MSU Extension

Weather report

Conditions were very warm over the weekend, and daytime temperatures reached into the mid-80s. Nighttime temperatures only fell into the low to mid-70s. The temperature hit 80.5 degrees Fahrenheit at the Northwest Michigan Horticulture Research Center on Monday, June 20. So far, we have accumulated 1,108 growing degree-days (GDD) base 42 and 633 GDD base 50. Future weather predictions suggest temperatures will remain in the 70s for the week and increase into the 80s for the weekend.

The next chance for rain is June 23 or 26. Rainfall has been variable across the Michigan State University Enviro-weather stations in the north, which fell on June 15 and 16. The Northwest Michigan Horticulture Research Center only received 0.25 inch. The remainder of the weather stations reported the following rainfall totals: 0.69 inch in Bear Lake, 2.55 inches in Benzonia, 0.83 inch in East Leland, 1.29 inch in Eastport, 0.42 inch in Elk Rapids, 0.73 inch in Kewadin, 0.53 inch in Northport and 2.14 inches on Old Mission Peninsula.

Crop report

Cherries are really starting to color with the recent heat, and both sweet and tart cherries are showing some straw color into pink. Some of the early sweet cherry varieties are pink to red in color. We are seeing some drop in sweet cherries, particularly in the variety Sams. Growers are questioning if spotted wing Drosophila (SWD) can lay eggs and develop in dropped fruit. We have a small research project underway to test this hypothesis. We have been observing cracks in developing sweet cherries, likely from the past few rain events. We are continuing to look into the non-bearing Ulster situation.

Growers are hedging apples at this time. The predicted harvest dates for apples are normal to ahead of normal by two to five days. More information on prediction harvest dates is forthcoming.

Earlier-blooming wine grape hybrid varieties, such as Frontenac and LaCrescent, are approaching full bloom at the research center. Noiret and St. Croix are showing some bloom. No bloom was found on any of the vinifera cultivars, but it will likely start before the end of this week.

We are now 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 few weeks. Rose chafer numbers have been low in a number of sites, but as is typical for this insect, there are hot spots where treatments may be needed.

Saskatoons berry samples from an untreated block showed a resurgence of apple curculio egglaying during the past week. Eggs and larvae of all sizes can be found inside fruits at this time. Saskatoon sawfly larvae have mostly completed their feeding and dropped out of fruits at advanced sites, but small larvae were still present in fruits at later locations. Rust has continued to be a minor problem this year, but there are still a couple of weeks before harvest begins and keeping fruit protected from this disease is advised. Rose chafers have been found in high numbers at a few sites. They can consume quite a bit of leaf material in a short time, so sprays may be required, especially in young plantings. At high numbers, rose chafers may even feed on the fruits.

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.

2016 growth stages as of June 20, 2016

• Bartlett Pear – 20 millimeter fruit
• Potomac Pear – 24 millimeter fruit
• Mac – 22 millimeter fruit
• Gala – 24 millimeter fruit
• Red Delicious – 29 millimeter fruit
• HoneyCrisp – 24 millimeter fruit
• Montmorency – 12 millimeter fruit
• Balaton – 14 millimeter fruit
• Hedlfingen – 16 millimeter fruit
• Gold – 13 millimeter fruit
• Napolean – 14 millimeter fruit
• Riesling – first bloom

Pest report

We are continuing to see shoots collapse from fire blight and some of these symptoms could be a result of either blossom blight during bloom or trauma blight from the high winds and stormy conditions on the evening of June 10. We have observed and had reports of fire blight-infected orchards with fresh ooze and if trees or leaves were damaged during recent windy conditions, fire blight bacteria could spread to wounded areas and cause trauma blight. Where it is feasible, some growers are pruning out fire blight-infected tissue as new symptoms appear and applying a material to kill the bacteria that are growing in the fire blight ooze. Continuing management of the bacteria until tree growth slows and fire bight symptoms subside will help to prevent the possibility of trauma blight during stormy weather this summer. Copper materials are the best chemistries to dry up fire blight ooze.

