Southwest Michigan fruit update – July 23, 2019

Mark Longstroth<$authorEmail>, William Shane<shane@msu.edu> and Michael Reinke<reinkem3@msu.edu>, Michigan State University Extension - July 23, 2019

Spotted wing Drosophila numbers jumped in the last week. Almost all our traps are catching flies in the double digits. Protect berries now.

Golden Delicious apples — Apples are about 2 inches in diameter. Protect against apple maggot, codling moth, oriental fruit moth and obliquebanded leafroller, as these pests will be more abundant in the next few weeks. Photo by Mark Longstroth, MSU Extension.

Weather

Last week’s weather was very hot and humid. High temperatures were in the upper 80s and 90s. Lows were in the 70s, with a dew point in the 70s. Thunderstorms and showers moved across the region Tuesday, July 16, and Thursday, July 18. A cold front moved across Michigan over the weekend, bringing strong winds and heavy rains in some areas. Rainfall for the week ranged from 0.6 to 4.2 inches. The regional average was 1.5 inches. Rainfall totals for the season are 14 to 20 inches across the region since April 1.

The forecast for this week starts with cooler and drier air, with highs in the 70’s and lows around 60. We will return to hot and humid conditions by the weekend. Last week’s rains returned soil moisture to adequate levels in many areas. With the hot temperatures, we accumulated heat units quickly last week, about 250 growing degree days (GDD) base 42 and 189 GDD base 50.

Southwest Michigan GDD summary from March 1 – July 21, 2019
Station	GDD 42 F	GDD 45 F	GDD 50 F
Benton Harbor (SWMREC)	2,119	1,813	1,363
Lawton (Lawton)	2,163	1,855	1,399
Fennville (TNRC)	1,952	1,659	1,230
Average for the SW region	2,132	1,836	1,375
Accumulation last week	250	229	194

Check out the animated weather forecasts from Jeff Andresen under the Weather tab on the Michigan State University Extension Fruit & Nuts Page. Articles and other regional reports can be found at the Fruit News page.

Tree fruit

Tree decline due to winter damage became more obvious in last week’s heat. First catch and biofix for first generation oriental fruit moth was May 6 (165 GGD base 45) at the Trevor Nichols Research Center. We are now at 1,800 GDD past the peak on the second generation. Trap catch for oriental fruit moth jumped sharply in several orchards last week. The third generation will begin to emerge after 1,900 GDD base 45 and peak at about 2,200 to 2,400 GDD.

First trap catch and biofix of obliquebanded leafroller was June 14, and larvae are feeding on the leaves. Scout for obliquebanded leafroller larvae in the growing shoot tips. We expect the summer generation flight to begin soon. Brown marmorated stink bug activity has been increasing, but summer adults are not expected to show up until approximately mid-August. Japanese beetle adults are becoming easier to find. Potato leafhopper are feeding and causing hopper burn on sensitive plants. The summer flight of male San Jose scale exploded with the heat last week. Estimated first crawlers will be 375 GDD51 after biofix or approximately two weeks from now.

Early-season peach varieties such as Harrow Diamond, Earlystar and Veeblush are being harvested for those places having fruit. Oriental fruit moth is the primary insect pest at this time and we are transitioning from the second into the third generation of this pest. Phomopsis twig dieback is becoming obvious on some trees. Bacterial spot infected leaves are dropping.

Cherry harvest has ended in southwest Michigan. Some cherry trees look pretty rough with partial defoliation and some yellowing leaves. This leaf loss was due to multiple factors, cherry leaf spot, bacterial canker and preharvest ethephon sprays. Most of the cherry leaf spot-infected leaves have fallen, but the return to wet, humid conditions will bring this disease back. Post-harvest chlorothalonil applications help reduce late season cherry leaf spot buildup without risk of resistance buildup. Cherry leaves are always susceptible to leaf spot, so management is needed to maintain a healthy leaf canopy during the entire season.

Plum varieties Shiro and Vibrant are ready for picking in some sites. The plum crop varies considerably from variety to variety and site to site. Potential insect pests now are obliquebanded leafroller, codling moth and cherry and apple maggot. Spotted wing Drosophila (SWD) is generally a problem of ripe plums.

