April 19, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, April 19, 2016, 8:00 – 9:00 AM
Guest speaker: George Sundin, Michigan State University, Professor of Plant Pathology
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

April 19th Call download: Click Here

Crop phenology
The warm temperatures over the weekend have pushed some early breaking cultivars to tight cluster or pre-pink. Throughout the region crop phenology varies by location and cultivar. The cooler temperatures this week may slow development going into bloom. Many growers have applied copper or an EBDC at the end of last week and should consider reapplying a fungicide to protect newly exposed tissue.

Continued pruning beyond tight cluster exposes tissue to the risk of fire blight infection. If additional pruning is necessary, it is recommended to make small cuts, e.g., < 1″ diameter, and do so when there is a window of dry weather of at least 48-72 hours.

Early season insect management
The cooler and wet weather this week may not be conducive to an oil application. For greatest efficacy apply oil when relative humidity is less than 65% and temperatures are warmer than 60°F.

Redbanded leafroller (RBLR), spotted tentiform leafminer and green fruitworm (GFW) flights are likely during the warmer nights. Whether or not traps are deployed, scouting can begin at tight cluster or pink for larvae of the spring lepidoptera complex, e.g., obliquebanded leafroller (OBLR), RBLR, GFW, near leaf and flower buds. Obliquebanded leafroller larvae overwinter as 2nd or 3rd instars, however 10x magnification may be necessary to see the newly hatched larvae of RBLR and fruit tree leafrollers and GFW. Note: If moths are currently being caught in codling moth (CM) and OBLR traps, they are likely to be a non-pest species, as the first flight of CM begins near bloom or approximately 180 – 200 degree days (DD), base 50. OBLR first flight begins near the fruit set stage or approximately 490 DD, base 50.

If any San Jose Scale (SJS) were found on fruit last year, you are encouraged to actively scout for and manage this pest because of its potential for explosive growth. Management strategies targeting the overwintering generation of immature scales involve the use of oil pre-bloom @1-2% concentration. The success of any SJS control depends on the use of sufficient spray volume to saturate all areas of the bark. There are several insect growth regulators (IGRs) available for SJS (Esteem, Centaur, Movento, etc) some of which have two application windows on their label for San Jose scale control, the first prior to bloom and the second in early to mid-June targeting first generation crawlers become active. If using a pre-bloom application of Esteem make sure the application goes on before any blossoms open to protect pollinators.

The April 18, 2016 Scaffolds Fruit Journal has a great article on managing San Jose scale and other early season insect pests, for more information visit: http://www.scaffolds.entomology.cornell.edu/2016/SCAFFOLDS-4-18-16.pdf

To subscribe to the Scaffold Fruit Journal, contact Art Agnello at: ama4@cornell.edu and include your name, location (city/state or province) and affiliation (e.g., commercial grower, home/hobbyist grower, fruit industry representative, consultant, university, government, etc.)

Cedar apple rust
Cedar apple rust is primarily a concern for organic growers that are growing scab-resistant varieties that require a minimal amount of sulfur or copper to being applied for scab protection during primary scab season. In these scenarios it is recommended to eliminate the amount of red cedar (alternate host) on your property to reduce the amount of inoculum. This method alone may not entirely prevent infection, since cedar apple rust spores can travel up to two miles.

For more information see: Efficacy of Selected Fungicides Against Apple Diseases, 2016 Midwest Fruit Management Guide, page 31

Question and Answer with guest speaker George Sundin, Michigan State University

To what extent does copper redistribute on expanding tissue, and is there any research indicating how particle size or formulation might affect this process?

• We believe there is a net loss of copper over time rather than redistribution on expanding plant tissue; redistribution is likely minimal. For example, a fixed copper, which has low solubility in water, will gradually disintegrate during light rains and release free copper ions that will come into contact with scab spores or fire blight bacteria and will destroy them. Two-inches of rain will wash-off all of the copper apparently independent of the particle size of the copper. Newer formulations containing smaller copper particles allow for better coverage, but it is the solubility that determines its longevity. Low solubility copper particles will persist on leaf surfaces, and gradually release copper ions when particles react with water. Highly soluble copper products, e.g., those containing copper sulfate pentahydrate, rapidly degrade and residues are more quickly removed by rain. Note: If there has been a lot of growth since you applied copper late last week, you apply a protectant fungicide before the next rain event.

