MSU Extension

Weather

Warm, wet weather over the last week has continued to quickly push the flowering and development of our fruit crops. Some of our small fruit crops, strawberries and fall raspberries for example, have “jumped out of the ground” and are finally looking more normal in terms of their growth.

There has been a series of showers starting late last week along with warmer temperatures that have been very challenging for growers to manage disease control in tree and small fruit crops. Some of our Michigan State University Enviro-weather stations had well over 50 hours of wetting for this period.

For the second week in a row we have accumulated a good number of growing degree days (GDD) in the last week, with some MSU Enviro-weather stations adding another 100 GDD base 50 to their totals. Our season has swung forward to currently running three to five days ahead of normal for GDD totals and about normal for flowering stages.

Much needed rainfall finally arrived in the last four days across the region, with most growers receiving close to 1.5 inches of precipitation. The rain was slow to start, doing a good job of wetting the top layers of the soil, then allowing subsequent showers to soak deeply into previously dry soils. Even with the most recent precipitation, many areas are running 2 to 4 inches behind normal for spring rainfall.

There is a chance of scattered light frost predicted for Wednesday night and Thursday morning, May 13-14, so strawberry growers need to be ready to frost protect.

East Michigan GDD totals from March 1 to May 11, 2015

Tree fruits

Apples are mostly at petal fall in the south to late full bloom or early petal fall in the Flint, Michigan area. Many apple varieties had a snowball bloom this season. The past five days have brought very high risk of fire blight in apples, some of the most challenging fire blight conditions I have seen in many years. Most growers applied streptomycin two or three times starting last Friday, May 8, and over the weekend to cover freshly open bloom, recovering due to wash-off and very high EIP numbers in the fire blight (Maryblyt) model at MSU Enviro-weather.

Cooler temperatures today have greatly reduced fire blight risk for the next few days. I have not seen any oozing cankers in orchards or wild trees, which is a good thing. Where growers have young blocks with susceptible varieties, blocks where there has been a history of fire blight in the past or where growers have not been on top of streptomycin applications in the past few days, application of Apogee may be encouraged. Michigan State University Extension suggests early timing of Apogee applications when shoots are just a few inches in length.

Apple scab was also a concern for this same period; most apple growers had three apple scab infection periods in the last week. More apple scab cover sprays were applied in the last week. High numbers of apple scab spores were caught in each of the many wetting events of the past week, so primary apple scab season continues. No apple scab lesions have been seen, but I would expect to begin to see some in the next few days from the April 29 and 30 infection periods.

Insect activity has quickly swung to full speed ahead with recent warmer temperatures. High trap catch of oriental fruit moths is starting to be seen, and continues for redbanded leafrollers. Plum curculio and apple curculio are just starting to be found in apples. Many small larvae are starting to be found feeding, including redbanded leafrollers, fruittree leafrollers, inch worms and green fruitworms. A few very small mullein bug adults are starting to be found, as are a few stinkbugs. European red mite egg hatch is starting in blocks with high numbers last season. A few rust mites are starting to be found as of yesterday, May 11. Spotted tentiform leafminer adult trap catch is now on the decline for the first generation flight, with a few eggs starting to be found.

As temperatures begin to warm up later in the week, I suggest there may be a good thinning window open for apple growers in the southern parts of our region. Regarding the use of the carbohydrate thinning model, my colleague Phil Schwallier reports, “The carbohydrate thinning model for southeast Michigan indicates moderate stress for the next few days. Thinners applied during this time should reduce crop load by perhaps 20 to 50 percent. If at petal fall, use Sevin or NAA (10 ppm) at normal rates. This week’s forecast is for less stress. If you thinned during bloom (May 2-5) – this is an estimate under the mild stress period (-10) – I would expect 10 to 20 percent thinning. There should be mild to little stress for May 12-15.” One last thought, cloudy weather at this growth stage will foster more fruit drop.

The Cornell Carbohydrate Thinning Model for southeast Michigan as of May 11, 2015 in Petersburg, Michigan.

Pears are at full bloom to early petal fall for early flowering varieties. The crop load appears extremely variable from variety to variety, from tree to tree and in some cases limb to limb. Pear psylla egg hatch has started as of late last week, with high numbers of adults continuing.

Peaches are at late bloom to still being in the shuck for those few growers with a crop this season. Most peach buds were killed this winter to extreme cold temperatures, with most trees that were stressed last season having just a few leaves on them this year. Most will not make it through our first period of stress this summer. Most trees that are flowering are younger. Cover sprays for brown rot are being applied where there is a crop.

Sweet cherries are at shuck split. I was encouraged to see a fairly good bloom in sweet cherries last week, but I see several blocks this week where there are only one or two developing fruit per cluster, so the crop load seems to be shrinking. Plum curculio cover sprays will be applied soon. Brown rot and cherry leaf spot cover sprays have been applied.

Tart cherries are at petal fall. There seems to be a good crop of tart cherries coming along this year, but as I said last week about sweet cherries, flowers at bloom time do not mean fruit later in the season. Brown rot and cherry leaf spot cover sprays are being applied.

European plums are at petal fall and Japanese plums are at shuck split. Some varieties of Japanese plums have severe damage from winter cold temperatures, with few fruits being seen; younger limbs have more fruit on them. Black knot, brown rot and leaf spot cover sprays have been applied at most farms.

Small fruits

Grape shoots are 1 to 2 inches in length for Concord types and just a few buds are emerging for European types. Many varieties have extensive winter kill. A few grape berry moths are just starting to be found.

Strawberries look much different than a week ago as they have finally put on some good growth and look more like how strawberries should look for this time of the season. Leaves are much larger this week and have greened up considerably. Flower trussed have emerged and are in early bloom in the south with a few early bloom in other areas. Strawberry clipper feeding damage on flower buds is just starting to be seen at a few farms. Gray mold controls will need to be applied at bloom. Angular leaf spot lesions on leaves have been seen at just a few farms, all where there is a history of angular leaf spot last season. Canadian thistle sprouts or shoots continue to be seen in many strawberry fields, more than I have ever seen in any season.

Raspberry canes of summer fruiting types are continuing to show leaf growth, except for the tips of canes that were killed during cold temperatures this winter. Flower buds are starting to be seen in a few varieties. Fall raspberry canes continue to emerge from the soil this week at a rapid pace. However, canes are not putting on much extension growth yet; the longest canes are about 4 inches in length.

Blueberries are mostly at late pink bud to a few early varieties at 25 percent bloom. I am encouraged to see as many buds that continue to swell, more than I expected. My initial bud assessments earlier this spring indicated more extensive winter cold damage in flower buds. More time is needed to determine crop load for this season.