April 21 AppleTalk Conference Call

AppleTalk Conference Call Summary

Tuesday, April 21, 2020 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM,
Moderator: Peter Werts, IPM Institute of North America; questions or comments, or send to Josie Dillon, .

April 21^st Call Stream: CLICK HERE

AppleTalk call and blog logistics

Thank you for registering for AppleTalk!  Your participation makes this program possible. After each AppleTalk, you can expect the call recording and agenda to be posted to the blog following the call. Written summaries will be posted when complete, within 24 to 48 hours, and distributed via email in PDF format. John Aue, Peter Werts and Josie Dillon will begin scouting orchards in the coming weeks and are available to answer questions as the season begins. If you still need to register for AppleTalk visit: https://ipminstitute.org/projects/specialty-crop-grower-services/appletalk/register/.

Facebook Page
Follow the AppleTalk Facebook page to receive additional insights into orchard production and pest management. This page will include call reminders, call summaries, relevant articles, scouting observations and photos, and questions for growers. Post comments, questions and connect with other growers: https://www.facebook.com/groups/261393341551191/

Guest Speaker Schedule

1. April 28: Dr. Amaya Atucha, University of Wisconsin-Madison presenting on Nutrient Management and Tree Stress
2. May 12: Dr. Kari Peter, Penn State presenting on Fire Blight Management and Streptomycin Alternatives
3. June 2: Dr. Brent Short, Trecé presenting on Codling Moth Lures and Mating Disruption
4. July 14: Dr. Sara Villani, North Carolina State University presenting on Summer Fruit Rots

Regional update

Location	Degree Days (Base 32°F)	Degree Days (Base 43°F)	Degree Days (Base 50°F)
Eau Claire, WI	329	46	10
Gays Mills, WI	381	63	10
Hastings, MN	358	61	12
Harvard, IL	442	93	22
La Crescent, MN	405	67	12
Mauston (Northwoods), WI	370	54	8
Mequon (Barthel), WI	362	50	13
Rochester (Ela), WI	419	76	19
Trempealeau (Ecker’s), WI	367	53	13
Verona, WI	402	68	11

Table 1. Degree-day accumulations as of April 21, 2020 using data reported by Cornell NEWA Network.

April orchard phenology
Green tip was first reported across the region in southern Wisconsin on McIntosh varieties and Zestar between April 8 to 10 and cooler temperatures over the last ten days have significantly slowed tree growth. More locations have reported green tip as temperatures occasionally reach the low 60s°F. In Galesville WI first green tip on Honeycrisp and ½” green tip on Zestar and McIntosh have been reported. Areas north of Lacrosse and through central WI are still at silvertip to first green tip. Along the Illinois and Wisconsin borders, a variety of growth stages have been reported to include ¾” green tip, first tight cluster on Zestar in Rock County WI and near Woodstock IL.

Green tip on McIntosh often occurs between ~38-63 DD base 50°F, based on historical observations in the northeast United States. Michigan State University uses a base 43°F for their degree-day model and predicts McIntosh green tip to occur between 90 and 130 DD base 43°F. As of today, many areas in southern WI and Northern IL are already reporting green tip on McIntosh, even though degree-accumulations are significantly behind the models. Our current base 50°F DD in southern WI and Northern IL are between 10-32 and base 43°F DD are around 68 (Note: NEWA uses base 43°F instead of 42°F).

Orchards from the Twin Cities to northern Illinois had between two and 25 hours of temperatures below 23°F on April 14, 15 and 16. Absolute lows ranged from 9°F to 23°F across the NEWA stations surveyed, with lowest temperatures recorded in Eau Claire and Afton, MN. During a hard freeze, microscopic cracks can form in one-year old wood and green tissue. When oil is applied after a freeze, it may penetrate these cracks, causing injury to the tree. However, when the forecasted low is only around 29-32°F, damage is much less likely. There is still some retained heat going into the evening and the cold temperatures are relatively short lived. Cultivars with buds at silver tip or green tip should be okay. If the cultivars were beyond green tip, damage is likely but should be manageable at ~10% loss depending on the length of time temperatures stayed below 23°F.

The forecast for the next 10 to 14 days will be slightly below normal temperatures. Wednesday, April 22 is the only day where temperatures are above 60°F and there will likely be significant leaf expansion, e.g., ¼ inch or more. If copper is applied in the next day or two, and significant leaf expansion occurs, the copper does not redistribute with the expanding leaf and unprotected tissue will be present. To protect this new tissue against apple scab, an additional fungicide to protect against apple scab will need to be applied, depending on the variety and amount of leaf growth over the next five days.

Note: Remember to record 50% McIntosh green tip dates for better ascospore development readings in NEWA. Some orchards reported 50% McIntosh green tip as early as April 8-10.

