MSU Extension

Weather report

Wet weather seems to be the norm so far this season, and there is more rain in the forecast for the remainder of the week. This wet weather has presented challenges for keeping good spray coverage—the rain is likely washing off materials, and these continued rainy conditions have prevented growers from making applications.

Thankfully, the wet weather has been accompanied with cooler temperatures, which will temporarily slowdown disease progress. Yesterday’s daytime high (June 26) capped out at almost 57 degrees Fahrenheit. June 27-29 are expected to warm up into the 70s and 80s, but then cool down again over the weekend.

We have accumulated 1,242 growing degree-days (GDD) base 42 and 706 GDD base 50. The amounts of rainfall vary across the different regions of northwest Michigan, but all stations have been recording wet conditions. At the Northwest Michigan Horticultural Research Center, we received 0.65 inch of rainfall on June 22, and just bit of moisture on June 23. The rain started up again on June 25 and lasted into June 26. Over these two days, the center received 0.48 inch.

2017 growth stages as of June 26, 2017

• Bartlett Pear – 24 millimeter fruit
• Potomac Pear – 27 millimeter fruit
• McIntosh – 40 millimeter fruit
• Gala – 30 millimeter fruit
• Red Delicious – 35 millimeter fruit
• HoneyCrisp – 32 millimeter fruit
• Montmorency – 15 millimeter fruit
• Balaton – 15 millimeter fruit
• Hedelfingen – 19 millimeter fruit
• Gold – 17 millimeter fruit
• Napoleon – 24 millimeter fruit
• Riesling – First bloom

Crop report

Most varieties of wine grapes are at 50-100 percent bloom in the Grand Traverse region. Foliage condition looks great in most sites despite the many rainy days we have experienced.

We’re still expecting to see some downy mildew, but have not found any. Powdery mildew may actually be less of a threat this year because frequent drenching rains can actually wash the spores off of the plants before they can infect tissues. Nonetheless, we are entering the prime window of time for protecting clusters from powdery mildew infections and spray coverage should be maintained.

No new insects have arrived since last week. Rose chafers should be done with their adult activity soon.

Early varieties of sweet cherries are coloring up at the Northwest Michigan Horticulture Research Center. We are testing cherries for firmness and brix for a spotted wing Drosophila choice and no-choice experiment, and our Ulsters are at 14 degrees brix as of June 23. The birds have noticed the ripening fruit, and bird pecks are not hard find in our sweet cherry blocks at the Northwest Michigan Horticulture Research Center. In particular, we have heard reports of bird problems with the variety Black Pearl.

Cracked fruit as a result of all of this rainfall has also been a concern. Cracked fruit and fruit damaged by birds are highly susceptible to American brown rot. Additionally, we observed last season that spotted wing Drosophila are opportunists, and they will take advantage of cracked fruit for egg laying. Lastly, our currently ongoing spotted wing Drosophila tests in the lab have indicated that most sweet cherries are susceptible to spotted wing Drosophila egglaying at this time. Ethephon will likely go on many blocks of sweet cherries toward the end of the week.

Tart cherries are also beginning to color. Tarts almost seem to be ripening or at least coloring faster than sweet cherries in some cases. Brix for tart cherries at the Northwest Michigan Horticulture Research Center are at 9 degrees. The size of the tart cherry crop across northern Michigan is estimated to be 130 million pounds. Please see document from the Cherry Industry Administrative Board in the FruitNet newsletter regarding set aside (about26 percent of the 2017 crop).

Apples are sizing nicely. Some growers are hand-thinning apples where they still had too many fruit after thinning.

Strawberry harvest is ongoing.

The saskatoon crop is large at most sites that have mature bushes. The earliest berries are beginning to color up, and harvest may begin in about a week at the most advanced sites. We’re expecting entomosporium leafspot and saskatoon-juniper rust to be troublesome this year due to the frequent wetting periods we have experienced. Growers will need to stay on top of these diseases with fungicides that have a short pre-harvest interval since harvest is approaching.

Pest report

As mentioned previously, keeping fruit protected from pests and diseases has been a challenge in the last two weeks with few decent days to get sprays on in the orchard. Although the region hasn’t been as wet in the last week compared with two weeks ago, we have had a few wet days and there is a chance for more wet weather in the coming week. Growers have been weighing options of when to put on covers and whether reapplications will be needed during this wet weather. Overall, fruit development is moving quickly and some areas are fast approaching sweet cherry harvest timing; these growers are planning their late season pest and disease management programs.

Spotted wing Drosophila numbers are on the rise in our regional trapping network, and many orchards have fruit that are straw-colored or riper and susceptible to spotted wing Drosophila egg-laying at this time. The Northwest Michigan Horticulture Research Center’s estimated tart cherry harvest date is July 20 meaning that we have about 24 days (or at least three to four full cover insecticide applications) that tarts will need to be protected from spotted wing Drosophila this year.

As growers are developing their late-season pest management programs, pest management costs are a key consideration as well as material and program efficacy for target pests, insecticide label use restrictions and guidelines, resistance development and concerns for possible mite outbreaks.

