University of Vermont

By Terence Bradshaw

As the calendar shifts into summer, things quiet down a bit in the orchard, and this year is no different. Especially with this dry weather we have been seeing, disease concerns are at a minimum. There have been few chances for sooty blotch and flyspeck to become established on fruit, but the upcoming rain expected this weekend could change that. Orchards without fungicide coverage in the past two to three weeks should receive an effective summer fungicide either before or soon after the rains. Fire blight continues to crop up, but these are symptoms of infections that occurred last month. If trauma (i.e. hail) occurs in your orchard and you have active fire blight (even if you’ve been cutting it out), be prepared to apply streptomycin within 24 hours to prevent spread of the disease to new sites. Some question the need for this now after terminal growth has subsided, but I feel it is cheap insurance in a heavy fire blight year like this one. Pay attention to harvest date, however, since strep products have a 50-day preharvest interval; an application today would mean no harvest until August 28.

Insects are of greater concern in midsummer. We are between generations of codling moth, with second generation flight expected to begin soon. Next sprays targeting this pest must target hatching larvae, which should occur in about three weeks. Obliquebanded leafroller (OBLR) is more active now, but likely only in orchards where this pest has historically been a problem. We caught our first OBLR in traps at the Hort Farm on June 7, and Eric Boire caught a few in Champlain Valley orchards in late May (which may have been the cousin redbanded leafroller) but the first sustained captures were caught the week of June 5 and all sites are showing increased flight activity beginning June 21. That said, trap captures at most orchards have been quite low, so a specific spray to manage this pest may not be necessary. That said, if applying a fungicide for summer diseases, consider applying an effective OBLR material at that time, even if it is just a Bt application. Apple maggot flies (AMF) have emerged and traps should be monitored to time sprays against this insect. At the UVM Hort Farm, we have an unrealistically high AMF population remaining from Dr. George MacCollom’s work with that insect in the 1980s in a now unsprayed orchard, and we reached management threshold this week. I expect most commercial orchards will have lower populations that may require management in the next couple of weeks. If you are not trapping for this insect, it may be prudent to apply a material effective against both AMF and OBLR (e.g. Altacor, Asana, Delegate, Imidan) next week.

Trees have been needing water, hopefully this expected rain July 9-10 will alleviate shortages of soil moisture. Dry soil conditions don’t just starve the tree from thirst, they also can lead to poor uptake of minerals such as boron, calcium, magnesium, and potassium. It is important to water trees if possible, and critical to water young and high density trees. All trees can use extra calcium during the rapid fruit expansion in summer, and all sprays moving forward this season should include a calcium material. If using calcium chloride (CaCl), that material will raise spray water pH to levels (i.e. pH 9-10) that can cause alkaline hydrolysis of materials like captan and Imidan, so 2/3 oz of plain white vinegar per pound of CaCl or a commercial formulated pH buffer like LI-700 should be added to the spray tank. Dr. Wes Autio has a good factsheet on Foliar Calcium Sprays for Apples available at: https://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/pdf/folcalcium.pdf.

By Terence Bradshaw

As we settle into summer, it’s time to shift our focus from weekly scab management to insects, and one disease in particular. Codling moth (CM) trap captures around the state declined last week, which indicates that the first generation flight has subsided. But it’s not the adult moths that we worry about, it’s the hatching larvae that will feed on fruit and cause damage (not to mention pupate and emerge as second-generation adults). Egg hatch is predicted to begin at 175-200 degree days (base 50F) after first sustained catch, but can extend for several hundred degree days after that. Spray treatment is recommended at 250-360 degree days, which were reached last week in most orchards; in orchards with heavy pressure, a second application may be warranted. Reduced-risk, CM-specific materials such as granulosis virus (Madex, CYD-X), molting disruptors (Intrepid, Rimon), and somewhat more broad-spectrum materials particularly active against lepidoptera (Altacor, Delegate) are good options at this time. Those last two materials are also effective against apple maggot (AM), and thus growers may want to save them for later applications when both CM and AM are targeted. Bt materials have little effect against CM, in my experience. Oriental fruit moth (OFM) have not traditionally been considered a major pest in Vermont, but trapping conducted by Eric Boire at CPS has shown high numbers in some orchards beginning around May 21 which is timed very closely with CM. Timing of spray materials against hatching larvae is the same for OFM as CM. Most materials recommended above (with the exception of CYD-X, which is specific to CM) will also target OFM, so management of one will typically target the other.

