West Michigan tree fruit update – June 13, 2017

Hot weather requires irrigation for tree fruits.

Fruit development continues and all tree fruits are beginning to size with many apples now in the 18 to 25 millimeter stage. June drop is occurring. The lack of rainfall since early May is starting to be noticeable in turf and on sandy soils. Most orchards with irrigation started their systems a couple of weeks ago. Avoid weed spraying and other spraying until after the 90 degree Fahrenheit days are over. Be especially careful of anything that contains oils or nutritionals as they could cause fruit russet issues in 90 F plus temperatures.

Disease update

Pressure from diseases in tree fruits has been minimal due to lack of rainfall. All primary apple scab ascospores should be mature and nearly all have been discharged. Rainfall amounts have been very light in the past two weeks which might not have been adequate to release the last of the primary spores. My gut tells me primary scab is over for the season, but my head tells me I need one more good rain to be sure.

It’s becoming easier to find scab on the 5th, 6th and 7th leaves on growing shoots. These would be from the long infection period that began on April 29 and lasted for 60 to 70 hours of wetting, depending on Michigan State University Enviroweather station location. Before you consider reducing fungicide rates, be very sure you are free from primary scab.

There might still be bloom present on newly planted trees that would be open to fire blight infection this week if we get rain. Be on the watch for stormy weather which might lead to trauma blight situations and spray as warranted. I would recommend avoiding anything that would damage trees and potentially lead to fire blight this week – the high temperatures, high relative humidity and threat for rain every day could lead to creating your own trauma event. Just hold off on feathering young trees and other orchards tasks that could damage trees. If you have blocks with active blight, remove the strikes as you see them but stay out of those blocks for pruning or any other activity that potentially injures trees unnecessarily.

Occasionally some powdery mildew can be found in apple susceptible apple cultivars but, overall, mildew infections continue to be low. The weather this week is perfect for mildew, so protect susceptible varieties as needed as long as terminal growth continues.

Insect update

Plum curculio adult activity should be coming to an end, but keep an eye on known hot spots.     

Codling Moth Trap numbers continue in varying levels – we should be past 50 percent emergence for first generation moths. A regional biofix was set for May 15 (250 DD50) and 404 degree days base 50 have been accumulated. First larvae starting emerging last week – we should be at 25 to 30 percent egg hatch now and sprays are important in blocks over the threshold of an accumulation of five moths per trap. Cover sprays need to be maintained well for the next three to four weeks to get through first generation codling moth egg hatch.

Obliquebanded leafroller adults in traps have had steady flight for about a week. A regional biofix was set for June 8 (1017 DD42) with 162 degree days accumulated since then. No management is needed in this stage. Early egg hatch is probably at least a week away and blocks with high pressure will need to consider management then. Low pressure blocks can scout for larvae and spray.

San Jose scale male scale flight has ended. Crawlers should be found at any time. A regional biofix was set for May 21 (318 DD50) with 310 degree days base 50 since then with is the right timing for the crawlers to show up. Crawler emergence estimated:  June 13 to 17 – cover sprays will be needed in blocks where San Jose scale was an issue on fruit in 2016.

First generation oriental fruit moth egg hatch should be ended. Second generation adult flight is just beginning and we are in between generations where cover sprays are less crucial for 10 to 14 days. A regional biofix was set for April 28 (307 DD45) and 654 degree days have accumulated since. This is a good time to change out lures for second generation flight

All stages of European red mite continue to be found. Predator mites are also present. This very hot and dry weather could push mite development so keep an eye on mites. The threshold for June is 2.5 mites per leaf.

Various species of aphids can be found in all tree fruits but overall numbers seem to be low this season. Green apple aphids are starting to build in some blocks. Continue to monitor for all aphid species in all tree fruits as well as the beneficials that attack them.

Rose chafer started to be found about a week ago and can now be found more regularly in blocks with sandy soils. Continue to monitor apples and stone fruits.

Spotted wing Drosophila flight is being reported which is earlier than ever for Michigan. Traps with lures need to be in place in susceptible crops – sweet and tart cherry, strawberry, raspberries, etc. This could be a high pressure year for spotted wing Drosophila – they have never been trapped this early in Michigan.

Overwintering adults of brown marmorated stinkbug can be found and newly laid eggs are hatching. They are not attracted to tree fruits at this time as a food source. Monitor for adults and nymphs. Management in tree fruits will target adults in summer when fruits near ripening and become attractive as a food source.

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