Northwest Lower Michigan fruit update
While our spring continues to advance slowly, growers must remain vigilant to conditions.
Nothing much has changed in the past week here in Northwest Michigan: we are still cool and wet. We are considerably behind our degree-day accumulations from our normal average. So far this season, we have accumulated 134 GDD base 42 and 40 GDD base 50, which are 100 and 60 GDD, respectively, behind the average.
Weather forecasts predicted a hard frost last evening (May 2), but for most of the evening and into the morning, temperatures remained above freezing in the region. Forecasts are predicting similar weather for the next 10 days with daytime temperatures in the 40s and 50s. Based on these predictions, we will only be at 202 GDD base 42 by 11 May.
We had rain on Tuesday, Wednesday and Thursday last week, but we have recorded no rainfall for the past four days. However, humidity levels have been relatively high, and we have had significant cloud cover for the last two days. Sunday brought high winds to the area.
Plant development remains slow across the region. A bit more green has started to show in apples and cherries, and plums and apricots are at bud burst. As ground has begun to dry out with the recent dry days, growers have been planting trees. Brush removal is also underway as tractors can move more easily throughout the orchards.
Apples. With the cool weather, it seems that things have ground to a halt in northwest Michigan orchards. Rain is in the forecast for the end of the week, bringing with it the potential for apple scab infections. Early season control with copper application may still be an option for some area growers (copper should not be applied past quarter inch green). Dormant copper applications also help manage the risk of fire blight by killing the fire blight bacteria as they reproduce and ooze from cankers that formed last season. Apple scab spore trapping during last week’s rain events captured very little ascospore discharge (one spore to be precise).
This early in the season and with the cold temperatures, it is likely that very few of the ascospores are mature and ready to be discharged. Based on work by Dr. Alan Jones, the scab model does not even begin accumulating degree days towards ascospore maturation until green tip in McIntosh, with an average of 450 DD32 required before 50 percent of the apple scab ascospores mature. This could be a long way off based on current conditions. Growers should be on the lookout for European red mite eggs and activity, too. Checking crevices in the bark and around buds are good ways to assess potential populations. European red mite eggs are bright red and relatively easy to spot with a hand lens.
Cherries. Things remain relatively quiet in cherry with development progressing slowly. Bacterial canker remains a concern as we head into more cool and rainy weather. Early copper sprays are the most common method of control for bacterial canker on cherry. Keep in mind that sweet cherry tissues are extremely sensitive to copper and the sprays must be accurately timed to reduce P. syringae inoculum without causing phytotoxicity.
If the trees are still in the dormant stage, two copper applications may be applied at one to two week intervals at a rate 1.2-2lbs of metallic copper with either one pint of spray oil per 100 gallons of water or 6-9 lbs of hydrated lime per acre. If the trees have broken dormancy and are in the pre-bloom stage (bud swell through white bud), copper rates should be reduced to 25-35% of the dormant rate. Up to two copper applications with a one week interval should be used at this time. In tart cherries, copper compounds can be used at the 1.2-2lb actual copper rate at bud burst with weekly repeated applications until late May.