Final Report for ONE15-242
Project Information
This year we successfully conducted and evaluated two string thinner studies on mature ‘Gala’ and ‘Honeycrisp’ apple trees with a cooperator in NY. All thinning treatments were applied on May 10 and 11 2015. Preliminary results of this technique have been promising. First evaluations began in 2014. More detailed studies were conducted in 2015 with SARE funding. We have had the concern that mechanical string thinning can damage apple trees and spread fire blight in a high density apple orchard. In this study (and at another conducted in 2014) the incidence and severity of fire blight was not increased for either cultivar by using the string thinner. Damage to the spur leaves, reproductive, and vegetative structures was more significant when the string thinner was applied at 240rpm in 2014. Increasing the rotational velocity of the string thinner (240 rpm vs. 220 rpm vs. 200 rpm) caused more string contact with the narrow canopy and increased leaf damage but this was not formally quantified in 2014. The string thinner at 240 rpm removed more Honeycrisp blossom clusters, spur leaves, and broke fruiting shoots compared with Gala. The most severe treatment removed 100 more Honeycrisp spur leaves compared to the control. In 2015 we quantified the damage to the spur leaves, reproductive, and vegetative structures. It was reduced when the string thinner was applied at 200 rpm and 220 rpm instead of 240 rpm.
Maxcel applied at 8-10 mm did improve fruit size and had a better effect than in 2014 when the string thinning at 240 rpm caused as much as 40 gr decrease in fruit weight compared to the control trees. At the 2015 harvest the string thinning at 220 rpm and the string thinning at 220 rpm followed by Maxcel caused as much as a 15 gr and 22 gr decrease in fruit weight compared to the control trees, respectively.
Although there is a concern that mechanical string thinning can spread fire blight in a high density orchard, our study showed no increase in the severity of fire blight in May 2015. This result needs to be confirmed over several season before this technique can be recommended, but we are very excited about the future of the Darwin machine when the US fruit industry won’t have carbaryl available anymore.
Introduction:
In the Northeastern US, almost all apple orchards are chemically thinned early in the season each year using a combination of either Naphtaleneacetic Acid (NAA, a synthetic auxin plant growth regulator) plus Carbaryl or Benzyl Adenine (BA, a synthetic cytokinin plant growth regulator) plus Carbaryl. Carbaryl, which is a carbamate insecticide, causes some thinning but also enhances the thinning efficacy of either NAA or BA. Carbaryl has been an essential component of chemical thinning programs for more than 40 years. However, there is concern that Carbaryl will be removed from the market by regulatory action in the US. If Carbaryl were removed from the market, apple growers in the Northeastern US would not achieve adequate thinning with NAA or BA alone. Since 2014, one US based supermarket chain has threatened to prohibit the use of Carbaryl on apples they have purchased even though it was still a legal product. At Cornell University we continue to research chemical thinning alternatives without Carbaryl, but there is significant interest in economical and safe nonchemical thinning strategies for use in high-density apple orchards. The main objective of this study was to evaluate the use of a single spindle string thinner on two high-value apple cultivars in the Western NY fruit region.
- To evaluate the use of a single spindle string thinner on two high-value apple cultivars in the Western NY fruit region by (a) determining the proper thinning severity, (2) the optimal application timing for Honeycrisp and Gala, (3) quantifying the potential spreading of fire blight, (4) supplementing the mechanical thinning with other chemical treatment, and (5) measuring return bloom and potential yields.
Cooperators
Research
In May 2015, we conducted two string thinner studies on mature ‘Gala’ and ‘Honeycrisp’ apple trees on B.9 rootstock at 2X11 ft. spacing. The ‘Gala’ and ‘Honeycrisp’ trees were 7 and 9 years old, respectively. Both were trained to a Super Spindle apple system at Lamont Fruit Farm Inc., Waterport, New York. The shape of the canopy was a narrow tree wall. The string thinner (Darwin machine) consisted of a tractor –mounted frame with a 10 ft. tall vertical spindle in the center of the frame. Attached to the spindle were 54 steel plates securing a total of 216 plastic cords each measuring 2 ft. in length. Speed of the clockwise rotating spindle was adjusted with a hydraulic motor. The string thinner spindle was operated at 200 or 220 rpm, and the mechanical thinner was driven through the orchard rows at 5 miles/hour. All treatments were applied at 70-80% bloom stage for the king flower and balloon stage for the laterals for Gala on May 10 and for Honeycrisp on May 11, 2015.
