MSU Extension

Weather

As I travel across the East Michigan region, there are wide swings of soil moisture supplies, from very dry to standing water in wet spots in fields. The majority of the region has now moved into the dry to very dry range of soil moisture. In these areas, growers have begun to irrigate, especially newly planted tree and small fruits. There are a few narrow bands where soils are finally dry enough, allowing growers to get back into fields to finish planting. What a season in terms of wide swings of rainfall across the region.

With the warmth of last week, our season has moved back to normal if one were to look at growing degree day (GDD) totals. However, it appears that we will be at least a week to 10 days late for the start of strawberry harvest.

East Michigan GDD totals for March 1 to June 2, 2014

Tree fruits

Apples near Flint, Michigan, are mostly 10 to 12 millimeters. We have had a good amount of growth in apples in the last week; they finally look much more normal. Many growers applied thinners in the last week, some now wishing they had either reduced their rates or even not applied any thinner at all. Growers continue to assess crop load in apples, but it is even more variable this week than last. Most growers have found that a good amount of fruitlets have shucked off in the last week. Many to a point where growers are disappointed with their crop load on the majority of varieties of apples and are starting to use terms like “shortest apple crop in 10 years” – excluding 2012, of course. The only two varieties that appear to require more thinning at most farms are Ida Red and Golden Delicious. It is unclear at this time what caused so much fruit to drop in the last week, but most growers suspect poor pollination and weather-related problems.

Two weeks ago I reported apple trees beginning to collapse or having very small leaves and being much further behind other apple trees. I have had many replies form apple growers saying they are seeing some of this collapse at their farm as well. It now appears that most of these trees will not survive. At first it appeared this collapse was related to rootstock and variety, but now that I am seeing the problem more widespread, this does not seem to be the case. The problem is not consistent from farm-to-farm or even block-to-block. For example, the same variety, rootstock and tree age combination may be severely affected on one part of the farm and appears to be unaffected on other parts of the same farm.

What appears to be the common thread for these collapsing trees in the farms that I have visited is where trees had some sort of stress in 2013 that they suffered winter injury, they are now collapsing. The stress could be caused by several things, including: crop load in 2013, dry soils last season, poor weed control, low fertility in the tree, leaf drop last season due to apple scab, topography or trees in lower areas more severely affected, and many other possibilities. In most cases, growers report that it was hard for them to see evidence of this stress last season.

The winter injury is to the tree trunk, just above the graft union. The cambium in the trunk is dark brown. More time is still required to determine the entire impact of this problem, but in the meantime, Michigan State University Extension advises keeping an eye out for this problem at your farm.

Most growers applied a petal fall spray last week and are close to putting on their first cover spray for the season. While I have no new apple insects to report this week, I am continuing g to find very high codling moth trap catch in the last week, especially in non-pheromone disrupted apple blocks. Very high numbers of plum curculio and apple curculio are being seen this week as well as San Jose scale males in traps. Several more growers are finding good numbers of European red mites and just a few are finding two-spotted spider mites.

New diseases to report in the last week include fire blight-infected branches just beginning to curl over and cedar apple rust lesions on apple leaves. We continue to have apple scab spore release with each rain event and spore numbers continue to decline. I am finding a few more apple scab lesions on leaf tops and bottoms at a few farms. Primary apple scab is still on in East Michigan, with the model indicating that we are just over the 1,000 GDD base 32 total to indicate that 100 percent of the ascospores are at maturity. However, just because the spores are natural does not mean that they have all been released. Once we get to that 100 percent point, then we generally need a few rains to discharge all the remaining spores. We are very near the end of primary, but staying covered for the next rain event is still highly recommended, just in case there are a few spores that need to be released.

Pears are 10 to 13 millimeters with a good crop coming along. Pear psylla adults continue to be very active with our warm days, with all stages now being present.

Peaches continue to look tough with trees that were under stress last season not leafing out at all. It appears that there is extensive winter damage in peaches this season, comparable to or now even worse than cold damage that occurred in the winter of 1994. I have not seen one peach flower this season, so there will not be any peach crop in the region this season. In the last three weeks or so, I am seeing a few more leaves emerging from the most vigorous shoots in the tops of younger and generally healthier trees. Growers can begin a light pruning in these trees, being sure not to remove any wood with leaves on it. In other words, trees need all the leaves they can have in order to foster healing for next year.

Sweet cherries are 10 to 13 millimeters with most growers reporting having 20 percent of a crop at best. Larger scaffold limbs on stressed sweet cherry trees are starting to collapse form winter injury. Here again as is the case in peaches, the cambium is dark brown from the winter injury.

Tart cherries have a wide range of fruit sizes this week, with most being 9 to 11 millimeters in size. Most growers have 40 to 60 percent of a crop of tart cherries this season.

Plums are mostly 9 to 15 millimeters for European types with many fruit remaining at 5 millimeters that will most likely drop. There are many doubles this season. Japanese plums are 12 to 16 millimeters in size with a very light crop on most trees.

Small fruits

Grapes have grown a great deal in the last week, now with 12- to 16-inch shots with flower clusters exposed for Concord and Niagara varieties. Wine grapes have extensive cane death in most varieties; it is too early to prune these back, as I hope to see some new buds break in the next few weeks.

Strawberries remain at full bloom for some varieties and others have thimble-sized fruit. Beginning of harvest is about 10 to 14 days away at most farms, which is later than normal. Most strawberry growers have applied one fungicide to control gray mold with another being needed fairly soon. Strawberry clippers and angular leaf spot disease seem to be under control at most farms. Growers need to do a thorough job of scouting at this time to check for the angular water-soaked translucent lesions on leaf surfaces. A copper application may be needed at this time to control angular leaf spot.

Raspberries are continuing to show signs of winter injury, especially summer red and black raspberries, and blackberries. Some varieties look normal in terms of growth, now these are beginning to bloom. Some growers have mowed off summer raspberry varieties because of lack of growth due to winter injury. These varieties will not have a crop this season.

This winter injury is variety specific. Canes of summer fruiting types have a significant amount of cambium browning, indicating potential winter injury. Fall raspberries continue to emerge from the ground and are now 16 to 18inches in length. New canes of blackberries continue to emerge from the soil with the tallest at 16 to 20 inches in length. All of the canes from last season are dead to the ground. Raspberry sawfly damage to leaves has been seen at a few farms.

Blueberries are mostly at late full bloom for Jersey and petal fall to small green fruit for most varieties. Small twigs continue to die in many blueberry varieties due to winter injury.