Tag Archives: peach

Late thinning of apple, return bloom, and peach hand thinning

Posted on May 22, 2014 by Greg Peck

LATE (“RESCUE”) THINNING

Where late (14-25 mm) thinning is still possible growers can use the following materials and combinations of materials in order of greater thinning potency:

ethephon (0.5 -1.5 pints/100 gal)
ethephon + carbaryl (1 pint)
ethephon + carbaryl + oil (1 quart)
ethephon + carbaryl + oil + NAA (5 ppm)

Ethephon applications can cause over thinning, so use the lowest rates and tank mix with the least number of other materials unless significant fruit removal is desired.

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.

Fruit Bud Damage in the Winchester Area

Posted on March 9, 2014 by Greg Peck

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.

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.

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

Posted on January 6, 2014 by Greg Peck

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. At 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.

Soil and leaf sampling for nutrient analysis by Greg Peck

Posted on July 30, 2013 by Greg Peck

Measuring the nutrient needs of orchards should be done by using both soil and leaf (also known as foliar) nutrient analyses. Soil analysis is best done before planting a new orchard so that lime and fertilizers can be incorporated deeper into the soil profile. Adjusting soil pH and getting less mobile nutrients into the rootzone is difficult once the orchard has been established, though there are times when these practices can and should be done. Soil sampling should continue throughout the life of an orchard every five or so years to monitor soil pH. In peach blocks where sulfur has been repeatedly applied for disease control, soil pH should be checked more frequently to ensure that the pH hasn’t fallen out of the acceptable range.

Since soil pH and nutrient content changes through the soil profile, soil samples should be taken from a consistent depth. Many labs will recommend a soil depth to sample, and then use that depth to calculate fertilizer and lime recommendations. The Virginia Tech Soil Lab recommends samples be taken from the top 6-8 inches of soil. When soil sampling prior to planting, it is recommended to take separate top- and sub-soil samples. Additional information on soil sampling can be found in the Virginia Tech Agronomy Handbook.

Soil nutrient analysis is a measure of the “plant available” minerals in the soil. However, due to the complex nature of the soil-root interface, minerals that are “plant available” are not necessarily taken up by plants and therefore soil testing does not always provide an accurate measure of the nutrient status of the trees in the orchard. Additionally, most soil analyses do not directly measure nitrogen content, but instead base nitrogen fertilizer recommendations on soil type and organic matter content. Additional information on soil nutrient analyses for orchards can be found in the following Virginia Tech publications

For commercial growers within Virginia, the Virginia Tech Soil Testing Lab conducts soil analyses at no charge. However, there is an additional charge for measurement of soluble salts ($2) and organic matter ($4). For the quickest processing time, be sure to use the official soil sampling boxes. Sample boxes are available from your local Virginia Cooperative Extension office. The Virginia Tech Soil Testing Lab will send you results via email. Please use the most recent submission form when submitting samples.

For mature fruit trees, leaf mineral content is a more accurate measure of the nutrient status than soil analyses. Leaf analysis can help determine if additional fertilizers are needed before there are any visual signs of deficiency in the tree. Leaf samples should be taken when most vegetative growth has subsided (terminal buds are set), which for most bearing apple trees happens in late July or early August. For the most part, by the time leaf samples are taken and analyzed there is little that can be done to impact the current season’s crop and next year’s flower buds. Therefore, to maintain optimal performance of your orchard, it is recommended to perform a leaf analysis for each block once every three years to ensure that you are consistently maintaining adequate nutrient levels.

Below are some additional recommendations for taking accurate leaf samples.

Collect 60-100 leaves to get a representative sample. Leaves should be taken at about the midpoint of the new growth and from all actively growing parts of smaller trees and between waist and head high on larger trees.
Choose between 8 and 10 separate trees that are representative of the block.
Don’t mix leaves from different varieties, rootstocks, ages, soil types, blocks, or farms.
Sample poorly growing or otherwise problematic trees separately from healthy trees, so that a comparison can be made between them.

Unfortunately, the Virginia Tech Soils Lab does not perform plant tissue analysis. Below is a partial list of regional service labs that perform leaf tissue analysis (this is not an endorsement of these labs and other labs may provide similar services):

1. Penn State Agricultural Analytical Services Laboratory (State College, PA)

Plant Analysis Kit, $24
N, P, K, Ca, Mg, Mn, Fe, Cu, B, Zn + crop specific interpretations

2. A&L Eastern Laboratories, Inc. (Richmond, VA)

PT2 package, $26.20 ($24 without recommendations)
N, S, P, K, Mg, Ca, Na, Fe, Al, Mn, B, Cu, Zn

3. Agro-One Soils Laboratory (Ithaca, NY)

Plant Tissue Analysis (#180), $24
N, P, K, Ca, Mg, Zn, Cu, Fe, B, Mn + recommendations based on Cornell University guidelines

4. North Carolina Dept of Agriculture (Raleigh, NC)

Plant Tissue Analysis, $25
N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B + recommendations

Suggestions for late thinning and return bloom applications

Posted on May 21, 2013 by Greg Peck

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 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