MSU Extension

Weather

Last week was cool. A cold front crossed the region Monday (Aug. 12) dropping rain and bringing cool temperatures. Highs were in the upper 60s Tuesday (Aug. 13) and lower 70s on Wednesday (Aug. 14). Lows dropped into the 40s all week long with heavy dews. Highs climbed back into the 80s by the weekend and much warmer temperatures are in store this week. Totals from Monday’s rain were about 2 inches.

Evapotranspiration (ET) is falling as the days get shorter and cooler. On sunny days in August, peak values are about 0.15 inches per day. On cloudy days, values are between 0.1 and 0.05 inches. Potential evapotranspiration for the week was about 0.9 inches. Areas south of I-94 have dry soils and some sandy sites have very dry soils, causing problems for young trees.

Temperatures this week will be in the upper 80s. There is a chance of rain mid-week. We are about a week behind the five-year average. Check your local weather station and conditions at Enviro-weather.

Southwest Michigan GDD summary from March 1 to Aug. 18

Tree fruit

Spotted winged drosophila (SWD) really jumped last week in southwest Michigan. We are catching SWD in almost all our Michigan State University Extension monitoring traps. Many traps are catching over 100 flies. Berry growers should assume that SWD is available to attack their fruit.

Japanese beetles continue to decline. Brown marmorated stink bugs catches have been very low in southwest Michigan, generally close to streams. Scout for this insect on field borders close to woods, especially close to water. San Jose scale can be found on fruit. New crawlers are expected to be out on or after Aug. 25. The window for sampling for foliar nutrient testing generally ends in mid-August. Honeybees have been feeding in clusters on ripe peach fruit.

Peach harvest of varieties such as Canadian Harmony, Allstar, PF17, Glowingstar, Coralstar and PF23 are underway in some area orchards. Quality is generally very good and demand has been keeping up with supplies. Brown rot, Rhizopus rot and peach scab are easy to find, but are easier to control with current dry conditions. Brown rot control programs and possibly insect control of SWD will need to be ramped up as we approach harvest. Oriental fruit moth trap catches have been steady at a relatively low level.

Cherry growers should continue to protect against cherry leaf spot. Pruning can be done on mature trees, but should not be severe to avoid devigorating the trees. Post-harvest pruning from now to early September will reduce bacterial canker infections that are favored by spring pruning under cool, wet conditions.

Plum harvest of Rubyqueen, Early Italian, Castleton and Fortune is underway in area orchards. Foliage looks tattered in sandy sites due to shot holes from earlier bacterial spot infections. Brown rot controls need to increase as fruit begins to color and ripen. Spotted wing Drosophila can be a problem, especially for fruit being picked relatively ripe for direct sales.

Apple harvest of Paulared, Gingergold and Zestar is underway. Red strain Gala varieties are coloring well, but do not yet show signs of starch conversion in maturity tests. The estimated harvest date for Gala for mid-Berrien County is Sept. 6. Growers should check the dates for applying Retain for stop drop control for the apple varieties they grow. Make sure you do not miss the application window – 30 days or less before anticipated harvest.

Sooty blotch and fly speck symptoms are present, but new infections are inhibited by current, dry conditions. Trap catches for oriental fruit moth and codling moth are generally low; however, a few sites are in their third week of high codling moth trap catch, indicating a strong flight at these sites. Apple maggot fly catch has been reported for four weeks in some area orchards. Growers who are participating in the Brazilian apple export program are reminded that the insecticides approved by this program as effective against maggots do not include many of the newer insecticides. White apple leafhoppers, European red mites, green apple aphids and wooly apple aphids have built to noticeable levels in a few orchards.

Pear growers should monitor for Fabraea leaf and fruit spot, and pear psylla activity. Pear fruit should be protected against second generation codling moth.

Small fruit

In grapes, veraison has begun in ’Concord.’ The tentative date for the beginning of ‘Niagara’ harvest by National Grape is Sept. 13. Trap catches for adult grape berry moth were low this week in monitored vineyards, averaging only two adult berry moths per trap. The percent of grape berry moth-infested berries this week dropped to 2 to 9 percent. Track grape berry moth pressure by checking 100 clusters on vineyard edges and woody borders and 100 clusters in the vineyard interior to determine the percent of infestation if grape berry moths are moving into the vineyard interior or remaining along the edges. The treatment threshold is 6 percent. Look for webbing on berry clusters and hollowed out berries.

