MSU Extension Fruit & Nuts

Weather report

This season continues to be warm and dry. Last weekend, we hit daytime highs in the 90s, and over the past weekend, we were slightly cooler in the mid-80s. The forecast is predicting continued warmth in the mid to high-80s. Conditions have also been humid. We have accumulated 1,681 growing degree-days (GDD) base 42 and 1,101 GDD base 50; we are currently ahead of our 28-year average of 1,579 GDD base 42 and 959 base 50.

The most pressing weather situation is the lack of moisture. The region has dried out and grass has almost seemed to brown overnight. Soils are dry and dry quickly following the little amounts of rainfall that we have received recently. Trees with a large crop load look particularly drought stressed and fruit size is small as a result of lack of moisture and hot weather. Young trees are also showing signs of drought stress.

The last substantial rainfall in the region was July 1 where the Northwest Michigan Horticulture Research Center’s Enviroweather station recorded 0.33 inch of rainfall. Rainfall totals at the Northwest Michigan Horticulture Research Center for June and thus far into July are 2.2 inches of rain. According to Jeff Andresen, MSU agricultural meteorologist and climate specialist, longer-term forecasts are predicting cooler and wetter weather around the third week of July. However, we will keep our eye on this forecast, as forecasts change quickly and frequently. There were brief rain showers recorded in East Leland (0.13 inch), Kewadin (0.05 inch), Old Mission (0.03 inch) and Northport (0.01 inch) last night, July 9.

Growth stages at the Northwest Michigan Horticulture Research Center as of July 9, 2018

• Bartlett Pear – 27 millimeter fruit
• Potomac Pear – 34 millimeter fruit
• Mac – 42 millimeter fruit
• Gala – 34 millimeter fruit
• Red Delicious – 37 millimeter fruit
• HoneyCrisp – 42 millimeter fruit
• Montmorency – 21 millimeter fruit
• Balaton – 20 millimeter fruit
• Hedelfingen – 19 millimeter fruit
• Gold – 17 millimeter fruit
• Napolean – 16 millimeter fruit
• Riesling – Buckshot berries

Crop report

Sweet cherry harvest has begun in the north. Again, fruit is on the smaller size as a result of the lack of moisture and likely a shortened growing season. With little rainfall, there is very little cracking in most sweet cherry blocks. Some brown rot is evident in bird-damaged fruit, but overall this disease level is low in the region. Some blocks of sweet cherries have a good crop load, and some orchards look like they have a very large crop.

Many tart cherries also have a big crop load on them. Tart cherries seem to be ripening quickly and there may be some logistical challenges to harvest tart and sweet cherries this season. Many growers will be relying on ethephon to manage the harvest timing. Lighten up ethephon rates if the hot weather continues.

Apples are sizing well. Many growers are pleased with their thinning efforts. There is some hand-thinning underway.

Strawberry harvest has finished.

Pest report

The weather has continued to remain dry and warm over the last week with several windy days, and these conditions have posed few challenges in terms of disease and pest management. This stretch of dry weather has been welcomed as it has provided growers with opportunities to maintain adequate coverage particularly for insect pests.

In cherries, we have received reports of phytotoxicity showing up in blocks where the product Syllit or copper products were used for cherry leaf spot management. Most areas have not had a leaf spot infection period since early last week; infections were possible during last night’s rain in East Leland, Northport and Old Mission.

Overall, disease incidence remains low with a few isolated cases of orchards with moderate infections. We have continued to find low levels of American brown rot in fruit clusters and overall incidence in the region remains low; drier weather has not been conducive for rapid development of American brown rot. However, dry weather has been favorable for powdery mildew in orchards with ongoing mildew infections.

Spotted wing Drosophila (SWD) numbers in traps have increased dramatically since our last regional report. At the station, we found a total of three flies two weeks ago and 180 flies last week. Regional trap numbers also increased from zeros two weeks ago, up to 90 flies last week. Additionally, we found a larva in untreated fruit at the station on Friday, July 6.

Maintaining coverage will be critical from now through harvest. Conditions have been dry, which has helped growers keep fruit protected from possible SWD egglaying. However, some pyrethroid materials could break down quickly in the recent hot, sunny weather. Avoid stretching intervals too far between sprays of these materials.

San Jose scale crawlers are still active in sweet cherries and apples at the station. However, many sweet cherry blocks are fast approaching harvest and insecticide pre-harvest intervals will limit control options. We will trap for the second flight of scale males that typically occurs in late summer (August); we will also monitor for the second emergence of crawlers. Some growers with heavy scale infestations in sweet cherry blocks have considered making a post-harvest application to target the late summer/early fall crawlers when they emerge.

Twospotted spider mite numbers have been building in tart cherry blocks at the station. This season’s hot and dry weather has been particularly conducive for mites.

Obliquebanded leafroller flight is ongoing with a decrease in activity at the station over the last two weeks. We have received reports of low numbers of obliquebanded leafroller larvae in commercial orchards.

Cherry fruit fly has not been detected at the station this season, but we have received reports that this pest was detected in our region last week.

In apples, fire blight disease progress has slowed recently. Previously infected shoots have dried and are noticeable in orchards, but we have not received reports of new ooze production.

The first flight of codling moth is ongoing and we found an average of three moths per trap in apples at the station. Two weeks ago, there was a lull in our trap counts, likely as a result of cooler evening temperatures that inhibited moth activity; with recent warmer evening temperature, activity has picked up. As mentioned in last week’s report, identifying distinct codling moth generations has been difficult due to relatively low pressure at the station. Based on our May 28 biofix, we have reached 798 GDD base 50, and second generation flight typically occurs 1,060 GDD base 50 after biofix.

We have not detected apple maggot at this time; apple maggots have been detected in other regions of the state, and anecdotally, numbers seem to be high this season in those areas. After emergence, apple maggot flies undergo a seven- to-10-day feeding period prior to egglaying, and this seven- to-10-day period is an optimal management timeframe.

We have not detected brown marmorated stink bug in orchards in the northwest region this season. In more southerly regions (north of Grand Rapids, Michigan), brown marmorated stink bug exploratory feeding has been observed in apples. Be on the lookout for this pest this season. At this time of the year, colleagues in the Grand Rapids area have observed that this pest seems to be particularly attracted to common buckthorn, an invasive shrubby plant. These insects attack many crop and non-crop hosts including several tree fruits. Although we did not find the pest in orchards last season, we observed feeding damage on apples in a commercial block that was suspect of brown marmorated stink bug.