Green apple aphids — Green apple aphid numbers are building. Now is the time to decide if beneficial insects such as ladybugs and lacewings will keep their numbers down. Photo by Mark Longstroth, MSU Extension.

Early-season apple varieties such as Lodi and Transparent are being spot picked. Include calcium in your cover sprays to reduce bitter pit. Fire blight infections are relatively rare. The Enviroweather sooty blotch and flyspeck model indicates fungicides to reduce these diseases may be necessary. The second generation of codling moth should be emerging now and we expect peak flight at about 1,600 GDD base 50 and peak egglaying at 1,700 GDD. Larvae of codling moth, oriental fruit moth and obliquebanded leafroller are threats to developing fruit. All three of these pests will be flying and laying eggs in the next few weeks.

Apple maggot flies catches have increased slightly over the last week, but we expect many more after last week’s rains. Yellow sticky traps are used to track emergence of this fly and red sticky sphere traps plus attractive scent lures are used to monitor egg laying. Potato leafhopper injury is fairly common on actively growing shoots. Apple aphid colonies are building on these shoots as well.

Pear terminal growth is slowing, reducing the attractiveness of foliage to pear psylla. The second generation codling moth adults should be emerging now and this generation does attack pears as they soften before harvest.

Small fruit

Jesery fruit — There is already ripe fruit in Jersey blueberries and spotted wing Drosophila (SWD) numbers are high. Protect ripe fruit as soon as SWD appears and maintain protection through harvest. Photo by Mark Longstroth, MSU Extension.

Spotted wing Drosophila (SWD) numbers jumped in many traps last week and we are catching them in almost all our traps. There are many wild fruits such as black raspberry, mulberry and bush honeysuckle, as well as berry crops available. Remember, under these conditions it only takes about 10 days for the fly to go from egg to egglaying adult. We expect SWD numbers to really explode in the next few weeks. Monitor this pest and protect fruit as it ripens. Last week’s hot humid weather did not seem to slow this pest down and the heat may have made insecticides degrade quickly. See “Plan to change when dealing with spotted wing Drosophila” from MSU Extension for more information.

Potato leafhoppers are common, protect sensitive crops.

Grapes are at berry touch and cluster tightening. Use this opportunity to get a fungicide active on botrytis into the interior of the fruit cluster to reduce the disease later in the season. Scouting has found most diseases are established in grapes; black rot on the berries, downy mildew and powdery mildew on leaves and fruit, and phomopsis on the leaves and stems can be found in vineyards now.

Grape berry moth sprays should have been applied now to control the larvae attacking the fruit. See the “MSU vineyard IPM scouting report – July 17, 2019” for more information.

Blueberry harvest continues. Growers are harvesting Bluecrop and there is ripe fruit in Jersey. The primary concern is controlling SWD. SWD numbers are increasing rapidly. Almost all our SWD traps are catching flies, so assume they are out in good numbers and protect your fruit. Sprays should be applied as soon as fruit starts to turn blue in the field. We have been dealing with this pest for almost 10 years and I put my thoughts down in 2017—see “Plan to change when dealing with spotted wing Drosophila.” Mummy berry and shoot collapse due to phomopsis canker are relatively common.

Strawberry field post renovation — This strawberry field has been renovated. The plants were mowed short, the rows narrowed with a rototiller and herbicides were applied followed by irrigation to bring up a new crop of healthy leaves. The new leaves need to be protected from insects and diseases. Photo by Mark Longstroth, MSU Extension.

Strawberries are putting out new leaves after renovation. The fields should be irrigated to get the plants off to a good start. After the leaves emerge, treat with a material to control potato leafhopper to prevent this pest from stunting the plants.

Raspberry harvest continues. Japanese beetles are out and feeding on raspberry leaves. Raspberries and blackberries are very attractive to SWD and fruit needs to be protected from this pest. Potato leafhopper are also feeding on raspberries and some susceptible varieties respond with crinkling and rolling up of young leaves.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).