MSU Extension

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. Initial harvest of Zestar and Paula Red apples is starting. Peach harvest continues and seems to have reached a peak

Tree fruit diseases

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.

Post-harvest diseases. The extended dry weather has allowed the stretching of apple fungicides, but don’t forget about the possibilities of preventing post-harvest rots with orchard sprays. There seems to be a bit more fruit rot being reported in the last few weeks, mostly from fruit hanging near the ground or in weedy situations.

Tree fruit insects

Codling moth adult flight continues. We estimate that the Sparta, Michigan area is around 20 percent egg hatch based on the July 30 biofix date. A second generation regional biofix was set for July 30, or 1,344 growing degree days (GDD) base 50. The GDD since biofix is 312. Peak egg hatch for second generation is expected around Aug. 27-30. For blocks over threshold, cover sprays are important for the next several weeks to prevent stings.

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.

European red mite hot spots are being reported, but overall numbers seem to be normal to even below normal. The presence of predators continues to be reported. Threshold is 7.5 mites per leaf for August. Michigan State University Extension recommends growers monitor for beneficials; one per leaf indicates wait a week and count again. Usually when we get to mid-August, miticide sprays are no longer necessary.

Two-spotted spider mites continue to be found in some apple blocks in high numbers, particularly those on sandier soils. Continue to monitor.

Obliquebanded leafroller second generation adult flight continues, but they are declining. Egg hatch should be underway. A summer generation regional biofix was set for July 30, or 2,130 GDD42. The GDD since biofix is 463. Scout for new larvae. In general, obliquebanded leafroller larvae continue to be difficult to find, but monitoring for new larvae is important as this generation is more likely to feed on apples directly.

San Jose scale adult male flight of the second generation is well underway and crawlers should again be active now at any time. Monitor with tape if you can. Cover sprays can target this stage if necessary. 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.

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.

Brown marmorated stinkbugs have not been trapped on the Ridge. Continue to monitor.

Green apple aphids are moving on to other hosts as terminal apple buds are set. Woolly apple aphids were first found on July 2, and really don’t seem to be expanding much. Continue to monitor for all aphid species and the beneficials that often attack them.

Japanese beetles seem to be declining and are overall very low in numbers this year. Continue to monitor for feeding damage through the month of August.

Potato leafhoppers are being seen more than white apple leafhoppers this year. Potato leafhoppers tend to roll leaves rather than the stippling that white apple leafhoppers do.

Oriental fruit moth second generation larval activity should be over and cover sprays not as critical in stone fruits. Adult flight is increasing for the third generation. A regional biofix was set for May 19, or 295 GDD45. The GDD since biofix is 1,929. Third generation flight is beginning and 8 to 10 percent egg hatch is estimated to take place around Aug. 30. Any late peaches still hanging at that time might be at risk. Third generation can sometimes be an issue in apples where adult numbers are high, especially in mating disruption blocks.

Black stem borer is a very small ambrosia beetle that has been found in several blocks on the Ridge. It mostly attacks dying or injured trees, but sometimes appears to attack nearby healthy trees. We know that it is attracted to ethylene which is often given off by injured trees – even when the injury is not visible. With all the winter injury we have seen so far, it could very likely be that trees have non-visible winter injury, but the beetles are attracted to their ethylene signal.

This is not a new insect to Michigan. It is well documented, but only seems to cause problems for commercial tree fruits every once in a while. It can infest all the tree fruits and could easily be confused with shothole borer. It seems to only be an issue in young trees in our area, but perhaps it is just not noticed in larger trees. It is usually happy feeding in the woods in fallen trees. A wooded area nearby a low frost pocket is a good site to look first. Monitor for tiny holes in the trunks, rootstocks or lower lateral branches. The beetles are tiny, about 2 millimeters long. They bore in the trunk from ground level to as high as 4 feet from the ground. The holes are very tiny too, only a few millimeters wide. Usually, you will first notice sawdust near or below the holes or weeping along the trunk of the trees.

The best management strategy is to remove the infested trees that also have extensive decline and burn them – they are the source of beetles that could move through the orchard. Trees that still seem healthy with a few borer holes in them might survive. This pest is also being reported in New York and they have seen marginally affected trees survive. Trunk sprays seem to be not as effective as for other borers, maybe because these beetles move into the tree as a nesting site and not as a food source, so their ingestion and contact with an insecticide are limited. They also fly for a long, extended period of several months, so a one-time pesticide spray might not be enough. They make galleries in the wood and line it with a fungus that is the food source for their larvae. This fungus could infect the tree’s vascular tissue and cause further decline.

The MSU fruit team is aware of this issue and would like to know if you have seem damage so we can get a full grasp of the situation. With all the winter-injured trees this season, it would be easy to miss this pest or misidentify tree decline as this pest. At this time, we have not witnessed direct fruit feeding damage, nor has this ever been documented. If you have seen damage, contact your county MSU Extension educator.