It is unlikely that all hosts of ZYMV and WMV2 have been identified. CMV, WMV2 and ZYMV overwinter in biennial and perennial plants and are usually carried to new plantings by aphids. Within plantings, CMV is spread chiefly by aphids, but may also be spread by cucumber beetles. WMV2 and ZYMV are also spread by aphids. While these viruses can be transmitted in plant sap through mechanical wounding (i.e., harvesting knives), spread by this means is considered minor.

Applying insecticides to cucurbits to control these viruses has not been effective. However, growers should be aware of surrounding crops and weeds that may serve as aphid sources. Insecticide applications to surrounding crops that are serving as aphid sources may be helpful. Reflective mulches, plastic coverings, and oil sprays when used experimentally have delayed and reduced infections, but have not been used commercially because of cost and disposal problems of mulches and covering materials. Weed control in and around plantings may help reduce infections, but will likely be inadequate by itself. Known weed hosts of WMV2 include (but are not limited to) lambsquarter and shepherd's purse. Planting a border crop that is attractive to aphids but not a host to the viruses around a susceptible vine crop has not been evaluated in Michigan. In theory, the aphids would feed first on the border crop greatly diluting any virus that the aphid might be carrying before feeding on the susceptible vine crop. Although this practice may be helpful, it would not eliminate occurrence of the virus. Currently, use of resistant varieties is the most effective approach in managing these virus diseases and should be coupled with weed control.

Regional reports
1 -- Southwest
Ron Goldy

Weather
Temperatures for the period were near to below normal with highs ranging from 69°F to 83°F and lows from 56°F to 69°F. We’ve received 3.6 to 4 or more inches of rain in the past week. This brings the August total in the area to 8 to 10+ inches of rain. Recent rains have seriously hindered field activities and reduced fruit quality and they have given us 50+ hours of continual wetness beginning the morning of August 28.

Commodity reports
Harvest conditions are similar to last week with maturity slowing due to cooler temperatures and cloudy skies. Harvest is complete on many plantings and growers should be removing plastic soon.

Mites continue to be a problem in some tomato and pepper fields and are at levels where control measures may need to be taken. However, recent rains may have reduced the populations to below threshold levels.

Pumpkin fields continue to look good for this late in the season. With the late set fruit this year, growers need to protect leaves as much as possible so fruit continues to grow and does not get sunburned.

2 -- Grand Rapids Area
Amy Irish-Brown

4 -- Mason-Newaygo counties
Jim Breinling

5 -- Macomb, St. Clair and Lapeer counties
Hannah Stevens

Weather news
Jeff Andresen
Agricultural Meteorology
Geography

A slowly-moving upper air trough over the Great Lakes and Ohio Valley regions will bring a continued chance for scattered light showers during the next day or two over southern sections of Michigan, while central and northern sections of the state will remain variably cloudy and dry. Clockwise flow around an area of high pressure centered over Ontario will lead to steady and brisk northeast to easterly winds through Friday. Most of the state is expected to remain dry for the next several days. However, one significant forecast challenge will be the remnants of Tropical Storm Ernesto, which may end up somewhere in the eastern Great Lakes region by late in the weekend. Depending on the exact path of these remnants, rainfall may be a possibility again by Saturday or Sunday, especially across southeastern sections of the state.

Temperatures during the next few days will generally average about 2 to 4 degrees below the climatological normals with highs generally ranging from the upper 60s far north to the low or mid-70s south with lows falling to the low 40s far north to near 60 south.

Medium range forecast guidance suggests the gradual formation of an upper air trough across the Great Lakes region by next week, which could lead to a period of cool and unsettled weather over Michigan. The NOAA Climate Prediction Center 6-10 day and 8-14 day outlooks (covering September 4-8 and 6-12) both call for temperatures to range from below normal across the southern half of the state to near normal across the north. Precipitation during the 6-10 day time frame is forecast to range from near normal levels over northwestern sections of the state to above normal levels in the southeast. During the 8-14 day period, precipitation is expected to fall back to a range from below normal levels over western Upper Michigan to near normal levels elsewhere in the state.