MSU Extension

Weather report

Summer-like weather was predominant over the holiday weekend. Daytime temperatures reached up into the high 70s and low 80s with nighttime temperatures in the low 50s. Humidity levels were relatively low, and we had windy conditions throughout the weekend.

We have accumulated 664 growing degree-days (GDD) base 42 and 357 GDD base 50. We also had some much-needed rainfall Thursday and Friday, May 26-27, and the Michigan State University Enviro-weather station at the Northwest Michigan Horticulture Research Center reported 0.22 inch of rain May 26 and 0.93 inch May 27. Conditions were extremely dry across the region prior to this last rainfall. Weather forecasts have been variable, and the rainfall predictions have been considerably different depending on the different forecasts.

Crop report

At the Northwest Michigan Horticulture Research Center’s wine grape variety trials, most vinifera are at the 3- to 6-inch shoot stage with a few at 6-10 inches. Hybrids are mostly in the 6- to 10-inch shoot stage. All clusters are showing and the crop load looks good. Last week’s heavy rain likely caused a discharge of powdery mildew spores, but the rains may have been so heavy that many spores were simply washed to the orchard floor rather than lodging on green tissues where they could infect plants. No significant pest insect activity was noted this week.

There is a “First Friday” meeting scheduled for June 3, 3-5 p.m., at L. Mawby Vineyards in Leelanau County. Main topics will be disease scouting, weather influences and fungicide selection presented by Michigan State University Extension plant pathologist Annemiek Schilder.     

Local saskatoon plantings are in the small green fruit stage. Activity of adult saskatoon sawfly has ended, and the number of apple curculio are lower than last week. An unsprayed block of plants at the research center has lots of fruit injury from sawfly and apple curculio. Some larger egglaying scars may have been the work of plum curculio, but none of these insects were seen in sampling. The same site also has a good number of larval green fruitworms feeding on foliage and foliar aphids in small numbers.

We have not seen symptoms of entomosporium leafspot or rust diseases, but they are likely to appear soon. These will be serious threats for the next few weeks if we get into periods of rainy weather.

A saskatoon field day has been scheduled for the morning of June 17. Participants will visit saskatoon production sites in Leelanau and Grand Traverse counties. For the full agenda or more information, contact Duke Elsner at elsner@msu.edu.

Tart cherries are coming out of the shuck, and sweet cherries are really starting to size with the recent heat and rainfall. We also have good growth on all tree fruits across the region.

There are still apples in bloom on later-blooming varieties. Growers were diligent about covering up for fire blight with the warm weather and the varying predictions of rainfall. Growers have begun to thin apples, and many growers began the thinning process at petal fall. We are approaching the key thinning window as the fruit is sizing, and the weather forecasts are predicting cooler temperatures in the coming days, which will make thinning more difficult. The most recent carbohydrate model (figure below) shows that we are entering a period of little stress, and MSU Extension recommends growers increase their rates of thinners to obtain the desired results. We recommend increasing rates by 30 percent when the carbohydrate model shows the four-day average of the carbohydrate balance to be greater than zero, which it shows below.

Carbohydrate model for the Northwest Michigan Horticulture Research Center for May 31, 2016.

Pest report

Last week was wetter and more humid compared to the season’s previous dry conditions; we have also had some mornings with foggy and heavy dew. These conditions have been favorable for disease development. Most growers were well-prepared and covered for the rains that came in Thursday, May 26, and continued through the weekend in some areas. The research center received over an inch of rain Thursday and Friday evenings; some areas were wetter and others were drier over the weekend. Most orchards will need reapplication of spray materials before the next rain comes, which is predicted for Tuesday, June 1.

Some orchards are past bloom, and fire blight blossom blight is not a concern in these orchards. However, hail was reported Thursday afternoon in northern Leelanau County, and trauma blight was a concern in areas that received hail. EIP levels remain high for the early part of this week, but temperatures are predicted to cool down and fire blight development will slow down in cooler conditions. Growers should keep all open blossoms and tag bloom covered for fire blight if conditions continue to be favorable.

Primary apple scab is ongoing and spores discharged during Thursday’s and Friday’s rain. Between one and three infection periods were reported in varying locations throughout the northwest in the last week; East Leland reported three infection periods. Primary apple scab is ongoing with about 100 percent spore maturity and about 84 percent discharge at the research center where our biofix is April 17. Primary scab season typically ends when 100 percent of spores have discharged according to the Enviro-weather apple scab model. We have observed a dramatic decrease in the number of spores discharged during recent rain, and we will continue to monitor for spore release to determine the end of primary.

 Like apple scab, cherry leaf spot infections were also triggered throughout the region following recent wet weather. Depending on location, one to four leaf spot infection periods occurred in the last week. Eastport reported four; Bear Lake, East Leland, Northport and Old Mission reported three; Northwest Michigan Horticulture Research Center, Elk Rapids and Kewadin reported two; and Benzonia reported one. The severity of these infection periods was variable among the locations due to varying weather conditions. Cherry leaf spot lesions are appearing at the research center and we have received reports of leaf spot in the area. Cherries are out of the shuck in many orchards and growers are planning first cover sprays for leaf spot and powdery mildew.

Plum curculio adults are active throughout the region and we have observed oviposition scars in many tree fruits (apricots, apples, sweet and tart cherries). Exposed fruits coming out of the shuck and developing apples should be protected from plum curculio feeding and oviposition as soon as possible.

Codling moths are flying, and we have received reports of high catches in some isolated areas in Leelanau and Manistee counties. The first codling moth was found at the station May 26, and we have received reports of earlier catches in the area. Some growers in hot spot areas set biofix last week. Once biofix is set, GDD accumulation should be monitored to determine when to manage for codling moth eggs and larvae. Codling moth egglaying has begun or will begin this week in orchards that set biofix last week. A cumulative catch of five or more codling moths per trap during the first generation may indicate the need for management; managing codling moth eggs typically occurs between about 100-250 GDD base 50 after biofix.

Other moth larvae are evident in terminals at this time. We have observed feeding damage, webbing and frass from green fruitworm and various leafrollers in apple and cherry terminals, as well as on developing fruit. Green fruitworm numbers seem to be high this season.

American plum borers are at peak flight this week; we found an average of 19 American plum borer moths per trap. We also found high numbers of lesser peachtree borers in traps this week with an average of 20 moths per trap. Trunk sprays to target these two borer species would be well-timed in early June. Greater peachtree borer activity has not been detected at this time.