Grand Rapids, Mich., area tree fruit regional report – June 10, 2013
Cooler temperatures have slowed insect development a bit.
Plum curculio damage has lessened in the last week, but they are still out there and most likely waiting for some warmer nighttime temperatures to do more egglaying. Cover sprays for plum curculio will be important until apples get to 20 or 25 millimeters in size when they become too hard for plum curculio to lay eggs into easily. According to Michigan State University Extension, stone fruits are susceptible to plum curculio for a longer time than apples and cover sprays should be maintained for at least two more weeks.
Codling moth has been trapped fairly regularly now for a couple of weeks, but some growers have told me they were catching male moths earlier than my May 28 biofix. I am now going to report growing degree day (GDD) totals for two different biofix dates that I’ve heard are common and I hope it helps you make decisions. The evening weather has a huge influence on codling moth activity and if it is below 50 degrees at dusk, or rainy and windy at dusk, they simply do not fly. You can use this information about codling moth activity to help you set a good biofix for your blocks as well.
So, for the May 18 biofix, 284 GDD base 50 accumulated at the Sparta Enviro-weather station indicate eggs should be starting to hatch (3 percent egg hatch) and timing for those early larvicide materials is right now. For the later May 28 biofix that is more likely to fit for most acreage on the Ridge, we have accumulated 177 GDD50 post-biofix, indicating eggs are being laid. Looking at the forecast, I estimate that around June 15 will be the timing for 3 percent egg hatch for the May 28 biofix, which is the timing for larvicidal insecticides.
Obliquebanded leafrollers are mostly very large larvae with some pupation beginning. This is not a good time to try to control Obliquebanded leafrollers, so save your sprays for the summer generation of larvae. I expect some flight of adults to start in 10 to 14 days, so you should have traps up in apples and sweet cherries soon to catch that first flight to set an adequate biofix.
Oriental fruit moth flight continues to be rather high in some blocks. Make sure you are maintaining the necessary insecticide covers in your stone fruits to prevent larvae damage to shoots and fruits. We are at 435 GDD45 since my regional May 15 biofix. This indicates egg hatch is most likely at a peak and cover sprays are really crucial at this time.