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Pest management guidelines for hailed and frosted orchards

A series of severe hail events hit southwestern Ontario last week resulting in considerable amounts of damage in orchards. The amount of damage in each area varies considerably from trace amounts of damage to severe fruit damage. Niagara, Hamilton, Chatham, London and Norfolk areas all reported hail damage. Many of these areas were also hit with a spring frost April 30/May 1 that resulted in a reduction in the amount of fruit. Combine the hail damage, frost damage, and poor weather during pollination time and some orchards have little or no fresh market crop (juice apples only). Growers with little or no crop still need to implement a pest management program. The extent of the program depends on the extent of the crop load in the orchard. Growers that have received hail damage may be concerned about trauma blight infections.

Hail can tear or shred leaves, puncture fruit and damage bark, making the tree more vulnerable to trauma blight infections. Traditionally OMAFRA has always recommended that growers apply Streptomycin within 12 hours of a hail event, especially on susceptible cultivars. However recent changes to the Canadian Streptomycin label indicate that the product can only be used up to 14 days after petal fall and the pre harvest interval for this product is 50 days which means that growers can not use it to manage trauma blight. Currently the only thing growers can do after a hail event is monitor the orchard carefully for fire blight and prune out infected wood wherever possible.

Orchards that have experienced a complete crop loss (juice apples only) should still make sure to follow a reduced spray program and pest monitoring should be continued. A scab program should be maintained. If growers are past the end of primary infection season and there is no scab in the orchard, then they can increase intervals between fungicide applications and adjust fungicide rates, as you would do with a normal sized crop. High scab populations will result in an increase in the overwintering populations of the scab fungus and may potentially cause more problems the following season. Management of direct pests is still important to prevent the build up of pest populations so sprays should continue to be applied for codling moth, oriental fruit moth and apple maggot. When using a reduced spray program growers may want to use border sprays of OP insecticides (Guthion, Imidan) to try to minimize costs. It is not recommended that growers use border sprays with neonicotinoids (Assail, Calyspo), insect growth regulators (Confirm, Intrepid, Rimon) and Ryanodine receptor modulators (Altacor).

Preliminary research suggests that resistance to OP insecticides is developing in codling moth populations in a few Norfolk orchards. In orchards with known OP resistance in codling moth populations, or in orchards that have a history of high damage from codling moth after using OP insecticides, it is recommended that growers use alternatives to OP's for codling moth including cover sprays of Intrepid, Assail, Calypso. Indirect pests (aphids, leafhoppers, leafminers) are less of a concern in these orchards. Miticides should only be applied when bronzing occurs or when the trees are stressed by drought.

Where hail/frost has resulted in a partial crop loss (spot picking) continue with a normal insect and disease management program. Growers looking at reducing their spray bills can use border sprays of OP insecticides for codling moth and apple maggot. However, be aware that these products may not be as effective in orchards with OP resistance. Be sure to maintain good coverage and use label rates. Cutting rates and improper coverage may result in inadequate pest management and potentially increase the changes of pesticide resistance developing. Managing the pests this year will help prevent insect and disease outbreaks in subsequent years.