Grand Rapids area tree fruit update

Warmer and drier has been nice.

Tree fruit growth stages

The warmer weather of late has moved us forward just a bit in degree day totals, but we are still about eight or nine days behind normal averages. Tree growth has improved with the warmer weather in the last few days. Apple growth is from tight cluster early pink depending on variety and site.

Tree fruit pests

Apple scab. The dry weather over the last week gave us a break from scab infections. Some very light rain moved through the area the evening of Monday, May 9. So far, this has not resulted in a scab infection according to the data from the local weather stations. Spore rods were checked Monday evening, and there were 2,190 spores per rod. This is the highest number so far this year and quite high given the very light rain of 0.01 to 0.05 inch. Spore maturity is most likely at 40 percent right now and will move quickly over the next week to nearly 80 percent by early next week. Therefore, the next two weeks are going to be critical for good scab spray coverage. Lesions from earlier infections in late April could start to show up in the next few days on spur leaves and the first true leaves.

Powdery mildew. All mildew susceptible varieties should have something added to the tank for mildew over the next two weeks. The very warm weather this week will push mildew along, so don’t let it get started.

Fire blight. With the very warm weather and potential rains this week, there could be a blossom blight situation for any pears or early apples with open bloom. The MaryBlyt model predicts that by Thursday, the EIP could go over the threshold of 100, which means that blossom blight could be an issue. With the predictions for stormy weather later this week, the other question will be about trauma blight Thursday and Friday. We don’t usually worry about trauma blight prior to bloom because cankers are not usually oozing that early, however, it would be a good idea to watch the weather closely for a trauma situation and be ready to cover blocks that have a history of fire blight and those with highly susceptible varieties. The Section 18 for Kasumin only allows for its use during bloom. Unless streptomycin resistance has been confirmed in your orchard, streptomycin is the material of choice for fire blight control. Oxytetracycline is really the only choice in streptomycin resistant areas to help prevent trauma blight outside of the bloom period, but it is not as effective for fire blight control as streptomycin once was.

Brown rot preventative sprays should be added in stone fruits now that bloom is open.

Insect development is slowly getting started. Spotted tentiform leafminer is flying regularly for the past week. Green fruitworm should be at peak flight. Oriental fruit moth is just starting to fly and a biofix will most likely be set this week. A few obliquebanded leafroller larvae can be found feeding in apple terminals. No European red mites hatch has been reported, but it’s expected to begin at any time this week. Rosy apple aphids are just starting to be found as well. If you had blocks with any damage from Campylomma (mullien bug) in 2010, you will want to be sure to add something into your pink spray for this sometimes pest. There are no codling moth flying yet, but it’s not too early to start putting up mating disruption dispensers.

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