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While there was a bit of a break in the heat this week, most areas still remain quite dry. Irrigation continues where it can. The latest Vegetable Crop Report for June 25, 2020 gives a great overview of growing degree days (GDD) and precipitation across Ontario. Overall, all regions have similar GDD to the 10 year average and are following the same increasing trend. Most apple growing regions, particularly Durham and Kemptville regions, lag behind the 10 year average for precipitation.
Rain showers are forecast for most regions over the weekend. With the high humidex, 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.
Until terminal bud set, young shoots can be easily damaged during summer storms. Fire blight is active in a number of orchards across the province, which means the potential for shoot or trauma blight can be quite high during these hot, humid conditions.
I’ve had a number of questions about what can be done to manage fire blight this time of year. In the previous Apple Pest Update: June 17, 2020, I included a number of links to resources and tips for management.
Now that we are moving back into some hot and humid weather, we could see some ideal bitter rot infection conditions, especially when followed by a rain storm. A general overview of bitter rot biology and symptom development can be found in the Orchard Network article, Bitter Rot Management in Apples. A Lunch ‘N Learn webinar from July 2019 with Dr David Rosenberger from Cornell University also provides a good overview of summer diseases.
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.
If spores land on fruit just before or during harvest, infection can occur with symptoms developing slowly in storage. For bitter rot, small lesions will begin to enlarge within a few days after the fruit is removed from storage.
Fly Speck & Sooty Blotch
Infection timing for fly speck and sooty blotch is quickly approaching. In wet years, infection typically begins 2-3 weeks after petal fall. With this season being so 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.
Fly speck and sooty blotch usually appear in orchards that have reduced summer fungicide programs due to a lack of apple scab. They can, however, also appears in September or October in orchards that have received summer sprays. In these cases, late summer rains often remove fungicide protection allowing fruit infection to occur prior to harvest. Studies have found fungicides applied in early summer for fly speck and sooty blotch do not eradicate pre-exisiting infections. These infections can resume growing and become visible late season when residues are depleted.
Management of Summer Disease
General chemical management recommendations for summer disease include:
- Rotate between registered products such as high rate captan (e.g., Maestro, Supra Captan), Granuflo-T (last date of use is June 2021), strobilurin/Group 11 (e.g., Pristine) and Allegro fungicides; however, refer to Table 3-5. Activity of Fungicides on Apple Diseases (pg. 113-114) in the 2020-2021 Publication 360A, Crop Protection Guide for Apples for all control options available.
- Follow a 14-21-day application interval until harvest to ensure fruit remains protected. Pristine can provide reasonable residual control of summer disease up to 3 weeks at the labelled rate in ideal conditions; however, captan should not be pushed further than 14-days between sprays particularly since it is not as strong on fly speck and sooty blotch as other control products.
- Reduce interval to 7 days during times of hot, wet weather.
- Reapply if more than 5 cm (2 inches) of rain has occurred since the last fungicide was applied especially on late-maturing varieties.
- Be aware of maximum applications per season and preharvest intervals.
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.
Egg hatch for 1st generation codling moth is on-going. There have been no reports of fruitlet damage yet. Activity has been fairly constant this year, so a follow up application may be needed to cover the extended egg hatch that will occur.
Following egg hatch, 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.
Trap catch still remains quite low for 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.
European apple sawfly fruit damage can be found. For many growers, they feel this damage is due to a late petal fall application.
Apple maggot traps are up in most regions and the first catch has been reported in Norfolk. Emergence is closely linked to soil moisture with flushes in flight often following periods of significant rainfall loosening soil. In a dry year, some pupae may even remain in the soil until the following season. Males generally begin emerging before the females but by peak emergence (about August) the sex ratio is about 1 to 1.
San Jose Scale
San Jose scale crawlers have been observed this week in Norfolk, signalling the start of 1st generation crawler emergence. 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 1-2 weeks 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 later 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.
Woolly Apple Aphid
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.
Potato leafhopper are quite active. Hopper burn and leaf cupping has already started in many orchards. This is caused by a toxin in the leafhopper’s saliva that blocks vascular system flow, preventing normal movement of water and nutrients to the affected area. In most high vigour blocks, leafhopper damage is manageable, particularly once terminals harden off. However, nursery trees and non-bearing blocks require control at first sign of injury since vigour and shoot growth can be significantly impacted.
Herbicide Resistence Testing
Do you suspect that you have herbicide resistant weeds on your farm? If so, why not get them tested for free through a genetic testing sample project. So far there are 16 genetic quick tests (with 5 more in progress) to assist in identifying herbicide resistance in 12 weed species. These tests deliver a diagnostic and a recommendation to the grower within the same growing season. For more information, check out Kristen Obeid’s latest ONfruit post.
Pick-Your-Own Apple Orchards Roundtable, July 7 @ 7:00 pm
On July 7th at 7:00 pm, we’ll be sharing guidelines for managing a pick-your-own orchard in 2020. We’ll hear from some experiences of pick-your-own strawberry operations, followed by an open discussion for the audience to ask questions and share some ideas or strategies.
Register in advance for this meeting:
After registering, you will receive a confirmation email containing information about joining the meeting.
High Tech Precision Orchard Spraying, July 20 @ 4:00 pm
On July 20th at 4:00 pm, Cornell Cooperative Extension will be hosting a webinar with Dr Jason Deveau (OMAFRA), Dr Heping Zhu (USDA) and Steve Booher (Smart Guided Systems) to learn what’s new in orchard precision spraying technology. More information can be found on the Cornell Cooperative Extension website.
Register in advance for this meeting: