MSU Extension

Weather report

We had very summer-like conditions over the weekend, and our growing degree-day (GDD) accumulations are consistent with our 20-plus-year average: 1,297 GDD base 42 and 766 GDD base 50. Our 2016 averages are as follows: 1,260 GDD base 42 and 743 GDD base 50. Temperatures cooled down yesterday, June 27, and today’s daytime highs are only predicted to be in the high 60s with nighttime temperatures dropping down into the 40s. Temperatures will vary for the remainder of the week from mid-60s to 80 degrees Fahrenheit.

Most Michigan State University Enviro-weather stations recorded some level of rainfall Saturday night into Sunday morning, June 25-26, and most stations received around 0.25 inch of rain or less. The Benzonia Enviro-weather station received just under 0.5 inch of rain. Rain is needed to size the crop, particularly in orchards that have a pretty heavy set. Some of the areas across the north are extremely dry, particularly just south of Elk Rapids, Michigan, where these orchards have received very little rainfall for the season (less than 1.4 inches of rainfall for June).

Crop report

Wine grape bloom has progressed nicely, with excellent weather for pollination and fruit set. The earliest blooming hybrid at the Northwest Michigan Horticulture Research Center, Brianna, already has buckshot-sized berries. Riesling was not quite at full bloom as of June 27.

We are still in the prime window for powdery mildew infections of berries. Blocks with a history of trouble with powdery mildew should be kept covered with protectant materials for the next couple of weeks. Rose chafer numbers have started to drop off at many sites.

A couple of unusual insect infestations have been found in area vineyards this year. Grape tumid galls, induced by the larvae of a tiny fly, are small swellings on the leaves that may be green or red in color. On certain occasions, the galls may be formed on tendrils or flower clusters. The galls have a hollow center where the larva develops. It is unusual for this insect to be numerous enough to cause significant injury to a grapevine.

Grape cane girdler is a small weevil that lays eggs in succulent shoots, then “drills” a series of small holes around the perimeter of the shoot somewhere below that point. The larva develops in the wilting shoot tip beyond the drilled holes. Infested shoot tips readily break off from wind or contact with equipment. So far, this insect has only been reported from a few hybrid varieties in northwest Michigan. It is not likely to occur at numbers that would cause significant injury.

There is a “First Friday” meeting scheduled for Friday, July 1, 3-5 p.m. at Hawthorne Vineyards, 1000 Camino Maria Drive, Traverse City, MI 49686, on Old Mission Peninsula. MSU entomologist Rufus Isaacs will be our featured speaker, presenting information on perimeter spray programs, new insecticide options and natural enemies.

Saskatoon berry samples from an untreated block indicate that egglaying by adult apple curculios has finally ended. Larvae of all sizes and some pupae can be found inside fruits at this time. All larval feeding by the saskatoon sawfly should be done by this time. Rust infections remain light in northwest Michigan. Rose chafers continue to do a lot of foliar injury and some berry feeding has been seen. With harvest coming up very soon, it is important to pay close attention to the pre-harvest intervals for any pesticide applications that are being considered.

Sweet and tart cherries are coloring up. The sweet cherry crop, particularly canners, looks a little lighter than we first observed. Brine cherries have a heavier set than dark sweets. Growers are considering ethephon applications, rates and timings with the dry conditions and potentially high temperatures that are predicted for the latter part of the week. Tart cherries are quite variable in terms of ripening. It is not unusual to see green fruit on the same branch with red and straw colored fruit. Tart cherry harvest will begin in southwest Michigan this week, and west central Michigan anticipates beginning harvest around July 6.

The Michigan Frozen Food Producers’ Association’s Guesstimate took place last week in Grand Rapids, Michigan. The total estimates for sweet cherries in Michigan are 27,000 tons/54,000,000 pounds. When we break up the cherry estimates into different categories, the following numbers were presented last week: 1,500,555 pounds of fresh market sweets; 3,000,000 pounds of canned product; 16,500,000 pounds of frozen cherries; and 33,000,000 pounds of brine cherries. Most growers thought they had good bloom, but there might be some variable pollination depending on when the orchards bloomed. We had some cold weather in the middle of sweet cherry bloom, so there may be some lighter than average crops. We have also been seeing considerable drop in sweet cherries. Overall, presenters at the Guesstimate estimated the sweet cherry crop across Michigan would be 90 percent of the 2014 crop.

