MSU Extension

Weather and crop report

Spring feels like it has arrived in northwest Michigan over the past few days. Daytime temperatures have risen to the mid-60s, and we have had some sunshine for bee activity in blooming sweet cherries. On Friday, May 6, the daytime temperatures reached almost 80 degrees Fahrenheit, and sweet cherry bloom really was accelerated by these warm conditions. Nighttime temperatures are still cool, and one Michigan State University Enviro-weather station reported below freezing temperatures (31 F) on Monday morning, May 9. We have accumulated 287 growing degree-days (GDD) base 42 and 114 GDD base 50. We are slightly behind our GDD averages here at the Northwest Michigan Horticulture Center: 316 GDD base 42 and 143 GDD base 50.

Soil moisture continues to decline with the lack of rainfall in the region. The last rainfall reported at the center was last week on Tuesday into Wednesday, May 4-5, where we received just over 0.25 inch of rain. Despite the lack of rainfall accumulation, weather forecasts have been predicting rainfall, so growers have been diligent in covering the growing green tissue in apples and the potential for American brown rot in sweet cherries.

With the dry conditions and still relatively cool temperatures, things have been quiet in the grower community. There is rain and warmer temperatures predicted in the near future, so growers will be prepared for these events. After the brief warm up, cool conditions are predicted for the weekend, so we expect development of trees, insects and disease slow down again. There seems to be many stops and starts to the season so far this year. We expect to be in bloom in tart cherries over the weekend into the start of next week. We are hoping for warmer temperatures for good bee activity.

All wine grape varieties are showing bud swell to some degree. In the research center variety trials, buds on canes that were severely injured by last year’s hailstorm appear to be swelling at the same pace as buds on uninjured canes. No pest insect activity has been seen. The window for dormant or delayed dormant applications for powdery mildew will be over soon.

In saskatoons, very little change has occurred since last week; most sites we’ve seen are still in the white tip stage of bud development. No pest insect activity has been seen. We are not certain of the prime infection periods for Entomosporium leaf spot or saskatoon-juniper rust, but these fungal diseases may now be releasing spores if rainy weather occurs.

2016 growth stages as of May 9, 2016

• Bartlett Pear – White bud
• Potomac Pear – First bloom
• McIntosh – Tight cluster
• Gala – Tight cluster
• Red Delicious – Early pink
• HoneyCrisp – Early pink
• Montmorency – Early white bud
• Balaton – White bud
• Hedlfingen – Full bloom
• Gold – First bloom
• Napolean – Full bloom
• Riesling – Early bud swell

Vineyard volunteers needed at the Northwest Michigan Horticultural Research Center

We still have a lot of pruning and tying left to do at the research vineyard. We are looking for volunteers to help finish the job this Wednesday and Thursday, May 11 and 12. Weather permitting, we’ll start at 8 a.m. and work until 5 p.m. With a big enough crew, it might be possible to wrap it up in one day.

Please contact Duke Elsner at 231-357-8353 or elsner@msu.edu if you can help out or would like more details. Please bring your own pruning shears and loppers. If the weather is questionable, call me before heading over to the research center.

Pest report

Recent dry conditions throughout the region have not been favorable for disease infections, and some growers did not spray for apple scab late last week as the forecast changed and no longer called for rain over the weekend. The region received rain May 3-4, but most areas did not have an apple scab infection period due to a short wetting event and cold temperatures. However, a light infection was reported at the Elk Rapids Enviro-weather station.

While there was no infection period, the center observed apple scab spore discharge following last week’s rain (see table below). The center set biofix on April 17 and according to Enviro-weather’s apple scab model, 36 percent of ascospores are mature and 13 percent have discharged at this time. Warm weather hastened spore maturity and the degradation of orchard floor leaf litter is noticeable this week. Currently, the forecast is calling for a chance of rain and thunderstorms on Thursday, May 12. MSU Extension suggests growers be ready to protect for apple scab if rain comes this week. If orchards became infected with scab during April 21-22 or 24-26 infection events, scab symptoms should show up this week.

Many growers protected sweet cherries from American brown rot infection over the weekend and early this week. Blossom blight is a concern as conditions are predicted to be warm and wet weather mid-late in the week, at least until the weekend when it is predicted for temperatures to cool down considerably. As mentioned in a previous report, several sterol inhibitors are available for American brown rot management; however, Rovral 4 F at 2.0 pints per acre is still the optimal option for excellent efficacy and resistance management. There are only two applications of Rovral 4 F allowed per season.

Although conditions are predicted to be warm and wet Thursday, May 12, temperatures are also expected to drop into the 40-50s overnight and into the weekend. There is also a possibility of rain over the weekend with daytime highs predicted in the 50s. Hence, European brown rot is a concern in tart cherries if this forecast is correct. All growers with Balatons and European brown rot-susceptible orchards should protect these trees from possible infection, as the currently cool and wet conditions predicted over the weekend will favor European brown rot infection.

Many orchards have cherry leaf spot-susceptible bract leaves present at this time, and these leaves and true leaves should be protected before rain this week. Preventing early leaf spot infections will help to minimize the risk of a cherry leaf spot epidemic this season. This is particularly important for trees stressed by early leaf loss last season to ensure that two years of early defoliation do not contribute to poor tree health in 2017. Most orchards likely have a high level of inoculum going into the 2016 season due to severe infections last season. Furthermore, because temperatures are predicted to be above 60 F during rain, there is the potential for a very high discharge of cherry leaf spot spores. For more information on managing cherry leaf spot this year, see “Fungicide efficacy update for cherry leaf spot management.”

The first American plum borer moths were detected in the center’s trapline this week (two per trap). Green fruit worm moths are in peak flight, and we caught an average of 26 moths per trap at the center. Green fruit worm have been active for several weeks, and we could see larvae this week. Oriental fruit moth has been detected in other regions of Michigan, but this pest has not been detected in northwest Michigan yet this season. Many apple growers in the region have made tight cluster timing applications targeting mites and sucking insects such as scale and aphids; apple orchards in more southerly areas of the northwest are at or approaching pink. Cherries are blooming, and we encourage growers to avoid applying insecticides that are toxic to bees during bloom to promote good pollinator management practices.