Northwest Michigan fruit regional report – May 19, 2015
Cool and dry conditions this week are not conducive for disease infections and will slow pest development.
The weather continues to change things up, almost on a daily basis. Last week, we had warm and seasonal weather conditions in the mid-50s and 60s. However, over the weekend, daytime temperatures rose to meet summer-like conditions. We were in the mid-70s to low 80s on Saturday, Sunday and Monday, May 16-18. On Monday evening, temperatures dropped to a low of 35 degrees Fahrenheit and today’s temperatures are not expected to be above the low 40s. Unfortunately, forecasts are predicting cold overnight temperatures in the low 30s for this evening, in particular in lower sites and outside the northwest Michigan fruit belt.
We have accumulated 438 growing degree days (GDD) base 42 and 211 GDD base 50. On Friday, May 15, we received 0.35 inches of rain, and we received a similar amount on Sunday, May 17, at the Northwest Michigan Horticulture Research Center (NWMHRC); Sunday’s rain fell fast and lasted under one hour. The remainder of the week is expected to be cool and dry.
In grapes, we are now at the point where the full extent of our winter kill of vinifera buds is evident. Buds that have not swelled by now are not likely to, so what you see is what you are going to get. There may be some development of latent buds on older wood as the season progresses.
At the research center vineyard there are very few live buds or shoot growth on vinifera varieties above 12-18 inches over the ground, clearly indicating where the snow cover line was. Commercial blocks are in the same condition, with differences in the live/dead line due to snow cover patterns. We have seen vineyards with live shoots up along the fruiting wire, but I fear these are exceptions.
In the newer hybrids at the center, LaCrescent is ahead of all others, getting to the 4-inch shoot stage over the weekend. Two years of harsh cold winters has taken a toll on the less cold-hardy of the hybrids. Chambourcin, Brianna, Corot Noir and an unnamed New York selection are looking very bad.
We have seen just a scattering of injury from climbing cutworms, far below significant levels.
Saskatoons are past full bloom and into petal fall and fruit set at most sites, but there is still a lot of open flowers which could attract pollinators, so be cautious about using insecticides for a few more days. Insect activity has been very light at the research center planting. We have received pictures of some entomosporium leafspot symptoms from one commercial site.
All tree fruit bloom seems to be overlapping this season, likely as a result of the starts and stops to our hot and cold weather. Most of the apples, cherries and pears are somewhere between later bloom and into petal fall.
Pollination is a concern this season as we have had some great pollinating weather for bee flight, but these warm conditions were followed by a few cool days in a row. If the bees have successfully accomplished their jobs, we hope temperatures were favorable to allow pollen tube growth down to the ovule to complete fertilization. As cherries come out of the shuck and apple fruitlets begin to size, we will have a better estimate about crop size.
Past and potentially future temperatures below freezing will also impact the fruit set and yields this season. We do have some spotty damage to tart cherries from past freeze events, likely from the low 20s on April 4 and 5, but most blocks still have the potential to set a full crop. Some areas across the region also had cold overnight temperatures last week, May 13, which may have impacted lower fruit sites. Planting is winding down and most growers are concentrating on early season disease control.
As mentioned previously, we received rain early in the morning Friday, May 15, and had hoped we would not receive additional rain that would trigger disease infection periods. However, more rain came Friday evening, which lead to a long wetting period that lasted through Saturday morning, May 16, and resulted in apple scab infection periods across the region. The research station’s biofix or “green tip” on McIntosh for primary apple scab is April 20 and based on this biofix, 69 percent of scab ascospores are mature and 35 percent of these ascospores have discharged at this time. The primary scab period ends when 100 percent of ascospores have been discharged, and at least .01 inches of rain is needed to soak overwintering leaves to initiate spore discharge.
In some northwest region areas, up to 0.33 inches of rain fell in a short period of time on Sunday, and this rain should have triggered spore discharge. Fortunately, there were no scab infection periods reported for areas near Benzonia, Elk Rapids, Northport and the NWMHRC because the wetting event was brief (about three hours). However, scab infection periods were reported for East Leland, Eastport, Kewadin and Old Mission following Sunday’s rain event. The current forecast is predicted to be dry for the remainder of the week with a chance of rain this weekend.
The Michigan State University Enviro-weather Maryblyt model reported high risks for fire blight blossom infection Sunday, May 17, in the Bear Lake and Benzonia areas. Moderate to high infection risks (75<EIP>100) were reported in Eastport, Elk Rapids, Kewadin and the NWMHRC Enviro-weather stations, and the risk of blossom infection was low to moderate (50<EIP>75) in East Leland, Northport and Old Mission. Average temperatures in the coming week are predicted to be cooler and as a result, the model is currently predicting the risk of fire blight infection will be low this week.
The long wetting period over Friday-Saturday also triggered cherry leaf spot infections throughout the region. Infection periods also occurred beginning overnight Sunday, May 17, into Monday, May 18. Again, because Sunday’s wetting period was brief in areas near Bear Lake, Benzonia and the NWMHRC, the cherry leaf spot model on Enviro-weather did not report a cherry leaf spot infection period for these areas.
Obliquebanded leafroller and green fruitworm larvae are active and some minimal flower bud feeding damage has been reported to Michigan State University Extension. Some northwest Michigan obliquebanded leafroller populations may have resistance to organophosphate (OP) insecticides and due to cross-resistance with OPs, the pyrethroid insecticide class may not be effective for control of obliquebanded leafrollers. American plum borer moths are active in low densities (about five per trap) in cherries at the research station. Spotted tentiform leafminers are still flying and no oriental fruit moths or codling moths have been detected at the research station at this time.