The specific treatments for ‘Gala’ were: (1) Control apple trees that received the grower standard chemical thinning program; 2pts/Acre Sevin XLR 5/27, 1 Galon/Acre Maxcel + 2pts/Acre Sevin XLR 6/1, 1 Galon/Acre Maxcel + 2pts/Acre Sevin XLR 6/9 (without the use of the string thinner), (2) Apple trees thinned with the string thinner at 200 rpm and 5 mph, (3) Apple trees thinned with the string thinner at 200 rpm and 5 mph, followed by Maxcel @85ppm sprayed at the 8-10mm fruitlet stage on June 1, 2015 (4) Apple trees thinned with the string thinner at 220 rpm and 5 mph, and (5) Apple trees thinned with the string thinner at 220 rpm and 5 mph, followed by Maxcel @85ppm sprayed at the 8-10mm fruitlet stage on June 1, 2015.
The specific treatments for “Honeycrisp/B.9” were: (1) Control apple trees that received the grower standard chemical thinning program; 2pts/Acre Sevin XLR 5/27, Fruitone L 4.25oz/Acre + 2pts/Acre Sevin XLR 6/2 (without the use of the string thinner), (2) Apple trees thinned with the string thinner at 200 rpm and 5 mph, (3) Apple trees thinned with the string thinner at 220 rpm and 5 mph, (4) Apple trees thinned with the string thinner at 200 rpm and 5 mph, followed by Maxcel @50ppm sprayed at the 8-10mm fruitlet stage on June 1, 2015, (5) Apple trees thinned with the string thinner at 220 rpm and 5 mph, followed by Maxcel @50ppm sprayed at the 8-10mm fruitlet stage on June 1, 2015.
The two field experiments were designed as randomized complete blocks with five replications consisting of 50 trees per plot. Before string thinning treatments were applied, the initial number of blossom clusters per flagged data tree was recorded. Immediately after treatment, blossom clusters were counted on the data trees. One extra data tree per plot was used to quantify the potential damage to the bark, shoots, leaves, and buds, and for assessing fire blight. In July 2015, ten trees were selected within the center of each plot to ensure consistent treatment, uniformity, and were used to quantify the final number and diameter of fruitlets per tree. In September 2015, whole tree fruit counts and fruit weight of three data trees per plot were collected at harvest one time for Gala and two times for Honeycrisp.
Effects of mechanical blossom thinning treatments applied on May 2014 on return bloom of Honeycrisp and Gala:
String thinner treatments had a significant negative effect on return bloom of Honeycrisp. There were fewer blossom clusters per tree when the string thinner spindle was operated at 240rpm in 2014. Based on the negative effect on return bloom of Honeycrisp we decided to decrease the rotational speed from 240rpm to 220rpm in 2015.
String thinner treatments had a significant positive effect on return bloom of Gala. There was no significant reduction in blossom clusters per tree in the low, medium, or upper section of the trees. The 220rpm treated trees had the higher number of blossom cluster per tree.
Effects of mechanical blossom thinning treatments applied on May 2015 on return bloom of Honeycrisp and Gala:
String thinner treatments had again a significant negative effect on return bloom of Honeycrisp. There were fewer blossom clusters per tree when the string thinner spindle was operated at 220rpm in 2015. Based on the negative effect on return bloom of Honeycrisp we decided to decrease the rotational speed from 220rpm to 200rpm and from 200rpm to 180rpm in 2016. We initiated a new experiment with same trees this past May 2016.
Both string thinner treatments and the treatments followed by Maxcel did not significantly reduce the blossom clusters per tree in the low, medium, or upper section of the trees compared with the grower standard trees.
Effects of mechanical blossom thinning treatments on number of fruitlets and clusters removed per tree in 2015:
We have had the concern that mechanical string thinning can damage apple trees and spread fire blight in a high density apple orchard. In this study (and at another conducted in 2014) the incidence and severity of fire blight was not increased for either cultivar by using the string thinner. Damage to the spur leaves, reproductive, and vegetative structures was more significant when the string thinner was applied at 240rpm in 2014. Increasing the rotational velocity of the string thinner (240 rpm vs. 220 rpm vs. 200 rpm) caused more string contact with the narrow canopy and increased leaf damage but this was not formally quantified in 2014. The string thinner at 240 rpm removed more Honeycrisp blossom clusters, spur leaves, and broke fruiting shoots compared with Gala. The most severe treatment removed 100 more Honeycrisp spur leaves compared to the control. In 2015 we quantified the damage to the spur leaves, reproductive, and vegetative structures. It was reduced when the string thinner was applied at 200 rpm and 220 rpm instead of 240 rpm.
Effects of mechanical blossom thinning treatments on fruit set, fruit number, fruit size, fruit weight, and yield in 2015:
Gala: All string thinning treatments reduced fruit set and did not significantly reduced fruit size and fruit weight. The string thinning treatment applied at 200 and 220 rpm followed by Maxcel caused greater thinning. Maxcel applied at 8-10mm did improve fruit size and had a better effect than in 2014 when the string thinning at 240 rpm caused as much as 40 gr decrease in fruit weight compared to the control trees. At the 2015 harvest the string thinning at 220 rpm and the string thinning at 220 rpm followed by Maxcel caused as much as a 15 gr and 22 gr decrease in fruit weight compared to the control trees, respectively. The grower standard chemical thinning treatment used multiple sprays of Maxcel which likely stimulated cell division and gave larger fruit size while the string thinner treatments reduced spur leaf area which likely inhibited initial fruit growth and cell division. There are incentives in the market for growers to produce large “Gala”; however, the smaller fruit size we obtained with the string thinner was a more serious problem for this strategy with Gala in 2014 than in 2015.