Data from our previous efficacy trials have shown that under high spotted wing Drosophila population pressure, full cover applications every seven days resulted in the fewest detectable spotted wing Drosophila compared with full covers at 10-day intervals and alternate row applications at seven or 10-day intervals. Although full covers every seven days is not feasible for all growers, the data suggest that intervals will minimize the chance of spotted wing Drosophila infested fruit, particularly if weaker chemistries are used or if wet weather washes away residues.

With the possibility of three or more sprays for spotted wing Drosophila before harvest, MSU Extension encourages growers to rotate insecticide modes to minimize the possibility of resistance development. Many of the efficacious materials for spotted wing Drosophila are in the pyrethroid class and there is a possibility for cross-resistance among pyrethroid and organophosphate (for example, phosmet/Imidan) insecticides.

Additionally, there are several generic and pre-mixes available, so carefully read labels for the maximum amount of active ingredient applied per season, number of allowable sprays, etc. The Northwest Michigan Horticulture Research Center will be coordinating effort with the MSU fruit team to begin monitoring for spotted wing Drosophila insecticide resistance this season.

Planning when to use different materials to target the mid- to late-season pest complex can help to maximize spray efficiency. For example, many of the pyrethroids that are efficacious for spotted wing Drosophila are also effective against plum curculio and cherry fruit fly, but efficacy data collected in cherries has shown that imidacloprid, the traditional chemistry used against cherry fruit fly, has weak activity against spotted wing Drosophila.

Therefore, we do not recommend imidacloprid as a standalone material to target both spotted wing Drosophila and cherry fruit fly. Cherry fruit flies have not yet been detected on traps at the station this season.

Obliquebanded leafroller activity is ongoing at the station (we have accumulated 291 GDD base 42 since biofix June 13), and some orchards in the region may have populations that warrant treatment before harvest for obliquebanded leafroller larvae; egg hatch typically begins 400-450 GDD base 42 after biofix. The spinosad insecticide Delegate is only rated good for spotted wing Drosophila, but it provides excellent obliquebanded leafroller control; the newer diamide product, Exirel, is rated excellent for spotted wing Drosophila and obliquebanded leafroller.

Lastly, growers should be cautious of possible mite outbreaks in orchards where multiple applications of pyrethroids have been made. The product Danitol is a pyrethroid-miticide premix insecticide with a short pre-harvest interval. As we approach harvest, we remind growers to discuss pest management options with processors.

Wet and warm weather has been optimal for disease development and growers have continued to diligently manage diseases in these conditions. Brown rot started to get a foothold in some blocks last week and this disease will continue to be a concern as fruit ripen and increase in sugar content. As mentioned above, fruit damaged by birds and cracked fruit are especially susceptible to brown rot.

Cherry leaf spot has also been a concern. Many growers have been optimistic about slowing the progress of cherry leaf spot lesions from early infections, but we have received reports that new lesions are showing up. Indar is an excellent material for brown rot, but we have seen reduced efficacy of Indar in recent years. Growers planning to use Indar should include a material for cherry leaf spot as Indar only provides fair control of the leaf spot fungus.

Additionally, growers planning to use the increased rate of 12 fluid ounces per acre will need to obtain the Special Local Need 24(c) label for Indar. The SDHI fungicides (Merivon, Luna Sensation) are excellent materials for both brown rot and cherry leaf spot, and an SDHI is typically suggested as the last fungicide spray prior to harvest. Previous data have shown that an SDHI applied to tart cherry trees at pre-harvest timing provided the longest residual cherry leaf spot control compared with other leaf spot materials.

In apples, primary apple scab is over in the northwest region and new fire blight symptoms became more prevalent late last week. Because fire blight incidence is low, growers are pruning out infected terminals. Sanitize pruners between cuts to minimize the spread of bacteria; a 10 percent bleach solution is an effective sanitizer. The fungal pathogen, nectria, has also been reported in the region.

Codling moth catches are down at the station this week (Table 1) and based on degree-day accumulations, larvae should be active at this time.

Catalpa trees came into bloom over the weekend and bloom of this species has been associated with San Jose scale crawler activity and timing sprays for crawlers. Determining when crawlers are active has been challenging because monitoring protocols are not very successful. We will continue to monitor for the second generation of male flight that typically occurs in late August (Table 1).

July “First Friday” Grape Meeting

The next First Friday Grape Meeting is July 14 (the second Friday in July, in order to avoid the Cherry Festival) at Ten Hands Vineyard on Old Mission Peninsula, located on Mission Road just south of the Old Mission General Store.

The topic of this meeting is “Foliar Fertilization Programs in the Vineyard” and will be led by Craig Cunningham of Cunningham Viticulture Services. Cunningham has utilized foliar programs in vineyards for more than 10 years, including Ten Hands Vineyard, owned by Tom Petzold.

We will also walk the vineyard for informal scouting, discussing issues as they come up. Tom will answer questions on his vineyard practices (composting, compost tea use, growing grass under the vines, etc.) to round out the session.