May 29, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, May 29, 2018, 8:00 – 9:00 AM
Guest speaker: Phil Schwallier, District Horticulture Agent, Michigan State University – Extension
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 29th Call Stream: CLICK HERE


Insect updates
European red mites and San Jose scale
High temperatures experienced across most of the region will affect typical pest patterns asymmetrically. While some insect populations will experience detrimental effects or no effect at all, European red mites and San Jose scale both favor the heat and are likely to grow in population much faster than previous years. Growers who typically put up tapes for San Jose scale should do this sooner than was in previous seasons. Scouting for both European red mites and San Jose scale should be performed sooner than usual as well.

Japanese beetle and spotted wing drosophila
In addition to European red mites and San Jose scale, Japanese beetle and spotted wing drosophila may also appear relatively early this season, if the trend of warm weather continues. Spotted wind drosophila is not a pest of apples, however, is of concern for growers who also grow strawberries and other susceptible crops. For more information, please visit the SWD webpage maintained by the University of Wisconsin,

Codling moth
All growers should have a biofix for codling moth in their orchards by now, with many growers setting biofix the week of May 20 to May 26. We typically discuss delaying the first codling moth treatments when gaps between flights occur, but these gaps only happen if cool weather prevents a codling moth flight. Since we are not expecting any cool weather this week, it is likely that growers will catch moths regularly. A continuous flight means treatments may be required as early as the 250-degree-day codling moth treatment threshold. If you are calculating degree-days by hand, be aware that codling moth has a top developmental threshold of 86°F, which means all temperatures above 86°F should be counted as 86°F, e.g., a high of 95°F would be changed to 86°F degrees, if calculating by hand. Degree days are also available from your nearest NEWA station here,

Note: For a full discussion on using the degree-day model to manage codling moth, please review the May 22, 2018 AppleTalk notes.

Plum curculio
Plum curculio is clearly delayed this year as recent nights in the 70s haven’t resulted in the start of plum curculio feeding and oviposition, i.e., egg laying, which is typically expected. When plum curculio first move in to the orchards, the insects must feed and mate before they can cause typical plant scarring, often taking up to a week to occur. Most damage on early varieties has been feeding injury, suggesting plum curculio has just moved into the orchard perimeter.

Note: For additional discussion on plum curculio, please review the May 22, 2018 AppleTalk notes.

Disease updates
Foliar burns observed on leaves
Foliar burning associated with captan applications, at this point in the season will be more intense if temperatures are high at the time of application. When applying captan during hot temperatures, avoid adding l surfactants and penetrants that have an oil component to them.

Apple scab
So far, the typical second wave of apple scab infections has not been seen. As temperatures reach into the mid-90s, mature ascospores may be destroyed by these high temperatures, prior to their release during a rain event. Orchard floors with knee-high grass and unkept plant debris present a hospitable habitat for fallen inoculum to survive, but ascospores in plant material that are left exposed on bare or mowed ground will disintegrate. At this point, spray intervals for materials like captan can be tentatively extended up to ten days unless a second wave of scab is seen.

Powdery mildew
While apple scab is hindered by 90°F weather, these hot and dry conditions are favorable for powdery mildew infections. If conventional growers haven’t reapplied their fungicide cover, this next spray would be ideal to add a sterol-inhibiting fungicide, e.g., Rally (myclobutanil), for powdery mildew control. Organic growers will have to use sulfur on new trees but should be careful when applying during high temperatures. Note: Hot temperatures that could cause phytotoxicity from sulfur, include highs in the mid-80s.

Fire blight
Risk of fire blight is not as high as it was during bloom, but bacteria still have the potential to replicate tenfold every couple of hours. Be observant for cankers and bacterial ooze that could spread infections, even as fire blight risk decreases. At the current stage of tree growth, fire blight transmission down shoots where new tissue can be exposed is a primary source of fire-blight infections. Rapid or easily transmitted fire blight will be a possibility until shoots stop growing.

Some orchards recently experienced hail damage to trees several days after petal fall. Hail is not as destructive when the fruit are 5 – 10 mm in size, as it would be during other parts of the season. Bacterial infection may be possible depending on how much bark was torn. While bacterial numbers have come down over the past week, all trees that have been injured during a hail storm will have significant risk of a fire-blight infection. To mitigate the risk of a fire-blight infection after a hail storm, streptomycin may be applied to all impacted trees.

Guest speaker, Phil Schwallier
George Sundin was on one of our early calls and he mentioned your research on the use of Apogee on young trees to delay their shoot growth, as a fire blight protection technique. If Apogee applications cease by the end of June, will any growth on that tree be lost by the time shoot elongation is over?

Experimental groups of two-year-old trees were treated with either one or two ounces per acre of Apogee at pink and again two weeks later. The goal was to reduce shoot growth through June while fire blight risk is greatest. Once the Apogee wore off around July, trees then grew vigorously in July and August with less risk of fire blight. Treated trees were three or four centimeters behind untreated trees but caught up fully once the Apogee wore off. There were no major differences between the one- or two-ounce experimental groups. If a severe fire-blight season is expected, a third application of one ounce per acre can be made two weeks after the second application. Note: Phil did not inoculate the trees with fire blight during the study, therefore this is not a true scientific study which confirms the Apogee was responsible for effective management of fire blight during the trial.

