Southwest Michigan fruit update - June 18, 2019

By: 
Michael Reinke, Mark Longstroth and William Shane, Michigan State University Extension

Strawberry harvest is underway. Grape bloom begins.
   Last week’s weather was a roller coaster of warmer, partly cloudy days and cold, rainy days. After a rainy weekend, Tuesday and Wednesday, June 11 and 12, were warm and dry with high temperatures around 80 and lows in the 40s. Cold rains with strong north winds moved across the region Thursday. Friday was warm and dry, but the weekend was cool and cloudy with scattered showers.
   Precipitation totals for the week ranged from 0.5 to 2.6 inches, with an average of 1.8 inches. Berrien County received the most rain, about an inch more than areas to the north and east. Rainfall totals for the season are 10.5 to 13.5 inches across the region since April 1.
   Soils are wet. Currently, precipitation exceeds plant water use by 4 to 6 inches.
   The forecast for this coming week is for cool conditions, with highs in the 70s and lows in 50s and 60s, which is cooler than normal for this time of year. There is a good chance of rain on Wednesday and Thursday and again on the weekend. Next week may be warm and dry with highs in the 80s. Sandy soils are beginning to dry out, but heavier soils are still very wet. Soil temperatures are in the 60s. With the warm soils and abundant moisture, plant growth is fairly rapid. There is standing water in poorly drained fields and wet spots.
   With the cooler temperatures, we picked up fewer heat units, about 140 growing degree days (GDD) base 42 and 85 GDD base 50. Locations away from Lake Michigan are picking up heat units slightly faster than those close to the Lake. We are still about a week behind normal heat accumulation for the season. Expect the cool, wet weather to continue this week.

Tree fruit
   There was strong insect activity last week with a continued flight of many moth pests. First trap catch of obliquebanded leafroller was this past week, setting biofix as June 14.
   Peach and nectarine fruit are attractive to tarnished plant bug and plum curculio. First catch of oriental fruit moth was on May 6 at the Trevor Nichols Research Center, and the flight has been ongoing since then. Shoot flagging due to oriental fruit moth entries should show up soon.
   Winter damaged trunks and weakened trees can be especially attractive to borers. Pheromone disruption for protection against peach tree borers should be out soon, if this is the chosen method for control. The same pheromone is effective for both greater and lesser peach tree borer as well as dogwood borer.
   At some locations, peach foliage seems pale, as if they are short of nitrogen. We think this is due to the cool conditions and the trees will improve with warmer temperatures. Conditions have been generally unfavorable for bacterial spot development and symptoms are not widespread.
   Cherries are beginning to change color ripen and swell. Sweet cherries are coloring and early cherry harvest could begin by the weekend. Tart cherries are yellow and beginning final swell.
   Fruit and leaf symptoms of bacterial canker have been found in sweet cherries and yellow leaves and leaf drop is reported in tarts. Cherry leaf spot symptoms can also be found. Both diseases cause yellowing leaves and leaf drop. Check the bottoms of the leaves for the white fruiting bodies of cherry leaf spot. Cherry leaves are always susceptible to leaf spot, so management is needed to maintain a healthy leaf canopy during the entire season.
   Ripening fruit are attractive to spotted wing Drosophila (SWD). We are catching only a few SWD at this time. Normally, cherry fruit fly do not emerge until the end of tart cherry harvest in southwest Michigan. Tart cherry harvest is estimated to begin about July 8, which is later than normal. Growers may need to apply insecticides to control these direct insect pests. Be sure to wait until all the fruit on the tree are yellow to apply Ethephon as a harvest aide to hasten ripening and facilitate harvest.
   The plum crop is light for most sites. Japanese plums are 22 millimeters and European plums (Castleton) are 20 millimeters in diameter in central Berrien County. We are seeing shot holing of the leaves and russeting of the fruit. This may be due to an interaction between our cool, wet conditions and fungicide sprays. Young plum fruit and foliage are tender and are prone to russeting from captan, especially under cool, slow drying conditions.
   Apple fruit are growing rapidly and are generally too large to respond to standard thinning sprays except Ethrel. The largest fruit are an inch or more in diameter. Cool weather has delayed fruit drop from earlier thinning sprays. Growers can gently pull on smaller fruit to see if they will still fall. With this season’s heavy rainfall, shoot and foliage growth have been spectacular. Excessive foliage growth increases the potential for bitter pit for apple varieties prone to this disorder. Include calcium in your cover sprays to increase the calcium levels in fruit. These early season calcium sprays are very important.
   Primary apple scab season is over. Look for scab lesions on the leaves and fruit and decide if you can drop fungicides from upcoming cover sprays. The Enviroweather sooty blotch and flyspeck model indicates that spray applications for these diseases can be delayed due to cool conditions. Codling moth egg hatch is underway.
   Pear fruit are sizing. Bartlett and Harrow Sweet fruit are 19 millimeters. The first generation codling moth is not a problem in hard pears but plum curculio can and will lay eggs in pears. The time of rapid shoot growth with succulent leaves is the primary treatment window for pear psylla. This treatment window is rapidly closing.