Honeycrisp: All string thinning treatments reduced fruit set and did not significantly reduced fruit size and fruit weight. The string thinning treatment applied at 220 rpm followed by Maxcel caused greater thinning. Both string thinning treatments followed by Maxcel increased fruit weight by August 19 and at harvest. There were as much as 48 gr and a 22 gr increase in fruit weight from the string thinning treatments at 200 rpm and 220 rpm followed by Maxcel at harvest, respectively. The highest yield reduction was achieved with the string thinning treatment at 200 rpm without Maxcel and there was a 56 gr decrease in fruit weight compared to the control trees.
This project allowed us to justify and get additional research funds for 2016 ($ 6,000 dollars from Apple Research and Development) and test more rates and timings of Maxcel to improve fruit size, specifically on Gala.
Education & Outreach Activities and Participation Summary
Participation Summary:
One publication has been submitted to the NY Fruit Quarterly magazine.
The grower cooperator Rod Farrow was invited to talk about “A Holistic Approach to Orchard Mechanization” at the IFTA annual conference session in Grand Rapids, Michigan, on Wednesday February 10, 2016. Rod discussed, among other things, our preliminary project results and the benefits of this technology for our industry to more than 350 registered participants (growers, fruit specialists, and consultants from all over the US and the world).
Tuesday July 19th, 2016: Rod, his partners, and have set up a field day where the results of our research are being presented at the same orchard blocks of Gala and Honeycrisp where we conducted mechanical blossom thinning in 2015. We feel very fortunate to have this possibility for such broad outreach and exposure to US growers and national media attending and covering this event. We will be providing the number of attendees after July 2016.
http://www.ifruittree.org/Events/2016-Study-Tour/2016-Study-Tour-Itinerary
and check the following information for this tour stop:
Tuesday July 19th - Orleans County.
7:30 am Depart Rochester Hotel
8:45 -10 am – Ledge Rock Farms, Medina
- Weed Management, Fireblight, Irrigation
- Geneva Rootstocks, Growing SnapDragon
- 10:15-11:30 am – Pettit Farms, Bates Rd, Medina
- New Varieties – NY1, NY2, Pazazz
- Tall Spindle System, NY1, NY2, Gala, Nutrition
- 11:45 am- 1:30 pm – Lunch, Leonard Oakes Estate Winery, Ridge Rd, Medina
- Catered Mexican Lunch
- Hard Cider Discussion and Heirloom Orchard Visit
- 1:45pm – 3:00 pm– Sandy Knoll Farms, Platten Rd, Lyndonville
- Established Tall Spindle, Pruning, Hedging, Trellis
- Platforms, Machine Harvest
- 3:30 pm – 4:45 pm– Lamont Fruit Farm, Stillwater Rd, Waterport
- Super Spindle – Hedging, Mechanical Blossom String Thinning, Crop Load Management
- Super Spindle – Economics, Precision Thinning
So far, these outreach efforts have shared the results with 270 stakeholders, extension, and researchers from 5 countries and multiple states from the US.
The project leader was interviewed by Good Fruit Grower magazine and an article about the research will be featured in the September or October issue, 2016.
thinning-without-carbaryl-darwin-work-good-fruit-grower-pages-36-37-october-2016
Project Outcomes
We again measured a crop value reduction in Gala and Honeycrisp (less crop value reduction if compared with a preliminary study conducted in 2014). We calculated as much as a 22 gr decrease for Gala and 56 gr decrease for Honeycrisp in fruit weight from string thinning treatments applied at 200rpm and 220rpm. The addition of a single application of Maxcel to the mechanical thinning program did not improve fruit size or crop value compared to the grower standard chemical thinning program (which it is a very aggressive thinning program). Among the string thinning treatments, a spindle speed of 200 provided the best overall thinning response and minimized injury to leaves.
We are now interested to improve fruit size with one and two applications of Maxcel in order to maximize crop value for treated Gala and Honeycrisp trees. The 2016 protocol included the addition of one more Maxcel spray at a higher rate to increase yield, fruit size, and crop value of treated trees.
Farmer Adoption
None at this moment.
Only experimental use of 2 acres for Gala and 2 acres for Honeycrisp with grower cooperator.
Same experimental acreage was again treated with Darwin machine this May 2016.
Areas needing additional study
The fire blight result needs to be confirmed over several seasons before the Darwin machine can be recommended.