Northwest Michigan fruit regional report – July 8, 2014
Cherries are ripening and growers need to be on high alert for spotted wing Drosophila and American brown rot.
Temperatures have felt summer-like across the northwest with daytime highs in the 70s and low 80s. Nighttime temperatures have cooled down into the 50s and 60s. So far this season, we have accumulated 1,412 growing degree days (GDD) base 42 and 860 GDD base 50. These accumulations continue to be slightly behind our 24-year averages here at the Northwest Michigan Horticulture Research Center (NWMHRC). We also have had rainfall this past week with varying amounts of precipitation across the region. We received just over 0.5 inches of rain last Wednesday, July 2, and another 0.11 inches on July 6. Rain was expected on and off July 7. Conditions have also been windy over this past week, which has been challenging for growers to make applications.
Wine grape bloom and fruit set is complete on all varieties. In general, berry set looks good on healthy shoots, but on shoots which are stunted in growth, the set is far worse. As was expected, we are now seeing some canes with all of their shoots collapsing as a result of winter injury to trunk or cane conductive tissues.
Powdery mildew has been slow to develop to this point in the season, but recent warmer weather and high humidity may have been sufficient to support colony growth and new infections. Downy mildew has been seen on wild vines. There are still a few lingering rose chafers in vineyards, but they are now of no consequence. Potato leafhopper populations have remained low. Adult grape berry moths should be active soon.
Sweet cherries continue to ripen across the region and first applications of ethephon are going on this week. Birds seem to be particularly problematic this season in ripening varieties. We have seen some cracking in some sweet cherries, likely as a result of the wet conditions. The crop of sweets looks good in northwest Michigan, and growers have been diligent about keeping fruit clean with the cracks and bird pecks.
Tart cherries are also ripening and starting to turn red. The crop is estimated to be between 107-125 million pounds in northwest Michigan. As the fruit turns red, the crop visually appears to be varied by tree and by block as estimated earlier in the season.
Apples are sizing well with the recent rains. Strawberry harvest continues, and growers are estimating a shorter than usual season.
American brown rot is showing up in isolated sweet cherry orchards across the region. We began receiving a few reports of American brown rot sporulating on non-pollinated fruit a few weeks ago and infected fruit is evident in heavy clustering varieties. However, we have had good weather conditions for the development of this disease and we expected to see American brown rot more widespread than we are currently seeing. Some of the American brown rot-infected fruit were previously damaged by birds, canker, insects, etc., but American brown rot can infect fruit that have not been wounded, particularly when the disease moves from cherry to cherry in a cluster. In some orchards where American brown rot has been detected, infected fruit are just above eye level and visible from the ground. However, American brown rot can be difficult to find because infected fruit are often high in the tree canopy where fungicide coverage is reduced.
American brown rot-infected fruit sporulate, in as little as three days in optimal conditions, and the disease can spread to nearby fruit. Temperatures between 59-74 degrees Fahrenheit are optimal for American brown rot spore production and optimal temperature range for infection is 67-77 F. This week, temperatures are predicted to be within the optimal infection range, and rain is forecasted. Because of these warm and wet conditions that have been typical this season, American brown rot has been and continues to be a priority, particularly now that sugar levels are increasing in sweet cherries. Michigan State University Extension advises growers to be diligent about maintaining adequate coverage and preventing infection to have clean fruit at harvest.
Once American brown rot infection is initiated, fungicides will not kill or stop American brown rot development. Sweet cherries are highly susceptible to American brown rot infection and the most effective materials should be used as a preventative measure. Currently, the SDHI fungicides are the best materials for American brown rot and although research has shown that American brown rot has reduced sensitivity to Indar, we are still recommending a rotation of Indar at 12 ounces per acre and the new SDHI fungicides. Therefore, growers should be using Indar at 12 fluid ounces per acre (the 24c label rate) plus captan in rotation with a SDHI fungicide such as Merivon and Luna Sensation plus captan. Based on our data, Indar, even at the highest rate, will only be effective for four to five days. Additionally, using the SDHI as the last spray before harvest will provide the longest effective American brown rot and cherry leaf spot control post-harvest.
We caught the first spotted wing Drosophila (SWD) at the research station this week; a single female in a Montmorency County tart cherry block. The first SWD, a single female in a trap, in northwest Michigan was captured Monday, June 30, in Grand Traverse County in tart cherries. SWD have also been detected in a vineyard in Leelanau County in the last week. Many sweet and tart cherries are ripening and susceptible to SWD. Strawberries are also susceptible to SWD at this time and SWD will be a concern in other small fruits, like raspberries, blackberries, etc., as soon as they begin ripening. In cherries, SWD can begin laying eggs in fruit as the fruit turn straw-colored. Growers will need to be protecting ripening fruit if SWD was caught in their area (Yuba area in Grand Traverse County, Ellsworth, and southern Leelanau County—near the NWMRHC, and East Leland, Leelanau County).
Cherry fruit flies and black cherry fruit flies have been captured in Leelanau County. Last week, cherry fruit flies were detected on Old Mission Peninsula. We have not detected either of the cherry fruit fly species on traps at the NWMHRC. Growers need to be diligent about controlling this pest through harvest to prevent infested fruit at harvest.
This is our third week of obliquebanded leafroller flight and obliquebanded leafroller trap numbers remain low at four moths per trap. At this time we have not received reports of high obliquebanded leafroller catches. We have received reports of lecanium scale crawler activity in sweet cherries in the East Leland, Michigan area. We have not detected San Jose scale crawlers in sweet cherry orchards where we are conducting a monitoring project for this pest; however, San Jose scale crawler activity has been reported in apples in the region. Birds have moved into many sweet cherry blocks and growers have been applying bird deterrents.
Most apple orchards remain clean of diseases so far this season. We called the end to primary apple scab last week and growers who have scab lesions will need to continue their scab program past primary to ensure scab-free fruit at harvest. Codling moth catches at the station remain low, an average of one moth per trap. Obliquebanded leafroller numbers in apples at the station remain low, an average of one moth per trap.
The next Parallel 45 vineyard meeting is this Friday, July 11, 3-5 p.m. at 2 Lads Vineyard And Winery on Old Mission Peninsula, 16985 Smokey Hollow Rd, Traverse City, MI 49686. Please park as directed, NOT in the tasting room lot. Our topics will focus on pests, diseases and the Michigan Agriculture Environmental Assurance Program (MAEAP).
Dr. Rothwell's work is funded in part by MSU's AgBioResearch.