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2018-2019 Fruit Disease and Insect Report

By Forrest Scharf (PAg) Provincial Specialist, Fruit Crops

Winter conditions in 2017-18 and 2018-19 were harsher than the prior five years and cold temperatures were sustained longer. In addition, fall and spring were significantly drier than average in most regions, except in the north-east where moisture levels remained relatively high. These conditions led to physiological stress of plants, especially sour cherry, but also resulted in less insect and disease pressure. Winter damage reports were received for cherries in 2018 and 2019 and some tip-kill occurred in raspberry patches in both years. The 2019 winter-kill was more severe with a lot of top-kill in raspberry and cherry. The 2018 tip-kill may have occurred when conditions warmed in mid-March followed by colder temperatures returning by the end of the month. Top and tip kill losses observed in 2019 may relate to prolonged drought stress, along with the coldest September (2018) and February (2019) in over one hundred years. The prolonged winter in 2018, and general lack of early flowering resources also led to significant loss in bee populations. The lack of early season pollination potential in 2018 resulted in lack of significant fruit-set for some haskap orchards. Locations with greater numbers and diversity of wild bees in 2018 were able to achieve much greater pollination success. As summer progressed in 2018, bee populations rejuvenated. This improvement was sufficient to sustain intrinsic fruit-set potential in later blossoming fruit species like raspberry. Bee populations appear to have been better sustained over winter in 2019, and no reports of poor pollination were received.

Late spring and early summer conditions were consistently warm and dry in both years. Upper soil layers became dry quickly after snow melt. Due to these conditions, iron chlorosis symptoms were negligible in most high pH soils, where plants had been chlorotic in previous years. In addition, due to lack of precipitation throughout the majority of the blossom period in 2018 and 2019, disease pressure was minimized in pathogens whose spores are spread via precipitation to flowers like fire blight, brown rot blossom blight phase, Entomosporium leaf spot. In 2018, for the earliest ripening crops like strawberry & haskap, some fruit quality was reduced due to dryness and inability to get water to the plants in the early development phases of fruit-set. Tent Caterpillars were not present in large numbers, continuing population decline from their peak in 2016. Commercial growers controlled isolated infestations with BT products, a few other insecticides and manual removal/killing of nests.

Snail on a haskap leaf
Snail on Haskap Leaf, July 2019
No economically significant diseases were detected in Haskap, but powdery mildew was present at low levels in sheltered pockets with a disease spread more significant than 2018. Control of powdery mildew is possible using conventional fungicides as well as “biorational” products like common hand soaps outlined in this study. Leaf scalding symptomology on haskap continues to be pervasive and is suspected to relate to stress, causing a lack of water and/or fertility, since plants pushed through this type of damage when irrigation along with moderate fertilizer applications were applied in sufficient amounts. The most significant fruit losses were from foraging birds like American robins, cedar waxwings and the most recent bird pest to discover haskap in large flocks, starlings. Cedar waxwings were particularly aggressive in the early stages of fruit ripening in 2018. They likely lacked other food sources due to delayed development of other crops, and therefore, foraged at less than desirable stages of fruit development. The main flocks migrated away for a few weeks, but returned again several weeks later when the fruit was almost ready to be harvested. American robins are more individualistic and sporadic foragers, but the starlings arrived in large flocks and foraged extensively. In 2019, starlings and cedar waxwings competed over desirable sites, but damage to commercial growers was generally less than in 2018, perhaps due to high yield wild fruit resource availability. Netting remains the most widely used business risk management strategy at present, but laser technologies from companies like Bird Control Group has been proving itself to be effective. In regard to insect pests, some reports of cutworm (species not determined) leaf foraging were made, but no economic damage was anticipated. Another type of pest that didn’t create economic loss are snails. They appeared to enjoy foraging on haskap leaves. In regard to starling control strategies, protocols like the starling control program that British Columbia Grape Growers Association initiated in 2003, to protect wine grapes may need to be initiated. Their program sets up traps in strategic locations and then captured birds are euthanized and donated to a local raptor rehabilitation program. With an annual budget of approximately $100,000 drawn from growers as well as local government, the program has managed to eliminate more than 800,000 starlings since its inception.

