West central Michigan tree fruit update – July 30, 2019
Tart cherry harvest will wind down by the end of the week, and peach harvest is just around the corner.
Several nice rains in the last two weeks have provided some welcome soil moisture. Warm weather continues to dominate the forecast as we move into August, lots of sun on the forecast for the next 10 days. Make sure you continue to monitor the soil moisture, particularly in young orchards. Soils got pretty dry during July, and while the recent rains have helped some, the soil could dry out again very quickly if we go through the first half of August without much rainfall.
The recent heat has helped move us closer to five-year averages on our degree-day accumulations. The Hart Enviroweather station is currently sitting at 2,004 growing degree days (GDD) base 42, 1,705 GDD45 and 1,253 GDD50. The five-year average for this date is 2,152 GDD42, 1,842 GDD45 and 1,369 GDD50. We are still behind in terms of crop development, but not nearly as behind as we may have expected given the start to the season.
Apples are showing some terminal bud set in most orchards, although more vigorous blocks are still pushing growth. The heat and lack of water helped slow many orchards down. Fire blight has continued to show up in the past couple of weeks on shoots, but it is slowing down now as terminal bud set arrives. This upcoming span of hot, dry weather is perfect for cutting out strikes if the amount of blight is small enough that the practice is warranted. Make sure to cut back at least a foot behind visible symptoms (the further back the better) when making these cuts to ensure that you remove all of the blighted tissue.
Growers should be monitoring the sooty blotch/fly speck Enviroweather model for 240 hours since 2 inches of rain have fallen on the last fungicide application. Captan will need to be mixed with a sterol inhibitor or strobilurin fungicide to effectively protect against this disease complex. The dry weather in the coming days is likely to keep these accumulations fairly stagnant, but if we end up getting scattered showers tomorrow, July 31, we could still see this stack up some. If we end up getting a dry August, using this model rather than your calendar to track your accumulated wetting hours can save you some good money.
Tart cherry harvest is mostly over in Oceana County, and growers in Mason County should be finished up by the end of the week. The crop is light, but quality has generally been good on fruit that have been shaken so far. Moving through harvest as quickly as crew speed and receiving lines will allow is in everyone's best interest as spotted wing Drosophila (SWD) starts to climb. This is going to be particularly critical (and extremely challenging) in the common situation where you hit your quota for a day on an orchard that is more than a week out on its last SWD material. To the best of your abilities, it's extremely important to try to plan how far you think you'll be able to get in a day and make sure everything that you won't be into is well-covered.
Growers will be making their final post-harvest fungicide sprays on tart cherry soon. If you are weighing your options given the current financial market, remember that young trees are going to be particularly devastated by early defoliation, so while keeping leaves through August is important in all tart cherry orchards, young blocks just moving into their prime can be particularly affected in the long run if they are neglected in the second half of the summer.
Sweet cherry harvest is largely over in the region. Brown rot was tough this year for a lot of farms. The effect of microclimate on brown rot formation within the field was very visible this year as I surveyed much of the damage around the area. In general, less dense fruit clusters located on the outside of sweet cherry trees or on younger trees with less dense canopies looks OK, but thick clusters of fruit hanging on canopy interiors or on pendent wood on standard sized trees was a disaster in many orchards this year.
It's tough to contemplate what the game plan is going forward when something like this happens. Given what has happened, it's in your best interest to try to prune trees back. This is best done in the hot, dry summer months when bacterial canker is not a concern. Big cuts to the canopy are well-timed right now because the hot dry weather will allow the wounds to scar over quickly and prevent bacterial canker from taking hold in the main scaffold of the tree. Thinning out tops of larger trees, removing pendant wood and cutting out shaded limbs to open up the canopy will help increase air flow and speed up drying time of fruit following a rain while decreasing humidity within the canopy, which will help reduce the favorability of the environment for the development of brown rot. This will also help to improve coverage, as getting good coverage in to the top and interior of a standard sized sweet cherry that has run away some on height is a tough thing to do. Good horticulture won't solve all the problems in a year like this one, but it does help.
Also, consider shaking any fruit you have walked away from onto the ground to help it break down before it can mummify fully. Brown rot mummies in the tree canopy are an extremely potent source of inoculum in subsequent years and should be avoided and removed whenever possible. Mummies on the ground also contribute inoculum, but most of the brown rotted cherries shaken onto the ground during the very early stages of brown rot infection or pre-infection will not mummify properly because they are broken down quickly by other secondary fungi and insects once they hit the ground. Brown rotted fruit left in the canopy will dry down quickly in the summer heat, stick tight to limbs and provide a healthy source of inoculum next season. It's always hard to stomach paying a crew to shake fruit on the ground, but it is in the best interest of the long-term health of the orchard to do so when brown rot claims an orchard.
We're working with George Sundin's lab to test local brown rot isolates for resistance to Indar and the SDHI's right now, and will have some results soon. It is possible resistance has played a role in the issues we are seeing this year, but unfortunately a significant player in this was the misfortune of highly conducive weather and some orchard systems that are highly favorable for the development of the disease.
Any sweet cherries that have not been harvested yet need to be well protected against SWD. The climb of this pest we are seeing this week means fields need to be well covered until harvest is complete. There are fewer short preharvest interval material options in sweet cherries, so planning ahead is particularly tough on this crop. To the best of your abilities, make sure you're not stretching a material past seven days until you're all finished up.
Peach harvest is already right around the corner as we move into August this week, which means the final stretch of brown rot control is upon us. There is a tremendous amount of brown rot inoculum out there this year, so make sure you are keeping a tight schedule and incorporating Captan as a protectant in your sprays. Indar at 12 fluid ounces, Flint Extra and Merivon/Luna Sensation are all viable systemic products but need to be tank-mixed with Captan to help manage resistance. Captan alone will provide some brown rot control and is a critical part of a good management strategy in peach.
A preventative strategy is critical for brown rot; none of these products work particularly well as a back-action option for the disease. This pathogen is extremely aggressive and develops in infected fruit quickly, so trying to eradicate existing infections with a late spray is not a practical solution for us.