Estimates were also presented for the tart cherry crop across the U.S. The total Michigan crop is estimated to be 253 million pounds: 165 million pounds from northwest Michigan, 68 million pounds from west central Michigan and 20 million pounds from southwest Michigan. This is the largest crop since 2009. Again, southwest Michigan will begin harvest around June 29 and 30.

New York had a frost on one-half of the state, but the overall estimate will be seven million pounds. Pennsylvania also had some cold spring temperatures, and there will only be 0.3 million pounds. Wisconsin is estimated to harvest 11 million pounds. Utah is estimated to harvest 50 million pounds, Washington 27 million pounds and three million pounds in Oregon. Oregon and Washington are already in harvest.

The total U.S. tart cherry crop is estimated to be 351.3 million pounds. In the restricted districts, the estimate that will be plugged into the Optimum Supply Formula is 348 million pounds and 3.3 million pounds are unrestricted. The free carry-in is 81.3 million pounds. The three-year free sales are 250 million pounds and the Board used a 25 million pound growth factor. Other factors the board considered are a carry-out of 57 million pounds, and they added another 22 million pounds in the “other category.” The total demand is 303 million pounds, which puts the restricted percentage at 29 percent (restricted tonnage 101 million pounds).

This year’s restriction is less than most growers have anticipated. In light of the challenges of spotted wing Drosophila (SWD), a lesser restriction will help us better manage this pest, particularly if fruit is put on the ground. Additionally, the Cherry Industry Administrative Board voted to temporarily suspend the zero-tolerance policy for 2016 because of concerns about SWD. In 2015, some growers had cherries infested by SWD, and these infestations may have been the result of unforeseen situations. Additionally, tart cherry crop insurance covers SWD-infested fruit if the grower did all they could to prevent this infestation. In keeping with the crop insurance policy, fruit infested with SWD can be used for diversion. However, MSU Extension highly recommends growers maintain good insecticide coverage to prevent SWD infestation. We remind growers that large SWD populations can overwhelm even the best spray programs. SWD-infested blocks can quickly escalate overall SWD populations, and these adult flies can move into blocks that are intended for harvest and compromise SWD control. Growers that intend to divert whole or partial blocks need to continue to control SWD to minimize impacts on adjacent blocks, neighbor’s blocks and SWD populations in subsequent years.

Pest report

Cherries are ripening across the northwest region, and spotted wing drosophila (SWD) has been the primary pest of concern in the last week. Thus far, the research center has found or confirmed a total of 24 SWD flies in northwest Michigan; no SWD have been found at the research center. The latest SWD catch numbers in our region are available in the table below. Until yesterday, June 27, most of the SWD catches were on Old Mission Peninsula and growers in this area have begun protecting cherries from SWD. Traps in Benzie County were checked yesterday; seven flies were found in tart cherry along the M-72 west corridor and two additional flies were found near Arcadia, one in tart cherry and one in gooseberry. Old Mission Peninsula, M-72 W corridors and growers in nearby locations where SWD have been detected should begin programs to prevent SWD egglaying into susceptible fruit if they have not done so already. Many orchards in northwest Michigan are susceptible to SWD at this time and if SWD has been detected on-farm or in a nearby location, growers with orchards in these areas should begin management programs. On-farm monitoring is the best means of having a timely detection of SWD to indicate when to begin management. Through research projects and the SWD Trap Swap program, the research center has over 250 traps in northwest Michigan, and we are working with local scouts and consultants to notify growers of SWD presence in more precise locations as this pest is detected.

Some growers are about a week away from early sweet cherry harvest and managing mixed variety blocks for SWD is a concern for meeting pre-harvest intervals (PHI) while also ensuring that spray materials will continue to provide SWD control. The pyrethroid insecticide Danitol is a three-day PHI material with good to excellent efficacy against SWD. As with most pyrethroids, Danitol is a relatively short-lived insecticide and will last five to seven days in the field. Pounce is also a three-day PHI material with the active ingredient permethrin, which has shown variable SWD efficacy in research center trials.

We remind growers that insecticides that have an efficacy rating in the “2016 Fruit Management Guide” have been tested by MSU for SWD efficacy. There are generic insecticides with the same or similar active ingredient as the materials that have been tested, but growers need to be aware that MSU has not tested all generics to determine comparable efficacy. Hence, we cannot be confident that generic materials will provide adequate or comparable SWD efficacy. For example, the pyrethroid insecticide Baythroid XL with the active ingredient beta-cyfluthrin has been tested and rated “good” for SWD efficacy; however, Tombstone is a generic with the similar active ingredient (cyfluthrin) and we cannot be certain that this material will provide comparable control at a similar rate because it has not been tested in MSU’s trials. Furthermore, growers should be aware that SWD is not listed on the Tombstone label.

