MSU Extension

Weather

Warmer day and night temperatures during the last week have continued to move our season back toward normal for growing degree day (GDD) totals. A few of our Michigan State University Enviro-weather stations have now cracked the GDD base 42 totals into the 1,000s. As a result of these warner temperatures, tree fruits have put on a great deal of new leaf and shoot growth in the last week. The exception here is winter-injured peach trees, which are continuing to produce poor growth and have larger scaffold limbs continuing to collapse.

Soils in most of the region are running on the dry side. Growers have been irrigating newly planted tree and small fruit blocks on a regular basis this past week, and even well-established plantings are requiring supplemental irrigation. Strawberry growers need to monitor soil moisture supplies closely as the smaller developing fruits can suffer and ripen before the cells enlarge, causing a significant loss of yield.

East Michigan GDD totals for March 1 to June 9, 2014

Tree fruits

Apples in the southern parts of the region are 24 to 29 millimeters, just under 1-1.25 inches, and in the Flint, Michigan area are mostly 18 to 20 millimeters. The thinning window is closed in the southern and mid-part of the region. Fruits are starting to differentiate in size with fruit that are set continuing to size and smaller fruit that will most likely drop are no longer growing, and most being around 10 millimeters in size. Growers are continuing to access crop load in apples with many growers disappointed with their crop load on the majority of varieties of apples. The only two varieties that appear to be heavy at most farms are Ida Red and Golden Delicious. We have had a good amount of growth in apples in the last two weeks.

Three weeks ago I reported younger apple trees beginning to collapse or having very small leaves and being much further behind other apple trees. In new developments since late last week, I am beginning to see larger, well-established trees with larger lower scaffold limbs starting to wilt, collapse and appear to be dying. It almost appears as if a contact herbicide, like Gramoxone, was applied with an orchard sprayer with only the lower nozzles turned on. I would expect the upper parts of these trees to collapse in a matter of time. It now appears that most of these trees will not survive.

At first, it appeared this collapse was related to the rootstock and variety, but now that I am seeing the problem more widespread, this does not seem to be the case. The problem of apples collapsing 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 effected 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 trees that had some sort of stress in 2013 are suffering from winter injury and 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 (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, keep an eye out for this problem at your farm.

Potato leafhopper numbers are quickly building in some apple blocks, and are the only new insect pest to report in apples this week. A few blocks are starting to see some hopper burn from this pest. Many apple growers are finding some plum curculio or apple curculio damage on fruit, mainly on the outside edges of blocks. Leafroller damage from several species has also caused a fair amount of damage in many apple blocks. Codling moth and oriental fruit moth trap catch has dropped off in the last week. The timing for codling moth cover sprays is quickly approaching for growers who biofixed around May 26, especially in non-pheromone disrupted apple blocks.

Very high numbers of San Jose scale males continue to be caught in traps, with no crawlers being seen. Where the aphids are this season is the question I have been asked many times during the past few weeks. It appears that the extremely cold temperatures of this past winter have greatly reduced the population. Good predator numbers are being found in many apple blocks in the past week.

No new diseases have been reported in apples this past week, with fire blight-infected branches being seen at just a few farms and cedar apple rust lesions on apple leaves also at just a few farms. We continued to have light or low numbers of apple scab spore release with the rain event on Sunday morning, June 8; however, the rain was so light that it was not a good test to check for the end of primary apple scab season. I am finding a few more apple scab lesions on leaf tops and bottoms at just a few farms.

Primary apple scab is still on in East Michigan with the model indicating that we are at 100 percent of the ascospores being mature. Just because the spores are natural does not mean 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 apple scab season, but staying covered for the next rain event is still highly recommended by Michigan State University Extension.

Pears are 18 to 21 millimeters with a good crop coming along on most varieties. Pear psylla adults continue to be very active with our warm days, with all stages now being present.

Peaches continue to look rough, 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. 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 18 to 20 millimeters, with most growers reporting having 20 percent of a crop at best. Larger scaffold limbs on stressed sweet cherry trees are continuing to collapse from winter injury. Here again is the case in peaches; the cambium is dark brown from the winter injury.

Tart cherries are mostly 10 to 12 millimeters. Most growers have 40 to 60 percent of a crop of tart cherries this season.

Plums are mostly 14 to 16 millimeters for European types with a good amount of fruit drop in the last week. Japanese plums are 17 to 20 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 16-inch shoots 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.

Strawberry harvest is just beginning at farms in the southern part of our region. Farms in the Flint, Michigan area are hoping to have enough ripe fruit to begin harvest late this week or over the weekend. I am concerned that many farms have not been applying enough irrigation in the past week to help size fruit, especially fruit that is still small and green. In these fruit, cells need to enlarge a great deal in order to be a good size when ripe. My concern is that growers may get two good pickings, and then berry size will quickly diminish.

Strawberry clipper feeding damage has been very high at a few farms, worse than I have ever seen it. The damage is mainly close to woodlots and on the outside edges of fields. It is too late to control them as the damage was done in the last two weeks and clippers have now completed their lifecycle for the season. I have had two farms where strawberry plants have begun to collapse just as berries are ripening. The cause of this plant wilting and collapse is yet to be determined, but I suspect winter injury.

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 now in full 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 18 to 22 inches in length. New canes of blackberries continue to emerge from the soil, with the tallest 24 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 small green fruit for most varieties. Small twigs continue to die in many blueberry varieties due to winter injury. This damage is variety specific, and is severe is some cases.