Spotted wing Drosophila numbers in traps bordering vineyards have been in the range of about 175 to 260 flies per trap, but grapes are currently not at risk because the berries are too hard for the flies to penetrate. We will continue to monitor these sites and report on catches as harvest gets closer.

Bunch rots are showing up in wine grapes with tight clusters, such as ‘Pinot gris.’ Powdery mildew is appearing on interior leaves and rachises of ‘Concord’ with dense canopies of foliage. Fog and heavy morning dew have been present most of the week, providing good environmental conditions for downy mildew. Downy mildew can easily become very serious at this time of year. There is considerable downy mildew in the unsprayed sentinel plots we monitor.

Some blueberry growers are still picking Bluecrop. Most growers are finishing Jersey and other late varieties and general picking of Elliott has begun. Because of the large volumes of fruit this season, it seems the season is running a little behind normal.

Growers need to protect against blueberry maggots and SWD. Blueberry maggots are being trapped across the region and most SWD traps are catching flies. Larvae of both flies have been found in fruit in the field and also harvested fruit. Growers who are not monitoring for these pests should be applying controls. Our trap catches last week ranged from 130 to 250 flies per trap. Rains earlier in August may have led to the wash off of protectant materials and loss of control. SWD numbers often spike about two weeks after a gap in protection. Protectants should be reapplied after significant rains or irrigation. The MSU Spotted Wing Drosophila website has management tips and weekly reports on SWD trapping across the state.

Many growers have shortened their harvest interval to reduce the amount of ripe fruit in the field. Under these wet conditions, growers should also apply controls to suppress anthracnose and alternaria fruit rots.

New strawberry growth looks good in most renovated strawberry fields. Continue to protect the new leaves from potato leafhoppers to prevent this insect from stunting growth. Everbearing strawberries are producing berries and should be protected from SWD. Infested fruit tends to have a soft spot on one side and very small, white maggots may be present.

Most of the emphasis on insect pest management now is on SWD, but sap beetles can also cause damage to ripe fruit. Strawberry sap beetles are small, about 0.125 inches long, oval and brown. They have knobbed antennae.

Strawberry sap beetle adult. Photo credit: Cornell University

In brambles, blackberry and fall raspberry harvest is underway. Spotted wing Drosophila is the most important pest to manage now. The “SWD Management Recommendations for Michigan Raspberry and Blackberry Growers” has been updated. Growers should be monitoring their plantings for SWD and applying insecticides. Sanitation is very important for managing SWD. Our trap catches in and around brambles is very high. We had several SWD trap catches last week in brambles with hundreds of flies. Frequent picking of ripe fruit and removal of overripe fruit is important to help reduce SWD populations. One sign of SWD infestation in raspberries is a red staining on the receptacle when the raspberry is picked.

High tunnel fruit are also at risk. Trap catches and SWD activity in the high tunnel at the Southwest Michigan Research and Extension Center (SWMREC) have climbed over the last week. One result of the increased infestation of raspberry fruit is a marked decline in the shelf life of the berries.

The dry weather has brought an increase in two-spotted spider mite activity. Be aware that multiple applications of insecticides to control SWD can also lead to mite population explosions. Where possible, choose products that will not flare mites. Insecticides to control SWD in brambles and other insect problems should not be applied while bees are actively foraging.

Upcoming meetings

The final in-season grape IPM meeting will be at Lemon Creek Winery Aug. 27 from 6-8 p.m. Contact the Berrien County Extension Office at 269-944-4126 to register and for more information about the program. Registration is $15 and includes supper. Speakers will be Stan Howell, Rufus Isaacs and Annemiek Schilder. Please register by Aug. 23 so we can have an accurate count for supper.

A peach and plum variety showcase will be held at SWMREC Aug. 27 from 4-7 p.m. The meeting will include a picnic dinner hosted by Summit Sales. There is no charge for the meeting. For further information, contact Bill Shane at shane@msu.edu or 269-208-1652.