May 31, 2017
Crop development: Day- neutral strawberry harvest continues. June bearing varieties are in full bloom and green fruit is present in early fields where row covers were used. Raspberry flower buds are present and bloom has started in early areas. Blueberries are in bloom and petal fall in southern Ontario.
Blueberries: Bravo can be used until petal fall for anthracnose fruit rot and phomopsis. Close to petal fall spray for cranberry and cherry fruitworm- sprays can be timed using pheromone traps or degree day models. Without traps or models time the first application at petal fall, followed by a second spray 7-14 days later.
White grubs can also warrant control at petal fall. White grubs are the larval stage of European chafer, June beetles, or Japanese beetles (Figure 1). Plants will be able to be pulled out of the ground easily, and white grubs will be easy to find in the root zone. They are typically a problem in light sandy soils. The larvae feed on plant roots in the spring and late summer. If white grubs are a problem target sprays right after the adult beetle and chafers are active prior to egg hatch, typically at petal fall, green fruit or post-harvest. Admire or Alias can be applied as a soil drench but not until after bloom.
Figure 1. C-shaped white grub larvae
Raspberries: Insect activity has been slow in raspberries. Continue to monitor for signs of raspberry fruitworm, strawberry clipper weevil or raspberry sawfly. Crop potential looks promising. Damage from spring feeding caterpillars has been seen.
Strawberries: Tarnished plant bugs counts continue to be low; we expect populations to increase in the next week so continue to monitor for these with your tapping trays. The threshold for June bearing varieties is approximately 1 in 4 flower clusters.
Thrips are not usually a problem in Ontario June bearing strawberries, however, problems with thrips have been reported in the mid-west US this year. Thrips can cause bronzing under the calyx, on the seeds and fruit, and can even cause the entire berry to become bronzed and cracked.
Monitor for thrips in June bearing and day neutral fields. If your tapping trays from tarnished plant bug monitoring are collecting a lot of thrips blow gently on the blossom to see if thrips crawl out. If you find 20-30 thrips per bloom in June bearing, and 30-40 thrips per bloom in day neutrals, consider using Delegate. Delegate will only provide suppression.
If thrips are a problem avoid using pyrethroids, which could kill beneficials that are naturally controlling this pest. Consider adding beneficials to your day neutral fields.
Bronzing on the fruit can also be caused by environmental conditions or from powdery mildew. Look for thrips or powdery mildew to determine what is causing the damage before applying insecticides or fungicides (Figure 2).
Figure 2. Comparing damage from thrips and powdery mildew.
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