The fifth Winchester Area Tree Fruit Meeting for the 2013 Season will be held this Thursday, May 30th at the Virginia Tech – Alson H. Smith Jr. Agricultural Research and Extension Center (Winchester Fruit Lab) at 7:00 p.m. with Dr. Tracy Leskey (USDA-Kearneysville) offering the program. Snacks will be provided.
I hope to see you at the meeting Thursday.
Mark Sutphin
Associate Extension Agent
Agriculture and Natural Resources, Horticulture
Attached are the final MaluSim carbohydrate models that I will run for 2013.
Please print out a copy of the below pdf file to add to your records. Later in the season, I will be asking for feedback from you about how you used the model, how well the model predicted thinner response in your orchard, and if I should continue running the model in future years. Please feel free to send me additional feedback at anytime.
By this time, apples in most of Virginia are 13-20 mm in fruit size. Once apples reach this size, the trees tend to be less responsive to the typical 10 mm (carbaryl plus NAA or 6-BA) applications. However, if additional thinning is needed, growers can still use ethephon (sold under the trade names Ethrel and Ethephon 2). Ethephon is most effective when fruit size is 14 to 28 mm in diameter. In most years, it is difficult to chemically thin apples larger than 24 mm.
Ethephon has variable responses due to air temperature and humidity, as well as spray water volumes. Overthinning is more likely with this material than with other thinners. For this reason, ethephon has been primarily used when earlier thinning applications were not successful, on very difficult to thin cultivars, and/or when return bloom has been a severe problem. Thinning results with ethephon varies amongst cultivars. Ethephon is not very effective on Gala, but it is very effective on Golden Delicious and Rome. Where water is alkaline, buffering the spray solution to a pH of 3 to 5 will increase chemical stability and effectiveness. Do not use before a light rain or dew or when post-application temperatures are predicted to be greater than 90˚F because excessive thinning may occur.
Ethephon is usually combined with carbaryl or oxamyl (Vydate L). For greater thinning activity, ethephon can also be tank mixed with NAA and/or spray oil.
I have several research trials underway to look at alternative and hopefully more consistent late thinning materials. However, at this time, ethephon is still the standard material when fruit size is greater than 14 mm.
Once fruit is larger than 28 mm, hand thinning will need to be used to remove additional fruit. Hand thinning will have a positive impact on final fruit size and return bloom for up to about 45 days after full bloom. In 2013, this is around the first week of June for central Virginia and the second week of June for the Winchester area.
PROMOTING RETURN BLOOM IN APPLE
Ethephon (sold under the trade names Ethrel and Ethephon 2) can promote flower bud formation when applied from petal fall to about 6 to 8 weeks after full bloom. The greatest effect is from applications made 0 to 4 weeks after bloom. However, since ethephon can cause substantial fruit thinning, multiple weekly applications at rates 1/2 that of the thinning rate are recommended starting when fruitlets are greater than 30 mm. When possible, it is best to wait until after “June” drop has occurred. At a minimum, wait 7-10 days after the last thinning application before starting ethephon return bloom sprays. Additionally, do not apply ethephon to trees that are stressed or trees that are low in vigor.
A single ethephon application can be used at a high rate (up to 900 ppm). However, more consistent results are often obtained from multiple (3-4) applications made at 10-14 day intervals using lower rates (150-300 ppm). One common, and often effective strategy, is to make two applications in June and two applications in July.
Another strategy is to make 2-4 applications of ethephon at 150 ppm tank mixed with NAA at 5-10 ppm (or 2.5-5 ppm when tank mixed with spray oil). This approach has been beneficial for strongly biennial cultivars.
Sensitivity to ethephon is very different amongst cultivars, thus it is important to choose a rate specific to each variety. Do not exceed 8 pints per acre per year. If trees are over-cropped ethephon may not effectively give adequate return bloom the following season. Higher soluble solids and lower starch levels at harvest may be expected with some cultivars, particularly with high rates and/or late season applications. No loss of firmness has been detected with ‘Red Delicious’ at the optimum harvest date.
Ethephon sprays can reduce tree growth (dependent on timing and amounts used) and thus may not be desirable for young non-bearing trees if maximum tree growth is desirable.
HAND THINNING PEACHES
Hand thinning peaches to 6-8 inches apart on the branch will result in increased final fruit size and help prevent limb breakage. This activity will be most effective when completed over the next couple-few weeks. Hand thinning peaches later in the season will not have as much of an impact on final fruit size.
On May 20, I ran the MaluSim carbohydrate model for Winchester and Central Virginia. This will be the last MaluSim posting using forecasted data for the season. Sometime in the week or two I will post a season recap using only recorded data.
In Winchester, as predicted, we have been experiencing hot and cloudy weather over the last few days. Thinning applications made from late last week through Monday will likely be fairly active, with some easy to thin cultivars (e.g. Red Delicious) potentially having significant fruit drop. However, from Tuesday through the end of the coming week, growers should expect an average response from their thinning applications.
In Central Virginia, there was a similar trend but with somewhat cooler daytime temperatures, the carbohydrate deficits were less severe. Similar to Winchester, thinning applications made over the next several days should have a fairly typical response.
Peck Winchester VA MaluSim 5_20_13
Peck Central VA MaluSim 5_20_13
Fruitlet sizes and growth rates at the Winchester AREC:
MaluSim models were run on May 16 for Winchester and Central Virginia.
