West Michigan tree fruit regional report – September 2, 2014

Insects are behind crop development stage this summer.

Crop update

Apples in west Michigan are coloring nicely and continue to size, but they seem to have slowed somewhat due to cooler temperatures. Insect development is also a bit delayed. Harvest of Zestar and Paula Red apples is complete on the Ridge and Gingergold harvest is well underway. There are a few other varieties being harvested for special markets such as juice and taffy apples.

Peach harvest continues and seems to have passed the peak.

Tree fruit diseases

Most blocks are free of apple scab, but there have been some recent reports of scab showing up expectantly, in particular on Romes. I’ve seen this before in Romes and have no good explanation for it, but it is a reminder that a low rate of Captan or other scab active fungicide is a good preventative to add to cover sprays for the rest of the summer.

Summer diseases. With the heavy rainfall and extended wet and humid conditions of late, sooty blotch and flyspeck protective fungicides are really important to have on developing apples. There is a great model on the Michigan State University Enviro-weather website to predict the need for summer disease fungicides. You can put in your spray date and it will calculate the need for a second application based on the weather in your area.

Some new powdery mildew has been seen in apples, so don’t let that slip by you. This is unusual to see new mildew so late in August, but the recent heavy rains have caused continued terminal growth in some varieties. Add in some hot and humid conditions and a stretched out fungicide program and it’s a recipe for late-season mildew.

Post-harvest diseases. The extended dry weather in July has caused the stretching of apple fungicides, which might explain the renewed appearance of scab and mildew, as well as some fruit rots. Now, with recent heavy rain and high relative humidity, I would suggest a hard look at a final fungicide application for the 2014 season. Fruit rots are being reported, mostly from fruit hanging near the ground or in weedy situations.

There are several fungicides that can help with rots, scab and mildew. Be sure to watch the pre-harvest interval (PHI) for late-season fungicides; three that have a zero-PHI are Captan, Pristine and Merivon. These can help prevent storage diseases such as fruit rots and pinpoint scab. Merivon seems to be especially good for fruit rots.

With a giant apple crop for the entire United States, only the best fruit will make it through to fresh sales; apples with slight damage will likely be culled. Fruit will likely need to be stored longer into 2015 and one final fungicide spray could help ensure better fruit for your pack coming out of long-term storage.

Tree fruit insects

Codling moth adult flight continues, but is declining. We estimate that the Sparta, Michigan area is just past peak egg hatch based on the July 30 biofix date, or 1,344 growing degree days (GDD) base 50. The GDD since biofix is 600. For blocks over threshold, cover sprays are important for the next several weeks to prevent stings, which are being reported in some blocks in low to normal levels.

Codling moth is slightly behind fruit growth stage and this is not the year to put the sprayer away on Labor Day, Sept. 1, if you are still catching codling moth adults. Be sure to take a look at your trap numbers two to three weeks ago – the eggs from those flying adults are hatching now.

Apple maggot adults continue to be trapped regularly on red spheres. Cover sprays should be initiated no longer than one week after catching on red spheres. Scouts in counties along the lakeshore – Oceana, Manistee and Mason – are reporting very high red sphere trap counts this year.

Most mite situations can just be let go this late in the summer. The exception would be blocks with a very heavy crop set and mite numbers well over the threshold of 7.5 mites per leaf with no predators present.

Obliquebanded leafroller second generation adult flight should be mostly completed. Egg hatch should be past peak and nearing an end for this year. A summer generation regional biofix was set for July 30, or 2,130 GDD42. GDD since biofix is 850. Larvae present this fall will overwinter and emerge again in early spring 2015. Unless larvae numbers are extremely high now, there is no need for cover sprays for obliquebanded leafrollers.

San Jose scale crawlers are still active, but this window is closing on the timing where cover sprays will still work well. Monitor for crawlers and treat if you find them. If you had a scale problem on harvested fruit in 2013 and have not sprayed them yet, now is the last chance to stop them before they settle on fruits. Reports of San Jose scale on fruit started last week.

Woolly apple aphid hotspots have been reported in some areas, but overall they are very difficult to find this year and small populations from several weeks ago have not grown much. This late in the season, the best integrated pest management tactic is to let the native parasitic wasps take care of them. However, high populations can cause worker distress, and this needs to be considered. If you are going to target them with pesticides, it is very important that you get excellent coverage with high water volumes and slow tractor speeds. If you don’t penetrate the waxy fluff in a wooly colony, you will be disappointed in the results of your pesticide application.

Spotted wing Drosophila (SWD) trap catches continue. SWD is not a feeder of healthy, sound apples. It could move into rotting fruit, similar to other vinegar flies. Late-season peaches should have traps up to monitor. Fall-bearing raspberries need regular cover sprays to prevent fruit damage.

Brown marmorated stinkbugs have not been trapped on the Ridge. Michigan State University Extension advises growers to continue to monitor.

Oriental fruit moth adult flight continues for the third generation. A regional biofix was set for May 19, or 295 GDD45. GDD since biofix is 2,274. Egg hatch for the third generation has begun and at the 8 to 10 percent egg hatch where cover sprays are again important in susceptible blocks. A peak egg hatch is expected in 10 days from now, around Sept. 11 or 12.

Any late peaches still hanging into next week or longer might be at risk for oriental fruit moth feeding. Third generation can sometime be an issue in apples where adult numbers are high, especially in mating disruption blocks.

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