min

77.5

16.3

12.4

4.1

1.7

29-30-Mar
* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

 

Empire Maturity Report 2002-2013

 

  
Year

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date
2002

42.0

25.3

10.4

2.1
2003

60.4

21.9

9.6

1.7
2004

78.1

17.2

10.9

2.2
2005

55.3

20.3

10.1

1.9
2006

46.0

19.7

10.7

2.1
2007

64.0

17.9

10.6

2.1
2008

66.3

18.2

11.0

2.1

21-Apr
2009

52.4

16.6

10.9

1.1

20-Apr
2010

44.3

18.1

10.7

1.8
2011

49.8

19.7

11.2

2.0
2012

85.9

19.2

12.5

1.7

0.01

29-Mar
2013

63.0

18.6

10.6

1.5

0.04

21-Apr
Mean

59.0

19.4

10.8

1.9

0.0

15-Apr
Max

85.9

25.3

12.5

2.2

0.0

21-Apr
Min

42.0

16.6

9.6

1.1

0.0

29-Mar
* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

 

Maturity Report – Other Varieties 2011
Cultivar

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*
HoneyCrisp

66.2

15.8

13.0

5.1
Idared

17.0

19.9

11.1

1.2
* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

Maturity Report – Other Varieties 2012

 

 
Cultivar

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date
Fuji Early Strain

65.5

16.7

14.7

4.1

0.03

5-Apr
Fuji Late Strain

26.0

20.9

12.1

2.1

0.03

5-Apr
Idared

36.7

17.0

12.3

1.3

0.00

2-Apr
Rome

39.8

22.5

12.3

1.5

.

12-Apr
York

41.8

22.4

10.7

1.0

0.00

3-Apr
* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

Maturity Report – Other Varieties 2013

 

 
Cultivar (number of orchards tested)

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date
Cameo (1)

33.5

18.1

10.2

1.7

0.53

N/A
Fuji Early Strain (2)

80.3

16.3

13.6

4.3

1.51

25-Apr
Ginger Gold (2)

3.9**

16.0

12.8

3.5

0.00

24-Apr
Idared (6)

41.1

17.5

10.1

1.2

0.12

23-Apr
Jonagold (1)

35.5

18.7

11.8

2.8

0.00

23-Apr
Rome (1)

21.2

24.6

9.2

2

0.00

1-May
York (1)

53.5

24.4

9.4

1

1.20

25-Apr
* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.
** 1 = green, 2 = light green, 3 = yellowish green, 4 = yellow.

Predicted Harvest Dates for Winchester and Central Virginia

Predicting harvest date depends upon many factors, including full bloom date, accumulated heat units (growing degree days) over the course of the growing season, physiological stressors (e.g., disease and insect damage or drought), day to night temperature differentials as harvest approaches, and the amount of precipitation. However, the number of days between full bloom and harvest has been shown to be the most reliable predictor of harvest date.

More than two decades ago, researchers in Michigan determined that there there are an average of 143 days between full bloom and the first commercial pick of Red Delicious apples that are to be held in controlled atmosphere storage (i.e., firmness between 17-18 lbs; starch between 2.5-4 on the 8-pt scale Cornell Starch Chart). Additional seasonal adjustments above or below the average number of days until harvest are made based upon the average daily minimum temperatures for the 15 days after full bloom.

For the past several seasons I have tested the Michigan model using fruit from a block of Bisbee Red Delicious on MARK rootstock. Results to date have shown that this model is very good at predicting harvest maturity in Virginia.

Based on the Michigan model, here are the predictions for 2013:

In Winchester, Bisbee Red Delicious full bloom was April 23 and average minimum temperature for the 15 days after full bloom was 8.0°F less than 50°F. Using this data in the Michigan model, harvest is predicted ~8 days more than 143 days between full bloom and harvest. This puts the predicted harvest date for the first CA pick of Red Delicious at September 19.

In Central Virginia (Piney River), full bloom for Red Delicious was estimated to be April 20 and the predicted harvest is September 14.

Since most growers have Red Delicious trees in their orchards, other cultivars (and strains of Red Delicious that ripen earlier than Bisbee) can be estimated based upon experience on their picking date relative to Red Delicious.

Another method for estimating harvest date uses the rule-of-thumb that says, “for each 2-3 days departure for the normal bloom date, there will be a one-day departure from the normal harvest date.” (Blanpied and Silsby, 1992).

You can find more information about harvest maturity indices in a post from last year.

In the next week or two, I will start conducting maturity evaluations of fruit from the Winchester AREC and surrounding orchards.

References

Blanpied, G. and K. Silsby. 1992. Predicting Harvest Date Window for Apples. Cornell Information Bulletin 221. <<pdf>>

Beaudry, R., P. Schwallier, and M. Lennington. 1993. Apple Maturity Prediction: An Extension Tool to Aid Fruit Storage Decisions. HortTechnology 3(2): 233-239.