• For more information on copper formulations see Kari Peter’s presentation, Demystifying Copper for Disease Management, http://extension.psu.edu/plants/tree-fruit/presentations/2016-winter-tree-fruit-meeting/demystifying-copper-for-disease-management

Fire blight development v. crop phenology
• There is not an exact indicator to compare fire blight bacteria development and crop phenology, yet the bacteria will become more active as the tree develops. In many years, fire blight cankers begin oozing around the start of bloom and this ooze will contain active bacteria.

• Only 10-20% of cankers that have bacteria will survive through the winter and survivorship is greater on larger limbs. However, when dormant pruning, it is important to remove all visible cankers to significantly reduce inoculum.

• Active cankers can produce enormous numbers of bacteria, so only a few cankers are needed to provide enough bacteria to infect an entire orchard. The bacteria travel easily and can be distributed through the orchard by wind, rain or insects. This is in stark contrast to the aeciospores of the apple scab fungus where most spores don’t travel beyond the perimeter of the tree where they were produced.

If fire blight cankers are not oozing, it is likely no bacteria are being spread. If the cankers are not oozing during bloom then there is a reduced risk of blossom blight. Following bloom, shoot blight can still occur in trees that have active cankers since the bacteria can spread systemically through the tree. Caution is advised to prevent these infections in older trees from traveling to nearby non-bearing, or newly planted trees that may bloom later in the season, as the amount of bacteria continues to increase as the summer progresses.

FRAC Group 7 (SDHI) fungicides
• SDHI options for growers include: Merivon (pyraclostrobin, fluxapyroxad), Luna Sensation (trifloxystrobin, fluopyram), Luna Tranquility (pyrimethanil, fluopyram), Fontelis (penthiopyrad) and new this year, Aprovia (benzovindiflupyr). These fungicides are all slightly different compounds with different spectrums of activity. If or when resistance occurs it will be very complex, e.g., resistance may appear to one compound, but not always with the others and could be specific to individual orchards. In Michigan there is resistance to strobilurins, e.g., pyraclostrobin, trifloxystrobin, which are included in Merivon and Luna Sensation.

• Growers should continue to tank mix a partial rate of an EBDC or captan when applying an SDHI. In Michigan there were resistance issues with half rates of EBDC and strobilurins, where the interval was extended too long between sprays. Currently, there is no science to support more than a half rate of a protectant fungicide is needed when tank-mixing with a systemic fungicide.

• However, tightening intervals and increasing rates of protectant will help ensure good coverage and kill the pathogen. The best way to protect against resistance is to eliminate the pathogen in the orchard.

• While protectants redistribute with rain or dew, many of the single-site fungicides (S.I.s, Strobilurins, SDHIs, but not AP’s) can move translaminarly through the growing leaf. This ability is more properly called translaminar movement or locally systemic, rather than truly systemic, as these compounds do not move throughout the vascular system of the tree. Translaminar movement allows for more thorough coverage while also allowing the protection to redistribute into expanding tissues from within the leaf. So think about the target size when deciding if or when to apply a “systemic” fungicide. For instance, half-grown leaves are more likely to receive sufficient single-site material to protect the leaf as it expands, compared to spraying these materials on just-emerging leaves.

How do the SDHIs activity on powdery mildew compare to the sterol inhibitors (DMIs) or strobilurins (QoIs)?
• SDHIs are at lower end of effective when compared to some of the sterol inhibitors or strobilurins. When comparing efficacy the most effective product on powdery mildew are least effective for scab.

• Strobilurins, e.g., Flint (trifloxystrobin), Sovran (kresoxim-methyl), are still very effective against powdery mildew and should still offer good control. The SDHIs that include a strobilurin, e.g., Merivon and Luna Sensation, will manage powdery mildew better compared to the other SDHI that lack a strobilurin in the pre-mix.

