Fruit Update - SW Michigan

June 10, 2001

Mark Longstroth
Bill Shane
Al Gaus

Last week brought warmer dryer weather. Average temperatures rose from 50 to 70. Plant growth and insect activity increased with the temperature. Rain on June 6 and 10 caused some infections for many fruit diseases. Precipitation totals ranged from 0.5 to 1.5 inches. Soils are still wet, with water standing in poorly drained areas. Soil temperatures are in the mid 60s. Frost hit the blueberry region two weeks ago on May 30 and caused severe damage to the crop in some areas.

Warm temperatures brought out the insects. Trap catches were high over the weekend for most pheromone traps. Rose chafers appeared late in the week. Little new plum curculio activity was noticed, but this pest is probably still around. We are seeing declining trees to due collar rot (Phytophthora). Declining yellow peach, plum and apple trees are easy to find. Soil drenches of Ridomil are effective at containing this disease but will not cure it. We are starting to see some mineral deficiencies (magnesium, iron) due to cool wet soils.

Apricot fruits are 1.25 inches in diameter. The lack of growth would indicate pit hardening, when the stone and seed develop and there is little fruit development. Bacterial spot is common on susceptible varieties.

Peach fruits are 1 inch in diameter. Growers are thinning. Few shoot strikes and flagging from oriental fruit moth have been reported. Tarnished plant bugs are scarce.

In cherries, bacterial canker is common. Broken trees, trunk splitting and broken limbs were common after Sunday evening's (June 10) storm. Sweet cherries are coloring. Fruit cracking is a problem. Growers need to maintain protection against brown rot. Tart cherries are straw colored. Cherry leaf spot symptoms appeared with the warm weather. Growers need to protect against plum curculio with this week's warm temperatures. We are catching lesser peach tree borer. Cherry fruit fly traps should be out.

European plums are 16-20 mm in diameter. Japanese plums are 20-24 mm in diameter. Sprays to control black knot are needed as long as new tissue is present. Cut out and remove black knots when you see them.

In Apple, the fruits are 20-25 mm. June drop has ending. Fruit set varies widely. Fireblight symptoms have increased with warming weather. Cool weather has delayed symptom expression. Up until this week all the symptoms that we found were associated with last year's cankers. Blossom blight symptoms from fireblight infections before the May 16 should be visible. Trauma blight infections conditions occurred on May 21, these symptoms should appear June 12. Shoot blight symptoms should begin to appear at the same time. Shoot blight symptoms are associated with blossom blight and will occur in orchards after blossom blight symptoms. Where there is little blossom blight cutting out shoot blight as soon as it is visible is a good way to control the summer spread of the disease. Orchardists with a lot of blight, who sprayed during bloom, should have their orchards tested to determine if antibiotic resistance is present in their orchards (call Bill Shane (616) 944-1477). Trees affected with rootstock blight last year are yellow with small leaves and poor growth. The graft union of most of these trees is completely dead and warm weather will cause their collapse. Apple fruit scab lesions are common is some orchards. Growers with scab in their orchards should continue fungicide applications. Powdery mildew symptoms are easier to find. We are also finding cedar apple rust.

Insect trap catches are up. Few Oriental fruit moth were caught. The first generation's flight is ending. But the second generation should be emerging at 950 GDD45. We are at 876 GDD45, 673 GDD45 since BIOFIX (203). We caught good numbers of codling moth after a 2-week lull. We are at 592 GDD50, 342 GDD50 since the first codling moth BIOFIX (250). Controls for codling moth should be applied about 200 GDD base 50 after BIOFIX. We should treat the second peak in the first generation as a separate event and time a pesticide application for 200 GDD base 50 after this resumption of flight at 790 GDD50. Many obliquebanded leafrollers were caught last weekend. BIOFIX for obliquebanded leafroller is Saturday at 1050 GGD42. Sprays to control were discussed last year in the Fruit CAT (July 7, 2000). Obliquebanded leafroller spray timing varies depending on the material used. Dogwood borer traps should be out to determine if sprays are necessary. Trunk sprays to control egg hatch and larval entry into the trunk should be applied in late June or early July after the adults begin flight.