Disease Management

Copper and oil applications
Copper may be applied to the whole orchard; certain varieties or not at all. Fire blight is the important risk factor that determines if a copper application is necessary. If fire blight has not been a problem in the last two years, copper may not be necessary. Copper may also offer utility on cool weather fungal diseases including silver leaf, anthracnose and Phomopsis. Silver leaf spread occurs early in the season and is associated with late pruning. When large-pruning cuts have been made, these cuts may be infected with silver leaf spores during rain events.

Copper applied at silver tip or bud-break target fire blight and apple scab. At this early growth stage and with cool temperatures, bacterial colonies in fire blight cankers are not actively growing. Fire blight cankers become much more active at pink and enough copper needs to be applied at this time to persist until early pink through bloom to inhibit bacterial growth. The downside of applying too high of a rate of copper, is that if excess copper is present at petal fall it can cause fruit damage and russeting.

Note: Once copper products are dry, they are no longer phytotoxic. If there is still enough copper residue remaining at petal fall, this can be redistributed by rainfall on to the developing fruitlets and cause russeting. For the standard copper products on the market, approximately three to four inches of rain between the application and fruit-set will mitigate this risk.

Functionally, copper sprays are only able to kill the fire blight bacteria (Erwinia amylovora) when a copper ion that has been dissolved in water encounters an active fire blight canker. A small amount of water is necessary for copper activation (air humidity can often be enough), however too much water, such as periods of heavy rainfall, will completely rinse the copper away. Even a small amount of copper residue remaining at petal fall will cause fruit russeting.

There are many copper-containing products that can be used for fire blight at bud-break. Formulations may contain copper hydroxide, copper sulfate, copper oxychloride, etc. All formulations function the same way by supplying copper ions, i.e., metallic copper, and it is these copper ions that inhibit bacterial or fungal growth. The hydroxyl or sulphate portion of the molecule does not. When choosing a copper product for fire blight, it is important to compare the amount of metallic copper contained in the different products. This is often represented on the package either as a percentage of dry metallic copper by weight or as pounds per liquid volume.

Another important factor in choosing copper is its longevity, which is dependent on the particle size of the copper salts in the formulated products. The smaller the size, the less likely it is to be dislodged by rain, and theoretically the better the copper will be distributed throughout fire blight cankers. Getting information on particle size for particular copper products can be difficult, however your distributor would likely be able to assist. Some options include:

• Kocide is 30% metallic copper
• COCS is 50% metallic copper
• Badge contains 2.18 lb. copper per gallon. Apply 2 – 4 qt per gallon.

For more information visit:

• Demystifying Copper for Disease Management, Brian Lehman and Kari Peter, Penn State, Click Here.

Copper and oil application rates
Traditionally, it is recommended to apply 2 lb. of actual metallic copper per acre between silvertip and bud break and applied with a high volume of water, e.g., 75 – 125 GPA, depending on tree size. This would equate to seven pints of Badge per acre, four pounds of C-O-C-S per acre or 6.7 pounds of Kocide 3000 per acre. It is not too late to apply copper if within ¼ to ½ inch green tip. Once beyond ½ inch green tip, applying 2 lb. of copper is not advised as it may cause phytotoxicity. Solubility can be decreased with the addition of hydrated lime to soluble coppers as well, which reduces phytotoxicity by acting as a buffering agent. The least soluble forms of copper include copper sulfate, pentahydrate, and cuprous oxide.

If copper has not been applied this year and phenology has advanced beyond ½” green tip, reduce the rate to 1 lb. of actual copper. For example, an orchard with Zestar at early tight cluster and Honeycrisp still at green tip, would benefit from this approach. By applying a lower rate of copper and oil, this reduces risk of toxicity to trees further along in their development, even though it is reducing copper residue at bloom.

Oil tank mixed with copper can act as a spreader and as an insecticide. For oil to be functional as an insecticide, temperatures need to be in the 60s°F and under these situations may be applied at a 1% solution. When temperatures are cooler, reduce this rate to 0.25% and only use as a spreader. If an oil application is planned this week, use as a spreader rather than an insecticide. Oil may still be applied during warm weather for mite and scale suppression.

Track rainfall from the application date, if three plus inches of rain has accumulated by bloom, it is likely the copper will be gone, and you will need to be more aggressive in controlling bacteria compared to a dryer spring.

To reduce the risk of phytotoxicity if applying during or near ½ inch green, there are several options:

1. Eliminate the oil or reduce the concentration to 0.5% or 0.25%.
2. Reduce the amount of copper applied per acre from two to one pound of actual copper:
   • Badge SC: 4 pints/acre (1.14 lb. actual Cu)
   • C-O-C-S: 2 lbs./acre (1.025 lb. actual Cu)
   • Kocide 3000: 3 lb./acre (0.90 lb. actual Cu)
3. Apply copper when it will dry quickly. The faster it dries, the more likely it will be nontoxic to green tissue.

Tips to mitigate risk of phytotoxicity and russeting:

• Apply when drying conditions are good (low humidity).
• Do not apply within 24 hours of a freeze event.
• Eliminate the oil from the application.
• Reduce the rate of copper per acre (but not the total gallons of water per acre).