Strawberry producers suffered relatively insignificant plant loss due to dry conditions in 2018, since most commercial growers employ drip irrigation. Most patches displayed less vigorous growth throughout May and early June, due to overwinter stress and delayed application of irrigation after the plants had come out of dormancy. Growth conditions in mid June and throughout July and August were stronger, but cold wetter conditions in September reduced the productivity of day-neutral varieties, whose fruit–set generally didn’t get enough heat to continue development and ripening. The most popular June-bearing cultivar (Kent) remained highly tolerant of iron chlorosis as were Sapphire, Serenity and AC Wendy, but day-neutral varieties like Seascape, and Albion were more stressed through winter than the other varieties and more susceptible to iron chlorosis and slow growth in early summer. The cold September was followed with the coldest February in over one hundred years and some poorly insulated and stressed strawberries perished. Plant death was more widespread in day-neutral varieties, but all cultivars experienced some loss. In the spring of 2019, conditions remained dry in the majority of the province, but this changed in June, July and August when more consistent rainfall was obtained throughout the province. Unfortunately; more consistent rainfall corresponded with cooler night temperatures, and the cool temperatures delayed ripening, and hindered fruit quality.

Fewer strawberry growers identified anthracnose as a major disease problem in 2018 and 2019 than in 2016 or 2017. In regard to this disease, anthracnose continued to be more infectious on berries than leaf and stem tissues. Most foliar diseases like powdery mildew, leaf spot, angular leaf spot, and leaf scorch were present but did not cause significant economic loss in 2018, and the spread of infection was less extensive than in previous years which may be due to the extended dry, hot conditions. In 2019, foliar diseases became more significant due to more widespread and consistent rainfall starting in late June. No significant strawberry root rot problems were reported in 2018 or 2019. In some patches in the northeast, some diseases like downy mildew, mucor, botrytis and other rot organisms could be found. This may be due to more consistent moisture allowing the diseases to survive. Many strawberry patches continued to experience tarnished plant bug infestation that required multiple applications of insecticide. No growers reported cricket infestation in 2018, but the population started to increase late 2019, and was foraging on late season day-neutral strawberries in particular. Wasps also foraged significantly on ripe strawberries in central Saskatchewan starting in late August 2019. Spider mite infestations were limited in severity and there were no reports of significant economic impact. This was consistent with the observation that in general most strawberry infesting insect populations declined over 2018 and 2019, likely due to dry summer and winter conditions.   

Unlike many other fruit species, pollination of raspberries was very strong in 2018. It appeared bee populations increased by the time raspberries came into bloom and the bees didn’t have a wealth of other foraging options so they concentrated on raspberries. Pollination was also strong for raspberries in 2019 and this was consistent with better bee foraging observed for all fruit crops. Growers continued to thin canes to allow better air movement through their raspberry patches, allowing better fungicide dispersal and limiting disease spread by reducing high humidity microclimates within dense canopies. Raspberry patches in the Northwest, and Southwest sustained improved management practices for control of botrytis and anthracnose and those patches did not report issues in 2018 or 2019, although some of the improvement in plant health may have been due to sustained dry conditions. Some spur blight, yellow rust and fire blight infections were detectable at various locations, but did not cause significant economic loss. Relatively few insect pests were reported in raspberry, but raspberry fruit-worm, raspberry sawfly and raspberry cane borers were present at levels below economic thresholds. Some mites were detected in the Saskatoon region and various types of mite were present in numerous other locations at low levels. Sap beetles were also found infesting late-season raspberries in central and southern Saskatchewan. Sap beetle populations didn’t become significant until late August 2019. Some Hutterite colonies experienced poor raspberry yields in 2019, and this may have been due to more severe winter-kill of fruit bearing floricanes . The Prelude cultivar continued to impress with respect to its productivity and growth habit. It produces fruit at early and standard summer production windows on floricanes and then produces a substantial yield later in fall on primocanes.

