MSU Extension

Weather report

As we head into the month of July, we look back at variable weather conditions for June 2014. We have seen temperatures swings from fairly high temperatures in the 80s down to daytime highs in the 50s and 60s, high humidity, and varying amounts of rainfall. These weather conditions would seem to be conducive for disease development, but orchards are looking clean across the region. Last week, we experienced our first full week of summer-like temperatures. Daytime highs were up into the 70s and 80s, and nighttime temperatures fell into the 60s. These temperatures were coupled with higher than normal humidity, which added to the summer-like feel to the week. We have accumulated 1,247 growing degree days (GDD) base 42 and 751 GDD base 50. We are only 100 GDD base 42 and 50 GDD base 50 behind our average accumulations.

Although conditions were humid last week, little rainfall was recorded at the Northwest Michigan Horticulture Research Center (NWMHRC). The NWMHRC recorded 0.02 inches on June 24, 0.03 inches on June 29, 0.17 inches on June 30, and 0.06 inches of rain yesterday on June 30. At the NWMHRC, the overall rainfall total for the month of June is 2.39 inches.

Crop report

Riesling and Chardonnay wine grape vines are in bloom to early fruit set at this time. Some early hybrid cultivars, like Frontenac and Brianna, already have berries approaching pea-size. Sucker growth has been very rapid. On vines with only a few live suckers at the base, shoot size is already too large, on the path to be poor-quality bull canes for 2015. There are still a lot of stunted shoots higher in the canopy of vinifera varieties.

The critical period for protecting fruit from powdery mildew will last for another two to three weeks. I have not seen powdery mildew infections on unsprayed “sentinel” vines at the research center. Rose chafers continue to feed on leaves and clusters, but their numbers have dropped off quickly this year. Adult potato leafhoppers are now in the area and nymphs may appear soon. The adult moths of the hornworm caterpillars are now flying, so small larvae may appear in the next couple of weeks.

Saskatoons are beginning to ripen with much red fruit showing in the research center plot. Berries that are very advanced in color can be found in the fruit clusters – these have been injured by the feeding by the larvae of apple curculio, saskatoon sawflies or leafrollers. Most of the injured fruit inspected were hollow inside and the offending larva had vacated the berry.

Saskatoon-juniper rust infections of fruit are now in the sporulation stage. It is getting late for treatments to defend against further fruit infections. Although Abound and Pristine have a zero-day pre-harvest interval, they do not have sufficient back-action to stop active infections which will continue to show new berry symptoms from now through harvest.

As mentioned above, orchards appear to be clean across the region. Growers have been diligent about keeping new tissue covered, particularly as we have had spotty rainfall and high humidity. Sweet cherries are coloring, and early varieties appear red at this time. Birds have been infesting early varieties of sweet cherries, and bird damage is evident in blocks where fruit is substantially colored. The sweet cherry crop looks good across the region, and growers remain committed to keeping this crop in good shape as the demand for sweet cherries, particularly canners, is high this season. We have seen some cracked fruit in early ripening varieties here at the NWMHRC, but overall reports of cracking are low.

Tart cherries are also starting to color, and many growers estimate to begin harvest during the third week of July. The tart cherry crop is variable, and at the Guestimate and the CIAB meeting, the estimate of the tart cherry crop was variable among meeting attendees. The estimate ranged from 110 million pounds up to 125 million pounds. For the Federal Marketing Order (FMO) formula, the CIAB board decided to use the USDA estimate for Northwest Michigan at 118 million pounds. Please see the attached documents on tart cherry estimates and the results from the CIAB meeting last week.

According to Perry Hedin, Executive Director of the CIAB, the following letter was distributed after the CIAB meeting in Grand Rapids, Michigan:

“At yesterday’s meeting, the CIAB met and to review various elements from the industry’s positions and to project the preliminary percentages under the OSF. In doing this, the CIAB considered the 2014 crop estimates, reviewed the 2013-14 sales data and considered the carry-over of product from 2013 to 2014.

As you will see in the attachment, the crop estimates from the USDA, the MFFPA Guesstimate and the CIAB members were consistent with each other. The OSF sets as the USDA as the default estimate to use in the formulation of preliminary percentages. Given the similarity in the estimates, the USDA’s estimate of 264 million pounds was used by the CIAB.

Sales of tart cherry products in 2013-14 were very good at 222 million pounds. This volume of sales following the 2012 crop failure was received as very good news. The sales were substantially better following the 2012 crop failure than were seen following the 2002 crop failure.

The reported carry-in of free inventories into the current crop year was 81.1 million pounds. This is based upon the actual reported inventories held at the end of May 2014. Considering all of these factors and applying them to the OSF, the CIAB set the preliminary free percentage at 90 percent and the restriction percentage at 10 percent.

