Crop Stage

Dry, sunny weather has been a welcoming sight in many areas of the province this past week. Unfortunately, the forecast doesn’t sound like the sun will be sticking around for much longer as we are in for more soggy weather.

Earlier regions such as Essex, Kent, Middlesex, Elgin, Norfolk, Brant and Niagara are now seeing petal fall in some – if not all – varieties. Other areas of the province such as Grey, Durham, Northumberland, Quinte and east to Ottawa valley are pink to early bloom.

Disease

Fire Blight

Conditions for fire blight infection were high to extreme in most areas across the province this last week according to the fire blight prediction maps. These maps use the Cougar Blight forecasting model to determine infection risk. According to this model, some of the most damaging fire blight epidemics have occurred under these optimum conditions, including in orchards that have never experienced fire blight.

Growers running the Maryblyt model also saw the epiphytic infection potential (EIP) exceed the spray threshold of 100. It is important to remember with this model, the EIP resets back to zero when a bactericide has been applied. However, with high temperatures, it does not take long for the EIP to jump back up above 100. A benefit to this model is that it also predicts when fire blight symptoms will appear.

If forecasting models are not being followed, bactericides should be applied from first bloom to petal fall when temperatures exceed 18⁰C with high humidity (>65%), heavy dews, rain or when spraying fungicides. According to Dr. George Sundin from Michigan State University, temperatures conducive for growth can result in fire blight populations multiplying to one million cells per flower within 1-2 days. Protective sprays are critical.

It seems as though the cooler temperatures will bring regional infection risk down for the remainder of the week. However, a cool forecast does not mean you are out of the woods entirely for fire blight blossom infection. The bacteria are capable of multiplying in temperatures ranging from 4⁰-32⁰C and will remain on the blossom until a wetting event occurs. As well, there is a possibility the day will be warmer than what was forecast or may be warmer in your orchard than elsewhere. In terms of fire blight infection risk, a few degrees can make a significant difference in disease pressure.

Despite some of the earliest regions seeing petal fall, secondary, or “rat-tail” blossoms are still possible. These late blooms are very susceptible to fire blight infection. Generally, continuing a protective program for a couple of weeks following petal fall will help ensure any late blooms are covered.

Regions that will be reaching bloom over the next week as infection risk potentially goes back down could consider the use of biopesticides such as Blossom Protect, Double Nickel or Serenade OPTI during extended periods of caution in early bloom. This will help establish a baseline protection on open blossoms should conditions change quickly. These products form a protective layer on the blossom and prevent the fire blight bacteria from invading. In cooler temperatures, while infection may not be occurring, the fire blight bacteria can still multiply and remain on the blossom. If temperatures climb above 18⁰C, the bacterial population can then increase exponentially in a very short period of time. Consider biologicals as a safety net for situations like this. Note, trials in the northeast have found an increased incidence of russeting when using Blossom Protect during extended wet weather particularly on sensitive varieties like Golden Delicious.

Apogee has started to be applied. Typical application is at king bloom petal fall for management of fire blight shoot infection; however, some growers are applying Apogee earlier between pink to bloom if there is terminal growth. This product works by:

1. Reducing vegetative growth of susceptible shoots and limiting spread of fire blight infection
2. Thickening the cell wall to provide a physical barrier from bacterial infection
3. Stimulating plant defense system and production of antimicrobial compounds to reduce infections.

Scab

The spring continues to be challenging for apple scab management. The continuous rainfall in recent weeks have resulted in several extended primary apple scab infection periods. While the cooler temperatures slowed new growth down, many growers have been concerned about maintaining protectant fungicide coverage with the heavy rains. Systemic fungicides have been a go-to for some looking for good kickback activity particularly in cooler weather. However, post-infection activity is calculated from the start of the infection period so may not provide full coverage in cases of extended infection periods.

Most areas are still within – though nearing the end of – the peak scab ascospore maturation period. Orchards have had a few rain-free days to help dry things up. However, that means there will be a significant build-up of mature ascospores ready to be released during the next rainfall. Very little moisture – dew, rain or spray – is required to trigger spore release during this time. Protectant fungicide coverage is critical as most of the available mature spores are discharged within 2 hours after the start of the wetting event.

At the present time, there have been no reports of scab lesions.

Rapid/Sudden Apple Decline

Early signs of tree collapse in Gala/M9 have been found in orchards that experienced rapid/sudden apple decline (RAD/SAD) in previous years. Generally, following a typically normal bud break, the tree appears to have low vigour, small and yellow leaves and small blossoms. Note in the image below the seemingly healthy tree on left with expanding green foliage compared to the collapsing tree on right.

As mentioned in last week’s update, if you notice signs of tree collapse in your orchard, please contact me at 519-420-9422 or kristy.grigg-mcguffin@ontario.ca.

Cedar Apple Rust

Reports of sporulating cedar apple rust galls on the winter, or alternate host (junipers including red cedar) continue east of Toronto. Orange, gelatinous spore masses called telia horns extend from the galls for a period of a few days typically about the same time apple trees are at pink, after a wet period caused by rain or heavy dew.