Interestingly, cherry fruit fly has not been detected at the station yet this season, and we have not received reports of cherry fruit fly activity in the region. We hypothesized that this pest would become active following rain last week, which was not the case. It is possible SWD management programs have impacted cherry fruit fly detections, particularly if pyrethroid or organophosphate insecticides have been used for SWD this season. We will continue to monitor for cherry fruit fly, and we ask local scouts and consultants to please notify the research center at 231-946-1510 when this pest is detected in the region.

Obliquebanded leafroller moth activity is ongoing and the research center biofix (i.e., first date of sustained catch) for this pest was June 17; some areas caught this pest earlier around June 14. According to Enviro-weather, the research center has accumulated 309 GDD base 42, and egg hatch typically begins between around 400-450 GDD base 42 after biofix. Obliquebanded leafroller trap numbers were down this week with an average of eight moths per trap with the highest catch at 22 moths per trap. Catches at around 20 moths per trap in an orchard indicates treatment may be needed.

Higher than usual obliquebanded leafroller catches have been reported in the region, and some growers are strategizing how to target obliquebanded leafroller and SWD in their pre-harvest spray program. We remind growers that obliquebanded leafroller resistance to the organophosphate insecticides and cross-resistance to pyrethroid insecticides has been documented and as a result, these chemistries alone should not be expected to provide adequate obliquebanded leafroller control. Diamide (Belt, Altacor) and spinosyn (Delegate, Entrust) insecticides are better options for obliquebanded leafroller.

Additionally, we remind growers that if a diamide was used earlier this season for obliquebanded leafroller, a different mode of action should be used for late season/pre-harvest larvae to prevent resistance development. Furthermore, we have not tested Belt or Altacor for efficacy against SWD, so growers should not rely on these materials for SWD control; however, Delegate has provided “excellent obliquebanded leafroller and SWD efficacy in research trials.

Our region has been fortunate that cherry disease and virus incidence has been relatively low this season because good leaf retention will be necessary for ripening the large cherry crop. We observed some orchards with powdery mildew mycelia growing on leaves near the centers of trees (Photo 1); there are no fungicides that will effectively eradicate mildew once it is established. We have had a few isolated reports of possible Syllit plus Captan phytotoxic symptoms following applications in hot conditions, but overall reports are low. The forecast is looking mostly dry for the coming week, and these conditions pose little threat for cherry leaf spot infection. Drier conditions are also less favorable for American brown rot development. However, growers will need to monitor the weather and the potential threat for diseases closely. Sugar content is increasing in cherries and brown rot could take off quickly in ideal wet, humid, warm conditions.

New fire blight symptoms are still appearing, but overall symptoms are slowing down; growers with fire blight-infected blocks are continuing copper programs to kill the bacteria at this time. Thus far, we have observed and collected fire blight samples in Grand Traverse (albeit not on Old Mission Peninsula), Antrim, Benzie and Manistee counties. We encourage growers to continue monitoring orchards for fire blight symptoms: flagging or “Shepard’s crook” terminals and ooze (Photo 2). We have found fire blight-infected fruit that appear to have a darkened or rotten looking spot where small, yellow- to orange-colored ooze droplets manifest (Photo 3). Keeping a low inoculum is the best means of preventing further spread of fire blight bacteria during windy, stormy weather that could lead to trauma blight.

Photo 2. Fire blight-infected terminal with ooze.

Photo 3. Fire blight ooze on apple fruit.

Codling moth activity is ongoing and we found an average of five moths per trap. Moth catches have been higher in our high density Honeycrisp block compared with the mixed block of dessert and cider varieties. According to the Enviro-weather codling moth model, we have accumulated about 560 GDD base 50 since the research center biofix of May 24, and codling moth are at peak egg hatch at this time.

Oriental fruit moth second generation are flying at the research center. Oriental fruit moth catches at the research center are often low and variable, and this scenario continues to be the case this season. If second generation populations are high and management is needed, action should be taken around 200 GDD base 45 after biofix (i.e., the first sustained catch of second generation oriental fruit moth) to target egg hatch.

The research center will deploy apple maggot traps next week; first emergence of apple maggot typically occurs at around 950 GDD base 50.