West Central Michigan tree fruit update
Extended wetting conditions resulted in a first apple scab infection in the west central region of the state.
Weather and crop development
Last week’s weather conditions were very unsettled. There was a very wide range of temperatures for both highs and lows. High temperatures were from high 30’s to mid-60’s and lows were from low 30’s to low 40’s. On a top of the cool conditions, it was cloudy and rainy…not a pleasant week for people nor for the plants. Two weather fronts brought us the most significant rainfall so far this season. Forecasted frost for tonight (May 3) is raising the anxiety level in all of us. In terms of degree-day accumulation, Manistee and Mason counties including a “pocket area” around Hart are three weeks behind 30-year average while most of the Oceana County is two weeks behind normal.
Fruit trees are pushing forward with sap movement and green tissue expansion. Apples are from advanced quarter-inch green in late blooming varieties to half-inch and very early tight cluster depending on the variety. Pears are at green tip. Peaches are at bud burst/calyx green. Sweet cherries are from bud burst to tight cluster depending on variety. Tart cherries at bud burst. Apricots are starting to show first white. At this stage of bud development fruit trees will tolerate temperatures in 26-28 degree range without significant damage.
West Central Michigan growing degree day totals since March 1, 2011. As of Sunday, May 1.
|Location||DD42||DD45||DD50||Rain last week||Rain since April 1|
Pear psylla is flying through orchards. Sunny days have intensified their activity. Light deposits of European red mite eggs are present in many area orchards. Scale on plums and peaches have been found in a few blocks. No other insects have been spotted yet.
Almost 80 hours of wetting span even at cooler temperatures resulted in heavy apple scab infection period throughout the area. Frequent checking of rods with collected spores revealed that the heaviest spore discharge occurred at the front-end of the wetting event. The first set of rods produced an average count of 74 spores per rod. Second set of rods produced an average of 9 spores with the grand total for the event reaching 83 spores per rod. This pattern of spore discharge could be considered as favorable news: spore viability has its upper limit so even in these prolonged wetting events, we can have good control with the protectant coverage prior to the infection period followed by post infection coverage with materials with kick-back action … the “fine print” is that requires full coverage.
Growers are advised to be on the lookout for root rot and collar rot (Phytopthora sp.) this spring. The long-term weather forecast is indicating above normal precipitation favoring disease development. Another disease that is accentuated by a wet and cool spring is bacterial canker (Pseudomonas syringae). Orchards that sustained winter injury will particularly be prone to it.
Stone fruit is developing rapidly. Apricots are already showing some white buds and sweet cherries and Japanese plums are not too far behind. This is the time to get organized for bacterial canker/spur blight control action. The established method of control is to apply metallic copper with either lime or oil. Lime will reduce phytotoxic effect of copper on the young sweet cherry leaves. For the same reason, reduced rate of copper (0.5 to 0.7 lb/A) is recommended at this stage of development and beyond.
More information can be found posted at MSU Extension News for Agriculture website.