MSU Extension

Weather report

Temperatures rose over the weekend, May 10-11, making it feel a little more like spring in Northwest Michigan. Daytime temperatures peaked in the mid-70s over the past three days and nighttime temperatures dipped into the high 40s and low 50s. We have accumulated 212 growing degree days (GDD) base 42 degrees Fahrenheit and 77 GDD base 50 F. We are still behind our 24-year average of 358 GDD base 42 F and 165 GDD base 50 F.

Although the spring is starting slow, tree phenology has moved along with the recent warm temperatures. We have also had substantial rainfall in the last week. We had almost a half-inch of rain on Thursday, May 8; 0.4 inches of rain on May 10; and an additional 0.48 inches of rain yesterday into this morning, May 13. Conditions continue to be cloudy and winds were high over the weekend. Even with our sandy soils, soil moisture remains high and soggy conditions are still evident in orchards with heavier ground.

Crop report

With the recent warm temperatures, tree and vine crops have advanced in development and green tissue is evident across the region. Growers have been applying early season fungicides on tree crops and most grape growers have applied dormant applications for powdery mildew. Windy and rainy conditions have posed challenges for growers to spray in the recent days. Pruning is ongoing and sweet cherry growers have been looking for optimal pruning conditions to avoid bacterial canker. Despite the slow start to spring, growers are busy with tree planting, fertilizing and wrapping up pruning for the season.

According to the forecasted data, bloom in sweet cherries is anticipated over the coming weekend at the Northwest Michigan Horticulture and Research Center (NWMHRC) and growers will be protecting for brown rot blossom blight. Temperatures are expected to cool on Thursday and Friday, May 15-16, and will be perfect conditions for European brown rot. Balaton growers should anticipate covering at popcorn and again seven days later. For growers that had a European brown rot infection in Montmorency in 2013, you should also protect against this disease this season.

We collected European brown rot mummies from both Montmorency and Balaton trees at the NWMHRC, and they have begun actively sporulating in less than one week. This sporulation indicates that the disease overwintered successfully and the fungi are active; forecasted cool and wet conditions are favored by European brown rot. For more information regarding these diseases and management, please refer to the Michigan State University Extension articles, “Be ready for European brown rot in tart cherries in 2014” and “Considerations for pre-bloom and bloom sprays for American brown rot.”

Wine grape bud swell has finally started in Riesling and Chardonnay. Later developing varieties still appear dormant, but bud development will likely be rapid from this point out. We are still in the window for dormant sprays against powdery mildew. There have been no reports of climbing cutworms or flea beetles so far, but expect them soon in sites with a history of these insects.

In saskatoons, individual flower buds are now visible on earlier varieties. No pest activity has been detected at the test planting at the NWMHRC.

Pest report

Apple growth has progressed substantially in the last week and green tissue is visible on several varieties. We continue to monitor for apple scab spores at a field site in Leelanau County to help growers determine primary apple scab infection. The site is a block of McIntosh, which is a variety that is highly susceptible to apple scab. During the previous season, these apples were managed commercially for the processing market. However, even with a scab program, apple scab was present in the block last year. Therefore, this site should provide a good indication of spore dispersal during the primary infection period. Furthermore, it is important to keep in mind that the number of apple scab spores that we report may be higher compared to fresh market orchards that have been managed more rigorously for apple scab and in varieties that are less susceptible to scab infection.

Since last Tuesday, May 6, three rain events were recorded on May 8, 9 and 12 at the NWMHRC. Two of these events resulted in apple scab infections on May 9 and 12. The average number of spores discharged during recent rain events has steadily increased, with a nearly four-fold increase to 1,443 spores per rod on May 9 compared with the 368 spores per rod collected on May 8. The table below shows the average number of spores discharged during rain events beginning at the end of April. With recent warmer temperatures and this ongoing wet weather, green tissue on most apple varieties is visible and it is important to continue to protect that tissue from scab infection. Many apple growers in the region started apple scab programs in the past two weeks. Michigan State University Extension reminds growers to be mindful to keep new tissues covered as development will increase quickly with warm and wet weather.

This is our second week of monitoring for insect pests at the research station and the recent warm up has resulted in increased insect activity. We caught our first green fruit worm moths last week; these moths are still active this week with an average catch of 7.3 moths per trap. We also trapped this season’s first catch of spotted tentiform leafminers this week with an average of 14 moths per trap.

No oriental fruit moth or American plum borer have been detected in our traps; cool temperatures have likely delayed the arrival of these insects. The first emergence of American plum borer moths typically occurs around 118 GDD base 50 F and adult oriental fruit moths typically emerge around 174 GDD base 50 F. We are also approaching peak activity of the first generation of obliquebanded leafroller larvae, which typically occurs between 205-254 GDD base 42 F.

Crop consultants and the NWMHRC research team observed San Jose scale on new growth of sweet cherries in an orchard in Antrim County where old scale damage was not prevalent. Finding San Jose scale on new growth is somewhat worrisome in that we had previously observed scale or masses of scales on older branches. These findings may indicate that San Jose scale moved into the orchard recently (last season) and are newly established colonies. Many sweet cherry growers made dormant applications targeting San Jose scale last week. The window for dormant oil applications is likely closed in many areas of Northwest Michigan.