Production and pest update brought to you by the OMAFRA Apple Team: Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist
Growth stages
Fruitlets continue to size in all regions. Depending on the variety and location, sizing varies, but most are past the 20mm stage.
Production
As June progresses, growers continue to irrigate, prune, and hedge their trees.
Although growers across the province have had to deal with the effect of frost, with certain pockets experiencing more damage than others, most growers are in positive spirits and are looking forward to the continued growing season. There have been reports of sporadic hail in some areas over the past few weeks, but there has not been any significant damages noted.
Thinning
Many growers are done using chemical thinners, as fruitlets are past the ideal sizes for high efficacy of product use, and now are shifting to hand thinning. Given that hand thinning is going to be heavily relied on due to the spring frost, and now that we can see the full extent of the damage, it is important to knock off any fruitlets that have been affected. Frost rings, described as russeting bands encircling the fruitlet, and shown in figures below, have been seen in many orchards. Fruit with frost rings should be dropped, as apples will not outgrow these rings. Although frost rings have been reported to not affect taste, they would not be saleable as a fresh apple.
Hedging
A topic that growers are currently discussing is hedging. There are many factors to look at if hedging is something you are interested in. As Karen Lewis from Washington State University put it,
“Mechanical hedging should not be considered for the sole purpose of saving money. Mechanical hedging should be considered for the following reasons: 1) filling in blind wood near the trunk; 2) restricting canopy depth and height for various reasons including to allow for additional mechanization and automation; and 3) light management in late winter/early spring, summer and close to harvest.”
With those 3 reasons in mind, you should also be aware of the following:
- Fire blight could be transferred through use of a mechanical hedger. As with any tool, going from tree to tree can spread bacteria.
- There are many factors that can change the results of hedging, including tree architecture (type of wood and placement), timing, cultivar, type, and operation of equipment, along with follow-up pruning.
- Hedging is not practical and beneficial for every system or every grower.
Now, the final “topic” of hedging, WHEN? This is a complicated question and depends on many factors, but from previous research, knowledge and experience these general statements are great rules of thumb.
- “Setting the box” should be accomplished during dormancy or early spring prior to bloom every year or every other year.
- Hedging is not a stand along technique as it’s not a selective process, making good and bad cuts. Follow up hedging with hand pruning to develop and maintain a narrow, productive canopy. This shortens up limbs and encourage renewal branches.
- To encourage buds on blank wood, and to set terminal buds, hedging at 12-14 new leaves has shown to be promising. This timing usually occurs in mid to late June and is ideal for hand pruning to further aid in colour development of fruit.
- Hedging in late summer will not stimulate as much vigour as dormant pruning, however, this timing may increase the risk of winter injury.
The size and structure of the trees are important considerations. Hedging is most efficient with small, central-leader trees with horizontal branches. As tree size increases, a progressively smaller percentage of the total pruning can be done by hedging.
Hedging is easiest to execute when it is considered in the design of a new planting, however, it is possible to incorporate hedging in an existing. To transition big limbs should be removed manually over several dormant pruning seasons. Keep in mind that during this phase some production will be lost.
As with any new method or tool, setting up a simple and small trial to evaluate the response of timings and combinations of manual and mechanical pruning is encouraged. You need to know what response you are after to determine when and how to use mechanical hedging.
Is hedging something you are considering in your orchard? If so, feel free to ask questions by commenting on this blog post or reaching out to Erika DeBrouwer directly (erika.debrouwer@ontario.ca, 1-226-931-4098).
Disease
With the warmer temperatures and higher humidex predicted over the coming days, this could bring unsettled weather to some areas including heavy rains, thunderstorms and/or damaging winds. These conditions at this time of year are ideal for disease development.
Apple scab
Low levels of apple scab infection can be found in some orchards across the province. Though overall, many orchards still appear to be clean at this time. The significant rainfall most areas welcomed last week likely brought the end of the primary infection period by releasing the last of the matured ascospores.
However, it is important to wait a few weeks after the last infection event before backing off of a scab program. Monitor for signs of scab lesions. Be sure to take a good look in the top part of the canopy as coverage can often be inadequate there. Before reducing fungicide rates, be sure your orchard is completely free from primary scab.
Powdery mildew
Some orchards continue to see powdery mildew and the warm, dry weather will favour development. Continue to protect susceptible varieties such as Gala, Honeycrisp, Cortland, Idared, Crimson Crisp, Goldrush, Russet, Fuji and Spy. Powdery mildew requires actively growing tissue to complete its cycle so fungicides with efficacy against this disease should continue until terminal growth stops.
Infected shoots will not cause damage to fruit at this point in the season. Fruit damage (see image below for an example of what this looks like) is a result of early infection that occurred in the flower buds and during bloom. However, infected shoots will be the inoculum source for next year. Prune out any strikes that are present.
