Fruit Update - SW Michigan

May 22, 2001

Mark Longstroth
Bill Shane
Al Gaus

Last week started with frosts and then highs in the 70s and lows near 60. Rain on the 14, 16 and 20 caused infections for many fruit diseases. Precipitation amounts ranged from 0.3 to 1.5 inches. Berrien County received much less rain than other areas in the region. Rain fell Monday and is forecast to continue through the week with much cooler temperatures. Soil moisture conditions are good. Soil temperatures are in the mid 60s.

New plum curculio egg laying scars were found. Cool temperatures this week should keep this pest out of sight. Stone fruit growers should be prepared after this rainy week as warm humid conditions return, bringing out plum curculio again. Growers need to protect stone fruit from egg laying.

Apricot fruits are 1.25 inches in diameter. We have a full crop. Growers need to be thinning. The water soaked lesions of bacterial spot were found Monday. The cool rainy weather forecast this week will surely spread this disease.

Peach fruits are 15 mm in diameter. In general there looks to be a good crop. There is a light crop in some areas due to winter cold. In these spots there is usually a distinct loss of crop in the lower portion of the tree. No shoot strikes have been reported from Oriental fruit moth. Tarnished plant bug has not yet appeared. Green peach aphid colonies have been found but once they start curling the leaves little can be done. Bacterial spot has not been found yet.

Cherries are at pit hardening. Growers need to protect against plum curculio. American plum borer and lesser peach tree borer adults are flying. These pests find weak trees and damaged trunks attractive for egg laying. Trunk sprays now will provide long term control. Tart cherries are 11 mm in diameter. Some growers report damage from frosts on the 12^th and 13^th. We have had many cherry leaf spot infections and growers need to control this disease. Loss of leaves before harvest will reduce fruit quality and weaken the tree. Sweet cherries are 14 mm in diameter. Sweet cherries are susceptible to brown rot at all times and growers need to maintain coverage during this upcoming wet week.

European plums are 14 mm in diameter. Japanese plums are 18 mm in diameter. Growers report a heavy June drop in some areas. Growers need to protect against plum curculio. American plum borer adults are flying. This pest finds black knot cankers and damaged trunks attractive for egg laying. Control this pest with sprays to the trunk and scaffold limbs. Cut out and remove black knots when you see them. Sprays to control black knot are needed during shoot growth as long as new green tissues are present.

In Apple, the largest fruit 16 and 18 mm. Most orchards have king fruit in the 13 to 15 mm range. Fruit set varies widely. Drop in some orchards has left singles that require little thinning. Other orchards have heavy set with 4 fruit per spur. Many growers are unsure of the effectiveness of their previous thinning sprays. The weather conditions forecast for this upcoming week are terrible for thinning. Cool weather with average temperatures BELOW 50 are forecast for the week. These cool temperatures will reduce and mask the effectiveness of thinning sprays. Growers need to wait until warm weather returns. The cool weather will also slow fruit growth. There should be an opportunity for a final thinning spray early next week when temperatures warm. Thinners are best applied at the beginning of warming trends when the highs will be above 70 F.
Fireblight symptoms from last year's cankers were reported late in the week. These included wilted leaves on girdled limbs. This week we are finding blossom blight and discolored spurs with no apparent bloom near last year's cankers. The spurs without bloom were probably infected by aerial spread from old cankers in the vicinity. Blossom blight symptoms should be apparent now from infections that occurred before May 9. May 10 was a major rain and new symptoms should continue to appear this week. Apple scab lesions are reported in many areas. We had scab infections on May 13,15,16 and 21. We are near the end of primary scab. Ascospores were caught during last week's rain. This week's rain should exhaust all the remaining spores but growers need to be sure to protect that fruit this week. Powdery mildew is appearing in apples and growers need to assess the need to spray to reduce this disease.
Oriental fruit moth trap catches are declining. We are at 662 GDD45, 462 GDD45 since BIOFIX for OFM. We should be at peak egg hatch for the first generation. Codling moth was first Biofixed May 4 at 250 base 50 GDD. Other orchards Biofixed May 7 at 290, or May 9 at 315. Controls for codling moth are applied about 200 GDD base 50. We will be picking up about 5 GDD50 each day, so the codling moth sprays should have been applied in first orchards to biofix. Growers who have not applied controls may want to wait until warm weather returns. This cool weather will halt moth flight and almost stop most insect development. Leafroller larvae are reported in large numbers. Obliquebanded leafroller are pupating. We should be catching adults when the temperatures warm. Put out your traps now. Growers should also be scouting for European red mite the treatment threshold is 2.5 mites/leaf. Look for spotted tentiform leafminer mines, you may need to treat the next generation. Potato leafhopper numbers are increasing and young plantings may need protection. White apple leafhopper adults are emerging now.

Bartlett Pears fruits are 18 mm in diameter. Pear psylla adults are active. Monday's rain was an infection period for pear scab.

Blueberry bloom is finished. The largest fruit are 12 mm in diameter. The frosts on May 12 and 13 caused damage in many areas. Wet conditions can spread blueberry fruit rots such Alternaria (cool no control?) and Anthracnose (warm weather). This cool weather will halt moth flights and almost stop most insect development. After bloom growers can use insecticides to control leafroller larvae as well as cranberry fruit worm and cherry fruit worm.

Grapes are almost in bloom. Wild grapes are at full bloom. Frost on May 12 and 13 damaged several hundred acres causing damage to the canopy and flower clusters. Rain on May 14, 15 and 16, 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 should delay bloom but flowers should open by Thursday (May 24) or Friday at the latest. A final application of protectant fungicides should be made to protect the flowers and rachis from phomopsis, during a wet bloom. Grape berry moth adults are being trapped. Grape growing degree-day totals from April 1 to May 20, 2001 are 456 GDD base 50.

Strawberries have red fruit. Harvest will probably begin late this week. Fungicides during wet weather will reduce fruit rots. Growers need to protect against tarnished plant bug that cat face the fruit.

Raspberries are in bloom. Winter injury to brambles has been severe. Thornless blackberries have been killed to the ground and many raspberry canes have had the upper portion killed. Avoid using insecticides but the application of fungicides during this wet weather will reduce fruit rots later. Growers should be scouting for rust in blackberries and black raspberries. Nova will protect against infection but will not eradicate a systemic infection.

Cranberries are nearing bloom and sprays of protectant fungicides will reduce fruit rots at harvest time.

Next Monday Fruit IPM meetings are in Allegan County on May 28 at the Alan Overhiser Farm north of South Haven and in Berrien County on June 4 at the Fruit Acres Farm south of Coloma and.

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Posted: May 22, 2001