Apple tree showing symptoms of Rapid Apple Decline
Apple tree showing symptoms
of Rapid Apple Decline
In apples; the same disease and insect problems remained present in orchards that experienced problems in prior years. Yields were average, but some growers reported experiencing what they believe is biennial or alternate bearing (AB) physiology. Management practices to reduce AB include application of proper pruning, irrigation, nutrient management and possibly application of Apogee (prohexadione calcium) to reduce the impact of gibberellins. Management of the bacterial disease fire blight remained a challenge in 2018. The recommended management protocol remains a modified non-antibiotic control of fire blight (from eOrganic eXtension), but experimentation with Apogee, combined with copper products and kasugamycin, may be another promising long-term management strategy. Apogee is particularly good at reducing the stem-blight phase of this disease. A few growers also had black rot, associated with fire-blight. The black rot did not appear to significantly infect fruit, but it does appear to have a strong correspondence with poor overall plant health. In 2019; orchards that had fire-blight, black rot, as well as various environmental stressors like saturated soils, sunscald damage, and cold overwinter temperatures, succumbed to a condition known as rapid apple decline (RAD). Initial experimental attempts to treat RAD in Saskatchewan have focused on use of Apogee to reduce vascular weakness in susceptible plants. It has particularly good efficacy, controlling the stem-blight phase of fire blight. Submission of samples for formal identification of RAD are being referred to Guelph’s Agriculture and Food Lab.

Apple growers continue to be referred to general recommendations in AAFC’s Crop Profile for Apple in Canada, 2016 and to OMAFRA’s Apple Calendar for control product usage. Canker diseases continued to be present in some orchards, with pruning and copper pesticides recommended to control spread. Apple scab was not reported to cause significant economic loss in 2018, nor was water core , but both were more easily detected in 2019, perhaps due to increased precipitation. Apple maggot was present in many commercial orchards, but economic impact was not reported to be significant, presumably because growers effectively controlled infestations. Apple maggots seemed to oviposit earlier in 2018, but appear to have been later in 2019. Late apple maggot activity may relate to cooler temperatures and delayed apple development.

Blind wood on dwarf sour cherry
Blind wood on dwarf sour cherry,
June 2019
In 2018, sour cherry yield was very significantly below average. Fruit size was also below average, but sugar content was relatively high. Under normal circumstances, dwarf sour cherries can sustain high levels of yield year-after-year, but the dry conditions combined with winter stress limited yield in 2018 and 2019. The plants came out of dormancy with relatively little dead wood, a condition that limits fruit yield, in 2018; but when they leafed out, the number of leaves were greatly reduced. Leaves were missing on large portions of stem. In addition, although blossoms opened at the same rate as average years, they soon wilted and were dropped from plants. It appeared the energy balance required to support fruit production was greatly depleted. Often when relatively few fruit are left on a plant they become larger and obtain higher sugar content. Although sugar content was slightly above average, fruit size was actually below average in 2018. In regard to diseases, spread of the blight phase of brown rot in dwarf sour cherry orchards was limited due to early hot-dry conditions and the significant early loss of flowers. That limited the potential of spores to spread flower to flower. Economic losses from brown rot were not reported in 2018, but increased in 2019, due to more consistent precipitation coupled with warm daytime temperatures during the fruit ripening phase where the rot can spread quickly from fruit to fruit. Relatively few mummy cherries remained in cherry orchards in 2018, but control of brown rot over the blossom period in 2019 was recommended.

