SW Michigan Fruit Update

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Southwest Michigan, May 19, 2008

Mark Longstroth, Bill Shane

Weather

Last week’s temperatures were cool with highs in the 60s and lows near 40.  There were scattered frosts with lows near freezing, Thursday (May 15) and Monday (May 19).  Little damage was reported.  Rain showers fell in the area Wednesday May 14 and Saturday May 17.  Rainfall totals were generally light (about a tenth of an inch).  Soil moisture levels are good, but light soils are beginning to dry out.  We expect continued cool weather this week until the weekend when we should see temperatures climb into the upper 70’s.  There is little chance of rain this week.  We need to be aware of the danger of frosts when we get clear calm conditions.  There is a chance of warm rain next Monday or Tuesday.  Our GDD totals have fallen back to levels not seen since the late 1990’s. 

Southwest Michigan Growing Degree Day Totals March 1 through May 18, 2008				Grapes, from April 1
Location	GDD 42	GDD 45	GDD 50	GDD 50
Berrien Springs:	594	471	306	296
Scottdale:	585	463	299	291
SWMREC:	535	423	270	264
Bainbridge:	561	446	291	284
Hartford:	525	416	269	265
Lawton:	590	470	307	302
Grand Junction:	607	486	324	318
South Haven:	507	402	260	253
Fennville:	494	385	245	241

Tree fruit

Insect activity remained generally low last week.  Oriental Fruit Moth trap catch continues.  Oriental Fruit Moth were caught and biofixed May 4 at SWMREC.  Trap catch has low but continuous.  Codling Moth trap catch has been sporadic.  Redbanded leafroller flight is finished.  Plum curculio is out and egg laying scars have been found.  Generally it has been too cool for egg laying, but warm temperatures return this weekend and growers should have their fruit protected.  We expect widespread egg laying early in the weekend warm up.

Apricots fruits are 12 to 18 mm in diameter.  Growers need to protect against plum curculio.

Peaches are out of the shuck.  Fruit are about 8 to 10 mm in diameter.  A lot of fruit disappeared due to fruit drop in the last week.  Oriental Fruit Moth was biofixed on May 4 at SWMREC.  Treatment is timed for 200 GDD45 after biofix and we are now at about 120.  We will need to apply controls during the weekend warm up.  We will reach the 200 GDD45 treatment window Monday or Tuesday.  Plum curculio egg laying should be a problem at the same time.

Sweet Cherry fruit are about 12 mm in diameter.  Growers should be prepared to protect against plum curculio egg laying during warm weather.  Sweet cherries are always susceptible to brown rot.  This disease requires wet and warm conditions, 5 to 6 hours of wetness at 70F.  We may see conditions that warm and wet early next week if it rains.  Remember to protect against cherry leaf spot.  We have not had many infection periods this year. 

Tart Cherries are emerging from the shuck and fruit are 4-6 mm in diameter.  Exposed fruit will be susceptible to plum curculio during the warm weekend.  The leaves are susceptible to cherry leaf spot.  Recent rains have been marginal infection periods due to cool average temperatures.  Growers should apply protectant materials before rains.  Because of widespread SI resistance in Cherry leaf spot, alternating sprays of Gem and copper are recommended for leaf spot control.  This saves the SI materials for brown rot control near harvest.

Plums are out of the shuck.  Japanese plums are about 8mm.  European plums are about 6mm.  Plum curculio egg laying scars were found in Japanese plums.  Growers also need to protect against black knot.  Indar or a tank mix of Topsin M and captan are the most common controls used.

Apples are at petal fall, with scattered late bloom.   Fruit size is in the 4 to 8mm range.  Rain last Wednesday, May 14, caused a wide spread scab infection.  We are nearing the end of primary scab season.  Most of the scab spores are mature and about ¾ of the spores have been released.  Scab protection will be necessary at least through the next rain event.  Last week was too cool for fire blight.  The cool weather will keep bacterial populations low this week.  We will not have enough heat for infection until the warm weekend.  Growers with open bloom should be prepared to apply controls Monday or Tuesday if we receive rain.  Some growers with small plantings of young trees plan to remove the blossoms.  Only those blossoms that open this week should be vulnerable since only young blossoms are susceptible to infection.  We are past the time to apply Apogee sprays to reduce the spread of fire blight.  To control vegetative growth into the season, applications are spread out at 14-day interval over the next 6 to 8 weeks. 

Southern Berrien County biofixed for Codling moth on May 14 at 278 GDD50.  There were only light catches elsewhere across the region and we have not set a regional biofix.  With the cool week and warm weekend we will be at about 100 GDD50 early (Tuesday) next week.  We expect most of the region to biofix Friday May 23 with the return of warm temperatures.  Spotted tentiform leafminer sap feeders should be out and they will move into the leaves soon.  European red mite motiles are moving about and we expect to see San Jose scale crawlers soon.