Oblique banded leafroller (OBLR) have been caught in traps since around June 1, but the overwintering larvae of that pest is generally well-managed with petal fall insecticides. Summer brood adults and newly hatching larvae may be controlled now with an application of any of the materials listed above for CM (except the carpovirusine materials CYD-X and Madex); additionally, Bt products are effective against OBLR. This pest has an extended flight and hatch period, with the worst damage occurring on fruit later in the season just prior to harvest. It would be prudent to ensure that all insecticide sprays in midsummer for orchards that have had a history of damage include a material with efficacy against OBLR. If not spraying for CM or AM, monitoring shoots for developing larvae is advised in order to best time control measure. The following is taken from an Ontario fact sheet on OBLR management; I have converted degree days (base 43F) to Fahrenheit: “The degree day accumulations for the obliquebanded leafroller degree model starts when first sustained moth catch occurs…

DDs are summed each day. At [439 DDb43F (degree days base 43F from date of first sustained trap catch)], egg hatch of the summer generation begins and at [780 DDb43F], 95% egg hatch has occurred. Immature larvae are very small and difficult to see. Larvae initially feed on tender growing terminals, water sprouts and developing fruit. After they reach the third instar, larvae cause more damage to fruit. Monitor for emerging larvae by examining 10 shoots and 10 fruit on 10 trees in a 4 ha block for the presence of larvae or feeding damage. Often damage is more apparent in orchards than are larvae. Management for the summer generation is recommended if 1% to 2% of terminals or fruit are infested. Resample the orchard in three to five days to ensure the population was not underestimated. Once [432-504 DDb43F] is reached and 1% to 2% of terminals or fruit are infested, an insecticide is recommended. Follow up sprays may be required because of the extended larval emergence of the summer generation (four to five weeks).” Note: June 7 was the first sustained catch at the UVM Hort Farm; 6/5 in the Shoreham area. I would use a date of 6/5 in the NEWA model to be conservative.

Apple maggot (AM) will soon emerge in Vermont orchards- now is the time to get sticky and prepare and deploy monitoring traps. Red sticky ball traps coated with Tanglefoot adhesive should be hung at four per ten-acre block and baited with an attractant to increase captures. AM traps are first and foremost visual traps, so they must be hung so that they can be seen from 10-20 yards away, which may mean trimming shoots and foliage around them. The traps should be located at the edge of the orchard, especially near woodlots and abandoned / unmanaged apples. Treatment is recommended when five adult flies per trap are caught. This typically occurs around mid-July, but variation in AM emergence can be great. More information on AM management may be found at: http://www.omafra.gov.on.ca/IPM/english/apples/insects/apple-maggot.html#advanced

Diseases, at least those which you can spray for, are quiet now, but fire blight remains a concern and I have heard many reports from growers with strikes in the orchard (and please, keep me posted). Keep cutting out every infection as soon as you see it; cut in dry weather only; and remove prunings from within the tree. If you have a lot of prunings, leave them on the ground but do not move or mow them until five or more days of dry, sunny weather dries them out. If it’s a more manageable amount, removing is advised as long as it can be done without dragging them through the orchard in contact with non-infected shoots. If you have fire blight strikes in blocks that were treated this year with streptomycin, let me know ASAP. A colleague in Connecticut is screening New England populations of Erwinia amylovera for streptomycin resistance, but any sample sent must be appropriately collected and handled.

Final horticultural notes: water those trees, especially new plantings. Include a calcium material ion all sprays for the rest of the season to increase fruit firmness and storability. Keep up with in-row weed management, but put the glyphosate away after July 1 to reduce likelihood of tree damage and make sure not to contact trunks or foliage any time you use it.

By Terence Bradshaw

After the past week of rain I expect any remaining apple scab ascospores to have been released. Maintain fungicide coverage through the next week or so, and check orchards methodically for scab lesions to determine if you’re really done managing the disease for 2016. Summer diseases, particularly sooty blotch and fly speck however will start becoming a concern next week or so when more leaf wetting hours accumulate, but for now, if your coverage was good during scab season, you’ve probably got a week off from managing fungal diseases.

Fire blight however is appearing in orchards across the state. Most growers are reporting sporadic strikes on trees that received no streptomycin; I haven’t heard of anyone with a major outbreak but please let me know if our orchard is venturing into that level of disease. Dry, sunny weather Wednesday – Friday will be good timing for cutting out strikes. Prune well below the site of infection, sterilize between cuts with alcohol or 10:1 bleach solution if you can, and for now just drop the cut tissue on the orchard floor until it can dry out, pick it up later. Time and effort this week should be spent on removing infected tissue from the tree.

Insect activity is high across the state. Plum curculio is winding down, orchards with recent coverage of a suitable material are probably okay for this pest. I am seeing higher than expected catches of codling moth in many orchards monitored by Eric Boire from CPS. For those with >5 moths per week trapped in the past couple of weeks, a second lepidopteran-specific spray (everyone sprayed for CM last week, right) is due.

The window is closing to apply nitrogen fertilizers for 2016. If you have a light crop or fire blight (or both), no more nitrogen should be applied this season to prevent excess vegetative growth which is susceptible to fire blight and some insect pests.

If you’re not cutting fire blight this week then focus on groundcover management. Small amounts of weed cover in the tree rows at this time of year turns into a real headache in late summer-early fall.