In 2019, more cherry winterkill was detected, and in many cases top-growth removal is recommended to improve canopy management issues in the long-term. Fruit yields in 2019 were significantly higher than 2018, and fruit quality was also better than 2018. Leaf spot remained detectable in some locations, but did not cause economic loss and was greatly reduced in prevalence compared to 2016 and 2017. Bacterial canker remained present, but did not cause significant damage in 2018 or 2019, although it may have contributed to some winterkill susceptibility. It is recommended growers attempt to control bacterial canker and leaf spot diseases using copper and other registered control products in future crop years.

Cherry fruit fly infections that had been significant in 2017, were not reported to be as significant in 2018 or 2019. In several locations where flies had an economic impact in 2017, the recommendation to spray was made despite lack of fly detection on sticky traps. Since infected fruit is not allowed to be processed at the Saskatchewan Food Centre, maggot control remains a significant priority. Insecticide control protocols were recommended from OMAFRA’s Tart Cherry Calendar (starting page 271) for these pests in 2019. Another type of larvae was also detected in sour cherry in 2018, and this was determined to be argyresthiidae. Investigation of the spread and severity of infection from these moths is ongoing. Control products for these moths may have to be considered for registration through the Minor Use Program. Another insect type reported to infect cherry leaves in central and southern Saskatchewan in 2018 and 2019 were Cherry slugs, also known as pear slugs, cherry sawfly. The insects can be controlled using conventional insecticides or organic products including sprinkling ash over leaves to desiccate the slimy exterior of the insect and cause its death.

Gulls were another bird pest noted by several cherry growers. One unique feature of gull foraging is that they consume the whole fruit and do not leave pits behind. As is typical with many birds, when they discover a nutrient source, a whole flock can be recruited to completely consume the entire orchard in a short period of time. Affected orchards were characterized as being very close to large bodies of water typically inhabited by gulls. Bird control strategies may offer some relief from this problem, and growers should consult with Saskatchewan Crop Insurance Corporation regarding their wildlife damage compensation program for possible assistance.

Shot hole and brown rot continued to infect chokecherry. Black knot also 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 of diseases in general, but growers continue to employ pruning removal as the primary practice to rid infected trees of this disease.

Disease pressure in Saskatoon berry was low for Entomosporium leaf spot, fire blight and Saskatoon-juniper rust in 2018 and 2019. Few other fruit or foliar diseases were significant in 2018 and 2019. In fact, 2019 was one of the best fruit production seasons for Saskatoon berry within collective grower memory. Fruit was large, sweet, abundant, and lacked significant pest damage. Hawthorn lace bugs were present in central areas of the grain belt in 2018; but populations were low, so control interventions were not warranted and growers did not report this insect to be a problem in 2019. Tarnished plant bug populations were above average in 2018, and it was recommended insects be controlled with registered control products, but populations were relatively low in 2019 and application of control products was not typically warranted. No Saskatoon berry orchards reported significant leaf gall problems caused by midges (Cecidomyiidae) in 2018 or 2019, and no infection was detected at the Canada-Saskatchewan Irrigation Diversification Centre orchard in Outlook. Growers in the Northwest quadrant of the grain-belt did not report spotted wind drosophila (SWD) larval infestations in their Saskatoon berries in 2018. If there had been any SWD, as had been suspected by growers in 2017, they must not have survived.

A grower located west of Saskatoon was reported, by a client, to have had a bad insect infestation in 2018. The insects were curculio, and the grower was advised to spray to control these pests in 2019. It was reported the grower has never sprayed to control insects, so it wasn’t overly surprising they ran into this issue. No curculio problems were reported in 2019.

Sea buckthorn orchard infections from Monilinia, anthracnose, and Botrytis were not detected in 2018 or 2019. Dry and sunny conditions throughout 2018 and early 2019, likely contributed to reduction in disease pathogenesis. It is recommended growers continue to monitor orchards for disease. Given the dry conditions experienced in spring and early summer of 2019, extensive application of fungicides was not recommended, but given more consistent precipitation since July, more disease pressure could be expected in 2020.

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