MSU Extension

Weather

Last week was warm with highs in the upper 80s and lows in the 50s and 60s. We continue to have heavy dews. Highs this week should be near 90 with increasing humidity. Lows are forecast in the 60s and 70s with a chance of showers most of the week. Many areas received rain last Thursday (Aug. 22). Totals from the region varied from under 0.2 inches to just under an inch. This warm rain was an infection period for most diseases.

Evapotranspiration for the week was about 0.17 inches per day and just over an inch for the week. With the warmer temperatures, the potential evapotranspiration for the week will increase to about 0.2 inches per day and the weekly total is forecast to be about an inch. Soils are drying out. We are almost two weeks behind the five-year average. Check your local weather station and conditions at Enviro-weather.

Southwest Michigan GDD summary from March 1 to August 25

 Tree fruit

Spotted winged Drosophila (SWD) continued to climb last week in southwest Michigan. We are catching SWD in all of our Michigan State University Extension monitoring traps. Trap numbers did fall for some traps and it seems the several weeks after harvest numbers fall because of lack of fruit, but many traps are catching hundreds of flies. The highest trap catch in Berrien County for a single weekly catch last week was 2,679. Berry growers should assume that SWD is available to attack their fruit.

Japanese beetles are becoming scarce. Brown marmorated stink bugs catches continue to be very low in southwest Michigan. Scout for this insect on field borders close to woods, especially close to water. The red spots on fruit due to the latest generation of San Jose scale crawlers should be showing up soon. Growers should check trees planted this year for evidence of water stress.

Peach harvest is moving rapidly with the ripening of later season varieties which seem to be bunching together. Varieties being harvested include Glowingstar, Cresthaven and PF24C Cold Hardy. The hot weather is bringing on some Captan fungicide-induced inking on the sun-exposed sides of some highly colored varieties. Quality continues to be good. A few varieties have noticeably bitter skin. Brown rot control programs and possibly insect control of spotted wing Drosophila will need to be ramped up as we approach harvest. Oriental fruit moth trap catches have climbed for several farms in the area.

Cherry growers should continue to protect against cherry leaf spot. Orchards are losing leaves in waves following various infections. Pruning can be done on mature trees, but should not be severe to avoid devigorating the trees. Post-harvest pruning should be concluded by early September to allow the wounds to harden.

Plum harvest of NY9 and Fortune is underway in area orchards. Stanley plum is not quite ready yet for most sites. Fruit size is suffering on sandy sites, especially where leaves are heavily tattered 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 Gala varieties is around the corner with Sept. 6 being the estimated harvest date for mid-Berrien County. 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 have increased for some orchards, but codling moth are generally low. Apple maggot fly catch has been reported for over a month in some area orchards. European red mites have built to noticeable levels in a few orchards.

In pears, Bartlett harvest began last week for some sites as fruit firmness has dropped below 10 pounds. Growers should monitor for Fabraea leaf and fruit spot and pear psylla activity. Pear fruit should also be protected against second generation codling moth.

Small fruit

In grapes, veraison is well underway in ’Concord’. The tentative date for the beginning of ‘Niagara’ harvest by National Grape is Sept. 13. Insect and disease wise, not much has changed since last week. Trap catches for adult grape berry moth averaged zero 16.5 last week in monitored vineyard blocks. The percent of grape berry moth-infested berries last week was 2 to 19 percent. Continue to check grape berry moth pressure on vineyard edges and woody borders to calculate percent infestation and determine 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.

For the Berrien Springs Enviro-weather station, we were at 2,009 GDD base 47 as of Monday (Aug. 26). The next generation of grape berry moth – beginning of fourth generation – is predicted for 2,430 GDD base 47. It is hard to say if that number will be reached before harvest.

Spotted winged Drosophila numbers in traps bordering vineyards and in other locations continue to climb. We will continue to monitor these sites and report on catches as harvest gets closer. In the last couple of years, very few SWD adults (about 5 percent of the total fruit fly larvae present) were reared out of grapes. The majority were other fruit flies. Bunch rots are increasing in wine grapes, especially those with tight clusters, such as ‘Pinot gris’. Levels of powdery and downy mildew are about the same as last week.

In blueberries, growers finished ‘Jersey’ and other varieties and are picking ‘Elliott’. Growers still need to protect against spotted winged Drosophila. Blueberry maggot is being trapped across the region and most SWD traps are catching flies. Growers who are not monitoring for these pests should be applying controls. Our trap catches in blueberries last week ranged from 40 to 60 flies per trap. Trap catches at the field edges are much higher with hundreds of flies per trap.

Rains can wash off protectant materials. See MSU entomologist Rufus Isaacs’ article “What are we learning about spotted wing Drosophila management in berries this season?” The MSU Spotted Wing Drosophila website has management tips and weekly reports on SWD trapping across the state.

In strawberries, new growth looks good in most renovated strawberry fields. Continue to protect the new leaves from potato leafhoppers to prevent this insect from stunting the growth. Everbearing strawberries are producing berries and should be protected from SWD. Infested fruit tend 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.

In brambles, blackberry and fall raspberry harvest continues. Spotted wing Drosophila is the most important pest to manage now. The Spotted Wing Drosophila Management Recommendations for Michigan Raspberry and Blackberry Growers has been updated. Growers should be monitoring their plantings for SWD and applying insecticides weekly. Be careful not to exceed the seasonal limits for insecticides and rotate modes of action.

SWD is an insect that prefers shady conditions. Be sure that your sprayer is properly calibrated to allow sprays to reach the interior of the canopy. Sanitation is the key for managing SWD. Our trap catches in and around brambles are very high. Frequent picking of ripe fruit and removal of overripe fruit is important to help reduce SWD populations. Look for and remove stray, overripe berries inside the canopy – you can often see a small cloud of flies hovering around overripe fruit that have been left on the bush. 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 tunnels at the Southwest Michigan Research and Extension Center have stabilized over the last week, but is still affecting fruit quality and causing a decline in the normal shelf life of the berries. Keep fruit refrigerated as soon as possible after picking and at the market to delay the development of larvae in berries. Freezing fruit immediately after picking will also stop larval development.

Two-spotted spider mite activity has increased recently, partly due to dry weather and partly due to the use of insecticides to control SWD. 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.