Bartlett Pears fruits are 22 mm in diameter. Pear psylla adults are laying eggs. Pear sawfly larvae are emerging from affected fruit. Fabraea leaf spot has been reported.

Blueberry fruit are 15 mm in diameter. We are finding lots of raised corky spots on green blueberry fruit. Cranberry fruit worm larvae have been found in the fruit. Affected fruit are purple and shriveled often webbed to other berries in the bunch. Fruit feeding from leafrollers and or rose chafer can be found. Frost hit the blueberry region two weeks ago on May 30 and caused severe damage to the crop in some low-lying areas. Severely affected fruit have a dark shrunken appearance. The inside of the berries is brown and hollow. Traps for blueberry maggot traps should be out.

Grape bloom is ragged. Clusters that are finishing bloom are next to clusters that are just starting to bloom. The calyptra (flower cap) is brown and clinging to the top of some of the flowers. These flowers will not be pollinated. Grape berry moths trap catches are up. Berry moth feeding was found in some vineyards. Rose chafer has arrived in force. Galls from grape tumid gallmaker were found on grapes near Paw Paw. Grape growing degree-day totals from April 1 to June 10, 2001 are 586 GDD base 50. The wet bloom conditions that we have had are excellent conditions for downy mildew in grapes as well as other diseases. Ridomil is an excellent material for controlling downy mildew. It is an eradicant and provides about one month of control for this disease. The PHI for Ridomil on grapes is 66 days. June 27 is 66 days before September 1 and growers should decide if they are going to use Ridomil by that date. Another disease that caused problems last year was phomopsis. We believe that the fruit and rachis are very susceptible to phomopsis infection from bloom on, even thought the fruit infections do not appear until veraison.

Strawberries harvest is in full swing. Growth was slow during the cool wet weather but fruit were firm. Fruit has ripened and softened rapidly with the hot weather. We are seeing some symptoms of pesticide leaf burns due to poorly developed cuticle and long drying conditions due to the cool wet weather of the last 2 weeks.

Raspberry bloom has ended. Small green fruit is a site for raspberry fruit worm. Orange rust has been reported from many growers but those who used Nova are pleased with how well it works.

Cranberries are still blooming. Most of the flowers have not yet opened. Those blooms that have been open may not have been pollinated. Fungicides should be applied when bloom is half completed.

RUP credits are available for all the meetings listed below.

Grape and Blueberry Meetings - Fruit specific summer meetings will be held for both Grapes and Blueberries on Wednesday June 20 at SWMREC. The grape meeting will be from 1:30 PM to 3 PM. The blueberry meeting will be in the evening from 7 to 9 PM.

Grape Post Bloom IPM Meeting will focus on post bloom insect and disease control. Dr. Rufus Isaacs will discuss control of grape berry moth, leafhoppers and Japanese beetle. Dr. Annemiek Schilder will discuss disease control after bloom.

Blueberry Preharvest Meeting will focus on preharvest insect and disease control. Dr. Rufus Isaacs will discuss control of blueberry maggot, cranberry fruitworm and Japanese beetle. Dr. Annemiek Schilder will discuss disease control after bloom and irrigation timing to reduce fruit rots. Dr. Eric Hanson will discuss weed control treatments at SWMREC. Form more information on these meetings call Mark Longstroth (616) 657-7745 or Al Gaus (616) 944-4126.

The weekly Monday Fruit IPM meetings cover all fruits and are held in Berrien and Allegan counties this year. The next weekly Monday Fruit IPM meetings are in Berrien County on June 18 at the Fruit Acres Farm south of Coloma and on June 25 at the Alan Overhiser Farm north of South Haven in Allegan County.

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Posted: June 12, 2001