Fruit Update - SW Michigan

May 29, 2001

Mark Longstroth
Bill Shane
Al Gaus

Last week started cool and stayed cool and wet. Average temperatures hovered near 50. Plant growth and disease activity slowed and insect activity stopped. Rain on the 23 began an infection period for many fruit diseases that stretched through the weekend until Monday. Precipitation amounts ranged from 1 to 1.5 inches. Berrien County received significant hail Thursday and Friday. Damage was severe in some areas. Soil moisture conditions are too good, with water standing in poorly drained areas. Soil temperatures are in the mid 50s.

Cool temperatures keep insects out of sight. Trap catches were zero for most pheromone traps. Stone fruit growers should be prepared when warm conditions return, bringing out plum curculio. Growers need to protect stone fruit from egg laying.

Apricot fruits are 1.25 inches in diameter. Growers are thinning. Bacterial spot is easy to find on susceptible varieties. The rainy weather will surely spread this disease.

Peach fruits are 25 mm in diameter. Shoot strikes and flagging have been reported from Oriental fruit moth. Tarnished plant bugs are scarce. Bacterial spot has not been found yet.

Cherries are showing symptoms of bacterial canker. Sweet cherries are 15 mm in diameter. Early varieties are beginning to color and fruit cracking is a problem due to the rain. Sweet cherries are very susceptible to brown rot and growers need to maintain protection until harvest. Tart cherries are 11 mm in diameter. No cherry leaf spot symptoms yet. Growers need to maintain protection to retain leaves until harvest and maintain fruit quality. Growers will need to protect against plum curculio when temperatures rise. The cool weather has shut down of insect activity, allowing more time for trunk sprays to control American plum borer and lesser peach tree borer.

European plums are 18 mm in diameter. Japanese plums are 20 mm in diameter. The crop is spotty with few growers reporting a good crop. 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 largest fruits are 26 mm. This is in early varieties with light fruit set. Fruit set varies widely. Many orchards still require thinning. The weather conditions forecast for this week are poor for thinning. Growers need to wait until warm weather returns. Thinners are best applied at the beginning of warming trends when the highs will be above 70 F. Orchards with fruit in the 15 to 18 mm range can still be thinned if conditions are right.

Fireblight symptoms are scarce. The cool weather has delayed symptom expression. Symptoms from May 10 should appear this week. Apple scab lesions are reported in many areas. We had a heavy scab infection period from May 23 to 28. We are near the end of primary scab. Last week's rain probably exhausted the remaining spores.

Insect trap catches were zero. For Oriental fruit moth we are at 719 GDD45, 559 GDD45 since BIOFIX (203). For Codling moth we are at 490 GDD50, 240 GDD50 since BIOFIX (250). Controls for codling moth are applied about 200 GDD base 50 after biofix. Growers who have not applied controls should wait until warm weather returns. The cool weather has stopped most insect development. Leafroller larvae are harder to find. Obliquebanded leafroller traps should be out now.

Bartlett Pears fruits are 20 mm in diameter. Pear psylla adults are active. Monday's rain was an infection period for pear scab. Fabraea leaf spot has been reported.

Blueberry fruit are 14 mm in diameter. Wet conditions can spread blueberry fruit rots such Alternaria (cool weather, no control?) and Anthracnose (warm weather). This cool weather has stopped insect development. Insecticides may be needed to control cranberry fruit worm and cherry fruit worm when it warms up next week.

Grapes are still about to bloom. Wild grapes are at full bloom. Cool weather with average temperatures near 50 have stopped grapes as well as their insect pests in their tracks. Rain last week caused infection periods for grape black rot and other grape diseases such as phomopsis. In wine grapes, powdery mildew is also a concern. The cool weather will continue to delay bloom. A final application of protectant fungicides should be made to protect the flowers and rachis from phomopsis, during a wet bloom. No Grape berry moths were trapped. Grape growing degree-day totals from April 1 to May 28, 2001 are 484 GDD base 50.

Strawberries have red fruit. Fruit from under floating row covers has already been harvested. Regular harvest will begin this week (then it will get hot). Fungicides during wet weather will reduce fruit rots. Cool wet weather can cause angular leaf spot, a bacterial disease controlled with copper. Tarnished plant bug is cat facing the fruit.

Raspberries are in bloom to petal fall. Blackberries are in bloom. Fungicides during bloom and the small green fruit stage will help control fruit rots later.

Cranberries are blooming.

Next Monday Fruit IPM meetings are in Berrien County on June 4 at the Fruit Acres Farm south of Coloma and in Allegan County on June 11 at the Alan Overhiser Farm north of South Haven.

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Posted: May 29, 2001