By Terence Bradshaw

Note: because I still cannot get my email program to post photos to this listserv, there will be references to pictures in the message below but nothing there. Growers who are very familiar with early fire blight symptoms should get out and inspect their orchards now; others might take the extra minute to view the pictures in the accompanying blog post at: http://blog.uvm.edu/fruit/2016/06/08/wet-weather-over-the-weekend-and-continuing/Fire-blight-symptoms-appearing-in-area-orchards

Fire blight symptoms are beginning to appear in area orchards where infection occurred. This first came to my attention when a grower from southern Vermont sent me a picture over the weekend for confirmation of whether or not the symptoms he was seeing were from fire blight. I’m still not sure that’s what we were looking at in that photo, but it’s entirely possible (and I’m beginning to think more likely).

Figure 1. Suspected fire blight on a shoot from southern Vermont.

Today I received notice from Eric Boire at CPS that growers in the Champlain Valley of New York are reporting shoot blight symptoms on susceptible cultivars: Cortland and Gala in particular. Cornell Extension Associate Anna Wallis has confirmed this and sent notice to area growers to be on alert. I immediately checked our organic orchard at the UVM Horticulture Research and Education Center and definitely saw symptoms of the disease.

Figure 2. Classic ‘shepherd’s crook’ symptom of shoot blight on Crimson Crisp at UVM HREC organic orchard.

Figure 3. Blossom blight symptoms shown on developing fruit.

As the name implies, symptoms look like tree shoots and / or fruit clusters were burned with a torch, although early symptoms may appear as water soaked tissues. A good fact sheet on symptoms and management may be found at: http://www.caf.wvu.edu/kearneysville/disease_descriptions/omblight.html

I did not see symptoms on trees that received streptomycin during bloom (strep is prohibited in certified organic orchards).

This is not a disease to underestimate, as, unlike most other tree fruit diseases which are fungal in nature, the bacterial pathogen associated with this disease enters the vascular system and can severely affect tree growth and production and even kill trees in a single season.

NOTE: It is CRITICAL that you not apply streptomycin to symptomatic trees in an attempt to manage the disease. You will NOT get control, and you will select for resistant strains of the bacteria.

Orchards should be scouted immediately for disease symptoms, and several courses of action should be considered. I will be referencing a 2014 post from Penn State Plant Pathologist Kari Peters for management considerations (found here). The primary courses of action are to cut the symptomatic tissue out of the tree, to reduce vegetative growth that is susceptible to shoot blight, and /or to spray a material with bactericidal activity (NOT STREP). A few notes:

1. If pruning out infections, only do so in dry weather and not within at least 8-12 (preferably 24) hours before rain, which could spread the bacteria throughout the orchard and increase infection. That shuts down most of this week for pruning.

2. When you do prune, cut shoots at least 8-12 inches below the extent of symptoms because bacteria can be present in vascular tissue below visibly affected regions. Focus on removing infected tissue and not saving this year’s crop- you’re saving the tree.

3. Concentrate first on susceptible cultivars like Gala, Honeycrisp, Cortland, Mutsu. A further list of relative cultivar susceptibility to disease may be found at: https://www.extension.purdue.edu/extmedia/BP/BP-132-W.pdf.

4. Young trees, especially on susceptible dwarfing rootstocks (M9, M 26, and others) will be most susceptible to tree damage or loss. Focus on them.

5. Application of Double Nickel (8 fl oz/100 gal dilute) plus Cueva (2 qt / 100 gallons dilute) fungicides have shown efficacy in reducing disease severity in past trials. These should be applied as soon as possible and repeated on 10-14 day intervals until shoot growth subsides. However, Cueva, a copper fungicide, may cause fruit russeting and should be applied in as concentrated a spray possible (low gallons per acre) and under good drying conditions, and not to wet fruit or foliage.

6. Shoot growth can be reduced by applying a high rate (8-12 oz/100 gallons) of Apogee now. Consider reapplying in 2-4 weeks if symptoms continue to appear and excessive growth continues.

All spray rates per 100 gallons are based on tree row volume calculations as referenced in the 2015 New England Tree Fruit Management Guide.

A couple of other considerations deserve mention. When scouting for infection, be careful not to over assess symptoms when you see fruit with yellowing stems, these are normal since we are still in the window where thinning practices will be apparent in the orchard.

Figure 4. Normal thinning response, the fruit with yellow stems will soon drop. This is not fire blight.

You also may note yellowing on leaves where streptomycin was applied during bloom. This is normal and will not greatly affect the tree, not anything like fire blight will.

Figure 5. Normal leaf burn symptoms from application of streptomycin during bloom.

Please let me know if you see symptoms of fire blight in your orchard, especially in orchards where strep was applied this year. I have a colleague interested in testing for strep-resistant strains of causal agent Erwinia amylovera, and I may be interested in collecting samples from affected orchards.