May 5, 1999

WEATHER:

Hot and dry! Evaporation since April 1 has totaled 5.47" (exceptionally high for this time of the year), with precipitation (rain and snow) since April 1 totaling 2.36", all of which fell in early April.  For irrigation scheduling purposes I have always considered the important time to begin accumulating evaporation data is approximately May 1, as this is approximately when tree growth begins.  But this year I feel we should consider that at least a portion of the April deficit would want to be replaced.  The rule of thumb for irrigation scheduling in orchards is to replace 75% of evaporation that occurs through a combination of rain and irrigation. For April, I suggest using a 25% to 35% replacement for the last 2 weeks.  This is designed to replace moisture evaporation from soil that occurred since the snow melted, but is lower than the 75% growing season figure because of the lack of leaf surface on the trees for moisture loss via transpiration. 

DEGREE DAYS at NWMHRS:

Base 42: 315; Base 50: 136

GROWTH STAGES:

Apricot: Harcot – petal fall
Plum: Stanley – 50% bloom
Apple: Red Delicious – pink
Sweet Cherry: Napoleon – full bloom
Tart Cherry: Montmorency – full bloom
Pears: Bartlett – 25% bloom
Peaches: Red Haven – full bloom
Grapes: Bud burst

INSECTS:

Cutworms – Activity has been very low this year. They remain a threat on recently planted trees and grapes.

European Red Mites – No hatch has been reported yet. Many of the orchards that I have looked at have had very low egg numbers. I suspect that the first of them have already hatched out. Oil applications can go on anytime before pink. 

Green Fruit Worm – Small larva have been found in cherries. Control should be aimed at the petal fall time period.

Spotted Tentiform Leafminer – Eggs are now being laid on the underside of leaves. Adult trap catches are average for this time of year, but continue to rise.

Pear Psylla – Nymphs should be hatching out within the next few days and begin feeding on the underside of leaves. Adults continue to lay eggs. Three good options are available for controlling psylla. Agrimek can be applied at first cover. The Pyramite label has been expanded to allow for higher rates. It should be used at no less than 8.8 oz, and 10 oz per acre is better. This should be applied at first cover. If applied at petal fall the residue will not be great enough to control the hatching nymphs. This is a more expensive control option, but it is an excellent resistance management strategy. Provado is another option that should work equally as well. Provado can be applied earlier at petal fall, as it is locally systemic.

Codling Moth – Growers who plan on monitoring for this pest should get their traps out at petal fall.

June Beetle - Adults are now emerging. The adult will feed at night on cherry leaves but more importantly, their larvae (white grubs) feed on the roots of fruit trees (particularly cherry). There is no good method of larval control, so it is wise to control the adults in young orchards to minimize egg laying. Guthion works well for June beetle adult control.

DISEASES:

Apple Scab – No scab infections have occurred yet this season. We can expect a large spore release with the next rain greater than ¼ inch. Even without any scab pressure growers should apply a fungicide for powdery mildew at this time on susceptible varieties like Idared and Jonathon.

Powdery Mildew – After another mild winter we can expect powdery mildew to have another banner year. When we have winters where the temperatures drop below –10*F. approximately 90% of the inoculum is killed. This winter the low temperature at the NWMHRS was –3*F. so there should be plenty of inoculum to get the season started. Nova is still the best at controlling PM, with Elite being the next best. Sulfur will provide some protection in cherries, but only for 3-4 days. Pink is the ideal timing for control in apples. 

Brown Rot pressure has been very low so far. If rain falls later this week, then sweet cherry in particular, should be treated to prevent blossom blight. Brown rot is a concern with any rains that may occur during bloom.

Cherry Leaf Spot – Once the leaves of cherry are fully expanded then the stomata on those leaves are opened and susceptible to infection. At that point growers need to control for leaf spot for the remainder of the season.

Black Knot can still be cut out in plums to lower inoculum. The most susceptible time for infection is from white bud to shuck split. Long wetting periods during this time should be considered infection periods and treated accordingly. Bravo, when used as a protectant, has been shown in Canada to offer superior control of black knot, when compared to a Benlate/Captan tank mix. 

MISCELLANEOUS:

Reminder on B9 Rootstock
By Gary Thornton, District Fruit IPM Agent

One of the dwarfing apple rootstocks that growers can choose from is B.9. B.9 is a stock which produces trees 10% smaller than M.9 EMLA, and in most situations it is not vigorous enough for northern Michigan. B.9 is also unique, as it is susceptible to crown gall. When growers are planting this rootstock into old stone fruit ground they should treat the roots with Galltrol. Galltrol is a gel mixture of Agrobacterium radiobacter, strain 84, which is a biological control for the crown gall bacterium. When the Galltrol is mixed with water, the roots can then be dipped or sprayed prior to planting.

Irrigation – If the rains bypass us this week, growers will want to get their irrigation going, particularly on young trees and apples. It is the cell division for the first 30 days after bloom that determines the full size potential in apples. Without good growth in this time period, then all the water in the world won’t swell that apple to a 3" apple. This extra size on each apple will greatly increase yields in bushels per acre.

Eight Old Cherry Tanks Needed at NWMHRS
By Jim Nugent, Station Coordinator

We need 8 old cherry tanks for a research project. They don't need to hold water. In fact, we will cut holes in the bottom for water drainage. We'll be planting some fruit trees in the tanks so that we can move them from one location to another. If you have some old tanks that you would like to get rid of, please let us know. We could either buy them or, if donated, you could get a tax deduction for a charitable gift of an item that you no longer use. Please give Bill Klein or me a call. Thanks!
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Please send any comments or suggestions regarding this site to: 
Bill Klein, kleinw@pilot.msu.edu

Last Revised:5-5-99