The primary phase of apple scab is over. Spore discharge numbers were at zero following Monday’s rain, and prior to this rain, spore numbers had been in the single digits for several wetting events (Table 1). Most commercial orchards are also at the end of primary apple scab at this time. However, if an orchard became infected during primary, scab management should continue until fruit and leaves are less susceptible to infection later this summer. Since biofix (April 17), the research center had a total of five scab infection periods, but we have not found scab lesions in apple blocks at the research center. Fortunately, there have been very few reports of secondary scab infections in the region this season. If scab is found, we ask growers and consultants to contact the research center at 231-946-1510 – we would like to collect samples for fungicide resistance screening.

Spotted wing Drosophila (SWD) adults have been detected in Leelanau and Old Mission so far this season. The rule of thumb for determining when to apply an insecticide for SWD is when one fly is caught in an on-farm trap or when 5-10 percent of traps in a region are catching SWD. Defining a region can be difficult, but our best use of this word is either county or a locale within a county. For instance, if we captured SWD in Benzie County, we would consider that county as a region. Manistee County would also be its own region. In the case of Leelanau County, we would consider the following “regions:” Bingham, East Leland, Centerville Township/Cedar, Northport-Omeana and just north of Suttons Bay. In Antrim County, the following areas could be considered regions: Elk Lake Road, Kewadin, Eastport and Central Lake. In Grand Traverse County, we have regions south of Traverse City, Yuba and Old Mission Peninsula.

We may not have traps in all of those regions, but we have over 250 traps in orchard across northwest Michigan. We will inform growers of the SWD catch with a precise location to assist with management decisions. The following chart shows the SWD trap catch through June 20.

The current forecast is calling for a slight chance of rain on Thursday morning, June 23, and if rain comes, cherry leaf spot protection could be needed. Temperatures this week are predicted to be in the upper 70s, a little cooler than last weekend’s temperatures. However, temperatures could jump back up in the 80s over the weekend and growers should be careful if they are planning to apply copper or Syllit.

We observed sporulating American brown rot on cherry mummies in some early sweet cherry varieties at the research center last week, and this fungus was starting to spread to adjacent healthy fruit. Some varieties have clusters that have many cherries and ensuring that these fruits are protected from brown rot is critical particularly in wet, humid and warm weather. Additionally, some orchards had high levels of first generation green fruit worm and obliquebanded leafroller larvae, and cherries that were damaged by insects and or birds or those that cracked after rainfall are favorable hosts for brown rot to get a foothold.

Damaged, poorly pollinated and June drop fruit have begun falling from trees at this time; however, keeping brown rot in check will be difficult if this fungus sporulates on June drop fruit that does not drop and spreads to good fruit clusters before the damaged fruit drop.

Cherry fruit flies have not been detected at the research center, and we have not received reports of fruit fly activity in the region. We anticipate fruit flies will become active this week possibly following Monday’s rain. After emerging, cherry fruit flies undergo a feeding period of seven to 10 days called the pre-oviposition period and control measures are typically implemented during this timeframe.

Obliquebanded leafroller adults are active, and we have received reports that populations of this pest are high in southwest Michigan. The research center biofix for this pest is was June 17, but there were earlier obliquebanded leafroller catches in the northwest region during the week of June 12.

At the research center, we found an average of 17 moths with the highest catch at 30 moths per trap. In recent years, obliquebanded leafroller numbers have been relatively low; however, as we observed previously in 2010, there is the potential for the larvae of this pest to be shaken from trees into tanks at harvest timing. Furthermore, populations of obliquebanded leafroller larvae earlier this season seemed higher than we have seen in a few years, and because pollinators were still in the orchard after bloom, many growers had a delayed or missed post-bloom spray for larvae that could contribute to a higher pre-harvest population this season.

We have had reports that mite populations are building, but mite populations are low at the research center. This season has been dry and some insecticides, in particular the pyrethroid class of insecticides, are toxic to mite predators and may cause a buildup of pestilent mites. While growers should review pesticide labels for pre-harvest intervals prior to application, MSU Extension reminds growers to pay particular attention to the miticides as some of these materials have long pre-harvest intervals of 21 to 28 days.

Codling moth catches were the highest of the season at the research center this week with an average of eight moths per trap. According to the Enviro-weather codling moth model, we have accumulated about 412 GDD base 50 F since the research center’s biofix (May 25), and we are approaching peak egg hatch.

Greater peachtree borers became active at the research center over the weekend. Lesser peachtree borer activity is ongoing with higher catches this week than last, but overall numbers are on the decline. American plum borers remain low, in the single digits.