Southwest Michigan Fruit update – April 16, 2019

Mark Longstroth, William Shane and Michael Reinke<reinkem3@msu.edu>, Michigan State University Extension - April 16, 2019

Warmer, wet weather will move plants quickly. Spraying season has begun.

Duke blueberries are at bud burst. Photo by Mark Longstroth, MSU Extension.

Weather

Last week was chilly. Lows were above freezing and high temperatures were in the 50s. Rain and snow fell Friday, April 12, and Sunday, April 14, with some snow on the ground Monday morning, April 15. Precipitation totals for the week were about 1.5 inches. The forecast for this week is for warmer temperatures with highs in the 60s and lows near 50. Rain and storms are forecast most of this week with only brief periods of clear weather between storms.

We are catching up on growing degree days (GDD) and are about a week behind normal but a week ahead of 2018, which was a very cool spring. Soils have begun to dry out. Soil temperatures are about 50 degrees Fahrenheit.

Southwest Michigan GDD summary from March 1 – April 14, 2019
Station	GDD 42 F	GDD 45 F	GDD 50 F
Benton Harbor (SWMRC)	122	84	41
Lawton (Lawton)	119	81	38
Fennville (TNRC)	90	60	25
Average for the SW region	118	84	39

Tree fruit

Tree fruit are moving past swollen bud to bud burst. Warmer temperatures will move buds quickly. There are no freezing temperatures in the forecast and freezing temperatures are not yet a concern. Expanding fruit buds would not be damaged by temperatures down to 23 F (see “Freeze damage depends on tree fruit stage of development”). Soils have begun to dry out. Check blocks for evidence of San Jose scale on branches to determine the need for oil sprays.

Apricots are scarce. Fruit buds are at red tip. At this stage, temperatures down to 23 F would not cause damage.

Peach and nectarine leaf buds have burst, and leaves are emerging. Low peach crops and wood damage due to January’s subzero temperatures will call for different pruning and fertilizing strategies (see “Cold damage to peaches”). Dormant sprays of copper or other appropriate fungicides will reduce peach leaf curl. Infection by this pathogen occurs when swollen peach buds with over 10 hours leaf wetness, temperatures between 46 to 53 F, and rainfall greater than 0.2 inch. Symptoms appear about 20 to 25 days after infection. Low levels of copper also suppress bacterial spot populations.

Tart cherries are at green tip. Photo by Mark Longstroth, MSU Extension.

Sweet cherry buds are at green tip. The buds have not yet burst. Montmorency tart cherry fruit buds are at green side and green tip. We are at the end of the window when copper sprays can safely be applied to sweet cherries. Copper applications may suppress bacterial canker in cherries. At this bud stage, cherries can withstand temperatures down to 23 to 25 F with little damage.

Japanese plums are at green tip and moving to tight cluster. Temperatures below 23 F would damage the flower buds. European plums are at swollen bud moving to white side and can withstand temperatures down to 20 F without damage. Prune out all black knot and dispose of the knots by burning. This is an important step in managing this disease. Ascospores of the black knot pathogen are released from knots from late April to early July, with the highest concentration in May.

Apple buds are generally at silver tip and green tip. Some early varieties are at half-inch green, depending on the variety. Apple flower buds can withstand temperature down to 20 F with little injury. With exposed green tissue, we are now in apple scab season. Low numbers of scab ascospores were caught in recent rains. Copper sprays will be going out soon for early scab control and fire blight suppression.

Pears have swollen buds and the bud scales are beginning to separate. Temperatures would need to drop below 20 to damage pears.

Small fruit

Concord grape buds have started to swell. Photo by Mark Longstroth, MSU Extension.

Grapes show some movement. Concord are at the beginning of scale crack at the beginning of bud swell. Many wine grape growers are cutting back their winter damaged vines.

Blueberry flower buds are swollen. The bud scales at the tip are beginning to open. Leaf buds are swollen and green and leaf tissue will be exposed soon. We are entering the window for mummy berry shoot strike, so scout for mummy berry mushrooms. Many growers have been applying Sulforix or other products to suppress early season diseases.

Strawberry leaves are emerging from the crown. Strawberry fields have a lot of brown leaves from desiccation of the leaves during the cold winter. Remove overwintering mulches and rake between the rows. Growers are looking at early season herbicides to control overwintering weeds.

Bramble buds are opening. Dormant pruning should be completed quickly. In summer bearing raspberries, last year’s primocanes should be headed (cut back) to the desired height and the number of canes in the row reduced to one every 8 to 12 inches. Remove all dead floricanes from last year. Cut or mow fall bearing raspberries to the ground. Lime sulfur treatments for anthracnose can still be applied.

Upcoming meetings

Our next Monday fruit IPM meeting will be April 22 at 5 p.m. at Fruit Acres Farms, 2559 Friday Rd, Coloma, MI 49038. These meetings are free and open to all. We review the current conditions in fruit crops and discuss pest control options with growers. Two Michigan RUP applicator recertification credits are available at these meetings.

There is a Grape Winter Damage Workshop planned for April 24, 2019, from 9 a.m. until 3 p.m. at the Southwest Michigan Research and Extension Center, 1791 Hillandale Rd., Benton Harbor, MI 49022. The morning portion will be indoor presentations and discussion. Following lunch, the afternoon will be in-field demonstrations on training and recovery strategies. Registration details will be announced later this week.

A Statewide Grape Kickoff Meeting is planned for April 26. This meeting will be held at both the Southwest Michigan Research and Extension Center and the Northwest Michigan Horticulture Research Center, which will be interconnected via the internet. This meeting will be a review of early season insect, disease and viticultural information for growers.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).