MSU Extension

Weather and crop report

Despite the warm weather in the southern part of the state, northwest Michigan was cool throughout the weekend and cool temperatures are predicted to continue into the near future. Tree development has progressed albeit slowly over the past week. Most growers have at least one to two sprays on apples where green tissue is showing; there are more rains in the forecast and tissues should continue to be protected. Development is slow in cherries. There is still some pruning underway, but growers should be aware of pruning sweet cherries under these cool and wet conditions. Bacterial canker is a disease that is favored by cold and wet.

Growers are reporting hail damage from last August’s storm. Unfortunately, some growers may need to remove younger trees that may not survive, likely as a result of the hail damage and the cold winters prior to this year. There is little we can do to help these trees other than pruning out the cankers and applying foliar fertilizers to try to keep the trees healthy. Canker is a particular concern in damaged sweet cherries, particularly in recent cold and wet conditions, but there are no sprays that will protect from this bacterial disease.

Tree planting continues across the region. Even with our sandy soils, the ground is fairly wet after the recent rain events. We received a little over a quarter inch of rain Sunday, April 24, and just over a half-inch of rain Monday. Rain is predicted to continue today, April 26, and small chances of rain continue for the remainder of the week. We have accumulated 190 growing degree-days (GDD) base 42 and 77 GDD base 50. If the predicted cool temperatures are accurate, we may hit sweet cherry bloom around May 6 or 7. However, there are considerable differences in predicted temperatures for the different weather forecasts.

Several cold days during the last week has kept the progression of wine grape bud development to a minimum. There is still plenty of time for dormant treatments against powdery mildew. No pest activity has been seen yet, but beneficials like ladybeetles and spiders have been seen on the warmer days.

The next “First Friday” meeting, co-hosted by Parallel 45 Vines and Wines, will be May 6 from 3-5 p.m. at 2 Lads Winery on Old Mission Peninsula. Mark Ledebuhr of Application Insight will be presenting information on sprayer rate controllers, drift management and visualizing deposition patterns.

Late last week most saskatoons fruiting buds were in the full green stage. Progression to tight cluster and white tip can be very rapid if just a few warm days occur. The 2016 pesticide recommendations for saskatoons are now available.

Michigan State University Extension is seeking grower assistance in tracking bud, flowering and fruit developmental stages in order to improve crop management and integrated pest management (IPM) practices in saskatoons. You can participate even if you only have a few bushes. See “Saskatoon bud and fruit developmental stages” or request the form directly from Duke Elsner at elsner@msu.edu. All you need to do is record the dates your plants reach the listed developmental stages and send in the information at the end of the season.

Pest report

The northwest region kicked off primary apple scab season last week, and the Northwest Michigan Horticulture Research Center set biofix on April 18. Since biofix timing, there has been one infection period on April 21, and there is currently an ongoing infection period that began Sunday, April 24. Fortunately, many growers were covered prior to both of these infection events.

We are monitoring for scab spore discharge and this year’s scab site represents a commercial McIntosh orchard with a high level of inoculum. The orchard was infected during the primary scab season last year, and the grower managed secondary scab infections for the remainder of the season. During the recent scab infection periods for this season, we found a total of 10 spores discharged on April 21 and 87 spores discharged following Sunday into early Monday rain (see table). Few spores were discharged during Monday-Tuesday morning rain (see table). Cool temperatures and less development time between rain events on Monday and Tuesday likely contributed to a lower spore discharge.

Although this week’s forecasted temperatures are cooler, scab spores will continue to develop at temperatures above 32 degrees Fahrenheit. Therefore there will be sufficient time between now and the next rain for spore development. Additionally, there will be new growth and substantial green tissue present that should be protected prior to future rain.

As mentioned previously, cool, wet weather is a concern for possible bacterial canker infections and because there is no effective treatment currently available, many growers are putting pruning on hold until we have drier conditions.

MSU’s Enviro-weather is currently reporting a low cherry leaf spot infection for the Benzonia, Michigan location. However, because susceptible green tissue (i.e., open stomata on the bract leaves) is not yet present, cherry leaf spot is not a concern at this time.

Few insect pests have been active in the recent cool weather. We found an average of 18 green fruitworm moths in traps at the station this week.