Fire blight
While many orchards may have got through bloom period without signs of fire blight, infection can still occur through open wounds caused by strong winds, heavy rain and hail, insect feeding, pruning or mechanical damage, or even microtears during rapid growth. Blossom blight does not need to be present for other parts of the tree to be affected such as shoots or rootstock. In fact, inoculum can be spread large distances throughout a region during storms.
Like the hail and wind storms experienced last week, these events can be very isolated, occurring in one area but not another nearby. Assess for signs of damage in all blocks following any storm.
Be sure to apply Streptomycin (PHI 50 days) or 0.5-0.8% Cueva as soon as possible after the trauma event, especially if foliage damage is extensive or fire blight is known to be active in the orchard (ie., cankers, etc). Ideal timing is 4 to 12 hours after a storm. Anything applied later runs the risk that the bacteria will have already established and begun to grow, reducing the efficacy of the product.
Efficacy of copper may be increased with the addition of Double Nickel.
Growth regulators (Apogee, Kudos) or SAR products (Lifegard, Regalia) will not have immediate activity needed followinga trauma event. While they can help limit future spread, these products should not be used as a stand-alone rescue treatment.
Other disease
When beginning to relax back on scab management for the summer, it is important to still consider fungicide sprays for summer diseases. While often considered mid- to late summer diseases, now is the time to start thinking about management of fly speck, sooty blotch, bitter rot and black rot.
Frog-eye leaf spot (black rot) can already be found in orchards. The developing fruitlets are now at risk of infection by these fungi despite symptoms not actually appearing until mid-summer.
Moving back into some hot and humid weather, we could see some ideal bitter rot infection conditions, especially when followed by a rain storm. Spread can be extensive with bitter rot as spores are produced on the fruit surface and rain splashed to other fruit resulting in further infections as the season progresses. Wounds do not need to be present for bitter rot infection unlike black rot.
Infection timing for fly speck and sooty blotch should also be considered. In wet years, infection typically begins 2-3 weeks after petal fall. With this season being relatively dry, it’s likely to be later than this. There is a fly speck forecasting model that predicts the start of infection at 185-190 leaf wetting hours after petal fall.
For management of summer diseases, follow a 14-21-day application interval until harvest to ensure fruit remains protected. Pristine or Merivon can provide reasonable residual control of summer disease up to 3 weeks at the labelled rate in ideal conditions; however, captan or Folpan should not be pushed further than 14-days between sprays particularly since they are not as strong on fly speck and sooty blotch as other control products. In all cases, reduce interval to 7 days during times of hot, wet weather.
Important cultural management recommendations include:
- Prune and thin clustered fruit to facilitate drying and improve fungicide coverage.
- Remove potential sources of inoculum such as dead branches, fruit mummies (where possible), infected fruit on the orchard floor and alternate hosts including brambles (blackberry, raspberry) from surrounding hedgerows or woodlots.
- Toss pruning cuts and thinned fruit in the row middle and mulch.
- Reduce tree stress by irrigating and/or applying a sun protectant, especially ahead of a heat wave.
Insects
San Jose scale
San Jose scale crawler activity for the 1st generation has begun. To spot these small yellow-orange nymphs, you’ll need to get close to the trunk with a hand lens as you can see in the picture below. While emergence may be slow at first, activity can pick up quickly, generally peaking early July. This generation will be active, however, for 4-6 weeks as crawlers move to new shoots and developing fruitlets. Once attached and starting to feed, these immature scales will form waxy coverings that protect them from insecticides.
Targeting sprays during the vulnerable time when crawlers are exposed will maximize the efficacy of products such as Closer, TwinGuard and Sivanto Prime. Since Movento is slow-acting, ideal application timing is prior to crawler emergence. If planning to use this product and it has not gone on yet, applying as soon as possible may still provide some efficacy for peak emergence due to the extended pest activity. While Purespray Green Spray Oil is registered for summer use on mites and aphids only, trials in Ontario have found weekly oil applications may provide some suppression of scale during the crawler stage.
Internal feeders
Egg hatch for 1st generation codling moth is on-going. There have been no reports of fruitlet damage yet.
Following egg hatch, codling moth larvae search out the fruit where they begin to tunnel in. This can happen as quickly as 24 hours after egg hatch which is why timing of control strategies are so important. After entering fruit, the larvae will feed for approximately 3 weeks before leaving the fruit to pupate (usually on tree trunk or larger branch of the tree). Pupation generally lasts 14-21 days. Some larvae do not pupate at this time, but remain as larvae until the next year. Second generation adults begin to appear in orchards as early as July and lay eggs over two months.
