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.
Today, I ran the first MaluSim Carbohydrate models for 2013. This includes a simulation for Winchester, and a simulation for Central Virginia (Piney River, VA). Thanks to Bennett Saunders for sending us the data to use for Central Virginia.
The Malusim model was developed by Drs. Alan Lakso and Terence Robinson at Cornell University to estimate the carbohydrate balance in an ‘Empire’ apple tree based upon many years of detailed research and information found in the scientific literature. In recent years, the model has been used by researchers and extension specialists in New York as a tool to help assess the application timing for applying thinning materials at the 10 mm fruitlet size. Carbohydrate status, and therefore the MaluSim model, is not as important for other times when chemical thinners might be applied (i.e., bloom, petal fall, 20 mm), so it is not as clear how well the model does to predict the response of chemical thinners used at timings other than 10 mm.
For the past several years, I have been running trials at the Winchester AREC to see how well the MaluSim model performs under conditions found in Virginia. Many researchers, including myself, are still working towards understanding the best way to use the model. From what we have found, when weather forecasts are used to predict the future carbohydrate status of an apple tree, the MaluSim model can provide a warning as to when there might be a chance for severe under- or over-thinning. This is particularly true when there are three- or four-day trends with large carbohydrate surpluses or deficits predicted. For this reason, in addition to the data points for each day, I show a four-day running average (the black line on the charts). To be consistent with other researchers and extension specialists, the four-day running average is calculated from the date the data is show to three days into the future.
Please keep these caveats in mind if you are using the MaluSim model to guide your thinning application timing:
In the below pdf files, I provide a chart of the weather data that are used to run each model (daily maximum temperature, daily minimum temperature, and daily solar radiation), a chart of the MaluSim model with day-by-day data and a four-day running average, and a chart with the potential response a chemical thinner might have for different levels of carbohydrate balance in the tree.
So, what do today’s models show? Some very advanced blocks of early blooming apple cultivars in Central Virginia are getting close to the 10 mm thinning stage. From applications that occur today and tomorrow, you should expect “normal” to “slightly aggressive” response from your standard thinning rates, but nothing that suggests sever overthinning. However, there is a period of unsettled weather predicted for Mon-Wed of next week that could cause the carbohydrate levels to drop in the trees. It all depends on the amount of cloud cover we get over those days. Temperatures are going to remain moderate over that period, so even with the potential for some cloud cover, it doesn’t look like a severe carbohydrate deficit. Cloud cover is the hardest thing to predict, and predictions are only good for 3 days at best.
In Winchester, we are still at late bloom to petal fall, so there’s probably another week before the carbohydrate model data needs careful interpretation.
I will talk more about the model at tonight’s In-depth fruit school in Winchester.
The table of contents in the 2013 Spray Bulletin was unfortunately printed with incorrect page numbers. Dr. Chris Bergh has manually updated the 2013 Spray Bulletin Table of Contents so that you can print a copy and insert it into the Bulletin.
We have been told that there are no more printed copies of the 2013 Spray Bulletin. However, the publication can be downloaded as a free pdf by clicking on the link on the Tree Fruit Extension and Outreach website.
Update (April 15): Dr. Alan Biggs still has about 20 copies of the 2013 Spray Bulletin for sale. If you want a copy, send a check for $14 made out to “West Virginia University” along with your mailing address to Dr. Biggs. He will send you a copy via USPS.
Dr. Alan Biggs WVU – KTFREC
There will be two commercial fruit grower meetings this week. On Tuesday (April 16) starting at 11:00AM, we will meet at Silver Creek Orchards in Nelson County to review current crop conditions and upcoming management decisions. On Thursday (April 18) at 7:00AM, we will meet at the Alson H. Smith, Jr. AREC for our first breakfast update meeting. Immediately following the breakfast meeting at the AREC, we will walk up the hill to view a Voen orchard covering system that was recently installed by Dr. Peck.
The Voen covering was funded in part by a grant from the Virginia Agricultural Council.
Future meeting dates and additional resources for tree-fruit producers can be found at the new Tree Fruit Extension and Outreach website.
The National Weather Service is predicting temperatures to drop to 22F by the morning of April 4 in the Winchester area. For the bud phenology that I’ve seen in the area, we will probably be spared from having very much damage.
Apples are still dormant with a few early blooming cultivars at silver or green tip. Even at green tip, there should only be 10% damage when temperatures drop to 18F. Peaches with a little pink showing may be susceptible to a low level ~10% of damage. Cherries are still in stage 1 or 2, and should be able to withstand temperatures down to 17F with minimal damage. So, fingers crossed that it doesn’t get any colder than predicted. Temperatures are forecasted to be more “spring-like” next week!
Here are pdf links for the Washington State University fact sheets on the critical temperatures for flower buds:
Additionally, Michigan State University has adapted the WSU critical temperature fact sheets into this easy-to-read fact sheet.
MSU has also put together an excellent set of resources about freezes and frosts in fruit crops.
Well, it’s hard to believe it given the cool temperatures that continue to prevail, but our Spring meetings start this week with an In-Orchard meeting at Crown Orchards on Tuesday starting at 11AM and an In-Depth meeting at the Alson H. Smith, Jr. AREC on Thursday evening starting at 7PM. Our first Rappahannock County meeting will be next Wednesday (April 10) at Jenkins Orchard starting at 11AM.
All tree-fruit meeting dates, times, locations, and directions can be found at the new Tree-Fruit Extension and Outreach Website by clicking on the Upcoming programs & events link.
To ensure that you don’t miss future announcements, please be sure to sign up for the Virginia Tech tree-fruit email delivery service by entering your email in the “Subscribe to commercial tree fruit updates” box on the Tree-Fruit Extension and Outreach Website.
The meetings are focused on commercial tree-fruit production. However, meetings are open to all, regardless of age, color, disability, gender, national origin, political affiliation, race, religion, sexual orientation, or veteran status. Virginia Cooperative Extension is an equal opportunity/affirmative action employer.
The scheduling of the 2013 fruit schools will be somewhat different than in the past, with two of the schools held on the same date. The Patrick-Carroll school (Mt. Airy) will be held on Tuesday, Feb 12. The Botetourt-Roanoke school will be held on the morning of Wednesday, Feb 13. The Nelson-Albemarle (Central Virginia) school will be held in the late afternoon-evening of that Wednesday. The Madison-Rappahannock school will be held on Thursday, Feb 14, and the Winchester school will be held on Friday, Feb 15 (Winchester Registration information).
Visit Dr. Pfeiffer’s Virginia Fruit Website: http://www.virginiafruit.ento.vt.edu/HotApple.html
