MSU Extension

Weather and crop report

As tart cherry harvest winds down, we reflect on a challenging season for tree fruit growers. As in every year, weather influences the agricultural crop. This season started out cool and wet and these trends continued through the season. However, we collect annual heat unit accumulations, and on paper, this season is fairly “normal.” We have accumulated 2,364 growing degree-days (GDD) base 42 in 2017, which is close to our 20-plus year average of 2,399.5 GDD.

This season was normal in some ways, but overall temperatures have been relatively cool sprinkled with a few hot days. Moisture, on the other hand, was higher than in most years. At the Northwest Michigan Horticultural Research Center, we have received over 11 inches of rain since May 1. This excessive rainfall has kept our grass green but has caused many disease problems in the orchard.

Cherry quality has declined over the past week. With all the rain this season, cherry size was large, but once the heat came early last week, quality diminished quickly. Since mid-week last week, tart cherries have been on the soft side, and with the excessive rain that came Friday, Aug. 4, fruit has become even softer. Some growers had difficulties getting back into orchards to continue with harvest after the rains last Friday. In addition to soft fruit, the rain resulted in low brix because fruit are saturated with water. Growers anticipate to finish harvest this week.

On a positive note, apple quality and size is looking excellent around the region. Apples are even starting to color up on some earlier varieties. According to Michigan State University Extension educators around the state, apple maturity seems to be moving along quickly. Although our predicted harvest dates are similar to 2016, we will monitor apple maturity throughout the season to keep growers informed. We will begin apple maturity testing in the near future.

2017 growth stages as of Aug. 7, 2017

• Bartlett Pear – 43 millimeter fruit
• Potomac Pear – 51 millimeter fruit
• Mac – 59 millimeter fruit
• Gala – 53 millimeter fruit
• Red Delicious – 61 millimeter fruit
• HoneyCrisp – 61 millimeter ftruit
• Montmorency – Harvested
• Balaton – Harvested
• Hedelfingen – Harvested
• Gold – Harvested
• Napoleon – Harvested
• Riesling – Green fruit

Pest report

In cherries, cherry leaf spot has been difficult to control with this season’s rain, and rainfall late last week continued this trend triggering infection periods across the region. Between May 5 and Aug. 8, the Northwest Michigan Horticultural Research Center Enviroweather station has reported 21 infection periods and 12 wetting periods that did not result in an infection—a total of 33 wetting events thus far in the 2017 season.

In comparison, 2015 was also a challenging cherry leaf spot year; from May 5 to Aug. 23, 2015, there were 15 infection periods and eight wetting periods that did not result in an infection—a total of 23 wetting events.

Defoliation is noticeable and widespread due to cherry leaf spot at this time. Foliar nutrient applications this fall will be helpful in cherry orchards that have leaves remaining on trees.

American brown rot was also difficult to control this season. We observed orchards that had substantial American brown rot infections prior to harvest and lingering fruit in blocks that have been harvested currently harbor the sporulating fungus. While the timing for management in harvested blocks has passed, American brown rot infected mummies will be an important inoculum source for next season.

Spotted wing Drosophila (SWD), the invasive insect pest, caused many problems for Michigan’s cherry growers. This season has been conducive for SWD population growth: excessive rainfall, humid conditions and relatively cool temperatures. Additionally, we caught our first flies during the week of May 22, which was an earlier catch than in previous seasons. Furthermore, other fruit growing regions in the state have seen faster than normal increases in SWD population growth.

Growers have done an excellent job controlling SWD, but as the season winds down, many orchards are faced with too much pressure from SWD to harvest. Some growers have left cherries in the orchard as a result of SWD.

Over the last three weeks, we have been monitoring for mites in tart cherries at the Northwest Michigan Horticultural Research Center. Overall mite pressure has been low, but we are noticing slight increases in twospotted spider mite numbers; mite numbers have remained below treatment threshold at this time. This season has not been our typical hot and dry summer weather that is usually conducive for mite development, but we encourage growers and scouts to be on the lookout for possible hot spots.

In apples, apple maggot emergence is ongoing at the center with higher than usual numbers; this trend is also true in other areas of the state. Apple maggots have been active for at least four weeks now, egglaying is also ongoing and newly emerged flies will undergo a pre-oviposition period before these flies lay eggs.

Be particularly cautious of apple maggot this season due to high populations; apple maggot damage results in deformed, unsightly fruit. Lastly, as mentioned in previous reports, this damage can be difficult to differentiate from brown marmorated stink bug feeding damage.

Brown marmorated stink bug activity and nymphs have been reported in southern parts of the state, but we have not observed or had reports of brown marmorated stink bugs in the northwest region. Brown marmorated stink bug eggs are laid in masses usually on the undersides of leaves. First instar nymphs are black and red/orange and tend to remain on the clusters of eggs until they molt to the second instar. Second through fifth instar nymphs are black and red/pink and very mobile; white-and-black-banded markings on the legs and antennae of the brown marmorated stink bug become more pronounced as the nymphs grow to later instars.

Anecdotally, our colleagues in southern Michigan have noticed brown marmorated stink bugs on buckthorn, but brown marmorated stink bugs have hundreds of known alternate hosts where this pest could be present. Visit Stop BMSB for more information and pictures to help with identification.

San Jose scale flight is ongoing at the center with relatively low numbers in the single digits per trap. We have not observed peak flight at the center, but peak male flight has been reported in southwest Michigan with crawlers expected to emerge in the next couple of weeks in that area. We have received more reports of San Jose scale damage in apples in recent years and many growers were diligent with programs targeting first generation crawlers this season.