MSU Extension

Weather report

The weather continues to be warm and dry across the region. Daytime temperatures reached into the 90s yesterday, July 27, and we will continue to be warm throughout the week. Conditions are extremely dry, and we could use a good rain. There is a 50 percent chance of rain tomorrow, July 29. The last measurable rain events at the Northwest Michigan Horticulture Research Center (NWMHRC) were July 13 and 14, where we received just under 0.25 inches of rain. Thus far this season, we have accumulated 1,618 growing degree days (GDD) base 42 degrees Fahrenheit and 974 GDD base 50 F.

Crop report       

Warm temperatures have allowed for some very vigorous growth of established or irrigated grape vines, but young vineyards without a well-established root system are likely to be suffering from drought stress if they are not irrigated. The progress of shoot growth of vinifera varieties is very encouraging – a fine recovery in progress. Berries are enlarging in hybrid blocks, with some early varieties approaching berry touch.

Powdery mildew is the only threat we have been experiencing during dry weather. So far, we have seen very little of it in the area. We are still in the critical control period for protecting fruit clusters from this disease. Insect activity has been light, but the timing is about right for the first generation of grape berry moths to be laying eggs. Vineyards with a history of grape berry moth problems should be scouted carefully for the presence of eggs on berries or cluster stems.

The 26th annual Viticulture Field Day and Steak Cookout will be held at the Southwest Michigan Research and Extension Center in Benton Harbor, Michigan, July 29. Informational sessions and the equipment show start at 9 a.m. and the day finishes with the ever-popular steak cookout.

Tart cherry harvest is in full swing this week. Fruit quality seems to be holding up even with this heat. Overall fruit size seems to be a bit on the smaller size, especially on trees with a good crop load. Despite the winds we had over a week ago, little wind whip or other mechanical damage is noticeable in tart cherries.

Most sweet cherries have been harvested except for a few orchards in the far north.

Apples continue to size and frost rings are evident in some blocks from the May 20 frost event.

Pest report

Cherry fruit fly activity is ongoing throughout the region and we have found cherry fruit fly larvae in cherries that were left hanging after harvest. Cherry fruit fly numbers continue to be high in some orchards and growers are thinking about targeting cherry fruit flies post-harvest to knock back the population for next season.

Spotted wing Drosophila (SWD) are also active and SWD catches are rising quickly in the northwest. We are running SWD efficacy trials this season and last week; we started to see SWD larvae in untreated cherries. Fortunately, many growers have been protecting from SWD infestation for several weeks, and Michigan State University Extension encourages growers to continue protecting blocks that have not yet been harvested to prevent SWD larvae in fruit.

Obliquebanded leafroller adult activity is ongoing and catches at the station are the highest we have seen this season, a high of 42 moths per trap. Obliquebanded leafroller larvae are also active; while these larvae are small, they are visible and can be found on terminals at this time.

For the second week in a row, apple maggot adults have been observed on ammonium-baited sticky traps, and we found a total of nine apple maggots at the station this week. The number of codling moths are lower this week with only one adult found in our traps at the station. Second flight of spotted tentiform leafminer adults is ongoing with an average of 293 spotted tentiform leafminers per trap.

Apple growers are continuing aphid and mite management programs, and because many non-crop plants are blooming in orchards at this time, we encourage growers to review the MSU Extension Bulletin, “Minimizing Pesticide Risk to Bees in Fruit Crops,” and consider incorporating practices to protect the pollinators that are currently active in orchards. A table of SWD adult catches can be found below.

The northwest has been very fortunate that conditions dried up in time for tart cherry harvest, leaving little opportunity for American brown rot development as well as inhibiting the spread of cherry leaf spot. After cherry shakers move through orchard blocks, there are few leaves left on some trees that were hit harder by disease and virus this season. Trees with significant defoliation now will be more susceptible to decline or death over the winter.

We have received reports of a “second leaf drop” due to virus and phytotoxicity. Viruses tend to impact individual trees rather than entire blocks and typically are not uniform across blocks. Unfortunately, there is no cure for virus and trees that are infected will continue to harbor the virus with which it is infected. In one orchard, we suspect some trees are infected with cherry green ring mottle virus. Cherry green ring mottle virus was also found in northwest Michigan tart cherry orchards in 2010 and 2012, and symptoms of this virus are usually expressed in late June to mid-July. The main symptom of the infection is bright yellow leaves with circular green blotches. These infected leaves can be easily removed from trees during shaking at harvest, or will defoliate naturally. In 2010, defoliation approached 40-50 percent of the leaves on each affected tree. We do not regularly observe this disease as most of our trees are certified virus-free. Leaves infected with cherry green ring mottle virus are similar to those infected with the cherry yellows virus, except the green spots within the yellow leaf are in a ring pattern.