Fruit Update - SW Michigan

June 5, 2001

Mark Longstroth
Bill Shane
Al Gaus

Last week stayed cool and wet. Average temperatures hovered near 50 (58-48). Plant growth and insect activity slowed. Rain May 31 to June 2 caused infections for many fruit diseases. Precipitation totals ranged from 1 to 1.5 inches. Soils are wet, with water standing in poorly drained areas. Soil temperatures are in the low 50s.

Cool temperatures kept insects out of sight. Trap catches were low or zero for most pheromone traps. Growers should be prepared when warm conditions return, bringing out plum curculio.

Apricot fruits are 1.25 inches in diameter. Bacterial spot is easy to find on susceptible varieties.

Peach fruits are 25 mm in diameter. June drop has begun and some growers have started thinning. Only a few shoot strikes and flagging have been reported from oriental fruit moth. Tarnished plant bugs are scarce.

In Cherries, bacterial canker is common. Sweet cherries are 17 mm in diameter and straw colored. Fruit drop and fruit cracking are problems. Sweet cherries are very susceptible to brown rot and growers need to maintain protection until harvest. Tart cherries are 13 mm in diameter. No cherry leaf spot symptoms yet. Growers will need to protect against plum curculio later this week when temperatures rise. We caught few American plum borers. 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 fruits are 20-25 mm. June drop is ending. Fruit set varies widely. Some orchards still require thinning. With cool temperatures it looks like a lot of small fruit will hang on. 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. Few orchards with fruit in the 15 to 18 mm range can still be thinned. Rescue treatments of combination sprays of Sevin and NAA or Sevin and Accel could result in pygmy fruit because of the NAA. Ethrel will be used in some areas.

Relatively little Fireblight symptoms have shown up so far this year. 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 the May 10 fireblight infection were found June 4. These are the first blossom blight symptoms of the season. Trees affected with rootstock blight are easy to recognize. They are yellow with small leaves and poor growth. Some collapsed early before bloom but many are hanging on. Warm weather will cause these trees to die rapidly. Apple fruit scab lesions are reported. Primary scab season is over. Growers who have no scab in their orchards can reduce fungicide applications. Powdery mildew symptoms are easier to find. We are also finding cedar apple rust.

Insect trap catches were low. The flight took place early last week before the rain. For Oriental fruit moth we are at 774 GDD45, 571 GDD45 since BIOFIX (203). For codling moth we are at 520 GDD50, 270 GDD50 since BIOFIX (250). Controls for codling moth are applied about 200 GDD base 50 after biofix. The cool weather has slowed insect development. Growers should wait until warm weather returns after the mid-week rain to apply controls. I believe that we will have a flush of eggs hatching, as the conditions become more favorable. An insecticide application then will provide good control of hatching insect larvae. We will then also get a strong flight of adults that have been waiting for warmer conditions. If these adults have been waiting long, they will be weak and mating and egg laying will be poor. However in the case of codling moth we are in the middle of the first generation and there will be lots of fresh moths out with the warmer conditions. We should treat the second peak in the first generation as a separate event and time a pesticide application for egg hatch of eggs laid immediately after the weather warms (i.e. we should use a second biofix to time applications). A few obliquebanded leafrollers were caught last week. Growers and scouts should have their traps out now. As with other insects I expect a major flight when temperatures warm up. This should allow a good biofix for this pest.

Inspections of fireblight affected rootstocks revealed that many of the trees had dogwood borers. In one orchard, affected trees almost always had several larvae in the dead rootstock tissue but not in the live tissue above the dead tissue. In another signs of old dogwood borer attack were common. Growers should inspect declining trees to see if dogwood borers are part of the problem. I think the dogwood borers are attracted to weak trees which makes dwarf apple attractive. The fact that many of these trees were infected with fireblight when dogwood borer was fling last year may have also made them attractive. In orchards that have a lot of dogwood borer larvae, trunk sprays to control egg hatch and larval entry into the trunk should be applied in July.

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 14 mm in diameter. We are finding lots of raised corky spots on green blueberry fruit. We think these are due to insect feed, but are not sure which insect it might be (probably a plant bug?). Cool weather has stopped insect development. Insecticides may be needed to control cranberry fruit worm and cherry fruit worm when it warms up later this week. We had the beginning of a large flight before the weather turned cool. I suspect that egg hatch has been low but that these eggs will not hatch until the weather turns warm. We will also see a large flight with warmer temperatures. We need to treat this second flight as if it was a new flight and treat accordingly.

Grapes are beginning to bloom. Cool temperatures slowed grape development and delayed bloom 10 days. Rain last week caused infection periods for grape black rot and other grape diseases such as phomopsis. Downy mildew symptoms have been reported in Berrien County. In wine grapes, powdery mildew is also a concern. Few grape berry moths were because of the cold temperatures. Some grape berry moth feeding was found in an abandoned vineyard. There are lots of hatched and unhatched eggs out in the vineyards but very few larvae were found associated with this feeding damage. We believe that a portion of the population was washed off or died due to the poor weather we have experienced. Expect more berry moth eggs to hatch as the conditions improve. There have been several reports of rose chafer. Warmer weather should bring rose chafer out in force. Time insecticide applications for rose chafer emergence. Galls resembling eriophyid mite galls (not phylloxera or grape tumid gallmaker) were found on grapes near Paw Paw. Grape growing degree-day totals from April 1 to June 4, 2001 are 514 GDD base 50.

Strawberries have red fruit. Some fruit has been harvested, but regular harvest has not begun. Fungicides during wet weather will reduce fruit rots. Cool wet weather can cause angular leaf spot. Tarnished plant bug is cat facing the fruit.

Raspberries and blackberries are still in bloom. Early varieties have small green fruit. Fruit set looks good but the winter damage suffered by most varieties will make for a short crop. Bloom was reported on Heritage primocanes.

Cranberries are blooming.

Next Monday Fruit IPM meetings are in Allegan County on June 11 at the Alan Overhiser Farm north of South Haven and in Berrien County on June 18 at the Fruit Acres Farm south of Coloma.

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Posted: June 4, 2001