Small fruit
   We are catching spotted wing Drosophila (SWD), so  set out traps to monitor this pest. Controlling this pest is focused on ripening fruit. Sometimes early season fruit, such as strawberries, early summer raspberries and early season blueberries, can be harvested before this pest builds to high numbers. With the late start of the harvest season, do not assume this pest will pass by. Monitor early ripening wild fruit near your fruit planting so you have an idea of the local population. If SWD numbers are high, monitor your fields and be prepared to spray to protect ripening fruit.
   Grape bloom has begun. The bloom and post bloom sprays are the most important sprays for controlling diseases on the berries. Use materials or a mix of fungicides to control all the fruit diseases, including downy mildew, phomopsis, powdery mildew and black rot, which can infect new green tissue as it is exposed. Black rot leaf lesions and phomopsis on the leaves and stems can be found in vineyards now.
   Many growers report finding tumid grape galls in their vineyards. Normally this is a sporadic pest that causes little real damage and treatment is seldom warranted. It is probably too late to apply a systemic material, such as Movento, to prevent damage from this generation. Our general recommendation is to cut out the galls and remove them from the vineyard.
   We are catching grape berry moth. Grape berry moth larvae can be found feeding in the clusters. This first generation causes damage to the clusters; but this early in the season, the loss is compensated for by later fruit growth. It is the second and third generations that are targeted for control.
   Bloom in wild grapes is used to set the grape berry moth model on Enviroweather and determine the spray timing for treating the second and third generations. Wild grape bloom began about May 31 in central Berrien County and June 1 in Van Buren County. Rose Chafer should appear soon and controls may be needed.
   Blueberries are past bloom and have small green fruit. The larger berries are 12 to 15 millimeters in diameter. Cherry fruitworm and cranberry fruitworm have both been caught. The warm weather this last week caused a good moth flight. Cherry fruitworm biofix for the region was set as June 3 and egglaying has begun. Cranberry fruitworm GDD biofix was June 14.
   Blueberry stem gall wasp is also flying. This is a major pest in Ottawa and Allegan counties and is becoming more common in northern Van Buren County. Chemical sprays may be necessary in susceptible varieties such as Jersey and Liberty. Time insecticide sprays a week apart and add 1% summer oil to help with stem penetration.
   The disease focus is on anthracnose as the small green fruit is very susceptible to infection, which does not appear until the fruit begins to ripen. Tailor your green fruit fungicide choice to control anthracnose under these wet conditions
   Strawberry harvest from conventional matted row plantings continues. The abundant moisture and cool weather make for good size and quality. Cool weather will lengthen the season and allow smaller fruit to gain more size as they ripen. Maintain fungicide coverage to reduce fruit rots. We have been catching SWD and you should be trapping for this pest.
   Bramble bloom has ended and we have lots of small green fruit. Growth of the new primocanes is looking better with warmer soil conditions. Orange rust is appearing on black raspberries and blackberries. Remove and destroy infected plants.
   Cranberry bloom is underway, but only a few flowers are open on the beds and many more flowers will open soon.

   This article was provided by Michigan State University Extension. For more information, visit www.msue.msu.edu.  To contact an expert in your area, visit expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).

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