Northwest Michigan fruit update – June 4, 2019
The weather has been warmer and drier, which has been a relief for disease management. We anticipate insect pest activity to pick up in the coming week with the anticipated warmer weather.
The region has been dry for the past six days. We had rainfall last Tuesday and Wednesday (May 28-29), and that two day total was over 1.25” of rain. The drier weather also brought a few days of warmer temperatures. We had a high temperature of 71 degrees Fahrenheit on May 29. Friday, May 31, we almost reached a daytime high of 80 degrees F. Temperatures cooled over the weekend again, and we have been hovering around the mid 50s and low 60s in recent days.
We have accumulated 470 GDD base 42 and 205 GDD base 50. We are still a good two weeks behind our average; our 30-year average are 691.8 GDD base 42 and 357.4 GDD base 50. We did have a bit of a low temperature scare on the evening/morning of June 3; the NWMHRC Enviroweather station recorded a low of 39.2 degrees F. The Bear Lake Enviroweather station was the only one in the region recording lows below 32 degrees F, and 31.1 degrees F was the lowest reading in Bear Lake was between 5 and 6 a.m.
MSU ag meteorologist Jeff Andresen gave his agricultural weather forecast on today’s MSU Fruit Team call, and he predicts the next best chance of rain to be tomorrow, June 5. We should have a few days of dry and potential rain will move in again early next week and will likely arrive on Tuesday, June 10. Andresen’s 6-10 day short term forecasts are suggesting temperatures will be closer to normal than in the past week. However, after the 10 day, he predicts temperatures will cool again and be cooler than our normal temperatures. Lastly, he predicts that our 14-day deficit, or the two weeks behind our average, will continue for the remainder of the growing season, indicating that we will not make up this deficit with warm temperatures into the future.
Bloom has finally ended in sweet cherry, and fruit are coming out of the shuck. If the temperatures warm in the coming days, these fruits will be susceptible to plum curculio oviposition. Most bees have been removed from sweet cherry blocks, and first insecticide sprays are being applied. Tarts here at the station are in late petal fall and bees have been removed from these blocks as well. We are still well into apple bloom throughout the region and bloom is variable among the different varieties and within the area on the tree.
Relatively drier weather over the last week has been a relief for growers and tree fruit disease management programs. Temperatures also have remained cool, and these conditions were welcomed for growers concerned with fire blight management in pome fruit. The forecast is calling for possible wet weather tonight and into tomorrow followed by another stretch of drier, warmer weather through the end of the week. Stormy conditions could be a concern for fire blight and susceptible tissue may need to be recovered if we receive significant rainfall. There is a possibility of some wet weather early next week, but it is still too early to tell whether the northern region will receive rain. With warmer temperatures, we are anticipating an uptick in pest activity.
Primary apple scab is ongoing across the region and the state at this time. Biofix for the NWMHRC is April 22 and according to the scab model on Enviroweather, we are approaching 100% spore maturity and ~80% spore discharge; the end of primary apple scab season ends when spore discharge reaches 100%. According to RIMpro, we had very high spore discharge numbers following recent rains at the end of May and beginning of June.
These model outputs match what we would expect in terms of spore discharge in relation to the disease cycle and crop development (i.e. high spore discharge numbers during bloom timing).
The risk for fire blight infections has been relatively low with the cooler, drier weather. The Bear Lake area reported some soft, slushy hail-like precipitation, but this weather did not cause damage that could have been a concern for trauma blight conditions. Warmer weather is predicted for the later part of this week, and as a result, epiphytic infection potential (EIP) values are exceeding the 70 mark that indicates the need for management if there is a potential for wet weather.
Any open or and newly open blossoms will need to be protected from possible infections if the warmer temperatures come and we receive wet weather. We remind growers that while four applications of Kasumin per year are allowable by label, there must be a different material applied between the second and third spray. Additionally, to minimize resistance development, only three applications of Kasumin are suggested per season. Due to low risk for fire blight thus far this season, “running out” of management tools for fire blight will not likely be a significant/widespread concern.
Black stem borer activity has been detected at the NWMRHC, East Leland, on Old Mission Peninsula, in the Central Lake area, and in the Williamsburg/Yuba area. Trap catches remain generally low at this time with a slight uptick in some areas. However, we have observed new entrance holes in weak trees already this season. Many orchards are still in bloom, and we do not suggest managing this pest during bloom, particularly if bees are still in the orchard. Trees showing stress symptoms and signs of black stem borer infestation later this season should be removed and burned to prevent the beetles from emerging and re-infesting in the orchard.
Two codling moths were detected in a trap in East Leland on Sunday, June 2. We have not yet detected codling moth at the station this season. A biofix is set for the first date of catch after two consecutive moth catches in a trap; hence, we have not set a biofix for this pest yet. Warmer evening temperatures around 60+ degrees F later this week, could facilitate more codling moth activity. Weather plays a significant role in codling moth behavior– temperatures below 60 degrees F in the evening and rainy weather inhibit codling moth flight and mating whereas 60+ degrees F around dusk are conducive for these behaviors.
In cherries, the last official cherry leaf spot infection period at the station was on May 25, but there have been a few close calls this season with Enviroweather’s progress toward infection outputs in the 90-100 percent range. Microclimates where leaf tissue remained wet for a longer period of time could have resulted in an infection, and therefore, maintaining coverage for this disease has been a good strategy. We have been fortunate to have relief from wet weather recently which will be suboptimal for leaf spot infections.
Plum curculio are active with reports of ovipositional scars on apricots. Warm conditions later this week could facilitate a flush of plum curculio activity. Most tart cherries are still in the shuck, but sweet cherries are exposed and could be vulnerable to plum curculio activity.
American plum borers and green fruit worm catches remain low. We have observed some lepidopteran feeding damage and frass on cherry fruit and terminals, but overall incidence has been low.
Spotted wing Drosophila traps have been deployed, but we have not detected this pest in northwest Michigan and sweet cherry fruit are still too green to be susceptible to oviposition at this time. Spotted wing drosophila has been detected in southwest Michigan.