Warm weather will move tree fruit growth quickly this week.
Posted on May 6, 2014 by Phil Schwallier, and Amy Irish-Brown, Michigan State University Extension
Daily temperatures have remained much below normal high and low readings, and tree growth has been in a stasis for the last seven days. Most apples are stuck in 0.5 inch green to tight cluster with some later varieties barely showing any green.
Stone fruits are slowly developing. Apricots are nearly in full bloom on the Ridge. Sweet cherry flower buds are expanding and the first white of bloom can be seen in the warmer sites. Tart cherries are just showing some bud expansion, but they seem very behind this year compared to sweets. Peach buds are slow to develop and while there may be some fruit bud damage, there appears to be a full peach crop potential at this time.
Tree planting continues on the Ridge and in Belding, Michigan, with very good soil moisture conditions to get this job done. As apple leaves begin to expand, it’s time to add foliar nutrients that can help with fruit set – nitrogen and boron in particular. Cooler weather will reduce nitrogen uptake in trees.
Tree fruit diseases
Apples. The very rainy conditions last week resulted in either a heavy infection or two separate apple scab infections, depending on the Michigan State University Eniviro-weather station site. The rainfall and intermittent dry times were quite variable across all of West Michigan. Spore numbers were rather high for this early in the scab season, with over 1,600 spores per rod for the entire rainy period last week. We expect we were at about 4 to 5 percent primary spore maturity when rain moved in, so numbers will be much higher with the next rain predicted for later this week when spore maturity will be nearing 25 percent.
Fungicide covers for the next two to three weeks are the most critical during primary scab and should not be stretched. Very warm weather predicted for later this week will push new leaf development quickly. Maintaining good fungicide covers on this newly expanding tissue will be very important in the next seven days.
It’s time to begin adding fungicides in for powdery mildew in apples. The very warm and humid weather predicted for later this week will be the perfect environmental conditions for mildew.
Sweet cherries. Copper applications on sweet cherries and other stone fruits can still be applied if there is no green tissue showing. As green tissue appears, the rate of copper needs to be reduced to prevent phytotoxicity.
Insects
Very cool weather has delayed the emergence of insects that are normally seen by the time we get to tight cluster, in particular apple grain aphids and obliquebanded leafrollers. With very warmer than normal weather in the forecast for this week, insects will become active and apples will move quickly toward the pink stage where many insects can be curbed.
If cool weather moves back in as the long range forecast suggests, it could be a long window for bloom and an extended period before petal fall insecticides can be used. This would be a good year to not skip a pink spray or rosy apple aphids might get established well before you can get in with a petal fall spray. Michigan State University Extension suggests pink is also a good timing for targeting San Jose scale.
This article was published by Michigan State University Extension. For more information, visit http://www.cnchemicals.com/. To contact an expert in your area, visit http://www.cnchemicals.com/, or call 888-MSUE4MI (888-678-3464).