It’s important to note for resistance management, if re-application is required for control of a pest with discrete generations, use the same product within a generation. For instance, codling moth is still in the first generation window. Second generation larvae activity will not begin for another few weeks – typically early August. Rotate to another insecticide class at that time to ensure each generation is only exposed to one active ingredient.
Control timing for 2nd generation oriental fruit moth is still a couple weeks away. This generation more commonly feeds on developing fruit. I have been in a few orchards in the province with terminal damage caused by oriental fruit moth. The 1st generation larva often enter growing terminals when other fruit sources (fruit) are still not present. Once terminal set occurs, this risk is reduced but can impact growth of new plantings. This damage can also be misidentified with shoot blight. Look for presence of brown frass and an entry hole at terminal tip.
Obliquebanded leafroller biofix has been set for some but not all regions. Control timing will begin over the next couple for weeks across the province.
Apple maggot traps are currently going up ahead of adult emergence. Emergence is closely linked to soil moisture levels. Those regions seeing drier than normal conditions may see a delayed emergence or sudden flush following a rain event. Apple maggot are even able to remain dormant until the following year if conditions are not favourable.
Aphids
While activity seemed a little delayed this year, aphid populations have picked up in recent weeks, in particular rosy apple aphid. Keep an eye on fruit clusters as feeding damage by rosy apple aphid can cause deformed fruit.
Woolly apple aphid colonies have been building. Still more commonly found inside the canopy around pruning cuts, cankers or split bark, there are some cottony masses that are beginning to move throughout the canopy. Most products timed for San Jose scale should have some efficacy on woolly apple aphid as well.
Dogwood Borer
Dogwood borer trap catch is beginning in early regions in orchards with a history of problems with this pest. However, adult emergence will continue through to early September with peak flight typically occurring mid-July. During this time, females lay eggs on the surface of burr knot formations, pruning cuts, cankers, and wounded bark, after which the larvae use as entry points to bore into the tissue to begin feeding.
If pheromone traps have not been placed in the problem orchard yet, these need to be installed as soon as possible since adult flight has begun. Four traps per site, placed in low scaffold limbs, are recommended. Use a minimum distance of 50 m between traps, and monitor twice a week. Record the number of adults captured – graphing the results – to identify peak flight time. This information can be used to time trunk applications of a registered insecticide.
Currently, pyrethroids, Altacor, Delegate and Rimon are registered for control of borers:
- Pyrethroids at this timing can have significant impacts on the natural enemy complex.
- Rimon 10 EC is an insect growth regulator (IGR) that must be absorbed by eggs or ingested by larvae to be fully effective. The optimal timing for this product is around 25-75% egg laying, or approximately peak flight.
- Delegate and Altacor must be ingested by the larva in order to work; therefore it must be applied at the beginning of egg hatch, or a few weeks following peak flight.
- With all products, a repeat application 14 days later is recommended.
An alternative management option for dogwood borer next year is the mating disruption product, Isomate DWB. Dispensers (250-375 dispensers/ha) should be applied before adult borer emergence, or approximately the end of May. Researchers from Rutgers and Cornell University feel that Isomate DWB can adequately control light to medium dogwood borer infestations and give equal control to trunk drenches after multiple years of use.
Other insects
Mullein bug stings on developing fruitlets have been reported in orchards. However, overall damage from this pest has been fairly low. This is especially surprising in some orchards especially given the high numbers of mullein bug nymphs were tapped out during weekly monitoring. At this point in the season, damage is not a concern as most mullein bugs are adults and fruit is larger than dime- to quarter-sized. In fact, mullein bugs are very effective predators of many orchard pests so supporting these populations from this point on in the season is encouraged.
Low levels of plum curculio damage has been found on developing fruitlets. Often movement into the orchard follows a period of sustained warm weather and rain. Activity is believed to be linked to weather patterns, so could be as long as 6 weeks during cooler, more dry conditions.
Adult flight for the 2nd generation of leafcurling midge has begun and egg laying can be found in growing terminals. New leaf curls will likely start developing in the coming week or so. Damage will continue until terminal set.
Overall, mite pressure continues to remain relatively low in most orchards.
Beneficial insects can be easily found in orchards now. Just this week, my counts have included lady beetle larva, mullein bugs, lacewings, hoverfly larva, assassin bug egg masses and evidence of aphid parasitism. Keep an eye out for these good guys. They’re doing a great job in the orchard this year!
Upcoming events
North American Virtual Orchard Meetup – Webinar 2
The 2nd webinar in this summer series will be held Thursday, June 29 at 7:00pm. The focus for this webinar is Managing the Uncontrollable: Water. For more information:
AgRobotics Field Tour
The AgRobotics Working Group is offering two demo days featuring a number of exciting new technology. For more information:
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