Northwest Michigan fruit regional report – July 23, 2013

The heat has moved out in time for the start of tart cherry harvest, which is well underway across the northwest region.

Tart cherry harvest has begun in northwest Michigan. Most of the sweet cherries have been harvested, and quality was good except in blocks where American brown rot was a problem. Tart quality is good, but there is some wind whip with the very high winds we had over the weekend. Last week’s heat was brutal, but on Friday night (July 19), cooler conditions moved in and we had almost perfect temperatures for harvest over the weekend.

We had little rain last week and soil moisture levels are extremely low. Some parts of the northwest received precipitation last night (July 22) and the Northwest Michigan Horticultural Research Center (NWMHRC) received 0.49 inches of rain last evening. We have accumulated 1,989 GDD base 42 and 1,322 GDD base 50 so far this season.

Apples. Dry conditions have kept apple scab at bay, but growers with some scab lesions have continued to protect new foliage and fruit. The warm conditions favor the development of powdery mildew, and there is some visible powdery mildew in orchards at this time.

Insect catch in apples is low this week, and codling moth numbers have been low across the region. We suspect that the hot weather last week was above the codling moth’s upper temperature threshold; they will likely begin to fly again with the cooler conditions. Spotted tentiform leafminer numbers are up this week, and we caught no apple maggots in the region. Obliquebanded leafroller adult numbers are also down again this week, but small larvae are visible in terminals.

Cherries. As mentioned above, most of the sweet cherry harvest is wrapping up and growers are moving into tarts. Cherry leaf spot lesions can be found in tart cherries, and Michigan State University Extension recommends a post-harvest application of chlorothalonil to keep leaves on the trees through September. Powdery mildew is evident on trees with good new terminal growth. There is phytotoxicity in both sweet and tart cherry blocks, and most of it is on older leaves. We are still trying to determine the cause of this damage, but we hypothesize that surfactants and heat together were the likely culprits. We will continue to look into this issue.

Obliquebanded leafroller larvae have been difficult to find in sweet and tart cherries, and adult catch in pheromone traps is low. July 1 was our peak catch of adults here at NWMHRC, and from that biofix date, we have accumulated 498 GDD. Summer generation obliquebanded leafroller egg hatch begins at 400 to 450 GDD base 42; therefore, we expect to see larvae in the orchards soon. Growers should be scouting for obliquebanded leafroller larvae in tarts, particularly in blocks that will not be harvested for some time.

American plum borer moth second generation flight has begun, and we trapped an average of 30 moths this week. Cherry fruit fly numbers are down again this week, and we trapped an average of six flies per trap, which is considerably lower than two weeks ago.

The major news of the week is that we trapped our first female spotted wing Drosophila (SWD) at NWMHRC in tart cherries today, July 23. Another female fly was trapped on Old Mission Peninsula. This insect will be challenging to control as it shows up so close to harvest. Delegate and Entrust are both rated excellent on SWD in cherries, and both have a seven-day pre-harvest interval (PHI). Imidan and Mustang Max are also rated excellent, but have a one-day PHI. Danitol (three-day PHI) and Baythroid (seven-day PHI) are rated good against SWD.

Wine grapes. Berries are sizing nicely, and some of the tighter clustered varieties are now at berry touch. It may be necessary to increase spray water volume from here on out to achieve good penetration through the canopy and into clusters.

Although powdery mildew is still surprisingly light in many vineyards, we have now seen the start of downy mildew symptoms at some sites. Anthracnose and black rot infections have been found on some table grape cultivars that are relatively susceptible to these fungus diseases, but we do not expect these to become an issue on our wine grape varieties.

Japanese beetles are now active downstate, and as the days progress they should appear here soon. A very high population of these beetles was seen in a Saginaw County vineyard on July 16, causing extensive skeletonization of the leaves.

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