MSU Extension Fruit & Nuts

Weather report

The weather continues to be cool over the past week. However, Jeff Andresen, our Michigan State University climatologist, predicts temperatures will warm for the remainder of the week and into the weekend. Tree phenology will certainly move along quickly with warm temperatures.

In addition to the cool temperatures, we have had substantial rainfall in the past few days. At the Northwest Michigan Horticulture Research Center, the MSU Enviroweather station recorded 1.11 inches of rain on Sunday, May 17, and 1.75 inches of rain on Monday, May 18. Conditions are still wet this morning, Tuesday, May 19, but expected to dry off through the day and be warmer and drier for the remainder of the week. Rain was welcomed as the soils were dry throughout the region.

We have accumulated 193 growing degree days (GDD) base 42 and 50 GDD base 50 thus far this season. We are still 10-14 days behind our normal: 413 GDD base 42 and 192 GDD base 50.

To watch a recording of Andresen’s weather report, visit MSU Extension Fruit & Nuts Weather.

Crop report

Crop phenology has moved slowly in cool temperatures, but rainfall helped to push development somewhat. With the predicted rain and warm weather, we expect crop development to move more quickly than it has previously. At the Northwest Michigan Horticulture Research Center, we are starting to see some white bud in sweet cherries. We have also seen some white showing north of Suttons Bay on some morel hunts over the weekend. The forecast continues to call for warmer temperatures and we are hopeful for a break in the rain to bring good pollination weather to the area during sweet cherry bloom.

We are at bud burst in Montmorency at the Northwest Michigan Horticulture Research Center and tight cluster in Balaton. We are at tight cluster in apples. We will be finishing pruning in sweet cherries at the station tomorrow.

Pest report

Diseases continue to be at the forefront of growers’ minds with the recent wet weather, which has brought more than 2.5 inches of rain and almost 40 hours of wetting to most orchards in the region. This wetting event resulted in a significant apple scab infection, and symptoms from this event could show up at the end of this month if infection occurred. Apples will be at tight cluster to early pink by the end of this week and with warmer temperatures powdery mildew could be a concern. Growers are planning to cover apples before rain forecasted for Saturday or Sunday.

Insect activity in our trap line continues to be relatively slow in apples at this time, but warmer weather ahead will bring more activity and growers have been considering when to begin managing for insects.

Spotted tentiform leaf miner numbers have risen over the last week to an average of 24 per trap, which is well below threshold for this pest.

We have not observed aphids on terminal leaves at the station, but it was difficult to see these insects in rainy weather. Continue to observe terminals for aphids toward the end of the week, as warmer areas will be approaching the growing degree day timing when the first aphids are predicted to show up (109 GDD base 50).

As noted in last week’s report, keep an eye out for small obliquebanded leafroller larvae, as they are showing up in unsprayed crab apples.

We have not detected black stem borer in our traps, but warm conditions could stimulate beetle activity. Additionally, excess moisture could cause tree stress in orchards that remain wet for an extended period of time. The beetles primarily attack young trees that are stressed and most of the cases of black stem borer infestation have been in apples in our region. However, this season, we received reports that black stem borer holes and galleries were found in young apricots with winter damage; the beetles would have infested these trees last season. We suggest monitoring for the beetles near orchards with a history of infestation, as well as near young blocks that may be stressed due to winter injury and/or saturated soils.

In cherries, before this long wetting period arrived, there was little concern for cherry leaf spot infection as there were almost no green leaves present on Montmorency. New bract leaves have emerged and are exposed to the cherry leaf spot pathogen under these warmer temperatures and the recent long wetting period. As of 9 a.m. on May 18 there were exposed and vulnerable bract leaves in some blocks at the research station (Figure 1). New observations from George Sundin’s Tree Fruit Pathology Lab at MSU observed open stomata on bract leaves as they were emerging from buds. This observation will help to further refine the timing when cherry leaf spot infections could get started under optimal infection conditions. Growers and consultants have been considering strategies for leaf spot management. Please refer to the article, “A long wetting period could be the start of cherry leaf spot infections for 2020,” for some management suggestions.

Sweet cherries are starting to show white and with warmer temperatures following this major precipitation event, American brown rot development is a concern. Recent resistance screening data has shown that this pathogen has substantial resistance to Indar and this product could provide weak efficacy against American brown rot. In cherries at popcorn, applications ahead of this weekend’s rain would be well-timed. Rovral is a good material for the blossom blight phase of American brown rot.

There is no insect activity to report in cherries at this time, but as noted previously, we do anticipate more activity in the days ahead.