What about delaying the subsequent rapid ‘catch-up’ growth? Did that influence the condition of those trees going into winter?

All trees were fertilized at the same time. Currently, there are no differences in the trees and there is no fire blight in that portion of the block. The tree’s ability to winterize may have been affected if growth was pushed too far into the season, but trees in the experiment were treated moderately until June.

In previous discussions it has been mentioned that carbaryl is not dose dependent. If this is true, then how does the carbohydrate model influence application rates of carbaryl?

Carbaryl is not dose dependent, so shouldn’t be varied according to carbohydrate model. Phil uses the one-pint rate rather than the one-quart rate. In an experiment comparing the thinning effects of one pound of Carbaryl 50W, one pint of Sevin XLR, two pounds of Carbaryl 50W and one quart of Sevin XLR, there was only a 1% difference in thinning, between the lesser and the greater dosages. The experiment was not done in combination with NAA. Sevin XLR won’t be effective at rates under half a pint, so a pint per acre is recommended.

We went from green tip to bloom in less than three weeks in many locations. According to the carbohydrate model, it may not be reliable when green tip to bloom is less than 21 days. Any thoughts on how to work with the model under these conditions?

Phil did not know the exact calculations that are used in the model, but he speculated the use of carbohydrates is not being accurately estimated. Day and night temperatures over the last few days have put trees under severe stress which supports the model’s predictions that trees will be sensitive.

What would you do if your king fruits were at 13-15mm and thinning was still necessary?

For Fuji or Gala that are difficult to thin, a heavy treatment is needed, especially during this high heat. If this is the first thinning spray of the season, Phil recommends 15 parts per million of NAA plus a quart of Sevin XLR. If a block has a history of thinning poorly, a surfactant like Regulaid may be helpful. Addition of Regulaid can account for 5-10% more thinning. Although there may be a thinning response due to the forecasted cooling trend, normal rates may be necessary if hard-to-thin fruit require thinning late in the season. There is also the option to only apply thinner to the top of the tree, targeting the top two thirds of the spray to the canopy. This will not thin fruit closer to the ground, but this fruit is easily hand thinned.

What about varieties that aren’t classified as hard to thin?

Varieties like Ginger Gold, Ida Red, McIntosh and Jonathan that are easy to thin would only need 10-15 parts of NAA for a first thinning application on big apples. If the first application is late, rates need to be increased. Trees have just come out of a period of high stress according to the carbohydrate model, and increased rates will thin trees. While the carbohydrate model only factors the current weather and the next three days’ forecasts, Phil thinks stress from conditions of up to two days prior may also play a role. Even if the carbohydrate model indicates lower stress, adjustments which consider the recent weather, may be necessary.

What about people who have already made a thinning application at a low rate last week?

What was put on a week ago before high-stress temperatures will now be showing a size separation in fruit. Fruits that are noticeably smaller are likely to drop off the tree. If a size separation is observed, a reduced dosage of 10-12 parts per million plus Sevin XLR without Regulaid should be applied. If a separation can’t be discerned six days after thinning, an aggressive application may be necessary with an aim to thin tree tops more heavily than lower branches, to reduce the risk of over thinning.

How might growers make use of a milder thinner like Amid-Thin W (NAD) at this time of the year?

Amid-Thin W (NAD) is usually applied at petal fall or even full bloom, but up until recently not much thinning has been done during full bloom. The very mild thinner is usually applied at eight ounces per hundred gallons of water. A low-set year with frost damage or fewer pollinators may only need NAD to achieve the right amount of thinning. NAD will generally under-thin trees year after year, but gets the thinning started and promotes return bloom. While NAD will thin about 20% in most varieties, 50-60% thinning is usually necessary.

At some NEWA stations the carbohydrate model has said, “Do not thin.” Does the extreme heat we experienced act as a thinner itself?

Natural thinning will occur in stressful conditions. In a period with 21 straight days of rain in Michigan, upwards of 90% of fruits were lost due to weather. Extreme heat will affect fruit all the way up to 18mm, but this effect won’t be noticeable for several days. When a tree drops fruitlets due to natural stress, these are expected to be the same fruits that would be removed by a thinner. Phil thinks recent heat stress will cause 15% thinning. Growers are encouraged to keep check trees, i.e., unsprayed trees, to verify the effect thinners are having.

Is Ethephon used for thinning with large apples?

Ethephon is a rescue thinner that tends not to be as predictable as other thinners, and easily risks under or over thinning. If apples are larger than 20mm and thinning is still needed, one quart of Sevin XLR per acre and one quart of Ethrel per acre can be used. Ethrel is dose dependent and should be adjusted based on heat conditions.

NAA may be applied to promote return bloom, after the normal thinning window. Please review the timing of these applications?

A typical schedule to apply NAA to promote return bloom has been at five, seven and nine weeks after full bloom. Recent data suggests flower bud initiation starts two weeks sooner on Honeycrisp, compared to other varieties. If NAA was applied at three weeks after full bloom, this application would have a thinning impact on Honeycrisp. Additional research is in progress, but Phil recommended growers start on Honeycrisp at four weeks after full bloom rather than waiting until the fifth week. Timing on other varieties may still be completed at five, seven and nine weeks after full bloom.