Spores are dispersed by wind to nearby apple trees. Golden Delicious, Idared, Mutsu and Russet are fairly susceptible to rust. Most scab fungicides used at this timing will have some efficacy on rust diseases. Refer to Table 2–3. Activity of Fungicides on Apple Diseases in the 2018-2019 Publication 360, Fruit Crop Protection Guide for efficacy ratings of registered fungicides.

Tree collapse in Gala/M9. Note the lush, green foliage of the healthy tree to left.

Orange telia horns extending from galls on alternate host of cedar apple rust. (Photo: Jennifer Dean)

Insects

Spring Feeding Caterpillar

Spring feeding caterpillars such as obliquebanded leafroller, eye spotted bud moth and tent caterpillar continue to be found along with terminal and cluster damage. Some orchards have reached threshold and growers will be applying a petal fall insecticide with activity on these pests.

Tarnished Plant Bug

Tarnished plant bug damage can be found on developing flowers. Damaged buds exude clear liquid ooze, which becomes amber after several hours. Affected buds  and flowers attacked prior to petal fall abort. Fruitlets stung after calyx typically fall off the tree during June drop, but those that hang on until harvest have a dimple or a deeply sunken conical area caused by the injection of a toxin during feeding.

Pre-bloom or petal fall insecticide applications targeted at other early season pests may suppress plant bug. Most often this pest moves to alternative hosts after petal fall.

Mullein Bug

Mullein bug activity has begun in some orchards, exceeding threshold of 7-9 per 25 taps in some blocks. A targeted spray may be required particularly on susceptible varieties, such as Red Delicious, Spartan, Spy, Empire, Cortland, Ambrosia, Gala, Jonagold and Golden Delicious. The critical time for damage from this pest is generally from dime to quarter sized fruit. However, mullein bug is also a very effective orchard predator for mites, aphids and leafcurling midge. Interestingly, mullein bug numbers were very high in some orchards last year yet fruit injury was minimal.

If planning to use Minecto Pro (pre-mix of AgriMek and Exirel) at petal fall, keep in mind Exirel does not have efficacy on mullein bug. Continue monitoring following application and apply a targeted control if populations exceed threshold.

Rosy Apple Aphid

Leaf curling and puckering typical of rosy apple aphid has been observed around bloom clusters. Colonies still remain in relatively low numbers. However, aphids thrive in cool, wet springs so we may see high pressure from this pest as a result. The most serious rosy apple aphid damage occurs when a toxin found in its saliva translocates from the leaves to fruit, causing apples to remain small, deformed (pigmy fruit) and unmarketable. Control is recommended if more than 5% of fruit clusters are infested.

Leaf curl and puckering caused by rosy apple aphid feeding. Note, leaves curl downward.

Rosy apple aphid colony developing on underside of leaf.

Apple Leafcurling Midge

Apple leafcurling midge egg counts are increasing and can be found near leaf folds or margins of young, developing leaves. Leafcurling caused by cream-colored larvae can be found in orchards with high midge pressure. This damage is expected to increase in the next week or two.

Small, orange apple leafcurling midge eggs along stem of new leaf.

Apple leafcurling midge terminal damage. Note, the leaves curl tightly upward.

Currently, only pyrethroids (Mako, Matador, Silencer, Decis) are registered for prebloom control of this pest. Movento is registered for suppression but can only be used postbloom. However, Ontario trials have found other products such as Purespray Green Spray Oil, Closer, Exirel and Delegate may also have efficacy when application timing is early in egg hatch/leafcurl stage.

San Jose Scale

Orchards in the Norfolk regions that are monitoring for San Jose scale observed the start of adult flight with a biofix of May 15/16. Interestingly, this typically aligns with 1st generation codling moth biofix for the region but moth activity has been delayed. Degree days for San Jose scale have begun to be accumulated to predict crawler emergence. Sticky tape is also currently being placed on infested branches in blocks with petal fall to monitor crawler activity. Typically, 1^st generation crawlers emerge mid- to late June in Ontario and are active for 4-6 weeks.

Control is rather targeted as most petal fall insecticides will be too early for scale. One option is back-to-back sprays of Movento starting 10-14 days after petal fall, or early June. This is a slower-acting product and requires a couple of weeks to see control so timing is best before crawler activity begins. Another option is a back-to-back spray of Sivanto Prime, Closer or TwinGuard (pre-mix of Delegate and Closer) starting at crawler emergence.

Internal Feeders

Sustained catch has occurred for oriental fruit moth in some areas monitoring for this pest. Biofix for Norfolk has been set for May 16.

Traps are up for codling moth and European apple sawfly. No catch has been reported.

Other

Mite activity continues to remain low, likely due to cool, wet weather.

Beneficial insect activity has also been increasing including spiders, lacewing and lady beetles.

Look closely! Can you spot the green spider?

Green lacewing

Lady beetle

Upcoming Webinar

There will be a noon hour thinning webinar this Thursday, May 30. For more information, see the blog post: Lunch N Learn Webinar: Fruitlet Thinning Review.