You will see two adjustments on the attached OSF calculation sheet. As it did last year, the CIAB adjusted the amount of cherries it projected were needed for sales. This adjustment was for 52 million pounds which, when added to the three year average of sales, yields a target sales volume of 250 million. The CIAB also adjusted the desired carry-out figure from the default of 20 million to 50 million pounds with a 30 million pound adjustment in the OSF.

As you all know, these figures are preliminary. The board reconvenes in September to review the OSF using actual production.”

Growers and processors were optimistic about the crop at last week’s meeting.

The apple crop is also looking good at this time. Most growers are pleased with their thinning efforts, but some hand-thinning may take place in orchards where fruit was difficult to thin. Apples are sizing well and jumped at least 10 millimeters since last week. Growers are breathing a sigh of relief to end the primary scab season this week.

Strawberry harvest is underway in Northwest Michigan. Size of the berries is good, and relatively cool temperatures for the remainder of the week will extend the harvest season. Hot temperatures are expected again on Sunday and Monday, July 6-7.

Pest report

Again, cherry orchards are looking clean in terms of disease symptoms so far this season. However, Michigan State University Extension has received reports of a few isolated incidences of powdery mildew on tart cherries, and some cherry leaf spot lesions are beginning to appear on new leaves. Very low or no infection at this point is a very good sign because a healthy tree canopy will help ripen fruit which is particularly important this year as cherry harvest may be later or longer than usual in some areas. Growers who have leaf spot infection now will need to maintain good spray coverage to prevent the spread of conidia to new tissue.

The warm and wet conditions have been worrisome for American brown rot infection and we have received more reports of American brown rot sporulating on sweet cherries injured by canker, birds, insects, etc. We found American brown rot sporulating on sweet cherries (variety Sams) at the station this week. Managing American brown rot can be problematic when cherries begin accumulating sugars, and growers should be diligent about controlling this disease.

Last week a handful of obliquebanded leafrollers were found in traps in cherry blocks. Numbers remain low this week – we found seven moths per trap. As mentioned last week, a consistent catch of 20 or more moths per trap for two to three weeks usually indicates that obliquebanded leafrollers may be a problem, and low-catch of less than 20 moths per flight period generally indicates a non-problematic pest density.

We have not detected cherry fruit flies on traps at the research station and have not received reports of cherry fruit flies on traps elsewhere in the region. However, a single cherry fruit fly was observed on a leaf at the research station on June 16. Sweet cherry varieties are well on their way to ripening and will be susceptible to cherry fruit fly damage when these pests emerge. In some areas, tart cherries that are ripening will also need to be protected from cherry fruit fly oviposition.

Spotted wing Drosophila (SWD) are emerging in Northwest Michigan. The first SWD in Northwest Michigan was captured Monday, June 30, in Grand Traverse County; there was a single female in the trap. SWD can oviposit into ripening fruit and growers will need to be diligent about controlling this pest to prevent larvae in fruit.

All three borer species, lesser peach tree borer, greater peach tree borer and American plum borer, were found in low numbers at the station this week. According to our trap data, peak borer emergence was around June 16. Birds have moved into early ripening sweet cherry blocks.

Most apple orchards are also very clean of diseases so far this season; we have received less than a handful of reports of apple scab lesions. Growers who have scab lesions will need to continue their scab program past primary to ensure scab-free fruit at harvest. Rain on Sunday, June 29, triggered the release of apple scab spores that were likely the last of the ascospores from last year’s infected tissue. An average of one scab spore per spore rod was found following rain on Sunday morning. Apple scab spores were not found on spore rods following rain on Monday night, June 30. Thus, we are calling an end to primary apple scab infection.

Apple trees damaged from winter injury are continuing to decline in orchards. Earlier this season, many of the trees that are now dying had pushed leaves and were using stored resources to grow. These winter-injured trees have now used up those resources and are collapsing.

No codling moths were caught at the station this week. However, codling moth adults are still active in the region and the number of codling moth found in traps has been variable from orchard to orchard. Codling moth adults fly at dusk and prefer warm temperatures for flight. We had a few warm nights over the weekend, some of which were also windy which could have inhibited codling moth flight in some areas. In orchards where GDDs have reached about 250 GDD base 50 F since codling moth biofix, larvae maybe hatching at this time.

Obliquebanded leafroller numbers in apples at the station are up from last week at 10.5 moths per trap; these numbers are still too low to set biofix. Green apple aphids have been active in the last few weeks and are feeding on new growth or terminal ends of shoots in orchards throughout the region. 

Dr. Rothwell's work is funded in part by MSU's AgBioResearch.