MSU Extension Fruit & Nuts

Weather report

Temperatures reached into the upper 70s on Thursday and Friday last week (April 8-9), but conditions began to get cooler and wetter toward the end of the week. Thursday kicked off wet weather and we received 0.3 inches that day, followed by 0.05 inches on Friday at the Northwest Michigan Horticulture Research Center. The warmest weather over the weekend was on Saturday, April 10, where the Northwest Michigan Horticulture Research Center’s Enviroweather station recorded a daytime high of 60.5 degrees Fahrenheit; we also received 0.11 inches of rain.

On Sunday, cool temperatures were coupled with a good rain event. Sunday’s rainfall totals varied across the region, and the station recorded 0.33 inches. Conditions continue to be damp, and we had a thick fog on Monday.

Temperatures have started off considerably cooler this week than last, and forecasts are predicting to get colder over the next two days. Today will be fair and dry, but the conditions currently still look overcast but are expected to clear later today. Cold weather will return tomorrow, and there is even some potential snow in the forecast for Wednesday. Thursday will remain cool and damp, nighttime temperatures are predicted to drop into the 30s.

The weekend is predicted to be brighter and warmer, but an Arctic trough will drop down next week, and conditions are predicted to be cold, which may be concerning with the current stages of bud development. However, Michigan State University climatologist Jeff Andresen commented that specific predictions so far away can easily change over the week.

Watch Andresen’s weekly weather report.

Crop report

Crop development is certainly moving along with last week’s warm temperatures. However, with the recent cooler weather, very little development has changed since last Friday. We are at early tight cluster in sweet cherries, and at green tip to late bud burst in Montmorency and Balaton. We are still holding at tight cluster in apples. Many growers have applied dormant applications in front of last week’s rain events. Growers should monitor the amount of green tissue before applied a first or second dormant spray; in communications with growers in the west central region, many cherry orchards have too much green tissue present for dormant applications. Growers should also hold back if there is still sweet cherry pruning to do. This cool and wet weather is ideal for bacterial canker development and pruning wounds can be an entry site for these bacteria.

Although it is still too early for Retain applications in sweet cherry, many growers, particularly those in the southern part of the region, should be approaching popcorn soon. With the cool weather in the forecast, ReTain may be a good option to extend the longevity of blossom life to ensure adequate pollination. Data has shown earlier applications have better results than later ReTain applications. In the recent past, we recommended first ReTain application at 10-20% bloom, but we have moved on from that recommendation to a popcorn timing for ReTain. We have good results with one pouch per acre for hard to set varieties, such as Regina.

Pest report

Apple scab management programs are well underway, and the station’s green tip date is set for April 5. Warm temperatures from Monday through Thursday last week accelerated growth from green tip to tight cluster in many varieties across the region and recent cooler weather has resulted in slower growth. Rainy weather came to the region late last week, initiating the first scab infection period of the 2021 season.

Because rain showers and foggy conditions have been intermittent, the duration of infection periods is quite long for most areas in the region. All of the Enviroweather scab models reported moderate to heavy infections over the weekend and some are still ongoing. Many growers were covered going into the weekend and recovered yesterday to protect the tremendous amount of new growth from infection. The current forecast is calling for cool temperatures in the 40s and 50s and trees will continue growing albeit at a slower pace in these temperatures. Continue monitoring the weather and new growth to determine when scab protection should be reapplied.

Sweet cherry flower buds are starting to show and although cooler temperatures will slow development, it is time to prepare for brown rot blossom blight protection. Currently, full bloom in sweet cherry is estimated to be around April 24 at the Northwest Michigan Horticulture Research Center, meaning that popcorn applications could be needed within the next week. Temperatures are predicted to be cooler which is less conducive for American brown rot development. However, inoculum coming into the 2021 season is high in many orchards due to difficulties managing this disease effectively last year.

In tart cherries, green tissue is starting to show, and growers should begin thinking about springtime cherry leaf spot management strategies. In recent years, we have observed the leaf spot fungus infecting bract leaves before bloom occurs in high pressure situations (i.e., long wetting events). As bract leaves start to emerge from buds and expand, keep a close eye on bud development in relation to the forecast to determine how critical it will be to protect bract leaves from possible cherry leaf spot infection.

The cherry leaf spot model on Enviroweather has been changed to reflect our new observations of bract leaf infections. In the past, early season wetting events before bloom were reported in red text, “No risk until after bloom,” if conditions would have favored an infection event; the model now reports, “No risk until first bract leaves have expanded,” in red text when the wetting period and temperature results in an infection period. If conditions do not meet the parameters for an infection to occur, the model output will report “None.”

A few warm days kickstarted insect activity, and we caught an average of 22 green fruitworm moths per trap at the station. Recent cool temperatures have slowed insect development. We have not detected oriental fruit moth and only a handful of spotted tentiform leafminer were trapped in apples over the past week. Black stem borer traps are up at the station and we will begin reporting on catches next week. Overall, we anticipate that the predicted cooler temperatures for the coming week will continue to result in relatively slow insect activity.