Apple fruitlets are 4 to 8mm in diameter, and we are just starting to see the early drop of injured and unpollenated flowers.  The cool weather forecast means that we will not have any good apple thinning windows until the weekend.  A warming trend when temperatures climbing above 70 for several days will offer us the best thinning window we are likely to see this spring.  Due to scattered frost injury and poor pollinating conditions fruit set may not be as heavy as the bloom indicates.  I am recommending a moderate thinning strategy.  I think the poor pollination and long bloom combined with the excellent thinning window means that the fruit will not be hard to thin.  We also run the risk of having high temperatures rise into the 80’s, which would make thinners very effective.  Growers need determine if any blocks need to be aggressively thinned.  There are wide differences in frost injury between varieties and sites.  Where there is a wide variation in bloom density.  Thin for the trees with the heaviest fruit set.  Thinners will remove more from heavy set trees and less from trees with a light set.  Where there is a heavy bloom on trees with a strong biennial bearing tendency, thin aggressively.  Using moderate thinning rates growers may need to apply follow up thinning sprays later.  There will certainly be another thinning window later but this one is likely to be the best. 

Winter injury has been reported in young apples.  Weak trees in last year’s plantings show poor growth and brown cambiums, while more vigorous trees show no damage.  Where the wood beneath the cambium is white the trees are likely to make a recovery.  If the wood is brown beneath the cambium, the trees are unlikely to recover and will remain stunted because of the dead wood in the interior of the trunk.

Pears fruit are 6-8mm in diameter.  Growers have been applying thinning sprays.  Pear psylla nymphs are hard to find.  Growers should protect against pear scab.

Small fruit

Blueberry bloom is well underway.  Because of the cool weather, I have received a lot of calls about the red or purple coloration of blueberry leaves.  This red color is normal during cool springs and when we warm up the leaves will green up.  Scattered cranberry fruitworm catch has been reported and we expect a general flight later this week when the weather warms up.  Mummyberry shoot strike symptoms from infections following the April 30 freeze are visible, and easy to find in some areas.  Some growers used their sprinkler systems for the frosts Thursday (May 15) and Monday (May 19).  Growers in cold pockets reported lows in the lower 20’s and suffered some damage.  More damage is being reported from the April 30 freeze in cold pockets.  Flower buds were killed at 19F at bud burst.  We are also seeing winter injury in young plants planted last year.  Shoot tips are growing poorly while leaves and shoots lower in the plant are growing well.  The dividing line between the injured upper part of the plant and the healthy lower part of the plant is probably the snowline on a cold calm night in the winter.  While the snow acts as an insulator, the temperatures above the snowline can get very cold during a calm clear winter night.  Blueberry stem gall wasps are flying.  There is no good control for this pest, which emerges during bloom and lays its eggs in the stem.

Grapes have six-inch long shoots, with two to three leaves out.  Vinifera grapes are a little behind in development and late varieties are noticeably behind.  Cool temperatures have slowed grape growth.  In vineyards damaged by the April 30 freeze, secondary and tertiary buds have begun do grow and are easy to find on and near live shoots, but no new growth is visible from dead buds in severely affected vineyards.  In the past it has taken four to six weeks for new growth to become apparent.  The conditions generally have been too cool for powdery mildew and, downy mildew, and marginal for black rot but phomopsis does well in cool damp weather and we have probably had a few infection periods.  Look for new phomopsis lesions at the base of this years shoots.

Strawberries are at past full bloom.  Most of the primaries have set fruit.  Avoid using insecticides during bloom.  Many growers irrigated during the recent frosts.  These cool wet conditions favor angular leaf spot a bacterial disease.  Applications of copper can reduce this disease (see notes on control in E154).  Fungicides are applied at bloom to reduce gray mold, anthracnose, leaf spot diseases and leather rot. 

Raspberry and Blackberry flower bud clusters have emerged. Orange rust symptoms are common in wild brambles.  Nova is an effective protectant for preventing infection by this disease. It suppresses symptoms but does not cure the disease after infection.

Cranberry beds are greening up and tip buds have burst.  Most of the movement is taking place on the edge of the beds.  When the shoots begin active growth before bloom is time for a protectant fungicide spray to protect new foliar and reduce fruit rots.

Miscellaneous

There is a pair of Grape IPM meetings are Wednesday May 21.  The morning meeting will be from 10 AM to noon at the Cronenwett Farm Shop at 70123 28th Street, east of Lawton. The afternoon meeting will be at 2 PM in the Berrien County MSU Extension Office at the Southwest Michigan Research & Extension Center.  These meeting are co-sponsored by National Grape Cooperative and MSU Extension and are open to all grape growers. 

There will be no Monday Fruit Update May 26 due to Memorial Day.  There will be a short Fruit IPM meeting at Fruit Acres Farm on Tuesday at 5 PM.  There will be no credits for this Tuesday meeting.  The next Monday Fruit Update meeting will be, Monday June 2, at the Fruit Acres Farm in Berrien County.