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Tree and Small Fruit Pest Report

By: Forrest Scharf (PAg) Provincial Specialist, Fruit Crops

Most fruit orchards suffered little “top-kill” or wildlife forage damage over winter 2014/15, as temperatures weren’t severe and snow cover was not generally excessive, allowing animals to forage from non-fruit sources. Spring and early summer conditions were generally drier, so negative effects from 2014 excess moisture were reduced. Since upper soil layers became relatively warm and dry, iron chlorosis was less significant than it had been the previous five years. This allowed many orchards to regain some vigour. The 2015/16 winter was also exceptionally mild, so plant response is likely to be similar, especially if spring conditions continue to match last year’s temperature and precipitation levels.

The majority of commercial fruit species did not suffer extensive frost damage in 2015. Since there was almost no precipitation over the bloom period, infection from diseases like fire blight, brown rot and Entomosporium leaf spot were less significant than in previous years. Early summer temperatures over the bloom period (for most crops) were warmer, allowing strong bee activity and pollination.

In addition, since nutrient status was improved due to warmer drier conditions, fruit-set and development for most crops was above average. However, in a few low lying orchards located in the northwest and northeast quadrants of the grain-belt (where early spring conditions were warm and plants came out of dormancy by early to mid-May), a deep spring frost on May 29, 2015, caused yield loss as a result of blossom freezing and top-kill.

Haskap

Haskap did not perform as well as other crops in 2015, as fruit size was smaller and yields were below average. Contributing factors may have included:

  • Frost damage during early spring and temperatures below -7 C during the blossom period, when other species had not started to flower;
  • Since haskap is shallow rooted, lack of consistent moisture reduced vascular transfer of nutrients and moisture to fruit;
  • Two flower structures need to be pollinated to allow the central ovary to develop. Insufficient pollination resulted in reduced fruit-set, since bees do not pollinate efficiently at temperatures below 8 C (for more pollination information, see Wild Bees as Crop Pollinators: a Case-Study in Haskap); and
  • Higher direct sunlight and heat levels in early to mid-summer reduced plant vigour and fruit size. It is recommended that photo-selective netting be tested to determine if their beneficial properties can improve haskap vigour and productivity, and that haskap nutrient deficiencies be carefully monitored via leaf analysis. No economically significant diseases were noted in 2015, but powdery mildew was detectable at many sites.

 Strawberry

The drying period that extended into summer was largely beneficial for tree and bush fruit, but some strawberry growers suffered loss. Strawberry producers that started ventures within the past six years had little experience growing plants under dry conditions, which are more typical for Saskatchewan. In many instances planting depth was too shallow, so crowns were propped above the soil line and roots were exposed above ground. Shallow planting had not caused plant loss in the previous six years, but dry conditions in 2015 resulted in crowns and supporting roots being desiccated, leading to widespread plant death.

Example of shallow-planted strawberry with
roots exposed (many plants like this became
desiccated under persistent hot dry conditions).

Growing everbearing varieties (like “Seascape”) in plastic mulch also created conditions that led to micronutrient deficiencies, despite providing sufficient fertilization. This was because excessive irrigation was provided in an attempt to prevent desiccation of crowns and exposed roots, making the soil cool and wet. It is recommended that growers walk fields during and after planting to ensure planting depth is sufficient so roots are not exposed, and that approximately 50 per cent of the crown tissues (below the apical meristem) be planted below ground level. It is also recommended that soil moisture sensors or diligent hand testing be utilized to ensure plants are not overwatered.

Some strawberry growers had fairly extensive Anthracnose damage. Anthracnose appeared to be more infectious on the fruit than on other plant tissues. In some cases it had been present in the patch from previous years, but in others it was introduced with recently purchased daughter plants. Some other foliar diseases, like powdery mildew, leaf spot, angular leaf spot, and leaf scorch were present, but in general these did not cause significant economic loss and their spread was far less extensive than in the previous five years.

Some strawberry patches also experienced strong tarnished plant bug infestations that required multiple applications of insecticides to bring them under control. A few growers also reported cricket infestations. Cricket populations have been building over the past five years, especially in the southern parts of the grain-belt; these insects feed on ripe strawberries and cause extensive economic loss. Their population appears to have declined in 2015, but application of control products is still recommended for 2016. Spider mite infestations were limited in severity, and there were few reports of it being a significant economic problem.

Raspberry

Some raspberry patches suffered with powdery mildew and botrytis, but in general production was strong. Some distilleries and wineries are using raspberries, so it is becoming increasingly important to control these diseases so that fermentation is not disrupted from the interaction with yeasts. Many growers need to thin their canes more to allow better air movement through the patch and more effective fungicide dispersal. Raspberry patches in the northwest saw improved management of botrytis and blight infections, and those patches are becoming more productive. Some anthracnose, spur blight, yellow rust and fire blight infections were detected, but did not cause significant economic loss.

Apple

Few new apple problems were reported and production was average. However, management of fire blight at a few sites remains a major challenge. Recommended management protocols can be found in Non-Antibiotic Control of Fire Blight (from eOrganic eXtension).

Silver leaf continues to be detected in apples, as well as dwarf sour cherry orchards. It is more prevalent in areas that have struggled under waterlogged soils and in orchards where pruning cuts are not made flush (where stubs are left on the remaining limbs). Spread of this disease was limited in 2015, likely due to drier conditions.

Canker diseases continued to be present in many orchards, and it is recommended that copper pesticides be employed to try to control spread. Apple scab did not cause significant economic loss in 2015, and water core was not reported by growers who had it in 2014. This is likely because pruning was reduced compared to previous years, plants have matured slightly and excess moisture conditions were not prevalent during the fruit ripening process.

Dwarf Sour Cherry

Spread of brown rot in dwarf sour cherry orchards was limited due to hot, dry conditions, but remains present in many orchards. Leaf spot is detectable in some locations, but has not caused detectable economic loss. Bacterial canker is widespread, but did not appear to cause significant economic damage in 2015. It is recommended that growers attempt to control bacterial canker and leaf spot diseases using copper and other registered control products.

Cherry fruit fly and apple maggot continue to infect dwarf sour cherry and apple, and growers have various insecticide options they can employ to control these pests.

Some shot hole and brown rot continued to infect chokecherry. Black knot continued to infect most wild chokecherry stands (especially along the Qu’Appelle Valley and east central regions of the province). There are a few control products registered to reduce infestation, but growers must also employ pruning to rid the trees of black knot.

Saskatoon Berry

Disease pressure in Saskatoon berry was moderate to low for both Entomosporium leaf spot and fire blight. Few other fruit or foliar diseases were present, but in some cases insect pest pressure was high. Hawthorn Lace Bugs were present in central areas of the grain belt. Although no economic thresholds exist for recommendation on when to control populations, it is recommended that growers control these insects, since they severely damage leaves and appear to weaken plants over time. Tarnished plant bug populations were also fairly strong, and those insects can also be controlled with a number of registered control products.

Sea Buckthorn

Sea Buckthorn orchards appear to have become infected with Monilinia, anthracnose and Botrytis. It is likely that these diseases have been building up in orchards over the past five years. These diseases had not previously been known to be a problem in Saskatchewan. More extensive monitoring and application of fungicides is recommended in 2016. The hope is that various disease management trials will be initiated at grower sites in 2016.

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