WEATHER:

A trace or more of rainfall has been recorded at the NWMHRS on 5 of the past 7 days, totaling 1.23". Since July 1 precipitation has totaled 8.12", with measurable precipitation occurring on 15 out of the 27 days to date in July. No wonder leaf spot is common!

GROWING DEGREE DAY ACCUMULATIONS

GDD 50:1497; GDD 42: 2311

COMMODITY REPORTS

Apples: The hot humid weather has created ideal conditions for the sooty blotch/fly speck fungus in apples. Fresh market apples should have a Topsin M or Benlate plus Captan or Ziram spray applied soon. A second spray may be needed towards the end of August if it continues to be wet. Apple maggot flies have been trapped in many, but not all, commercial apple blocks. Remember that 2 flies caught in a block is the threshold. Codling moth trap catches were very low this past week. Considering our degree days, we should be seeing the second generation soon, and trap catches should rise. European red mites are above threshold in some apples. Aphids are building in some apple blocks. Young trees, in particular, should be scouted for infestation. 

Cherries: Tart cherry harvest is nearing conclusion in NW Michigan. The crop appears to be picking out below the USDA estimate. Wind damage is common, but firmness has been excellent. Cherry fruit fly adults are being caught in very high numbers. If you expect to be harvesting for over 4 or 5 days more, then the later fruit should be protected. Last Wednesday we had a heavy infection period for cherry leaf spot. If adequate protection was not applied prior to infection, then a sterol inhibitor fungicide should be included with Bravo in the post harvest spray. Brown rot pressure has been extremely high in unsprayed tart cherries.

Peaches: Peach growers should heed the warning about brown rot and make sure an appropriate fungicide is used on them during this pre-harvest period.

Other Fruit: In young apples, plums, grapes, and strawberries, potato leafhoppers continue to be a threat.

MISCELLANEOUS

Apple Leafminer
By Gary Thornton

In the last several years we have seen this pest in a few locations throughout northwest Michigan. It does not seem to be a devastating pest, but it is one that you may want to consider controlling for in young apple blocks as this article suggests.
 

SCAFFOLDS Fruit Journal, Geneva, NY, Volume 8, No. 17, July 12, 1999
(Dick Straub, Entomology, Highland)

As occurs most years about this time, I have recently received some inquiries from Hudson Valley growers regarding considerable foliar damage by a leafminer. The pest is neither the spotted tentiform leafminer nor the apple blotch leafminer -- gracillariid species that are commonly found in this region. The culprit, apple leafminer (Lyonetia speculella Clemens), has been occurring sporadically here in isolated orchards since 1987.

Female moths oviposit in tender new foliage by piercing the undersides of leaves and depositing single eggs inside the leaf tissue. The hatched larvae form serpentine mines, which are visible as wavy brown lines on the tops of leaves. As the larvae grow, they enlarge their mines into brown blotches, within which they consume all of the tissue between the upper and lower epidermis. Unlike other leafminers of apple, L. speculella is characterized by frass (small black pellets) that is constantly expelled on a silken thread from the mine by the feeding larvae. Just prior to pupation, larvae spin cocoons, which are suspended by threads and resemble a hammock. Apple leafminer probably has 4 to 6 generations per year in southeastern New York. 

Moreover, unlike our other leafminers, larval damage is confined to the youngest foliage, particularly terminal leaves of vigorously growing shoots. Root initials or water sprouts that are partially shaded are the preferred sites for feeding and pupation. Severely mined leaves turn brown and die; most such leaves drop off prematurely, thereby decreasing the number of the most photosynthetically active leaves. The potential for damage is greater in young orchards than in mature ones, and vigorous trees usually sustain higher infestations than do less vigorous trees.

Populations normally do not achieve high abundance or cause critical damage until the beginning of the harvest period of our earliest cultivars. Insecticidal control of larvae or adults at this time may not be a reasonable tactic because of the pre-harvest interval of most materials and, just as importantly, because infestations do not damage fruit or cause premature drop of fruit. Broad-spectrum insecticides typically used in cover sprays (OP's) are unlikely to provide significant control of adults or larvae. The optimum control tactic would be 1 or 2 sprays of either methomyl, oxamyl, endosulfan or a pyrethroid at petal fall or 1st cover. Undoubtedly, Provado at the same timing would also do some good. We consider that sprays are necessary only on non-bearing trees where vigor is essential, or on bearing trees that had high infestations the previous season.
 

NW Michigan Horticultural Research Station
Insect Trap Count Averages - 1999 
 

Date	Codling  Moth	Spotted Tent Leaf Miner	Lesser Peach Tree Borer	Greater Peach Tree Borer	American Plum Borer	Oblique Banded Leaf Roller	Grape Berry Moth
5/18	0	660	8		30
5/24	0	88	1.3		14.3	0
6/1	.6	85	17		4.6	0	9
6/8	2	15	17.3		2.7	0	7.7
6/14	1	342	11	6	.3	7	4.3
6/21	.33	511	10	5	0	2.3	1
6/28	.75	455	6.3	1.6	.75	2.3	16.3
7/5	0	357	7.3	1.6	2.6	.3	2.3
7/12	.3	274	6.6	3.6	7.6	2	.3
7/26	.3	233	4.6	4	11	1	5

Please send any comments or suggestions regarding this site to: 
Bill Klein, kleinw@pilot.msu.edu

Last Revised:7-27-99