Northwest Lower Michigan fruit uptdate
Warmer temperatures bring an increase in crop development and a wary eye on pests.
The past week saw cool temperatures, mostly in the 50s and 60s for daytime highs. Nighttime temperatures remained chilly. However, Sunday (May 8) and Monday brought warmer temperatures and daytime highs reached into the low 70s. Overall, we have accumulated 195GDD base 42 and 68GDD base 50, which are still behind our 21-year averages. We recorded rainfall in the area, and precipitation is expected to continue throughout Tuesday and Wednesday. Hail was reported in the region.
With the recent warm temperatures, crop development has picked up in the last few days. We are starting to see white in sweet cherries and green in apples. Apricots are now in bloom, and depending where they are in the region, they range from first to full bloom. Growers have been spraying orchards for early season diseases, and planting continues across the region. Growers are anxious for the season to get moving along.
Apples. Green apple aphid nymphs were observed this week on opening buds. There was also evidence of two-spotted spider mite activity, with webbing and cast skins leftover from last year, which is a good reminder to keep an eye out for European red mite, rust mite and two-spotted spider mite this season. Refer to the article Control Options for Mites in Fruit Crops for more information on management.
With the scattered precipitation forecast for this week, apple scab control should be a priority. Despite the dry weather over the past week, ascospores on last year’s leaves continue to mature on orchard floors, and a proportion of these spores will likely be discharged during this next rain event. A preventative scab program is critical with the recent discovery of fungicide resistant scab isolates identified in Michigan apple orchards. Preventing scab infection at green tip helps delay the start of the secondary disease cycle until after the period of maximum susceptibility and leaf expansion (around bloom) has passed. Apple tissue should be kept covered with protectant fungicide applications. Early in the season when fruit scab is not a concern and temperatures are cooler, Scala and Vanguard are good options to tank mix with EBDCs for scab control. As we move into warmer weather and the risk of fruit scab increases, growers should be considering second generation sterol inhibitors (Indar and Inspire Super) or captan tank mixed with EBDCs.
Cherries. As we approach bloom, European brown rot is of concern to many area growers, particularly on susceptible European-type varieties. Indar applications for European brown rot should be applied with two applications: the first at white bud and a second at bloom are recommended on susceptible varieties such as Balaton and Meteor. We have occasionally observed this rot on Montmorency under cool and wet conditions.
For American brown rot control, sterol inhibitors (Indar, Rally, Orbit, or Elite) or Rovral sprays may be used. Rovral may not be used after petal fall and is a good option prior to petal fall as it is a different mode of action. Spray programs for the blossom blight phase of American brown rot are initiated at 10 to 20 percent bloom. Infection rarely occurs at white bud, but if there is a large amount of inoculum from last year and a prolonged wetting period occurs during temperatures above 60°F, the maximum rate of Indar should be applied.
Green fruitworm moths were caught in the plum borer traps this week. Immature larvae of the green fruitworm feed on flower buds and new foliage, but have not yet been observed. Mature larvae feed on blossoms, developing fruit and leaves. Early feeding injury often causes fruit to abort. Fruit remaining on the tree after feeding exhibit deep holes sealed over with corky scar tissue.