MSU Extension

Weather report

The past week was extremely warm and, as a result, we are two days ahead of our long-term averages. This warm weather has been coupled with significant rainfall, and tree growth and fruit size have moved along quickly. Temperatures cooled off Sunday and Monday, June 18 and 19, and cool weather is expected for the next few days.

We have accumulated 1,097 growing degree-days (GDD) base 42 and 617 GDD base 50. The region received rainfall throughout the last week, but the actual amounts were variable depending on location. At the Northwest Michigan Horticultural Research Center, we received just under 0.75 inch of rain on June 12, almost 0.25 inch on June 13 and another 0.75 inch of rain on June 14. We did receive just a bit of rain on June 15. We had a day of dry weather on June 16, and more rain fell (about 0.37 inch) on June 17 and 18.

More rain is in the forecast for later this week. All these wet days have been challenging for growers to make spray applications.

2017 growth stages as of June 19, 2017

• Bartlett Pear – 21 millimeter fruit
• Potomac Pear – 23 millimeter fruit
• McIntosh – 33 millimeter fruit
• Gala – 24 millimeter fruit
• Red Delicious – 27 millimeter fruit
• HoneyCrisp – 24 millimeter fruit
• Montmorency – 13 millimeter fruit
• Balaton – 14 millimeter fruit
• Hedelfingen – 15 millimeter fruit
• Gold – 14 millimeter fruit
• Napoleon – 16 millimeter fruit
• Riesling – 10 to 16 inch shoots

Crop report

Many wine grape varieties have reached 2-3 feet of shoot growth. The potential crop looked very good at the sites we visited this week.

Rose chafer populations have already started to decline. Adult potato leafhoppers are easily found in vineyards, so watch for them or their symptoms in very susceptible varieties such as Pinot Gris and Pinot Noir. Young caterpillars of the larger sphinx moths should be appearing soon.

We have not yet seen infections of powdery mildew or downy mildew at the research center vineyard, but all vineyards should be examined closely for these two diseases. Downy mildew is much more likely this year due to frequent rain events. Sprays to protect clusters from powdery mildew are recommended from now on through to three to four weeks after bloom.

Fruit is sizing well with the recent rains and warm weather. Some early varieties of sweet cherries are starting to color. We continue to subject fruits at different stages of ripening to spotted wing Drosophila flies to determine when the fruit becomes susceptible to spotted wing Drosophila oviposition. We also are checking wild host ripening to determine when to begin those studies.

Apples are sizing, and many growers are hand-thinning blocks where they did not have good thinner activity. We are currently hand-thinning our Honeycrisp at the research center.

Strawberry harvest began late last week in more northerly plantings.

Pest report

This last week’s wet weather challenged growers’ pest and disease management programs and opportunities to get into orchards. In particular, cherry leaf spot has been a concern as many orchards have at least a low level of infection at this time.

Since June 12, the Michigan State University Enviroweather has reported four infection events for the research station and five infection events in areas that received more rainfall. Growers will need to be diligent with spray programs to stop the spread of leaf spot infection. Our observations indicate wet weather during the end of May is likely where trees became infected initially and recent rainy weather has been very conducive for leaf spot development.

In 2015, leaf spot was problematic, and the research station had 12 infection periods from May 10 to the end of July. This year, the Northwest Michigan Horticulture Research Center Enviroweather station has reported nine infection events in a little over a month from May 22 to June 20. MSU Extension encourages growers to use full fungicide rates and full covers, as well as slow down to ensure good coverage to prevent possible leaf spot epidemics before we reach harvest.

Apple scab spore rods were collected following rain over the weekend and we did not catch spores following these rain events. Last week, most growers in the northwest region were planning one or two more covers for primary this season. The Ridge and Hart areas have called the end of primary apple scab.

Although many orchards appear to be free of scab, we have received reports of isolated orchards with substantial scab infections. Orchards that have active scab will need to be actively managed to prevent fruit scab.

Growers will also want to prevent premature defoliation. For example, if trees have an apple crop, adequate numbers of leaves are needed to support fruit growth and ripening. Orchards with a light crop can tolerate more leaf loss. Significant early defoliation reduces carbohydrate storage, which can impact winter hardiness and overall tree health.

Most apple blocks do not have fire blight symptoms. Where fire blight has been observed, it is usually just one or two strikes in a block. If orchards were impacted by windy and stormy conditions, or if an orchard had hail about two weekends ago, trauma blight symptoms should be visible.

Codling moth activity is ongoing at the research center with consistent trap numbers in the last two weeks (see table below). Based on the research center biofix of May 31, we have accumulated about 350 GDD base 50 and egg hatch is ongoing. We remind growers and consultants that cumulative threshold counts of codling moth should be reset to zero after an application has been made. Trap count reports from across the region have been variable with some hot spot orchards having codling moth catches in the high 20s.

We did not find San Jose scale males in traps at the research station this week, indicating the likely end of male flight in our area (see table below). We have not detected crawlers, and we have continued to observe active yellow-bodied scales under their waxy coatings. Crawlers became active in the Ridge area last week and, as a rule of thumb, crawler activity usually coincides with bloom of catalpa trees.

Spotted wing Drosophila is becoming more of a concern as sweet cherries are beginning to turn color in some areas. Trap catches remain relatively low in orchards with higher catches in traps set in alternate hosts adjacent to orchards. Fruit in most tart cherry orchards are still green, but be prepared to start management programs when green fruit begin turning straw-colored. Please refer to the most recent FruitNet newsletter for more detailed information on trap catches in the region.

Other late season or pre-harvest pests are also on growers’ minds. Cherry fruit fly have not been detected at the research center. While imidacloprid is affordable and has been very effective for cherry fruit fly management, this material has not shown excellent efficacy against spotted wing Drosophila in cherries.

Obliquebanded leafrollers have been active for two consecutive weeks at the research center, and we set our obliquebanded leafroller biofix for June 13. Growers typically target the obliquebanded leafroller larvae at pre-harvest timing to prevent shaking larvae into tanks. Setting a biofix will help us estimate when the larvae will be active.

Rose chafers became active last week and growers had difficulty planning sprays between rainy and windy weather. Many materials growers use for rose chafers provide quick knockdown efficacy of this pest, but residuals do not last long particularly in wet weather. Furthermore, this pest can re-infest blocks quickly—continue monitoring problem blocks for this pest.

Borer activity is ongoing at the station (see table below). While lesser and greater peachtree borer numbers remain consistent with last week, we have received reports that some orchards have higher populations this season.

July “First Friday” Grape Meeting

The next First Friday Grape Meeting is July 14 (the second Friday in July, in order to avoid the Cherry Festival) at Ten Hands Vineyard on Old Mission Peninsula, located on Mission Road just south of the Old Mission General Store.

The topic of this meeting is "Foliar Fertilization Programs in the Vineyard” and will be led by Craig Cunningham of Cunningham Viticulture Services. Cunningham has utilized foliar programs in vineyards for more than 10 years, including Ten Hands Vineyard, owned by Tom Petzold.

We will also walk the vineyard for informal scouting, discussing issues as they come up. Tom will answer questions on his vineyard practices (composting, compost tea use, growing grass under the vines, etc.) to round out the session.