• Sterol inhibitors, e.g., Indar 2F (fenbuconazole), Inspire Super MP (difenoconazole), Rally (myclobutanil), Topguard (flutriafol), are all great options for powdery mildew. Rally and Topguard are the most effective against powdery mildew and least effective against scab, compared to Inspire and Indar that have greater efficacy against scab and less on powdery mildew.

• Fungicides applied for powdery mildew that have greatest efficacy on scab, should be saved for application made during primary scab season.

What fungicide use behaviors are driving resistance?
• Increase use over time is likely the greatest driver of resistance. For strobilurins, in particular, the number of sprays over the history an orchard drives resistance, and it appears, after 20 applications of a strobilurin you will have resistance.

• SDHIs likely have a similar “life expectancy” to the strobilurin where resistance is developed over time and can be reduced by limiting the number of applications per season. It is recommended to limit to two applications per year for any of the SDHIs. When resistance to SDHIs does develop in the apple scab fungus it will likely spread rapidly within orchards and persist.

• Tank-mixing with a protectant fungicide, e.g., EBDC or captan, and alternating FRAC (Fungicide Resistance Action Committee) group codes between applications will help reduce the risk of resistance developing. We are concerned we don’t know the exact number of applications, before resistance will develop to the SDHIs, so two applications per year for ten years is better than making four application per year and only having it last five years or less.

• Growers need to commit to the higher application rates to prolong the life of a fungicide. The scab in your orchard is yours! Scab spores do not travel far and the likelihood of resistant strains moving between orchards is low, unless you are in a region with back-to-back orchards. Effectively controlling the scab population in our own orchards and preventing resistance is dependent on using higher rates that will effectively destroy the fungi.

What is the ideal fungicide rate for growers on a protectant-only program?
• The captozeb strategy, mancozeb (3 lb. /acre) + captan (2.5 lb. /acre), offers a good blend of retention ability (mancozeb) and redistribution capability (captan). However when employing a protectant-only program the spray intervals will be tighter compared to tank-mixing with a systemic, e.g., SDHI, that has translaminar activity.

• There is no risk of fungicide resistance when using a protectant-only program.

Powdery mildew disease cycle and management strategy
• Powdery mildew overwinters in infected shoots and buds. Temperature below -20°F will kill buds infected by the pathogen; during warm winters there will be better survival of the pathogen. Some cultivars are more susceptible than others and susceptibility of many new cultivars has yet to be determined.

• Fungicide resistance is difficult to establish with powdery mildew since it cannot be grown in the lab on culture media and only grows on the trees. It is very likely there could be field resistance to the strobilurins and sterol inhibitors but be difficult to prove.

• The powdery mildew fungus overwinters in the infected buds and new infections can occur as soon as new, green tissue begins develop. Powdery mildew will begin sporulating at tight cluster.

• It is recommended to begin applying fungicides targeting powdery mildew at tight cluster to protect new tissue. Sulfur can be used as an early spray when there is less green tissue to protect and less pressure from the fungus. Sulfur is a broad spectrum, protectant fungicide and is also effective against scab, yet it has a low residual and may be phytotoxic if applied to close to oil. It is recommended to use stronger fungicides, strobilurins or SDHIs, later in the disease cycle when infection risk is greatest, i.e., first to third cover. Factors that influence infection risk may include: amount of shoot growth and unprotected tissue, fungal activity when it is producing the most spores and warm temperatures.

• Growers with powdery mildew issues in the recent past should begin their powdery mildew fungicide program relatively earlier, e.g. at tight cluster rather than pink or early bloom. Use the highest label rate when using a systemic fungicide with one mode of action, e.g., Fontelis. Rates can be reduced for the pre-mixes, e.g., Luna Sensation, Merivon, where both the strobilurin and SDHI component (two different mode of action) will provide control.

• For more information see: Efficacy of Selected Fungicides Against Apple Diseases, 2016 Midwest Fruit Management Guide, page 31

Flower Bud Damage Assessments of Hudson Valley Apple, April 8th, 2016, The Jentsch Lab, http://blogs.cornell.edu/jentsch/2016/04/09/flower-bud-damage-assessments-of-hudson-valley-apple-april-8th-2016/