First EBDC applications
The forecasted temperatures for April will be conducive to scab development and John does not recommend delaying first scab spray. If you had scab last year, it is recommended to start management in high inoculum blocks earlier, rather than later, since there may be significant ascospore maturity before tight cluster.

The amount of ascospore development in terms of pre-bud break is typically small. During spring rains, mature spores could be released (pre-bud break), but would require green tissue to be present for an infection to occur. The bulk of ascospore release will occur between tight cluster and petal fall stage. John does not recommend using any of the biological fungicide until there is significant leaf surface present and temperatures are warmer. Additionally, copper applications may negate the impact of these biological products.

If there is very minimal bud maturation five to seven days after an initial copper application, a mancozeb application may not be needed. Look at leaf growth and degree day accumulations (NEWA station) to have a better understanding of the maturation and reproductive rate of the fungi. Do not mix copper and mancozeb as there is no advantage for this.

The full rate of mancozeb, referred to as the “Pre-bloom schedule” is 6 lb./acre and the half rate or “Extended-spray schedule” is 3 lb./acre and interpreting these two schedules can be confusing. The full rate is four six-pound applications where the half rate is seven three-pound applications up to the 77-day pre-harvest Interval (PHI). If the goal is to apply mancozeb past bloom, then it is important to only use 21 pounds maximum for the season and not apply past the 77-day PHI

Organic scab management at green tip
Reducing the inoculum on the orchard floor within the leaf litter is one of the most effective strategies organic and low-input orchards can do to improve scab management. Chopping, mulching, etc., is very important and has been proven to reduce overwintering scab inoculum by 50%. Biological fungicides can be used by organic and non-organic growers for apple scab and other diseases later in the season. However, many of these products are live cultures and require a minimum amount of leaf surface and warmer temperatures to thrive, they may not be very effective at green tip and are best saved until there is much more leaf tissue present. If fungicides need to be applied in organic systems, sulfur and lime sulfur are the primary pre-bloom options. Lime sulfur is best applied post-infection as it offers some eradication and too frequent of applications as a protectant can reduce yields, tree, and soil health. Lime sulfur must be applied when it is not too hot and is not compatible with oil. Sulfur alone does not redistribute or adhere very well to tissue and has a short length of efficacy and could be applied as a protectant prior to rain events.

Insect management

Mites and San Jose scale
Oil applied between silver tip and bloom is important to suppress mites and San Jose scale. Dormant oils are easiest to work with when temperatures are at least 60 °F or higher. As temperatures increase, overwintering mite and San Jose scale respiration rates increase, and the oil application will do a better job at suffocating mite eggs and San Jose scale. There is a very wide range of application rates growers like to use. Most growers apply a 1 – 2% oil, but 3 – 5% oil has also been observed. These higher rates may be necessary where scale and mite pressure is most severe. We will discuss mites and scale in greater detail later this spring, but the dormant oil spray is one of the most important opportunities to manage these two pests. The post from the Jentsch Lab on San Jose scale management offers some important insights to consider: http://blogs.cornell.edu/jentsch/2020/04/11/tight-cluster-going-heavy-on-scale-management/.

Esteem (pyriproxyfen) may be applied pre-bloom to improve management of San Jose scale and early leafrollers. San Jose scale is found on the bark and significant green tissue is not needed for efficacy. In the past John has recommended ½ inch to tight cluster at a minimum for applying Esteem. Most of the developed tight cluster buds are apical, or at the ends of last year’s growth or fruit spurs. These are important buds to protect, however they do not represent a high percentage of all the buds on the tree. Wait until most buds are at tight cluster. There is no rush to apply Esteem this week and the northern region may have an extended pre-bloom schedule due to cooler temperatures.

Weed management

Rapid apple decline/sudden apple death and herbicide use
Over the last six to seven years, research has been conducted to show evidence that rapid-apple decline (RAD) may be partly associated with herbicide use, along with a combination of susceptible rootstock/varieties, latent viruses, and winter damage. Organic growers typically do not apply herbicides and are not reporting this damage. Most of the evidence is pointing to herbicide damage associated with mass tree collapse. Most post-emergent herbicides have precautionary statements on the labels about being careful to not allow products to contact the bark of young trees. Extension agents and consultants often make the exact same comment. However, Extension and consultants typically define young trees as those which are four years old or younger, non-bearing or have not reached full crop-load capacity. On the other hand, many of the manufactures define “young” as any tree that can have green bark when scraped with a fingernail. This condition persists much longer and can still have sensitive bark on trees beyond four years old and trees may need to be much older before they are safe for them to have contact with post-emergent herbicides. Rely (glufosinate), Gramoxone (paraquat-dichloride) and Roundup (glyphosate) are the most common post-emergent herbicides used in tree-fruit production. Research conducted at Rutgers University suggests that bark injury can occur on any age tree from glufosinate applications and that glufosinate products should never come into direct contact with tree bark.