As I spoke about at the Winchester breakfast meeting on Thursday morning, the Winchester forecast is calling for warm and cloudy weather starting today and running through most of next week. From many year’s of research, we know that these are the conditions under which there is a fair amount of natural thinning and that chemical thinners can be particularly active. When the weather data is run through the MaluSim model, we see that there is a carbohydrate deficit between -40 to -60 g CHO/day predicted for the next 10 days. This means that chemical thinners that are applied over the next several days will likely be fairly active. With this in mind, growers should consider reducing rates and/or not using a surfactant. Growers with blocks that sustained freeze damage on Tuesday morning, should consider further reducing rates. As always, you should be checking your trees and making decisions based upon the conditions in your own orchard.
For Central Virginia (Piney River), the carbohydrate deficits over the next week will remain in the negative, but not be as low as the Winchester area. This means that chemical thinners applied from today through the weekend will likely be slightly aggressive when used at standard rates. Growers should be regularly checking their blocks for current conditions. By now, you should be able to see some effect of the cloudy weather that the region experienced early last week.
Here are the pdf files that contain the weather data and the MaluSim models:
Peck Central VA MaluSim 5_16_13
Peck Winchester VA MaluSim 5_16_13
The MaluSim carbohydrate model was run on May 13 for both Winchester and Central Virginia.
In Central Virginia, many later blooming cultivars are around 10 mm fruitlet size and can still be chemically thinned. From applications made over the past weekend, growers can expect average responses to chemical thinners. As we move through the week, greater and greater carbohydrate deficits are predicted, which will increase the potency of chemical thinners.
For Winchester, the model is predicting mild carbohydrate deficits early in the week, and much more severe deficits towards the end of the week and over the weekend. Applications made this past weekend through the middle of the week will likely have an average to slightly aggressive response. However, applications make towards the end of the week may result in very aggressive thinning activity. If the weather forecasts hold up, growers should consider reducing rates for applications made towards the end of the week.
I will run the model again on Thursday, May 16.
Fruitlet sizes from the Winchester AREC:
One more note, there are widespread frost/freeze predictions for most of Virginia for Tuesday morning. If a significant frost/freeze event occurs, growers should be cautious with their thinning applications until they can assess if damage has occurred. However, the forecast for Winchester predicts the temperature will only go to 32F, which will not be cold enough to cause significant damage. The forecast for fruit growing regions to the south of Winchester appears to be in the mid-30s to low 40s.
To see more information, click on the linked pdf files below:
On Wednesday (May 15) starting at 11AM, we will have the next Rappahannock County In-Orchard meeting at William’s Orchard.
And, on Thursday morning (May 16) starting at 7AM, we will have a breakfast meeting at the Winchester AREC with plant pathology, entomology, and horticulture updates.
Meeting dates, times, and locations can be found at: http://www.anr.ext.vt.edu/tree-fruit/index.html by clicking on the “Upcoming Programs & Events” link on the righthand side of the screen.
MaluSim carbohydrate models for Winchester and Central Virginia were run on Thursday morning.
Over the next day or so, for Central Virginia, the carbohydrate balance will remain in the negative, but quickly move to the positive over the weekend. From thinning applications made Thursday (5/9) or Friday (5/10), growers should expect a fairly “normal” response. However, forecast data from Intellicast.com, suggests that sunnier, but cooler weather will move into Virginia early next week, followed by a warming trend starting on Wednesday. Based on the MaluSim model, this weather pattern will cause apple trees to have positive carbohydrate values through the early part of next week, and thus standard rates of thinners used on Saturday or Sunday will be less effective than expected. In blocks where heavier thinning is needed, growers should consider holding off on their 10 mm thinning application until Tuesday or Wednesday when warmer temperatures return. However, once fruit gets to be 15 mm or larger, NAA and 6-BA are less effective thinning agents. The other approach is to increase the rates used in thinning applications made over the weekend through Monday.
The above scenario is similar for Winchester but since fruit size is smaller (generally 6-8 mm), growers can wait for next week’s warming trend to make the 10 mm thinning applications. Additionally, with the smaller fruit size in Winchester, the cloudy weather that we’ve experienced over the last few days should cause less natural thinning than what might occur in Central Virginia.
I’ll run the model again on Monday.
Current fruitlet sizes at the Winchester AREC:
For more information, download pdfs of the models:
On Wednesday May 8, we will have a commercial fruit growers’ meeting at Saunders Brothers Orchards starting at 11AM. The meeting was requested by growers in the Central Virginia area to discuss fruit thinning, as well as current disease and insect management issues.
For more information, please contact Michael Lachance at Lachance@vt.edu or 434 263 4035.
MaluSim models were run on Monday May 6 for Winchester and Central Virginia (Piney River). The outputs from both locations were fairly similar, with carbohydrate deficits predicted over the next six or so days. This is mostly due to the cloud cover from a series of storms that will pass through the region. With sunnier conditions and warmer temperatures, the model predicts a carbohydrate surplus by Saturday.
Apple trees are still at late bloom to 4 mm fruitlet size in the Winchester area, and growers will probably not need to start thinning until later in the week or early next week.
In Central Virginia, fruitlets are ranging from 8 to 15 mm. Growers should consider reducing rates over the next few days as the model is predicting an aggressive response to standard rates of chemical thinners. However, as we move towards the end of the week, growers should use full rates to ensure an effective response.
It is unclear how much “natural” thinning will occur from this prolonged stretch of cloudy weather. However, work by Dr. Byers suggests that 3 days of cloudy weather with temperatures at 70F (this was a controlled study in growth chambers) can cause 50% of the fruitlets to abscise. With the prolonged stretch of cloudy weather that we are experiencing, growers should consider being less aggressive with rates until the end of the week.
